Raw image format

This article is about a digital photography topic. For storage virtualization topic, see IMG (file format).
".srf" redirects here. For the ATL file type, see ATL Server § SRF files.
"Camera raw" redirects here. It is not to be confused with Adobe Camera Raw.

Raw image file
Filename extension .3fr,
.ari, .arw,
.crw, .cr2,
.data, .dcs, .dcr, .dng,
.eip, .erf,
.k25, .kdc,
.mdc, .mef, .mos, .mrw,
.nef, .nrw,
.obm, .orf,
.pef, .ptx, .pxn,
.r3d, .raf, .raw, .rwl, .rw2, .rwz,
.sr2, .srf, .srw,
Type of format Image file formats

A camera raw image file contains minimally processed data from the image sensor of either a digital camera, image scanner, or motion picture film scanner.[1][2] Raw files are named so because they are not yet processed and therefore are not ready to be printed or edited with a bitmap graphics editor. Normally, the image is processed by a raw converter in a wide-gamut internal colorspace where precise adjustments can be made before conversion to a "positive" file format such as TIFF or JPEG for storage, printing, or further manipulation. This often encodes the image in a device-dependent colorspace. There are dozens, if not hundreds, of raw formats in use by different models of digital equipment (like cameras or film scanners).[3]


Raw image files are sometimes called digital negatives, as they fulfill the same role as negatives in film photography: that is, the negative is not directly usable as an image, but has all of the information needed to create an image. Likewise, the process of converting a raw image file into a viewable format is sometimes called developing a raw image, by analogy with the film development process used to convert photographic film into viewable prints. The selection of the final choice of image rendering is part of the process of white balancing and color grading.

Like a photographic negative, a raw digital image may have a wider dynamic range or color gamut than the eventual final image format, and it preserves most of the information of the captured image. The purpose of raw image formats is to save, with minimum loss of information, data obtained from the sensor, and the conditions surrounding the capturing of the image (the metadata).

Raw image formats are intended to capture as closely as possible (i.e. at the best of the specific sensor's performance) the radiometric characteristics of the scene, that is, physical information about the light intensity and color of the scene.

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".

File contents

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), CR2 (Canon), ERF (Epson), MEF (Mamiya), MOS (Leaf), NEF (Nikon), ORF (Olympus), PEF (Pentax), RW2 (Panasonic) and ARW, SRF, SR2 (Sony), are based on the TIFF file format.[4] 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 tagged data.

Panasonic's raw converter corrects geometric distortion and chromatic aberration on such cameras as the LX3,[5][6][7] with necessary correction information presumably included in the raw.[8] Phase One's raw converter Capture One also offers corrections for geometrical distortion, chromatic aberration, purple fringing and keystone correction emulating the shift capability of tilt-shift in software and specially designed hardware, on most raw files from over 100 different cameras.[9][10] The same holds for Canon's DPP application, at least for all more expensive cameras like all EOS DSLRs and the G<n> series of compact cameras.

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/or standards, including Exif metadata, XMP metadata, IPTC metadata, CIE XYZ coordinates, ICC profiles, and JPEG.[11]

Sensor image data

In digital photography, the raw file plays the role that photographic film plays in film photography. Raw files thus contain the full resolution (typically 12- or 14-bit) data as read out from each of the camera's image sensor pixels.

The camera's sensor is almost invariably overlaid with a color filter array (CFA), usually a Bayer filter, consisting of a mosaic of a 2x2 matrix of red, green, blue and (second) green filters.

One variation on the Bayer filter is the RGBE filter of the Sony Cyber-shot DSC-F828, which exchanged the green in the RG rows with "emerald"[12] (a blue-green[13] or cyan[14] color). Other sensors, such as the Foveon X3 sensor, capture information directly in RGB form (using three pixel sensors in each location). These RGB raw data still need to be processed to make an image file, because the raw RGB values correspond to the responses of the sensors, not to a standard color space like sRGB. These data do not need to be demosaiced, however.

Flatbed and film scanner sensors are typically straight narrow RGB or RGBI (where "I" stands for the additional infra-red channel for automatic dust removal) strips that are swept across an image. The HDRi raw data format is able to store the infrared raw data, which can be used for infrared cleaning, as an additional 16-bit channel. The remainder of the discussion about raw files applies to them as well. (Some scanners do not allow the host system access to the raw data at all, as a speed compromise. The raw data are processed very rapidly inside the scanner to select out the best part of the available dynamic range so only the result is passed to the computer for permanent storage, reducing the amount of data transferred and therefore the bandwidth requirement for any given speed of image throughput.)

To obtain an image from a raw file, this mosaic of data must be converted into standard RGB form. This is often referred to as "raw development".

When converting from the four-sensor 2x2 Bayer-matrix raw form into RGB pixels, the green pair is used to control the luminance detail of the processed output pixel, while the red and blue, which each have half as many samples, are used mostly for the more slowly-varying chroma component of the image.

If raw format data is available, it can be used in high-dynamic-range imaging conversion, as a simpler alternative to the multi-exposure HDI approach of capturing three separate images, one underexposed, one correct and one overexposed, and "overlaying" one on top of the other.


Providing a detailed and concise description of the content of raw files is highly problematic. There is no single raw format; formats can be similar or radically different. Different manufacturers use their own proprietary and typically undocumented formats, which are collectively known as raw format. Often they also change the format from one camera model to the next. Several major camera manufacturers, including Nikon, Canon and Sony, encrypt portions of the file in an attempt to prevent third-party tools from accessing them.[15]

This industry-wide situation of inconsistent formatting has concerned many photographers who worry that their valuable raw photos may someday become inaccessible, as computer operating systems and software programs become obsolete and abandoned raw formats are dropped from new software. The availability of high-quality open source software which decodes raw image formats, particularly dcraw, has helped to alleviate these concerns. An essay by Michael Reichmann and Juergen Specht stated "here are two solutions – the adoption by the camera industry of A: Public documentation of RAW formats; past, present and future, or, more likely B: Adoption of a universal RAW format".[16][17][18] "Planning for [US] Library of Congress Collections" identifies raw-file formats as "less desirable file formats", and identifies DNG as a suggested alternative.[19]

DNG is the only raw image format for which industry-wide buy-in is being sought. It is based upon, and compatible with, the ISO standard raw image format ISO 12234-2, TIFF/EP, and is being used by ISO in their revision of that standard.

The ISO standard raw image format is ISO 12234-2, better known as TIFF/EP. (TIFF/EP also supports "non-raw", or "processed", images). TIFF/EP provided a basis for the raw image formats of a number of cameras. For example, Nikon's NEF raw files are based on TIFF/EP, and include a tag which identifies the version of TIFF/EP they are based on.[20] Adobe's DNG raw file format was based on TIFF/EP, and the DNG specification states "DNG ... is compatible with the TIFF-EP standard".[21] Several cameras use DNG as their raw image format, so in that limited sense they use TIFF/EP too.[22]

Adobe Systems launched this DNG raw image format in September 2004. By September 2006, several camera manufacturers had started to announce support for DNG in newer camera models, including Leica, Samsung, Ricoh, Pentax, Hasselblad (native camera support); and, Better Light (export).[23] The Leica Digital-Modul-R (DMR) was first to use DNG as its native format.[24] In September 2009 Adobe stated that there were no known intellectual property encumbrances or license requirements for DNG.[25] (There is a "Digital Negative (DNG) Specification Patent License",[26] but it does not actually state that there are any patents held on DNG, and the September 2009 statement was made at least 4 years after this license was published).

TIFF/EP began its 5-year revision cycle in 2006.[27] Adobe offered the DNG specification to ISO to be part of ISO's revised TIFF/EP standard.[28][29] A progress report in October 2008 from ISO about the revision of TIFF/EP stated that the revision "... currently includes two "interoperability-profiles," "IP 1" for processed image data, using ".TIF" extension, and "IP 2" for "raw" image data, ".DNG" extension".[30] It is "IP 2" that is relevant here. A progress report in September 2009 states that "This format will be similar to DNG 1.3, which serves as the starting point for development."[31]

DNG has been used by open-source developers.[15] Use by camera makers varies: the largest companies such as Canon, Nikon, Sony, and some others, do not use DNG. Smaller companies and makers of "niche" cameras who might otherwise have difficulty getting support from software companies frequently use DNG as their native raw image format. Pentax uses DNG as an optional alternative to their own raw image format. There are 15 or more such companies, even including a few that specialize in movie cameras.[22] In addition, most Canon point & shoot cameras can support DNG by using CHDK.


To be viewed or printed, the output from a camera's image sensor has to be processed, that is, converted to a photographic rendering of the scene, and then stored in a standard raster graphics format such as JPEG. This processing, whether done in-camera or later in a raw-file converter, involves a number of operations, typically including:[32][33]

Note that demosaicing is only performed for CFA sensors; it is not required for 3CCD or Foveon X3 sensors.

Cameras and image processing software may also perform additional processing to improve image quality, for example:

When a camera saves a raw file it defers most of this processing; typically the only processing performed is the removal of defective pixels (the DNG specification requires that defective pixels are removed before creating the file[38]). Some camera manufacturers do additional processing before saving raw files; for example, Nikon has been criticized by astrophotographers for applying noise reduction before saving the raw file.[39]

Some raw formats also allow nonlinear quantization.[40][41] This nonlinearity allows the compression of the raw data without visible degradation of the image by removing invisible and irrelevant information from the image. Although noise is discarded this has nothing to do with (visible) noise reduction.


Nearly all digital cameras can process the image from the sensor into a JPEG file using settings for white balance, colour saturation, contrast, and sharpness that are either selected automatically or entered by the photographer before taking the picture. Cameras that produce raw files save these settings in the file, but defer the processing. This results in an extra step for the photographer, so raw is normally only used when additional computer processing is intended. However, raw has numerous advantages over JPEG such as:


Software support

Cameras that support raw files typically come with proprietary software for conversion of their raw image data into standard RGB images. Other processing and conversion programs and plugins are available from vendors that have either licensed the technology from the camera manufacturer or reverse-engineered the particular raw format and provided their own processing algorithms.

Operating system support

Apple Mac OS X and iOS

In January 2005, Apple released iPhoto 5, which offered basic support for viewing and editing many raw file formats.

In April 2005, Apple's OS X 10.4 brought raw support to the operating system's ImageIO framework, enabling raw support automatically in the majority of OS X applications both from Apple (such as Preview, OS X's PDF and image viewing application, and Aperture, a photo post-production software package for professionals) as well as all third party applications which make use of the ImageIO frameworks.

Semi-regular updates to OS X generally include updated support for new raw formats introduced in the intervening months by camera manufacturers.

In 2016, Apple announced that iOS 10 would allow capturing raw images on selected hardware, and third party applications will be able to edit raw images through the operating system's Core Image framework.[46]

Microsoft Windows

Windows Camera Codec Pack

Microsoft supplies the free Windows Camera Codec Pack for Windows XP and later versions of Windows, to integrate raw file viewing and printing into some Windows tools.[47] The codecs allow native viewing of raw files from a variety of specific cameras in Windows Explorer / File Explorer and Windows Live Photo Gallery / Windows Photo Gallery, in Windows Vista and Windows 7.[48] As of October 2016, Microsoft had not released an updated version since April 2014, which supported some specific cameras by the following manufacturers: Canon, Casio, Epson, Fujifilm, Kodak, Konica Minolta, Leica, Nikon, Olympus, Panasonic, Pentax, Samsung, and Sony.[48]

Windows Imaging Component (WIC)

Windows supports the Windows Imaging Component (WIC) codec standard. WIC was available as a stand-alone downloadable program for Windows XP Service Pack 2, and built into Windows XP Service Pack 3, Windows Vista, and later versions. Windows Explorer / File Explorer, and Windows Live Photo Gallery / Windows Photo Gallery can view raw formats for which the necessary WIC codecs are installed. Canon, Nikon, Sony, Olympus and Pentax have released WIC codecs for their cameras, although some manufactures are only providing codec support for the 32-bit versions of Vista.[49]

Commercial DNG WIC codecs are also available from Ardfry Imaging,[50] and others; and FastPictureViewer Professional installs a set of WIC-enabled image decoders.[51][52]


Android Lollipop 5.0, introduced in late 2014, can allow smartphones to take RAW images, useful in low-light situations.[53]

Free and open source software

Proprietary software

In addition to those listed under operating system support, above, the commercial software described below support raw formats.

Dedicated raw converters

The following products were launched as RAW processing software to process a wide range of raw files, and have this as their main purpose:


HTML5 browser-based apps

A new class of raw file processing tools appeared with the development of HTML5 - rich Internet applications.

Raw filename extensions and respective camera manufacturers

See also


  1. http://www.luminous-landscape.com/tutorials/understanding-series/u-raw-files.shtml
  2. "Camera Raw Formats". Digital Preservation. Library of Congress. 2006-10-04. Retrieved 2014-03-11.
  3. Decoding raw digital photos in Linux
  4. "Exif Tool, Supported File Types".
  5. The Online Photographer: Panasonic LX3 Barrel Distortion Controversy
  6. Panasonic LX3 Lens Distortion
  7. "Panasonic LX3 Lens Distortion". Seriouscompacts.com. Retrieved 2011-12-11.
  8. Panasonic Lumix LX7 Review - Imaging Resource
  9. "Review: Capture One 6 Pro". IT Enquirer. Retrieved 5 October 2011.
  10. "Phase One Capture One 6 Pro Review". ePhotoZine. Retrieved 5 October 2011.
  11. Adobe: DNG Specification
  12. "Sony 4 colour (RGB-E) filter on DSC-F828 sensor".
  13. "Sony Japan announces new RGB+E image sensors". imaging-resource.com. July 16, 2003.
  14. "Sony announce new RGBE CCD". dpreview.com. 15 July 2003.
  15. 1 2 "Raw storm in a teacup?". Dpreview.com. 2005-04-27. Retrieved 2007-12-09. Dave Coffin, creator of the dcraw program, discusses some of his successful reverse-engineering in this interview, and mentions his enthusiasm for the DNG format.
  16. Reichmann, Michael; Specht, Juergen (May 2005). "The RAW Flaw (at The Luminous Landscape)".
  17. Reichmann, Michael; Specht, Juergen (May 2005). "The RAW Flaw (at The Luminous Landscape)" (DOC).
  18. Reichmann, Michael; Specht, Juergen (May 2005). "The RAW Flaw (at The Luminous Landscape)" (PDF).
  19. Planning for US Library of Congress Collections: Preferences in Summary
  20. Barry Pearson: What is in a raw file?
  21. Adobe: DNG Specification (June 2009) (scroll down a bit)
  22. 1 2 Barry Pearson: Products from Camera Manufacturers that use DNG in some way
  23. Barry Pearson: DNG support, to end-September 2006
  24. Barry Pearson: A brief history of DNG
  25. Adobe Labs: CinemaDNG (final bullet point)
  26. Adobe: Digital Negative (DNG) Specification Patent License
  27. I3A (International Imaging Industry Association): WG18, Ad Hoc groups and JWG 20/22/23 Meet in Tokyo
  28. Web archive of widely distributed email: Forwarded Message from a member of the ISO TC42 (technical committee for photography) working group 18 (electronic imaging) standards group
  29. DPReview: Adobe seeks International recognition for DNG
  30. I3A (International Imaging Industry Association): ISO 12234 Part 2 – TIFF/EP (scroll down a bit)
  31. NPES: Minutes of ISO/TC 130/WG2, 39th Meeting, see 14f
  32. R. Ramanath; W.E. Snyder; Y. Yoo; M.S. Drew. "Color Image Processing Pipeline in Digital Still Cameras" (PDF).
  33. Keigo Hirakawa. "Color Imaging Pipeline for Digital Still & Video Cameras Part 1: Pipeline and Color Processing" (PDF).
  34. Understanding What is stored in a Canon RAW .CR2 file, How and Why
  35. Ron Day. Understanding & Using the RAW File Format
  36. Nanette Salvaggio (2008). Basic Photographic Materials and Processes (3rd ed.). Focal Press. p. 206. ISBN 978-0-240-80984-7.
  37. William E. Kasdorf (2003). The Columbia guide to digital publishing. Columbia University Press. p. 270. ISBN 978-0-231-12499-7.
  38. "Digital Negative (DNG) Specification" (PDF): 14.
  39. "Comparative test: Canon 10D / Nikon D70 in the field of deep-sky astronomy".
  40. 1 2 "Digital Negative (DNG) Specification" (PDF): 61.
  41. 1 2 "Is the Nikon D70 NEF (RAW) format truly lossless?".
  42. "Understanding Camera Raw".
  43. http://www.rawdigger.com/howtouse/sony-craw-arw2-posterization-detection
  44. Kevin Carter (March 3, 2014). "RED Epic Dragon review: First camera to break the 100-point DxOMark sensor score barrier".
  45. Larry Strunk (2006-03-19). "The RAW Problem". OpenRAW.
  46. "Advances in iOS Photography". Apple. 14 June 2016. Retrieved 16 June 2016.
  47. Microsoft RAW Image Thumbnailer and Viewer for Windows XP
  48. 1 2 "Windows Camera Codec Pack". Microsoft. 2014-04-22. Retrieved 2015-02-18.
  49. Understanding RAW Image Support in Windows Vista: Windows Vista team blog
  50. DNG Thumbnail and Preview Support for Windows Photo Gallery and Windows Live Photo Gallery
  51. FastPictureViewer's Image Formats Compatibility Chart
  52. FastPictureViewer 32/64-bit raw codec pack for Windows
  53. Paul Monckton. "Android 5.0 Camera Tests Show Update Instantly Improves Every Smartphone". Retrieved December 27, 2014.
  54. "Libraw".
  55. "AZImage".
  56. "ImageMagick Image Formats".
  57. The LightZombie Project - About
  58. "Capture One".
  59. "ACDSystems Supported RAW Formats".
  60. ideaMK: DNG Viewer
  61. http://www.fastrawviewer.com/usermanual/supported-cameras
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