Raw image format

A camera raw image file is a file that contains unprocessed data straight from a digital camera. Such data can later be changed into a photo, either within a digital camera itself or by usage of external tools. Raw files are so named because they are not yet processed, and contain large amounts of potentially redundant data. Normally, the image is processed by a raw converter, in a wide-gamut internal color space where precise adjustments can be made before conversion to a viewable photos for storage, printing, or further manipulation. There are dozens of raw formats in use by different manufacturers of digital image capture equipment.

Raw image files are sometimes described as "digital negatives". Like transparency film and unlike negative film, raw image pixels contain positive exposure measurements. The raw datasets are more like undeveloped film: a raw image can be developed by software in a non-reversible manner to reach a complete image that resolves every pixel in an RGB or other viewable color space. Raw development adjustments include color, contrast, brightness and details recovery. A given raw dataset can be developed many times with different adjustments.

In contrast, developing an exposed film transforms it irreversibly; thus, development cannot be repeated on the same exposed film. If the film is negative, the printing process must invert the image to a positive result.

Like negative photographic film, a raw digital image may have a wider dynamic range or color gamut than the positive print. Unlike physical film after development, the Raw file preserves the information captured at the time of exposure. The purpose of raw image formats is to save, with minimum loss of information, data obtained from the sensor.

Raw image formats are intended to capture the radiometric characteristics of the scene, that is, physical information about the light intensity and color of the scene, at the best of the camera sensor's performance. Most raw image file formats store information sensed according to the geometry of the sensor's individual photo-receptive elements (sometimes called pixels) rather than points in the expected final image: sensors with hexagonal element displacement, for example, record information for each of their hexagonally displaced cells, which a decoding software will eventually transform into the rectangular geometry during "digital developing".

Raw files contain the information required to produce a viewable image from the camera's sensor data. The structure of raw files often follows a common pattern:

Many raw file formats, including IIQ (Phase One), 3FR (Hasselblad), DCR, K25, KDC (Kodak), CRW, CR2 (Canon), ERF (Epson), MEF (Mamiya), MOS (Leaf), NEF NRW (Nikon), ORF (Olympus), PEF (Pentax), RW2 (Panasonic) and ARW, SRF, SR2 (Sony), are based on TIFF, the Tag Image File Format. These files may deviate from the TIFF standard in a number of ways, including the use of a non-standard file header, the inclusion of additional image tags and the encryption of some of the tag data.

DNG, the Adobe digital negative format, is an extension of the TIFF 6.0 format and is compatible with TIFF/EP, and uses various open formats and standards, including Exif metadata, XMP metadata, IPTC metadata, CIE XYZ coordinates, ICC profiles, and JPEG.