Progressive scan
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Progressive scanning (alternatively referred to as noninterlaced scanning) is a format of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence. This is in contrast to interlaced video used in traditional analog television systems where only the odd lines, then the even lines of each frame (each image called a video field) are drawn alternately, so that only half the number of actual image frames are used to produce video.[1] The system was originally known as "sequential scanning" when it was used in the Baird 240 line television transmissions from Alexandra Palace, United Kingdom in 1936. It was also used in Baird's experimental transmissions using 30 lines in the 1920s.[2] Progressive scanning became universally used in computer screens beginning in the early 21st century.[3]
Interline twitter
[edit]
This rough animation compares progressive scan with interlace scan, also demonstrating the interline twitter effect associated with interlacing. On the left there are two progressive scan images. In the middle there are two interlaced images and on the right there are two images with line doublers. The original resolutions are above and the ones with spatial anti-aliasing are below. The interlaced images use half the bandwidth of the progressive ones. The images in the center column precisely duplicate the pixels of the ones on the left, but interlacing causes details to twitter. Real interlaced video blurs such details to prevent twittering, but as seen in the pictures of the lower row, such softening (or anti-aliasing) comes at the cost of image clarity. A line doubler shown in the bottom right picture cannot restore the previously interlaced image in the center to the full quality of the progressive image shown in the top left.
Note: Because the refresh rate has been slowed by a factor of three, and the resolution is less than half a resolution of a typical interlaced video, the flicker in the simulated interlaced portions and also the visibility of the black lines in these examples are exaggerated. Also, the images above are based on what it would look like on a monitor that does not support interlaced scan, such as a PC monitor or an LCD or plasma-based television set, with the interlaced images displayed using the same mode as the progressive images.
Usage in storing or transmitting
[edit]Progressive scan is used for scanning and storing film-based material on DVDs, for example, as 480p24 or 576p25 formats. Progressive scan was included in the Grand Alliance's technical standard for HDTV in the early 1990s. It was agreed that all film transmission by HDTV would be broadcast with progressive scan in the United States.[4] Even if a signal is sent interlaced, an HDTV will convert it to progressive scan.[5]
Usage in TVs, video projectors, and monitors
[edit]Progressive scan is used for all LCD computer monitors and most HDTVs. Most cathode-ray tube (CRT) computer monitors and CRT-type displays, such as SDTVs, needed to use interlace to achieve full vertical resolution, but could display progressive video at the cost of halving the vertical resolution. Before HDTV became common, some televisions and video projectors were produced with one or more full-resolution progressive-scan inputs, allowing these displays to take advantage of formats like PALPlus, progressive scan DVD players, and certain video game consoles. Early HDTVs supported the progressively-scanned resolutions of 480p and 720p with 1080p displays available at higher cost. At the debut of UHD, TVs had emerged on the consumer market in the 2010s, also using progressive resolutions, but usually sold with prohibitive prices[6] (4K HDTVs) or were still in prototype stage (8K HDTVs).[7] Prices for consumer-grade 4K HDTVs have since lowered and become more affordable, which has increased their prevalence amongst consumers. Computer monitors can use even greater display resolutions.
The disadvantage of progressive scan is that it requires higher bandwidth than interlaced video that has the same frame size and vertical refresh rate. Because of this 1080p is not used for broadcast.[8][obsolete source] For explanations of why interlacing was originally used, see interlaced video. For an in-depth explanation of the fundamentals and advantages/disadvantages of converting interlaced video to a progressive format, see deinterlacing.
Advantages
[edit]The main advantage with progressive scan is that motion appears smoother and more realistic.[9] There is an absence of visual artifacts associated with interlaced video of the same line rate, such as interline twitter. Frames have no interlace artifacts and can be captured for use as still photos. With progressive scan there is no need to introduce intentional blurring (sometimes referred to as anti-aliasing) to reduce interline twitter and eye strain.
In the case of most media, such as DVD movies and video games, the video is blurred during the authoring process itself to subdue interline twitter when played back on interlaced displays. As a consequence, recovering the sharpness of the original video is impossible when the video is viewed progressively. A user-intuitive solution to this is when display hardware and video games come equipped with options to blur the video at will, or to keep it at its original sharpness. This allows the viewer to achieve the desired image sharpness with both interlaced and progressive displays.
Progressive scan also offers clearer and faster results for scaling to higher resolutions than its equivalent interlaced video, such as upconverting 480p to display on a 1080p HDTV. HDTVs not based on CRT technology cannot natively display interlaced video, therefore interlaced video must be deinterlaced before it is scaled and displayed. Deinterlacing can result in noticeable visual artifacts and/or input lag between the video source and the display device.
See also
[edit]- 1440p
- Deinterlacing
- High Efficiency Video Coding
- Progressive segmented frame: a scheme designed to acquire, store, modify, and distribute progressive-scan video using interlaced equipment and media
References
[edit]- ^ "Interlacing". Luke's Video Guide. Archived from the original on 2014-02-22. Retrieved February 12, 2014.
- ^ Burns, R.W. John Logie Baird, Television Pioneer, Herts: The Institution of Electrical Engineers, 2000. 316.
- ^ Poynton, Charles A. (2003). Digital Video and Hdtv: Algorithms and Interfaces. Morgan Kaufmann. p. 56. ISBN 1558607927. Retrieved 27 January 2013.
- ^ Abramson, Albert; Christopher H. Sterling (2007). The History of Television, 1942 To 2000. McFarland. p. 245. ISBN 978-0786432431. Retrieved 27 January 2013.
- ^ Hurley, Danny Briere (2008). Home Theater For Dummies. John Wiley & Sons. p. 200. ISBN 978-0470444375. Retrieved 27 January 2013.
- ^ 4k resolution wikipedia page, that includes a table of 4k display devices with their corresponding prices. Retrieved 29 May 2013.
- ^ Sharp 8k TV launch, Displayed at CES 2013, the Sharp 8k UHD TV. Retrieved 29 May 2013.
- ^ Zettl, Herbert (2011). Television Production Handbook. Cengage Learning. p. 94. ISBN 978-0495898849. Retrieved 27 January 2013.
- ^ Andrews, Dale (2011). Digital Overdrive: Communications & Multimedia Technology 2011. Digital Overdrive. p. 24. ISBN 978-1897507018. Retrieved 27 January 2013.
Progressive scan
View on GrokipediaFundamentals
Definition and Principles
Progressive scan is a video imaging technique that captures, stores, transmits, or displays each frame by sequentially scanning all horizontal lines from top to bottom in a single continuous pass, thereby constructing a complete image without dividing it into separate fields.[8] This method ensures that the full vertical resolution is rendered progressively, providing a cohesive frame that avoids the temporal offset inherent in other scanning approaches.[9] At its core, progressive scan operates on the principle of raster scanning, where an electron beam in traditional cathode-ray tube (CRT) displays or equivalent signal in digital systems sweeps horizontally across each line, modulating intensity to represent pixel brightness, before advancing to the next line in sequence.[8] Each frame comprises the entire set of lines—such as 480 or 720—delivered in full without field separation, enabling higher temporal and spatial fidelity compared to field-based methods like interlaced scanning.[9] This frame-based approach aligns well with both legacy CRT raster principles and contemporary flat-panel displays, which inherently process images progressively.[8] The notation for progressive scan formats uses a lowercase "p" to indicate the progressive nature, as in 480p (denoting 480 progressive lines per frame) or 720p (720 progressive lines), distinguishing it from interlaced formats marked by "i."[8] This convention, standardized in digital video interfaces, emphasizes the complete vertical resolution achieved in one scan.[9] Visually, a progressive frame is built by drawing line 1 at the top, followed immediately by line 2, and continuing downward to line N at the bottom, forming the image in a unified sweep that minimizes artifacts and supports smooth motion portrayal. For illustration, this sequential process can be outlined as:Line 1: ---------------- (top of frame)
Line 2: ----------------
...
Line N: ---------------- (bottom of frame)
This linear progression ensures the entire frame is complete before the next one begins.[8]
Comparison to Interlaced Scanning
Interlaced scanning operates by alternately capturing and displaying odd-numbered lines (field 1) followed by even-numbered lines (field 2) to form a complete frame, which halves the vertical resolution per field and reduces bandwidth requirements compared to progressive scanning while doubling the field rate to mitigate flicker on cathode-ray tube (CRT) displays.[10] This approach was designed to balance spatial detail with temporal update rates in bandwidth-constrained analog systems.[11] In comparison, progressive scanning transmits and displays all lines of a frame sequentially from top to bottom, delivering the full vertical resolution in every frame for consistent spatial detail and smoother motion rendering, especially in dynamic scenes where interlaced fields can misalign.[12] Progressive formats, such as 1080p, provide better separation of spatial and temporal information, avoiding the half-resolution limitation of interlaced fields like 1080i, which can lead to perceived judder during fast motion due to the temporal offset between fields.[10] Progressive scanning eliminates interlaced-specific artifacts, including combing—jagged, tooth-like edges on moving objects caused by combining temporally displaced fields—and interline twitter, a shimmering effect on fine horizontal edges or patterns.[10] Line flicker and edge crawling, which occur in interlaced signals on progressive displays without proper processing, are also absent in progressive formats, resulting in higher vertical resolution and no flashing between lines during motion.[13] Interlaced scanning, however, remains advantageous in bandwidth-limited environments like traditional broadcasting, where it achieves effective flicker reduction without doubling the data rate—progressive requires approximately twice the bandwidth for equivalent frame rates.[12] Perceptually, progressive scanning excels in applications requiring fluid motion, such as computer-generated graphics or film-originated content, by maintaining full resolution throughout the frame sequence and reducing motion blur.[14] Interlaced scanning, optimized for CRT-based television, prioritizes flicker suppression in static areas but introduces judder and resolution loss in high-motion scenarios, making it less ideal for modern progressive displays.[10] To bridge these formats, deinterlacing techniques convert interlaced signals to progressive by methods such as weaving (spatially merging adjacent fields, prone to combing in motion) or bobbing (temporally repeating fields to form frames, avoiding artifacts but potentially reducing smoothness).[15] These conversions, while essential for compatibility, can introduce compromises if motion detection is inadequate, underscoring progressive's native superiority for artifact-free playback.[16]Technical Aspects
Scanning Process and Signal Generation
In progressive scan systems, image capture begins at the source, such as a video camera, where sensors acquire a complete frame of the image in a single, sequential pass from top to bottom, without dividing the frame into separate fields.[17] This full-frame acquisition contrasts with interlaced scanning, which alternates between odd and even lines across two fields. The scanning process involves several key steps to generate the signal. First, the captured frame is processed into a raster format, where pixels are read out line by line. Horizontal synchronization pulses (H-sync) are then inserted at the end of each line to define the timing for the start of the next line, ensuring precise alignment across the frame.[8] Vertical synchronization pulses (V-sync) mark the conclusion of the full frame, signaling the return to the top for the next frame. The pixel clock rate governs the horizontal resolution by determining how many pixels are sampled per line, typically operating at frequencies like 25.175 MHz for standard 640x480p formats.[18] Finally, the frame rate, such as 24p or 60p, sets the vertical refresh interval, with the entire frame refreshed progressively at that rate.[19] In analog progressive signals, such as those using YPbPr component video, synchronization is achieved through sync pulses embedded on the luminance (Y) channel or provided separately, without distinct field sync pulses since the signal represents a single frame rather than alternating fields.[20] Blanking intervals—horizontal periods during line retrace and vertical periods during frame retrace—suppress the video signal to prevent visible flyback artifacts, allowing time for synchronization.[8] In digital pipelines, like HDMI, the progressive format is explicitly flagged using the Auxiliary Video Information (AVI) InfoFrame in the CEA-861 standard, where Video Identification Codes (e.g., VIC 1 for 640x480p) and a non-interlaced bit in the EDID timing descriptors indicate the sequential full-frame structure.[18] Progressive scanning inherently avoids field mismatches by transmitting the complete frame as a unified entity, eliminating the risk of odd-even line discrepancies that can arise from timing errors in interlaced systems; blanking intervals further support reliable synchronization by providing stable periods for receiver lock-in.[8]Resolution, Frame Rates, and Bandwidth Requirements
Progressive scan video resolutions are defined by the number of horizontal pixels and vertical lines, with common formats including 720 × 480 for 480p, 1280 × 720 for 720p, and 1920 × 1080 for 1080p, where the total pixels per frame equal the product of horizontal and vertical dimensions, such as 2,073,600 pixels for 1080p.[21][22] These metrics stem from standards like SMPTE ST 274 for 1080p and SMPTE ST 296 for 720p, ensuring compatibility in digital video systems. Frame rates in progressive scan denote the number of complete frames per second, with 24p commonly used in cinema for a film-like aesthetic, 30p standard for NTSC broadcast video, and 60p for smoother motion rendering in gaming or sports content.[23] The choice of frame rate relates to shutter speed via the 180-degree rule, where shutter speed approximates 1/(2 × frame rate)—such as 1/48 second for 24p—to balance motion blur and natural movement without excessive sharpness or strobing.[24] Bandwidth requirements for progressive scan are calculated as bitrate (in bits per second) = horizontal pixels × vertical lines × frame rate × bit depth per pixel, often adjusted for chroma subsampling in YUV formats; for uncompressed 8-bit RGB (24 bits per pixel), this yields approximately 3 Gbps for 1080p at 60 fps (1920 × 1080 × 60 × 24 bits).[25] Higher resolutions like 4K (3840 × 2160) quadruple the pixel count compared to 1080p, escalating uncompressed bandwidth to around 12 Gbps at 60 fps, while elevated frame rates further amplify demands by linearly scaling data throughput.[25] Compression standards such as H.264 (ITU-T H.264) address these trade-offs by achieving significant bitrate reductions—typically 4.5–9 Mbps for high-quality 1080p60 video—enabling practical transmission and storage without proportional resource increases.[26][27] This mitigation is crucial for applications where raw bandwidth exceeds network or media capacities, prioritizing efficiency in progressive formats over interlaced alternatives that inherently halve field transmission rates.[26]| Format | Resolution (Pixels) | Common Frame Rates | Uncompressed Bitrate Example (8-bit RGB, 60 fps) |
|---|---|---|---|
| 480p | 720 × 480 | 30p, 60p | ~0.5 Gbps |
| 720p | 1280 × 720 | 24p, 60p | ~1.3 Gbps |
| 1080p | 1920 × 1080 | 24p, 30p, 60p | ~3 Gbps |
| 4K | 3840 × 2160 | 24p, 60p | ~12 Gbps |