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Infrared photography
Infrared photography
Infrared photography
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A tree photographed using the near infrared range
Alternative
photography

In infrared photography, the photographic film or image sensor used is sensitive to infrared light. The part of the spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is the domain of thermal imaging. Wavelengths used for photography range from about 700 nm to about 900 nm. Film is usually sensitive to visible light too, so an infrared-passing filter is used; this lets infrared (IR) light pass through to the camera, but blocks all or most of the visible light spectrum. These filters thus look black (opaque) or deep red.[a]

When these filters are used together with infrared-sensitive film or sensors, "in-camera effects" can be obtained, false-color or black-and-white images with a dreamlike or sometimes lurid appearance known as the Wood effect, an effect mainly caused by foliage (such as tree leaves and grass) strongly reflecting infrared in the same way visible light is reflected from snow.[b] There is a small contribution from chlorophyll fluorescence, but this is marginal and is not the real cause of the brightness seen in infrared photographs. The effect is named after the infrared photography pioneer Robert W. Wood, and not after the material wood, which does not strongly reflect infrared.

The other attributes of infrared photographs include very dark skies and penetration of atmospheric haze, caused by reduced Rayleigh scattering and Mie scattering, respectively, compared to visible light. The dark skies, in turn, result in less infrared light in shadows and dark reflections of those skies from water, and clouds will stand out strongly. These wavelengths also penetrate a few millimeters into skin and give a milky look to portraits, although eyes often look black.

History

[edit]

Until the early 20th century, infrared photography was not possible because silver halide emulsions are not sensitive to longer wavelengths than that of blue light (and to a lesser extent, green light) without the addition of a dye to act as a color sensitizer.[1] The first infrared photographs (as distinct from spectrographs) to be published appeared in the February 1910 edition of The Century Magazine and in the October 1910 edition of the Royal Photographic Society Journal to illustrate papers by Robert W. Wood, who discovered the unusual effects that now bear his name.[2][3][4] The RPS co-ordinated events to celebrate the centenary of this event in 2010.[5] Wood's photographs were taken on experimental film that required very long exposures; thus, most of his work focused on landscapes. A further set of infrared landscapes taken by Wood in Italy in 1911 used plates provided for him by C. E. K. Mees at Wratten & Wainwright. Mees also took a few infrared photographs in Portugal in 1910, which are now in the Kodak archives.[citation needed]

Infrared-sensitive photographic plates were developed in the United States during World War I for spectroscopic analysis, and infrared sensitizing dyes were investigated for improved haze penetration in aerial photography.[6] After 1930, new emulsions from Kodak and other manufacturers became useful to infrared astronomy.[7]

Album cover of Are You Experienced (1967) by The Jimi Hendrix Experience; the photographer captured the trio with a fisheye lens on color infrared film

Infrared photography became popular with photography enthusiasts in the 1930s, when suitable film was introduced commercially. The Times regularly published landscape and aerial photographs taken by their staff photographers using Ilford infrared film. By 1937, 33 kinds of infrared film were available from five manufacturers including Agfa, Kodak and Ilford.[8] Infrared movie film was also available and was used to create day-for-night effects in motion pictures. A notable example being the pseudo-night aerial sequences in the movie The Bride Came C.O.D., starring James Cagney and Bette Davis.[9]

False-color infrared photography became widely practiced with the introduction of Kodak Ektachrome Infrared Aero Film and Ektachrome Infrared EIR. The first version of this, known as Kodacolor Aero-Reversal-Film, was developed by Clark and others at the Kodak for camouflage detection in the 1940s. The EIR film became more widely available in the form of 35 mm film in the 1960s but has been since discontinued.

Infrared photography became popular with a number of 1960s recording artists, because of the unusual results; Jimi Hendrix, Donovan, Frank Zappa and the Grateful Dead all issued albums with infrared cover photos. The unexpected colors and effects that infrared film can produce fit well with the psychedelic aesthetic emerging in the 1960s.[citation needed]

Techniques and special equipment

[edit]

Infrared filters

[edit]
Infrared-passing filters

Infrared light lies between the visible and microwave portions of the electromagnetic spectrum. Infrared light has a range of wavelengths, just like visible light has wavelengths that range from red light to violet. "Near infrared" light is closest in wavelength to visible light, ranging from approximately 700 to 5000 nm, and "far infrared" is closer to the microwave region of the electromagnetic spectrum, ranging from approximately 25 to 350 μm.[10] The longer, far infrared wavelengths are about the size of a pinhead and the shorter, near infrared ones are the size of cells, or are microscopic.

Historically, black-and-white infrared films are sensitive to near infrared wavelengths shorter than approximately 860 nm, and retain significant sensitivity to blue wavelengths.[11]: 3, 5, 21 [12] Infrared-passing filters are used in black-and-white infrared photography to block blue wavelengths and limit the photograph to infrared wavelengths only. Without filters, infrared negative films look much like conventional negative films because the blue sensitivity lowers the contrast and effectively counteracts the infrared look of the film.[13][14]: 16  Typically, a red filter (Wratten #25) is recommended as the best compromise, which removes blue wavelengths while still passing enough visible light for focusing.[12][14]: 16 

Wratten IR filter nos.[15][16]: 35, 64–66, 81 
No. 50% (nm)[c]
15 530
21 560
23A 580
25 600
29 620
70 675
89B 720
88 735
72B 740
88A 750
87 795
87C 850
87B 930
87A 1050

Some photographers use orange or red filters to allow slight amounts of blue wavelengths to reach the film, and thus lower the contrast. The majority of black-and-white infrared art, landscape, and wedding photography is done using orange (Wratten #15 or 21), red (#23, 25, or 29) or visually opaque (#72)[d] filters over the lens to block the blue visible light from the exposure. Very dark-red (#29) filters block out almost all blue, and visually opaque (#70, 89b, 87c, 72) filters block out all blue and also visible red wavelengths, resulting in a more pure-infrared photo with a more pronounced contrast.

Instead of the Wratten number, some manufacturers embed the transition or cutoff wavelength in the name of the filter. For example, Hoya markets the R72 (720 nm cutoff, 750 nm 50% transition)[17] and RM90 (900 nm cutoff) filters for infrared photography.[18] B+W (Schneider Kreuznach) and Heliopan sell filters using glass sourced from Schott AG, including types RG695 (695 nm transition, considered approximately equivalent to Wratten #89B), RG715 (715 nm, #88A), RG780 (780 nm, #87), RG830, RG850, and RG1000.[19][20]: 26, 38 

Focusing infrared

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Nikon lens for Nikon F mount; the infrared index mark is the small red dot under one yellow hash mark for hyperfocal range at f/8.

Many manual focus lenses for 35 mm single-lens reflex cameras (SLR) and medium format SLR have a red dot, line or diamond, often with a red "R" called the infrared index mark, which can be used to achieve proper infrared focus; many autofocus lenses no longer have this mark. For these lenses, after visual focus is achieved for the intended subject, the distance indicated by the visual focusing mark is then re-set to the infrared index mark.[21] Without refocusing, a sharp infrared photograph can be taken by proper hyperfocal settings, which generally requires a tripod, a narrow aperture (like f/8);[citation needed] however, wider apertures like f/2.0 can produce sharp photos when the lens is meticulously refocused to the infrared index mark, and only if this index mark is the correct one for the filter and film in use. Diffraction effects inside a camera are greater at infrared wavelengths so that stopping down the lens too far may actually reduce sharpness.

Some lens manufacturers such as Leica never put IR index marks on their lenses. The reason for this is that any index mark is only valid for one particular IR filter and film combination, and may lead to user error. Even when using lenses with index marks, focus testing is advisable as there may be a large difference between the index mark and the subject plane.

Most apochromatic ('APO') lenses do not have an Infrared index mark and do not need to be refocused for the infrared spectrum because they are already optically corrected into the near-infrared spectrum. Catadioptric lenses do not often require this adjustment because their mirror containing elements do not suffer from chromatic aberration and so the overall aberration is comparably less. Catadioptric lenses do, of course, still contain lenses, and these lenses do still have a dispersive property.

When a SLR camera is fitted with a filter that is opaque to visible light, the reflex system becomes useless for both framing and focusing, one must compose the picture without the filter and then attach the filter. This requires the use of a tripod to prevent the composition from changing.

Zoom lenses may scatter more light through their more complicated optical systems than prime lenses, that is, lenses of fixed focal length; for example, an infrared photo taken with a 50 mm prime lens may have more contrast than the same image taken at 50 mm with a 28–80 zoom.

Film cameras

[edit]
Infrared negatives fogged by the frame counter of a Minolta Maxxum 4

Many conventional cameras can be used for near-infrared photography, where the portion of the infrared is light of a wavelength only slightly longer than that of visible light. Photography of the far-infrared spectrum with longer wavelengths is called thermography and requires special equipment.

With some patience and ingenuity, most film cameras can be used. However, some cameras of the 1990s that used 35 mm film have infrared sprocket-hole sensors that can fog infrared film (their manuals may warn against the use of infrared film for this reason). Other film cameras are not completely opaque to infrared light.

Arguably the greatest obstacle to infrared film photography has been the difficulty of obtaining infrared-sensitive film. Kodak typically manufactured just one or two batches of infrared films per year.[12]: 100 [22]: 25  In addition, the popularity of digital photography has pushed film manufacturers to discontinue niche film products, including infrared-sensitive films. The discontinuance of Konica Infrared 750 (2006),[23] Kodak High-Speed Infrared (2007),[24] and Efke IR820 Aura (2012) has now narrowed the selection for black-and-white infrared film to Agfa Aviphot films, made for areal photography.[25] These films are not available directly to consumers and must be purchased in large quantities and non-consumer formats. This film is often bought by large companies and sold in consumer quantities and formats under different brands, such as Rollei Infrared 400 film.[26]

Black-and-white infrared film

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Black-and-white infrared negative films are sensitive to wavelengths in the 700 to 900 nm near infrared spectrum, and most also have an inherent sensitivity to blue light wavelengths.[27]: 37–38  Kodak High-Speed Infrared (HIE), which produced negatives for photographic prints, was one of the most common black-and-white infrared films used. Because HIE was so prevalent, black-and-white infrared photographs have been associated with a notable halation effect or glow often seen in the highlights, similar to the soft focus effect of uncorrected spherical aberration.[28]: 55  This halation is an artifact of the clear polyester film base used for HIE and not inherent to infrared photography; it is caused by the absence of an anti-halation layer on the back side of Kodak HIE film, which results in a scattering or blooming around the highlights that would usually be absorbed by the anti-halation layer in conventional films. In addition, the clear backing means that Kodak HIE must only be loaded and unloaded in total darkness.[e][29]

Frank Lloyd Wright's Rudin House: panchromatic film on the left, infrared on the right

Infrared black-and-white films require special development times but exposed film can be processed using standard black-and-white photographic developers and chemicals, including D-76;[29]: 4  the choice of chemical may affect the characteristic exposure/density curve.[12]: 44–47  Kodak HIE film has a polyester film base that is very stable but extremely easy to scratch, therefore special care must be used in the handling of Kodak HIE throughout the development and printing/scanning process to avoid damage to the film.

Kodak HIE was sensitive to 900 nm. Other infrared black-and-white films include:

  • Agfa Aviphot (sensitive to approximately 770 nm) Widely available in most formats, such as 135 film, 120 film, and sheets by larger resellers (such as Rollei as 80S, 400S and IR 400) and individuals. Occasionally 220 film, 70mm film, and other formats not sold at scale may be available from individual sellers.[30]
  • Fotokemika/Efke IR 820 (also sensitive to approximately 800 nm)[31]
  • Ilford SFX 200 ("extended" sensitivity in the near-infrared range to 740 nm)[32]
  • Konica Infrared 750 (sensitive to approximately 800 nm)[33]

Color infrared film

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Kodak Ektachrome Infrared Color 35mm Color Film (expired in the 1970s)

Like HIE, the most commonly used infrared color reversal film, also called transparency or slide film, was manufactured by Kodak and sold as Ektachrome Infrared (EIR), under code 2236, packaged as a 36-exposure roll; in addition, Kodak made EIR in bulk lengths (for the motion picture industry) and the similar Aerochrome III Infrared for aerial photography (codes 1443 and SO-734).[22]: 19  EIR originally was developed during World War II as a means to detect camouflaged objects, taking advantage of the difference in infrared reflectance between plants and green paint,[34] and was adopted by the military and scientific communities after the war. It was not marketed to consumers until the 1960s.[22]: 12–13  To improve camouflage paint, companies began incorporating infrared-reflecting materials.[35]

Color reversal film
During exposure, light selectively sensitizes each of the three wavelength-sensitive layers; an internal blue-blocking filter is used to prevent false sensitization of the red- and green-sensitive layers
After E-6 development process, with subtractive color negative layers

The structure of all color reversal films (both standard and infrared-sensitive) contains at least three separate photosensitive layers. Each layer is specifically sensitized to respond to a different set of wavelengths; for instance, a standard color reversal film has red-, green-, and blue-sensitive layers.[36] During the modern E-6 process of development, grains of silver halide that were sensitized by the appropriate wavelengths of light in each layer react with a reducing agent to form metallic silver particles. The unexposed grains are then sensitized chemically during a second development step and produce oxidized developer, which react with dye coupler compounds embedded in the film emulsion layers to form negative images in various color dyes, respective to how the silver halide was originally sensitized for each layer.[citation needed]

In conventional color films, the topmost (blue-sensitive) layer gets exposed to light prior to the green- and red-sensitive layers stacked behind it. Since the green- and red-sensitive layers also retain an inherent sensitivity to blue light, a yellow filter layer is placed behind the blue-sensitive layer, in front of the green and red-sensitive layers. This serves to minimize undesired passthrough of shorter wavelengths that are not supposed to expose the bottom layers.[citation needed]

During development, each emulsion layer forms a negative image in the appropriate subtractive color (cyan-magenta-yellow): the blue-sensitive layer forms a yellow-dyed ("minus-blue") negative image, the green-sensitive layer forms a magenta-dyed negative image, and the red-sensitive layer forms a cyan-dyed negative image. When the slide is viewed or projected by passing white light through these stacked layers, the visible wavelengths are filtered correspondingly with the reversed colors. For example, blue light will result in no yellow dye formation in the blue-sensitive layer, but cyan and magenta dye will form in the red- and green-sensitive layers. By projecting white light through the combined layers, blue is produced: cyan (aka negative-red) removes red and passes blue and green, and magenta (aka negative-green) removes green and passes blue and red; when these layers are stacked, only blue light is passed.[citation needed]

Since silver halides are sensitive to wavelengths of light outside of the visible range of the electromagnetic spectrum, longer wavelengths corresponding with infrared light can be captured by using suitable dyes. Without specialized dyes, silver halides are only sensitive to a wavelength shorter than around 450 nm.[37]

Comparison of color reversal film structure (E-6 process)
Conventional[36]   Infrared[38]
Layer Present Final dye color Final dye color Present Layer
Yellow filter (external) Not used — — During exposure Yellow filter (external)
Blue-sensitive Present Yellow Cyan Present IR-sensitive
Yellow filter (internal) Present Carey Lea silver, bleached clear — Not present Yellow filter (internal)
Green-sensitive Present Magenta Yellow Present Green-sensitive layer
Red-sensitive Present Cyan Magenta Present Red-sensitive
Color infrared reversal film
During exposure, light selectively sensitizes each of the three wavelength-sensitive layers; an external blue-blocking filter is used
After development, with false-color remapping

Color infrared reversal films share a similar three-layer emulsion structure with conventional color reversal films, with the blue-sensitive layer replaced by an infrared-sensitive layer, and different dyes used for each of the layers.[38] An external yellow photographic filter is used (Wratten #12 or equivalent) to block the blue and violet wavelengths, which results in a false-color image by translating or remapping the captured spectrum (from green through infrared) to the visible spectrum: Infrared wavelengths are mapped to the red color, even though the infrared wavelengths are not normally visible. Similarly, visible red wavelengths are remapped to green, and visible green band wavelengths are remapped to blue. The filter and color remapping means visible blue and violet wavelengths are not captured. The infrared-sensitive layer will form cyan dyes (negative-red), while the green-sensitive layer will form yellow dyes (negative-blue) and the red-sensitive layer will form magenta dyes (negative-green).[39]

The external yellow filter is used because each emulsion layer in color films (both conventional and infrared) has an inherent sensitivity for short-wavelength radiation (blue and violet visible wavelengths of light) due to the silver halide chemistry. Since there is no blue-sensitive layer, color infrared films also omit the internal yellow filter layer built into conventional color films to protect the following layers. This requires photographers to use an external blue-blocking filter to absorb blue and violet wavelengths of light, which gives the filter a yellow color.[citation needed]

  • 'False-color' (remapped) infrared film examples
  • View of the Hollywood Hills. Kodak Infrared color slide film, no filter used and developed with E-6 process
    View of the Hollywood Hills. Kodak Infrared color slide film, no filter used and developed with E-6 process
  • An example of color infrared
    An example of color infrared
  • Lüdinghauser Tor in Dülmen (1981); remapped false color represents infrared wavelengths (as reflected by foliage) as shades of red
    Lüdinghauser Tor in Dülmen (1981); remapped false color represents infrared wavelengths (as reflected by foliage) as shades of red
  • Ribiera da Janela Valley on Madeira Island, using Kodak EIR (2003)
    Ribiera da Janela Valley on Madeira Island, using Kodak EIR (2003)
  • Bluebeard's Castle, Charlotte Amalie (1980)
    Bluebeard's Castle, Charlotte Amalie (1980)

Early color infrared films were developed in the older E-4 process, but Kodak later manufactured a color transparency film that could be developed in standard E-6 chemistry, although more accurate results were obtained by developing using the AR-5 process.[40] Like HIE, EIR uses a clear polyester film base and must be loaded in complete darkness. In general, color infrared does not need to be refocused to the infrared index mark on the lens.[22]: 28 

Kodak EIR loses its infrared sensitivity as it ages, giving photographs a cyan cast, as fewer grains in the infrared-sensitive (cyan-forming) layer will be sensitized.[22]: 59  Anecdotally, EIR is most sensitive up to approximately 21 days after purchase, and stabilizes at a decreased sensitivity thereafter.[22]: 26 

Availability

[edit]

Kodak discontinued production of HIE Infrared 35 mm film at the end of 2007, stating that, "Demand for these products has been declining significantly in recent years, and it is no longer practical to continue to manufacture given the low volume, the age of the product formulations and the complexity of the processes involved."[24][29] At the time it was discontinued, HIE Infrared 135-36 was available at a street price of around $12.00 a roll at US mail order outlets.

Also in 2007, Kodak announced that production of the 35 mm version of their color infrared film (Ektachrome Professional Infrared/EIR) would cease as there was insufficient demand.

In 2008, Los Angeles photographer, Dean Bennici started cutting and hand rolling Aerochrome color Infrared film. Most Aerochrome medium and large format which exists today came directly from his lab. The trend in infrared photography continues to gain momentum with the success of photographer Richard Mosse and multiple users all around the world.[41]

Since 2011, all formats of color infrared film have been discontinued. Specifically, Aerochrome 1443 and SO-734.[citation needed]

Digital cameras

[edit]
  • Digital infrared photograph examples
  • A view in infrared of Montréal as seen from Mont Royal, taken with filter made of a floppy disk
    A view in infrared of Montréal as seen from Mont Royal, taken with filter made of a floppy disk
  • Bending Cypress: infrared shot by Sigma SD10 with B+W 093 filter, ISO 100, f/8, 1/160 s
    Bending Cypress: infrared shot by Sigma SD10 with B+W 093 filter, ISO 100, f/8, 1/160 s
  • Digital infrared using a 50mm lens, D810 and the program Exposure. Infrared photography typically produces false-color artifacts, such as turning greens into pinks and purples as shown in this example.
    Digital infrared using a 50mm lens, D810 and the program Exposure. Infrared photography typically produces false-color artifacts, such as turning greens into pinks and purples as shown in this example.

Digital camera sensors are inherently sensitive to infrared light,[42] which could interfere with normal photography by confusing the autofocus calculations, because infrared light wavelengths may focus at a different point than visible light wavelengths, or by softening the image, if the red channel becomes oversaturated. Also, some clothing is transparent in the infrared, leading to unintended (at least to the manufacturer) uses of video cameras.[43][44] Thus, to improve image quality and protect privacy, many digital cameras have infrared blockers or hot mirrors installed in front of their sensors.[45] Depending on the subject matter, adding a infrared-passing filter to the lens may not be practical with these cameras because the exposure times become overly long, often in the range of 30 seconds, creating noise and motion blur in the final image. However, for some subject matter the long exposure does not matter or the motion blur effects actually add to the image. Some lenses will also show a 'hot spot' in the center of the image as their coatings are optimized for visible light and not for IR.

There is no currently available digital camera that will directly produce the same results as Kodak color infrared film although equivalent images can be produced using a full spectrum converted infrared digital camera and a Kolari Vision Color IR Chrome lens filter.[46] Similar effects can be achieved by taking two exposures, one infrared and the other full-color, and combining in post-production. A yellow (minus-blue) filter can also be used, which produces a single image that can also be post-processed to emulate the Ektachrome look.[47] The color images produced by digital still cameras using infrared-pass filters are not equivalent to those produced on color infrared film. The colors result from varying amounts of infrared passing through the color filters on the photo sites, further amended by the Bayer filtering. While this makes such images unsuitable for the kind of applications for which the film was used, such as remote sensing of plant health, the resulting color tonality has proved popular artistically.

Color digital infrared, as part of full spectrum photography is gaining popularity. The ease of creating a softly colored photo with infrared characteristics has found interest among hobbyists and professionals.

Hot mirror removal

[edit]
An example of color digital infrared photography. The camera's infrared blocking filter has been removed. Red and blue channels have been swapped for more conventional sky color.

One method of infrared photography using digital cameras is to remove the infrared blocker in front of the sensor and replace it with a glass cover that either removes or restricts visible light (infrared-only conversion) or one that passes infrared wavelengths ("full spectrum" conversion). This filter is behind the mirror of DSLRs, so the camera can be used normally - handheld, normal shutter speeds, normal composition through the viewfinder, and focus, all work like a normal camera. Metering works but is not always accurate because of the difference between visible and infrared refraction.[48] When the IR blocker is removed, many lenses which did display a hotspot cease to do so, and become perfectly usable for infrared photography. Additionally, because the red, green and blue micro-filters remain and have transmissions not only in their respective color but also in the infrared, enhanced infrared color may be recorded.[49]

Since the Bayer filters in most digital cameras may also absorb a significant fraction of the infrared light, converted cameras are sometimes not very sensitive to infrared wavelengths and can sometimes produce false colors in the images. An alternative approach is to use a Foveon X3 sensor, which does not have absorptive filters on it; the Sigma SD10 DSLR has a removable IR blocking filter and dust protector, which can be simply omitted or replaced by a deep red or complete visible light blocking filter. The Sigma SD14 has an IR/UV blocking filter that can be removed/installed without tools. The result is a very sensitive digital IR camera.[28]: 32 

While it is common to use a filter that blocks almost all visible light, the wavelength sensitivity of a digital camera without internal infrared blocking is such that a variety of artistic results can be obtained with more conventional filtration. For example, a very dark neutral density filter can be used (such as the Hoya ND400) which passes a very small amount of visible light compared to the near-infrared it allows through. Wider filtration permits an SLR viewfinder to be used and also passes more varied color information to the sensor without necessarily reducing the Wood effect. Wider filtration is however likely to reduce other infrared artefacts such as haze penetration and darkened skies. This technique mirrors the methods used by infrared film photographers where black-and-white infrared film was often used with a deep red filter rather than a visually opaque one.[citation needed]

Post-processing

[edit]

Another common technique with near-infrared filters is to swap blue and red channels in software (e.g. Adobe Photoshop), which retains much of the characteristic "white foliage" while rendering skies a glorious blue.[50]

Phase One digital camera backs can be ordered in a modified form suited for infrared photography.

Applications and specific implementations

[edit]
  • Digital infrared applications
  • An example of the use of infrared photography in aerial archaeology to delineate sub-surface features
    An example of the use of infrared photography in aerial archaeology to delineate sub-surface features
  • The reverse of the United States five-dollar bill has two rectangular strips that are blanked out when viewed in the infrared spectrum, as seen in this image taken by an infrared camera.
    The reverse of the United States five-dollar bill has two rectangular strips that are blanked out when viewed in the infrared spectrum, as seen in this image taken by an infrared camera.
  • Nightshot infrared photography of a stove with 600 nm red-filter and polarizing filter at daylight
    Nightshot infrared photography of a stove with 600 nm red-filter and polarizing filter at daylight
  • Thermographic image of coffee cup
    Thermographic image of coffee cup
  • The starburst galaxy IC 10 is hidden behind dust in the Milky Way, but infrared light is less strongly absorbed by dust than visible light. Green patches in the galaxy are its star-forming H II regions.
    The starburst galaxy IC 10 is hidden behind dust in the Milky Way, but infrared light is less strongly absorbed by dust than visible light. Green patches in the galaxy are its star-forming H II regions.

The health of foliage can be determined from the relative strengths of green and infrared light reflected using color infrared film; this shows in color infrared as a shift from red (healthy) towards magenta (unhealthy).

Several Sony cameras had a feature branded as Night Shot, which physically moves the blocking filter away from the light path, making the cameras very sensitive to infrared light. Soon after its development, this facility was 'restricted' by Sony to make it difficult for people to take photos that saw through clothing.[44] To do this the iris is opened fully and exposure duration is limited to long times of more than 1/30 second or so. It is possible to shoot infrared but neutral density filters must be used to reduce the camera's sensitivity and the long exposure times mean that care must be taken to avoid camera-shake artifacts.

Fuji have produced digital cameras for use in forensic criminology and medicine which have no infrared blocking filter. The first camera, designated the S3 PRO UVIR, also had extended ultraviolet sensitivity (digital sensors are usually less sensitive to UV than to IR). Optimum UV sensitivity requires special lenses, but ordinary lenses usually work well for IR. In 2007, FujiFilm introduced a new version of this camera, based on the Nikon D200/ FujiFilm S5 called the IS Pro, also able to take Nikon lenses. Fuji had earlier introduced a non-SLR infrared camera, the IS-1, a modified version of the FujiFilm FinePix S9100. Unlike the S3 PRO UVIR, the IS-1 does not offer UV sensitivity. FujiFilm restricts the sale of these cameras to professional users with their EULA specifically prohibiting "unethical photographic conduct".[51]

Remote sensing and thermographic cameras are sensitive to longer wavelengths of infrared (see Infrared spectrum § Commonly used sub-division scheme). They may be multispectral and use a variety of technologies which may not resemble common camera or filter designs. Cameras sensitive to longer infrared wavelengths including those used in infrared astronomy often require cooling to reduce thermally induced dark currents in the sensor (see Dark current (physics)). Lower cost uncooled thermographic digital cameras operate in the Long Wave infrared band (see Thermographic camera). These cameras are generally used for building inspection or preventative maintenance but can be used for artistic pursuits as well, such as this image of a cup of coffee.[citation needed]

See also

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Notes

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References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Infrared photography

View on Grokipedia
from Grokipedia
Infrared photography is a technique that records images using in the near- , typically with wavelengths ranging from 700 to 1200 nanometers, which extends beyond the visible detectable by the . This method produces distinctive visual effects, such as the reflection of by in , rendering foliage bright white or glowing while skies and appear unusually dark—a phenomenon known as the Wood effect. Unlike conventional , it captures details invisible in standard visible , enabling unique artistic expressions and scientific insights into materials' reflective properties. The foundations of infrared photography trace back to 1800, when British astronomer Sir discovered radiation by measuring temperature increases beyond the red end of the solar spectrum using a prism and thermometers. Practical photographic applications emerged in the early ; American physicist captured and published the first infrared photographs in October 1910 in the Journal of the Royal Photographic Society, demonstrating the technique's potential for revealing hidden visual qualities in landscapes and portraits. By , advancements in photographic emulsions and sensitizing dyes made film commercially viable, with introducing specialized products that facilitated broader adoption in fields like document analysis and . Traditional infrared photography relies on films or plates sensitized to infrared wavelengths, paired with deep-red or opaque filters to exclude visible light and isolate the desired , often requiring standard cameras, tripods for stability, and sources like or lamps. In digital workflows, common approaches include professionally converting cameras by removing the built-in infrared-blocking filter from the , allowing direct capture of light, or affixing external infrared-pass filters (such as 720nm or 850nm) to unmodified digital single-lens reflex (DSLR) or mirrorless cameras, which necessitates long exposures of 1 to 90 seconds at low ISO settings like 100–200 and apertures around f/16. Post-processing in software such as is essential, involving RAW file adjustments, channel swapping for false-color effects (e.g., inverting and channels), and contrast enhancements to accentuate the surreal, ethereal qualities of infrared imagery. Beyond aesthetics, infrared photography serves diverse practical purposes, including art conservation where it non-destructively reveals underdrawings and alterations in paintings by penetrating surface layers. In and forensics, it visualizes subsurface details like bruises, tattoos, or such as bloodstains that are obscured under visible . Scientific and environmental applications encompass aerial surveys to assess via near-infrared , military for detection, and astronomical to study heat emissions, underscoring its enduring value across disciplines.

Fundamentals

Infrared Spectrum and Sensitivity

Infrared photography primarily utilizes near-infrared (NIR) light, defined as with wavelengths ranging from approximately 700 nm to 1100 nm, extending just beyond the (400–700 nm). This range is invisible to the , which perceives only up to about 700 nm, allowing NIR to capture scenes that differ markedly from visible-light images. NIR light interacts uniquely with materials due to its longer wavelengths, which reduce compared to visible light; for instance, healthy foliage reflects up to 50% of incident NIR —a phenomenon known as the Wood effect—because strongly absorbs visible wavelengths (400–700 nm) but not NIR, leading to high internal scattering within leaf mesophyll layers. This selective reflection enables NIR photography to highlight vegetation health and structure, with stressed plants showing reduced NIR reflectance due to altered leaf . Additionally, NIR's penetration properties allow it to pass through atmospheric haze more effectively than shorter visible wavelengths, as intensity decreases with the fourth power of wavelength per Rayleigh's , improving image clarity in foggy or smoky conditions. Photographic emulsions and digital sensors exhibit sensitivity to NIR through specific chemical or semiconductor properties; traditional silver-halide emulsions in infrared films peak in sensitivity around 750–950 nm, while silicon-based (CCD) and complementary metal-oxide-semiconductor () sensors in digital cameras respond up to about 1100 nm, limited by the silicon bandgap energy of 1.1 eV. This sensitivity captures reflected NIR from ambient sources like , distinguishing it from thermal infrared (typically 3–14 μm), which detects emitted heat radiation rather than reflected light and requires specialized uncooled detectors not used in standard NIR photography.

Photographic Effects and Characteristics

Infrared photography produces distinctive visual effects due to the reflection, absorption, and transmission properties of near-infrared light by various materials, differing markedly from visible light imaging. One of the most prominent characteristics is the "Wood effect," where healthy , such as leaves and grass, appears unusually bright or white because strongly reflects infrared wavelengths while absorbing visible light. This effect, first noted in early experiments, creates high-contrast landscapes with glowing foliage against darker backgrounds. Skies in infrared images often render as dark or nearly black, particularly in black-and-white photography, as atmospheric scattering of shorter visible wavelengths (like blue) is reduced for longer infrared wavelengths, minimizing the typical sky brightness seen in standard photographs. This results in dramatic cloud highlights and enhanced atmospheric depth. In portraits, skin tones take on a smooth, milky appearance because infrared light penetrates several millimeters into the epidermis, reducing surface texture visibility, while subcutaneous features like veins and birthmarks become more prominent due to differential absorption by hemoglobin. In false-color infrared rendering, common in both analog films and digital processing, color channels are remapped to simulate the spectrum, leading to surreal hues; for instance, vibrant red foliage may appear or , while water bodies and urban surfaces shift to deep blues or blacks, emphasizing vegetation through intense reds for vigorous growth. Infrared imaging also offers improved resolution in hazy conditions compared to visible light photography, as longer wavelengths penetrate atmospheric aerosols like fog, smoke, and dust more effectively, reducing scattering and revealing distant details that would otherwise be obscured. This haze-penetration property, stemming from the inverse wavelength dependence of , is particularly useful for aerial and landscape work. Photographers working with infrared must consider safety limits for near- exposure, as prolonged direct viewing of intense sources like the sun can pose risks to the eyes and , potentially leading to or cataracts; guidelines recommend limiting exposure and using protective eyewear compliant with standards like those from the International Commission on Protection (ICNIRP), which set spectral irradiance limits (e.g., 10 mW/cm² for wavelengths 700-1400 nm over 1000 seconds).

History

Early Discoveries and Experiments

The discovery of infrared radiation traces back to 1800, when British astronomer Sir conducted experiments dispersing sunlight through a and measuring temperature changes across the using thermometers placed in each color band. He observed that the highest temperatures occurred beyond the red end of the spectrum, where no visible light was present, leading him to infer the existence of an invisible form of radiation that he termed "calorific rays," later identified as . This finding laid the foundational understanding of the portion of the , adjacent to visible red light and characterized by longer wavelengths that primarily manifest as heat, sparking initial scientific interest in non-visible radiation's potential applications. Advancements in infrared photography emerged in the early through experimental efforts to sensitize photographic plates to these wavelengths. In 1910, American physicist pioneered the first known infrared photographs by treating glass plates with specialized dyes to extend their sensitivity into the near- range, capturing landscapes that revealed striking contrasts due to differential reflection of infrared light by foliage and other materials—a phenomenon now known as the Wood effect. Wood's work, published in the Royal Photographic Society Journal, demonstrated the feasibility of recording images despite requiring long exposure times, and it influenced subsequent optical research. During (1914–1918), -sensitive plates were employed by U.S. units for , where they proved effective in penetrating atmospheric and smoke, allowing clearer detection of terrain features and structures obscured in visible light photography. The saw further experimentation with infrared photography, including early applications in forensics to reveal alterations, erasures, and ink differences in documents invisible under normal light. By the 1930s, these developments culminated in the commercialization of infrared-sensitive films by , which produced emulsions capable of capturing near-infrared wavelengths for practical use. These films were initially adopted for scientific and military purposes, including enhanced aerial surveys; for instance, 's products were later adapted during preparations for detecting by exploiting vegetation's strong infrared reflectance against artificial coverings. This era marked the transition from rudimentary experiments to reliable photographic tools, setting the stage for broader adoption in the mid-20th century.

Film and Digital Advancements

During the 1940s, Kodak developed color infrared film in collaboration with the United States military to aid in aerial reconnaissance during World War II, enabling the detection of camouflage by rendering vegetation in magenta hues against a cyan sky. This innovation, initially known as Kodacolor Aero Reversal Film, evolved into Ektachrome Infrared (EIR) by the 1960s, with peak sensitivity around 730 nm extending to 900 nm, facilitating applications in camouflage detection, vegetation analysis, and medical imaging. By the 1970s, Kodak introduced Aerochrome III Infrared Film 1443, a refined false-color reversal emulsion that maintained military and scientific utility through the 1980s, though civilian use remained niche due to specialized processing requirements. The decline of analog infrared film accelerated in the late 2000s as digital alternatives emerged, with announcing the discontinuance of Aerochrome III Infrared Film 1443 in 2009 due to diminishing demand, marking the end of mainstream production for color IR emulsions. Black-and-white options like Kodak High-Speed Infrared (HIE) had already been phased out by 2007, shifting the medium toward hobbyist use of expired stocks. Niche revivals persisted through limited resellers and custom processing services, sustaining interest among analog enthusiasts into the 2020s. In the 1990s, the inherent near-infrared sensitivity of silicon-based digital sensors—extending up to approximately 1100 nm—was recognized as a byproduct of (CCD) and complementary metal-oxide-semiconductor () technologies, originally designed for visible light but requiring internal filters to block IR for accurate color reproduction. This discovery spurred the infrared conversion market in the early 2000s, with the 2003 launch of the affordable digital SLR catalyzing widespread sensor modifications by removing the IR-blocking filter to enable full-spectrum capture. Through the , companies specialized in these conversions, transforming consumer cameras into dedicated IR tools and democratizing access to digital infrared photography for artistic and scientific purposes. From 2020 to 2025, infrared photography saw increased accessibility through cost-effective sensor conversions, with services offering full-spectrum modifications for under $400 on entry-level mirrorless cameras, broadening adoption among amateurs. Smartphone-compatible IR attachments, such as external 720 nm filters and clip-on lenses, emerged as budget options, allowing mobile devices to produce false-color effects without permanent alterations, as demonstrated in practical tutorials for and Android users. Concurrently, the near-infrared (NIR) camera market expanded rapidly, driven by applications in , , and , with projections estimating growth to $518 million by 2031 at a of 8.8%. This digital surge underscored the transition from film-based to hybrid and fully electronic workflows in .

Equipment and Techniques

Infrared Filters and Accessories

Infrared filters are essential tools in infrared photography, designed to isolate wavelengths by blocking visible , thereby enabling the capture of IR-specific effects such as enhanced foliage glow and surreal skies. These filters primarily fall into two categories: long-pass and band-pass. Long-pass filters, the most commonly used in IR photography, transmit all wavelengths above a specified cutoff while attenuating shorter ones; examples include 720nm and 850nm variants, which allow starting from those thresholds to reach the film or . Band-pass filters, in contrast, permit a narrower range of wavelengths, often employed for specialized applications like vegetation analysis, but they are less prevalent for general artistic IR imaging due to their restricted transmission. Filter materials significantly influence performance, with being a preferred choice for its high purity, selective absorption, and durability in blocking unwanted spectra. Schott glasses, such as those used in RG series for long-pass IR, provide excellent transmission in the near-infrared range (typically 700-1100nm) while minimizing internal reflections and heat buildup. Selection of a filter depends on the desired photographic effect: a 720nm long-pass filter yields subtle false-color results with some residual visible red light, ideal for vibrant, otherworldly landscapes, whereas an 850nm filter produces high-contrast images emphasizing deep blacks and glowing whites, suited for dramatic black-and-white compositions. Beyond filters, several accessories enhance IR photography workflows. IR flash gels, thin sheets of IR-transmissive material, are clipped or adhered to standard flashes to convert their output to infrared illumination, enabling fill lighting in low-light scenarios without visible light contamination; these typically transmit 800-1100nm while blocking below 700nm. Tripods are indispensable for stabilizing cameras during the extended exposures often required in IR shooting, preventing blur from even minor movements. Lens hoods help mitigate , which can be exacerbated in IR due to heightened surface reflections from foliage and . Compatibility considerations differ between film and digital systems. In analog IR photography, external long-pass filters are mounted directly on the lens, as IR-sensitive films like Ilford SFX inherently respond to near-IR without internal blocking. For digital cameras, external filters work with both unconverted and converted models, but unconverted sensors demand thicker or higher-cutoff filters (e.g., 850nm) to overcome the built-in IR-blocking layer, resulting in longer exposures; converted cameras pair well with lower-cutoff options like 720nm for versatile external use.

Focusing, Exposure, and Camera Adjustments

Infrared photography presents unique focusing challenges due to the focal shift caused by the longer wavelengths of , which typically range from 700 nm to 900 nm compared to visible 's 400-700 nm . This shift means that a lens focused visually for visible will not produce sharp infrared images without adjustment, as rays converge at a slightly different point behind the lens. Photographers must rack the lens forward slightly after visual focusing, effectively treating the subject as nearer, to achieve optimal sharpness. To address this, many lenses from the film era include dedicated infrared focusing marks on the focus scale, allowing users to align the visual focus distance with the IR mark for correction. In digital workflows, live view mode is particularly useful, enabling real-time preview and manual fine-tuning of focus under infrared conditions, often combined with small apertures to leverage and minimize discrepancies. Rule-of-thumb adjustments for unknown lenses suggest advancing the focus by approximately 0.3% to 0.75% of the , though testing is recommended for precision. Exposure in infrared photography requires careful management, as reciprocity failure is pronounced in infrared-sensitive films, where efficiency drops at longer exposures beyond 1 second, necessitating additional time to maintain density—for instance, Infrared 400 may require exposures several times longer than indicated at ISO 3 for times exceeding 1 second. In digital infrared capture, high ISO settings (often 800 or above) are commonly employed to compensate for the light-blocking effects of infrared filters, though low ISO (100-400) paired with extended shutter speeds (10-30 seconds) is preferred to reduce during long exposures. exposures—typically in ±1 to ±2 EV increments—is essential due to the high variability in infrared reflection from subjects like foliage, which can lead to clipped highlights or underexposed shadows in high-dynamic-range scenes. Camera adjustments for infrared shooting favor manual mode to provide full control over , , and ISO, avoiding automated metering that may misinterpret the filtered scene. White balance should be set custom in-camera using green foliage or a neutral as a reference under the shooting , filling the frame and ensuring neutral exposure before selecting the image for —this prevents color casts and allows flexibility. Apertures of f/8 or smaller are standard to maximize , accommodate the focal shift, and reduce lens hotspots where concentrates unevenly. Sunlight serves as the optimal light source for infrared photography, providing abundant near- in direct midday conditions, while skies significantly reduce available by longer wavelengths. For indoor or low-light scenarios, incandescent () lamps are effective artificial sources, emitting substantial output— a 100W produces approximately 95 W in —though they necessitate higher ISO or longer exposures compared to due to their deeper spectrum.

Analog Infrared Photography

Infrared-Sensitive Films

Infrared-sensitive films are specialized emulsions designed to capture wavelengths in the near-infrared , typically extending beyond the visible light range of standard photographic films. Black-and-white infrared films, such as SFX 200, offer extended red sensitivity up to approximately 750 nm, allowing photographers to achieve the characteristic ethereal effects of infrared photography when paired with appropriate filters. This medium-speed film has an ISO rating of 200 and is coated on a 0.125 mm grey acetate base for effective halation protection, making it suitable for creative applications in 35 mm and 120 formats. Color films, like the discontinued Aerochrome III (type 1443), produce false-color images by rendering light in the red channel, resulting in vibrant, surreal renditions where foliage appears and skies turn . Developed primarily for , this exhibited medium resolving power and fine grain, with a daylight sensitivity of ISO 100 when processed via the E-6 method adapted for . discontinued Aerochrome III in 2009 due to declining demand, leaving it unavailable in new production but highly prized in expired stocks among enthusiasts. These films generally feature speeds ranging from ISO 100 to 400, balancing sensitivity with manageable grain structure—often fine to medium, which contributes to sharp yet textured renderings without excessive . To maintain integrity and prevent fogging from unintended exposure, -sensitive films require storage in cool, dark conditions, ideally below 13°C (55°F) and away from heat sources, with prompt processing recommended to preserve speed and contrast. As of 2025, options remain niche, with SFX 200 available through suppliers like Harman Technology, while true color films like Aerochrome have no direct modern equivalents, though expired rolls persist in limited supply via specialty retailers.

Film Processing and Development

Infrared-sensitive black-and-white films, such as Kodak High Speed Infrared (HIE), are processed using standard black-and-white developers like Kodak D-76, with development times typically ranging from 6.5 to 11 minutes at 18–24°C depending on the desired contrast index and agitation method. For films like Ilford SFX 200, equivalent developers such as Ilford ID-11 (similar to D-76) are recommended, requiring about 10 minutes at 20°C for an exposure index of 200 with stock solution and continuous agitation. Extended times compared to conventional panchromatic films help achieve full emulsion speed and fine grain while compensating for the film's extended red and near-infrared sensitivity. Handling infrared films demands precautions to avoid fogging from stray , as many emulsions lack anti-halation dyes and standard canisters transmit IR light. Highly sensitive types like Kodak HIE require total darkness for loading and unloading, with no use permitted, while moderately sensitive films like Ilford SFX 200 can be managed in subdued light. Processing temperatures must be precisely controlled, usually at 20°C, to ensure uniform development and prevent variations exacerbated by the film's response. Fixing follows standard procedures with rapid fixers like Ilford Rapid Fixer for 2–5 minutes, followed by thorough washing in running water at the same temperature. Color infrared films, exemplified by Aerochrome, undergo reversal processing via the E-6 or proprietary AR-5 method using chemicals like EA-5, yielding positive transparencies at temperatures of 46–49°C across steps including first developer, color developer, bleach, and fixer. This produces the film's signature false-color rendering, with a bias in vegetated areas due to infrared recording as red and as blue. Alternative C-41 processing is feasible but introduces caveats, such as negative results with pronounced color shifts toward or , necessitating strict 38°C control to minimize imbalances and achieve usable negatives. Post-development, infrared films are scanned at high resolutions—often 2400–4800 dpi—to capture their subtle halation effects and tonal gradations without loss of detail. Dust prevention is paramount given the films' fine emulsions; pre-scanning cleaning with anti-static brushes and is essential, and for color variants like Aerochrome, infrared-enabled scanner tools detect and remove particles by analyzing the IR channel where dyes are transparent. A key challenge in color processing is managing inherent biases, such as Aerochrome's dominance, which amplifies surreal visuals but can require selective density adjustments during evaluation.

Digital Infrared Photography

Sensor Modifications and Conversions

Digital cameras designed for visible light photography incorporate an internal infrared-cut filter, commonly known as the hot mirror, positioned in front of the image sensor to block infrared wavelengths and prevent color contamination in standard images. Sensor modifications for infrared photography involve the precise removal of this filter through camera disassembly, followed by thorough cleaning of the sensor area to eliminate dust particles that could cause artifacts in images. This process typically requires specialized tools and is conducted in a controlled environment, such as an ISO Class 5 cleanroom, to maintain optical quality; improper handling risks permanent sensor damage or voiding the manufacturer's warranty. After removal, the camera undergoes focus recalibration using test lenses to compensate for the shift in focal plane caused by the absence of the original filter. Two primary types of conversions exist: full-spectrum modifications, where the hot mirror is replaced with clear fused-quartz glass to allow passage of , visible, and light, necessitating external filters for specific applications; and dedicated conversions, such as a 720nm internal filter, where the hot mirror is substituted with an -pass filter that blocks visible light below 720nm, enabling direct capture of near- imagery without additional attachments. The 720nm variant produces the classic effect with strong wood/leaf reflection and blue sky darkening, while full-spectrum offers versatility for both standard and shooting. While DIY conversions are possible for experienced users— involving careful prying of the filter with a craft and sensor access— they carry significant risks, including electrical shock from high-voltage components, focus misalignment, and costly repairs exceeding professional fees. Professional services, such as those from Kolari Vision or LifePixel, are recommended for reliability, with costs ranging from $275 to $350 for DSLR conversions as of 2025, including a one-year against post-conversion defects. Compatibility favors older DSLR models like the (Rebel XT), which are affordable, have accessible sensor assemblies, and perform well in due to their unmodified filters responding effectively to near- light. Mirrorless cameras offer advantages in conversions, such as electronic viewfinders and live preview for real-time composition and focusing in invisible wavelengths, though some models may exhibit minor issues like internal IR LED interference requiring additional shielding.

Full-Spectrum and Specialized Cameras

Full-spectrum cameras are digital devices modified by removing the internal hot mirror, or IR-cut filter, that typically blocks and light from reaching the , enabling capture across a broad range of wavelengths including UV, visible, and near-infrared (NIR). This modification allows users to switch between spectra using external filters, such as those blocking visible light for pure IR imaging or UV for specialized applications, while maintaining functionality for standard visible-light photography without additional hardware. Popular models for full-spectrum conversions include the Canon EOS R series, Sony α7 series, and ES, which offer high-resolution s and live view for precise composition in IR. These cameras are favored for their versatility and compatibility with interchangeable lenses, making them suitable for both and workflows. Specialized infrared cameras build on this foundation by incorporating fixed or optimized IR filters during conversion, such as 720nm or 850nm cutoffs, to focus exclusively on NIR capture without the need for frequent filter swaps. In 2025, converted versions of the (45 MP full-frame) and Sony α7 Mark III (24 MP full-frame) rank among the most sought-after for their excellent dynamic range and low noise in IR spectra, providing ready-to-use solutions from services like Kolari Vision and Life Pixel. models, including the X-T2 and X-T4 ES, are also prominent due to their , which enhances post-processing of IR images, and their compact design for field use. These specialized setups prioritize IR sensitivity while retaining core camera features like and electronic viewfinders. For more accessible options, smartphone and compact camera users can employ clip-on IR filters and mounts to approximate full-spectrum or specialized IR capture without permanent modifications. Systems like the Moment 67mm snap-on filter mount for iPhone 12 through 17 series allow attachment of 720nm IR filters directly to the phone's lens, enabling NIR photography via apps that process the resulting images. These portable solutions are ideal for casual users, though they may introduce minor vignetting or require manual exposure adjustments. Advancements from 2020 to 2025 have introduced hybrid multispectral sensors in drones, combining visible RGB with NIR and red-edge bands for integrated IR capabilities. The DJI Mavic 3 Multispectral, released in 2022, exemplifies this with its 20 MP RGB camera paired alongside five 5 MP multispectral sensors, facilitating real-time vegetation analysis and environmental monitoring without separate conversions. Similarly, the MicaSense Altum-PT integrates thermal and multispectral imaging for synchronized data capture, enhancing applications in precision agriculture and remote sensing. More recent developments include the DJI T70 agricultural drone series launched in 2024, which features advanced multispectral payloads for crop monitoring, and the AgEagle RedEdge-P Green camera introduced in 2025 for high-accuracy vegetation health assessment.

Image Processing

Color Mapping and Channel Adjustments

In digital infrared photography, color mapping techniques transform the raw infrared data captured by modified sensors into visually interpretable images, often requiring adjustments to account for the shifted response where near- predominantly registers in the channel. This process begins with handling the raw files from converted cameras, which preserve the full for subsequent corrections. Channel swapping is a fundamental method to create false-color representations, particularly for landscapes where foliage appears bright due to high . In software like , this involves using the Channel Mixer adjustment layer to reassign the red channel's data to the channel and vice versa, for example, setting the red output to 100% input and the blue output to 100% input, while leaving the green channel unchanged (R=B, G=G, B=IR). This swap produces striking effects, such as skies and golden foliage, by inverting the typical color response. White balance adjustments are essential to neutralize the dominant red or cast inherent in uncorrected captures, ensuring more balanced tones before further mapping. Custom white balance settings are set in-camera or during post-processing by targeting a neutral reference like green foliage or a under the shooting conditions, which recalibrates the to represent "white" accurately in the . For illumination, a common setting is around 2000K, the minimum available in many tools like Adobe , though the eyedropper tool on a neutral area may be needed for finer tuning below this threshold. This step prevents overwhelming color shifts and provides a neutral starting point for subsequent enhancements. To optimize the of infrared images, which often exhibit flat contrasts due to the sensor's sensitivity, levels and curves adjustments enhance tonal distribution and detail visibility. Levels adjustments involve sliding the black and white point markers in the to clip extremes and expand the midtones, thereby increasing overall contrast without losing -specific details like subtle textures. Curves, applied via an adjustment layer, allow more precise control by plotting input versus output values; the auto curves function in tools like Photoshop effectively boosts midtone contrast in files, making faint highlights in foliage pop while preserving shadow details. These techniques are particularly vital for 's extended range, where visible light adjustments alone would underperform. For efficiency in handling series of infrared images, batch processing applies these color mapping and adjustment steps uniformly across multiple files, maintaining stylistic consistency across a shoot. In Adobe Photoshop, this is achieved by recording an Action that sequences channel swapping, white balance application, and levels/curves tweaks, then applying it via the Batch command to a folder of raw or processed images. This method ensures repeatable results, such as uniform false-color rendering in landscape series, while minimizing manual repetition for large datasets.

Software Tools and Post-Production Techniques

and Photoshop are widely used for post-production in photography, offering tools such as the Channel Mixer for basic channel swapping and custom actions to automate false-color effects. supports -specific DCP profiles for accurate color rendering during RAW import, while Photoshop provides actions like those from experts for efficient channel adjustments and . facilitates processing through its white balance dropper tool applied to foliage for neutral starting points and by setting exposure levels to individual RGB channels to handle the unique spectral response. Other tools include ON1 Photo RAW, which incorporates presets and LUTs for streamlined workflows, and the Collection's Silver Efex Pro for enhancing images with structure and clarity adjustments. Layer blending techniques in Photoshop enable the creation of composites by stacking adjustment layers, such as Hue/Saturation for selective color shifts and Curves for contrast enhancement, often blended in mode to preserve tonal details in captures. For high-ISO shots prone to noise from long exposures, is applied using plugins like DeNoise AI, which selectively smooths grain while retaining edge sharpness in foliage and skies. HDR merging leverages the wide exposure latitude of infrared imagery by combining bracketed exposures in Photoshop's Merge to HDR Pro, which aligns images, removes ghosts from motion, and applies via Local Adaptation to reveal details in high-contrast scenes like sunlit landscapes. Since 2020, AI-driven tools have advanced infrared post-production, with Luminar Neo's Infrared Mastery AI templates automating color mapping and stylistic enhancements across 16 presets for both color and black-and-white outputs, reducing manual adjustments for artistic results. As of 2025, 2.6 and later versions integrate AI features like automatic subject selection to facilitate precise layer blending and in photo edits, including infrared images.

Applications

Artistic and Creative Uses

Infrared photography has long captivated artists for its ability to render familiar scenes in otherworldly tones, transforming everyday subjects into surreal visions through the unique reflectance properties of infrared light, such as the prominent "wood effect" where appears luminously bright. This technique emphasizes aesthetic experimentation, allowing photographers to explore dreamlike qualities that challenge conventional perceptions of color and form. In , infrared captures produce ethereal effects, with foliage and trees glowing in brilliant whites or unnatural hues due to high infrared reflectance, contrasted against and water bodies that absorb the light, creating dramatic, dreamlike compositions. Photographers like Pierre-Louis Ferrer have utilized this to depict rural and urban fringes in vibrant yellows and reds, evoking an alien vitality in natural environments. These visuals gained prominence in creative circles during 2024, as evidenced by entries in international contests that highlighted such surreal landscapes. For portraits, infrared photography offers surreal skin rendering, often appearing smooth and luminous with a porcelain-like quality, while deeper penetration of wavelengths reveals underlying veins as subtle dark lines, adding an intimate, anatomical layer to the imagery. This effect lends itself to artistic nudes, where the visibility of veins and ethereal tonality create introspective, dreamlike studies of the human form, as explored by photographers like Edward Thompson in series that uncover hidden bodily details. Such portraits evoke a sense of and otherworldliness, distinguishing them from standard visible-light work. In urban and experimental contexts, infrared accentuates architectural glow, where building materials reflect light variably to produce haunting contrasts, turning structures into luminous silhouettes against inky backgrounds. Ferrer’s views of , for instance, infuse brutalist facades with fiery, surreal energy, reimagining as a fantastical realm. Experimental techniques, including with sources during long exposures, further enhance these effects by tracing invisible paths of light, yielding dynamic, ghostly abstractions in cityscapes. The infrared photography community fosters creativity through events like Kolari Vision’s 2024 "Life in Another Light" contest, which received over 3,000 submissions across categories emphasizing , with winning landscapes and portraits showcasing the technique’s transformative potential in . These competitions highlight infrared’s role in pushing artistic boundaries, inspiring photographers to blend technical innovation with expressive vision.

Scientific, Forensic, and Industrial Applications

In forensic document examination, photography reveals erased or altered entries by exploiting differences in absorption and reflection properties between inks and the underlying . For instance, non-destructive techniques differentiate inks that appear identical under visible , allowing examiners to detect overwritings or erasures without damaging the document. Similarly, reflectography uncovers abraded or faded inscriptions in historical documents, such as marks, by penetrating surface alterations. Guidelines from forensic standards organizations emphasize 's role in documenting such alterations, recommending specific wavelengths (typically 700-1100 nm) for optimal contrast in questioned document analysis. At crime scenes, infrared photography enhances the detection of latent bloodstains obscured by dark surfaces, paint, or soot, where hemoglobin's infrared reflectivity contrasts with surrounding materials. Studies demonstrate that reflected infrared imaging can visualize blood beneath up to six layers of paint or dense soot deposits exceeding optical density 2.3 at 550 nm, aiding in pattern reconstruction even after environmental interference. On common crime scene floor coverings like dark carpets or tiles, infrared successfully identifies bloodstains on approximately 71.7% of tested materials, outperforming visible light in low-contrast scenarios. This technique has proven particularly valuable in fire-damaged scenes, where soot masks evidence, enabling non-invasive documentation for evidentiary purposes. In scientific applications, infrared photography assesses plant health by capturing near-infrared reflectance from chlorophyll, which indicates photosynthetic efficiency and stress levels. Healthy vegetation strongly reflects near-infrared light (700-900 nm) due to chlorophyll fluorescence, while stressed plants show reduced reflectance, allowing early detection of water deficiency or nutrient imbalances through color infrared imagery. Chlorophyll fluorescence imaging in the infrared spectrum further quantifies photosystem II activity, providing non-invasive metrics for environmental stress phenotyping in crops and ecosystems. In astronomy, converted digital cameras sensitive to infrared wavelengths penetrate cosmic dust clouds to image nebulae, revealing structures invisible in visible light; for example, full-spectrum modifications enhance capture of hydrogen-alpha emissions in emission nebulae like the Orion Nebula. Industrial and medical uses leverage infrared photography for non-destructive analysis in art conservation and diagnostics. In art conservation, infrared reflectography (800-2500 nm) detects underdrawings and pentimenti by rendering certain pigments transparent, exposing preparatory sketches or alterations in paintings without physical intervention; this has been applied to works like Botticelli's Virgin and Child to reveal carbon-based underdrawings. The technique distinguishes between paint layers and supports authentication by identifying hidden modifications. Medically, near-infrared imaging maps subcutaneous veins for diagnostics, visualizing structures 1-3 mm deep with diameters as small as 0.5 mm, aiding in varicose vein detection and improving venous access accuracy during procedures. Recent advancements from 2020-2025 integrate drone-based photography in for crop stress detection, using and near- sensors to monitor canopy temperature and indices over large fields. These systems calculate crop stress indices from data, identifying drought-affected areas with resolutions down to centimeters, enabling targeted and yield optimization in arid conditions. Such drone applications have reduced monitoring costs compared to ground-based methods while providing for precision farming. Historically, infrared photography found early military applications during for , detecting camouflaged positions through vegetation differentiation.

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