Digital Negative

For the informal use of "digital negative", see Raw image format.
Digital Negative (DNG)
Filename extension .dng
Developed by Adobe Systems
Initial release September 27, 2004 (2004-09-27)
Latest release
1.4.0.0
(September 2012 (2012-09))
Type of format raw image format
Container for Metadata may be embedded in XMP, Exif or IPTC formats.
Extended from TIFF/EP
Open format? Yes
Website helpx.adobe.com/photoshop/digital-negative.html

Digital Negative (DNG) is a patented, open, non-free lossless raw image format written by Adobe used for digital photography. It was launched on September 27, 2004.[1] The launch was accompanied by the first version of the DNG specification,[2] plus various products, including a free-of-charge DNG converter utility. All Adobe photo manipulation software (such as Adobe Photoshop and Adobe Lightroom) released since the launch supports DNG.[3]

DNG is based on the TIFF/EP standard format, and mandates significant use of metadata. Use of the file format is royalty-free; Adobe has published a license allowing anyone to exploit DNG,[4] and has also stated that there are no known intellectual property encumbrances or license requirements for DNG.[5] Adobe stated that if there were a consensus that DNG should be controlled by a standards body, they were open to the idea.[6] Adobe has submitted DNG to ISO for incorporation into their revision of TIFF/EP.[7]

Rationale for DNG

Given the existence of other raw image formats, Adobe's creation of DNG as a competing format implies that DNG is unusual and satisfies objectives that other raw image formats do not. These objectives and the associated characteristics of DNG, as well as assessments of whether these objectives are met, are described below. Increasingly, professional archivists and conservationists, working for respectable organizations, variously suggest or recommend DNG for archival purposes.[8][9][10][11][12][13][14][15][16]

Objectives

These objectives are repeatedly emphasized in Adobe documents:[1][6][17][18]

Characteristics

All of the above objectives are facilitated or enabled by most of these characteristics:[25]

Technical summary

A DNG file always contains data for one main image, plus metadata, and optionally contains at least one JPEG preview.[2] It normally has the extension "dng" or "DNG".

DNG conforms to TIFF/EP and is structured according to TIFF. DNG supports various formats of metadata, (including Exif metadata, XMP metadata, IPTC metadata), and specifies a set of mandated metadata.[28]

DNG is both a raw image format and a format that supports "non-raw", or partly processed, images.[2] The latter (non-raw) format is known as "Linear DNG".[33] Linear DNG is still scene-referred[34] and can still benefit from many of the operations typically performed by a raw converter, such as white balance, the application of a camera color profile, HDR compositing, etc. All images that can be supported as raw images can also be supported as Linear DNG. Images from the Foveon X3 sensor or similar, hence especially Sigma cameras, can only be supported as Linear DNG.

DNG can contain raw image data from sensors with various configurations of color filter array (CFA). These include: conventional Bayer filters, using three colors and rectangular pixels; four-color CFAs, for example the RGBE filter used in the Sony Cyber-shot DSC-F828; rectangular (non-square) pixels, for example as used in the Nikon D1X; and offset sensors (for example with octagonal pixels) such as Super CCD sensors of various types, as used in various Fujifilm cameras. (Or combinations of these if necessary). DNG specifies metadata describing these individual parameters; this is one significant extension to TIFF/EP.

When used in a CinemaDNG movie clip, each frame is encoded using the above DNG image format. The clip's image stream can then be stored in one of two formats: either as video essence using frame-based wrapping in an MXF file, or as a sequence of DNG files in a specified file directory.

Contrary to its name (Digital Negative) the DNG format doesn't distinguish negative and positive data[35] - all data is considered to be describing a positive image. While this is not an issue when working with images from digital cameras (which are always positive), working with scanned (by a film scanner or DSLR copy stand) film negatives saved as raw DNG files is complicated, because the resulted image is not automatically inverted and thus impossible to be used directly. A way to get around this is using an inverted curve in the photo editing application, however this reverses the effect of the image controls (Exposure, Shadow and Highlight details, etc) which complicates the photo editing.

Timeline

This provides a mixture of the dates of significant events (such as "the first X") and various counts of usage at the anniversaries of the launch (each 27 September).

Counts of products and companies that use DNG in some way are provided primarily for illustration. They are approximate, and include products that are no longer sold. The purpose is mainly to demonstrate that such products and companies exist, and to show trends. Convertible raw image formats (camera models whose raw images can be converted to DNG) only include official support by Adobe DNG converters; not unofficial support by Adobe products (sometimes reaching about 30), nor support by other DNG converters.[24]

During the first 5 years when about 38 camera models were launched that wrote DNG, Adobe software added support for about 21 Canon models, about 20 Nikon models, and about 22 Olympus models.

Reception

The reaction to DNG has been mixed.[24] A few camera manufacturers stated their intention to use DNG at launch. The first supported DNG about 9 months after launch. Several more niche and minority camera manufacturers added support after this (e.g. Leica). The largest camera manufacturers have apparently never indicated an intention to use DNG (e.g. Nikon and Canon).

Some software products supported DNG within 5 months of launch, with many more following. Some only support DNG from cameras writing DNG, or from cameras supported via native raw image formats.

OpenRAW was an advocacy and lobby group with the motto "Digital Image Preservation Through Open Documentation". They became opposed to DNG.

Some photographic competitions do not accept converted files, and some do not accept DNG.[42]

DNG conversion

"DNG conversion" refers to the process of generating a DNG file from a non-DNG image. (This is in contrast to "raw conversion", which typically refers to reading and processing a raw file, which might be a DNG file, and generating some other type of output from it). DNG conversion is one of the sources of DNG files, the other being direct output from cameras and digital backs.

Several software products are able to do DNG conversion. The original such product is Adobe DNG Converter or DNG Converter, a freely available stand-alone utility from Adobe.[17] Other Adobe products such as the ACR plugin to Photoshop or Lightroom can also generate DNG files from other image files.

Most DNG converters are supplied by companies other than Adobe. For example:

The process of DNG conversion involves extracting raw image data from the source file and assembling it according to the DNG specification into the required TIFF format. This optionally involves compressing it. Metadata as defined in the DNG specification is also put into that TIFF assembly. Some of this metadata is based on the characteristics of the camera, and especially of its sensor. Other metadata may be image-dependent or camera-setting dependent. So a DNG converter must have knowledge of the camera model concerned, and be able to process the source raw image file including key metadata. Optionally a JPEG preview is obtained and added. Finally, all of this is written as a DNG file.

DNG conversion typically leaves the original raw image file intact. For safety, many photographers retain the original raw image file on one medium while using the DNG file on another, enabling them to recover from a range of hardware, software, and human, failures and errors. For example, it has been reported in user forums that some versions of the Adobe DNG Converter don't preserve all the raw data from raw images from some camera models.[43][44]

Summary of products that support DNG in some way

This section summarizes other more comprehensive lists.[45][46]

Adobe products

All raw image file handling products from Adobe now support DNG.[3] Adobe DNG Converter was published by Adobe Systems on September 27, 2004. It converts different camera raw format files into the Digital Negative (DNG) standard. It also supports lossless data compression when converting. The program is free of charge. It can be downloaded at Adobe's site (for Microsoft Windows[47] and the Apple Macintosh[48]).

Digital cameras and related software

Use by camera manufacturers varies; there are about 15 camera manufacturers that use DNG, including a few that specialize in movie cameras:[23]

Some digital cameras that support DNG.:[23]

Some of the Canon cameras can shoot as DNG using additional free software CHDK.

Third-party software

Support by software suppliers varies; there are of the order of 200 software products that use DNG.[45][51]

The majority of raw handling software products support DNG. Most provide generic support, while a few support it only if it is output directly from a camera. The type of support varies considerably. There appear to be very few third party software products that process raw images but don't support DNG. This may reflect the difficulty of discovering all of those that do not.[52]

Versions of the specification

All versions of the specification remain valid, in the sense that DNG files conforming to old versions should still be read and processed by DNG readers capable of processing later versions. DNG has a version scheme built into it that allows the DNG specification, DNG writers, and DNG readers, to evolve at their own paces.[29] Each version of the specification describes its compatibility with previous versions.[2]

1.0.0.0, published September, 2004
This version accompanied the launch of DNG and related products. It was a rare, possibly unique, example of a raw image format specification published by its owner. It was adequate for representing typical images, but it had a few errors and deficiencies (specifically the lack of support of "masked pixels" and an inadvertent deviation from the JPEG specification) that required it soon to be replaced by the next version.
1.1.0.0, published February, 2005
This version corrected the flaws in the first version. It has proved capable of representing raw images for a large variety of cameras (both when written in-camera or via conversion from other raw image formats) for a few years, and it is the version still typically written in-camera.
1.2.0.0, published May 2008
This version was based on experience and feedback from other companies about DNG since its launch. It introduced many new features, especially several new options for color specification under the general heading of "Camera Profiles". These are mainly of value to software products wanting their own flavor of color handling. This version permits administrative control of Camera Profiles, including calibration signatures and copyright information.
1.3.0.0, published June, 2009
This version added various improvements, but the major change was to introduce "Opcodes". A Opcode is an algorithm to be applied to some or all of the image data, described in the specification, and (optionally) implemented in the product that reads and processes the DNG file. The DNG file itself holds lists of Opcodes to be executed, together with the parameters to be applied on execution. In effect, the DNG file can contain lists of "function calls" to be executed at various stages in the raw conversion process. For example, the WarpRectilinear Opcode "applies a warp to an image and can be used to correct geometric distortion and lateral (transverse) chromatic aberration for rectilinear lenses". This is an example of an algorithm that cannot be applied to the raw image data itself before it is placed into the DNG file, because it should be executed after demosaicing. There are 13 Opcodes described in this version, and each Opcode is accompanied by a specification version so that more can be added in future.
1.4.0.0, published Sept., 2012
This version added Floating Point Image Data, Transparent Pixels, Proxy DNG Files, and additional tags. It also added SampleFormat and Predictor.
CinemaDNG, published September 2009
CinemaDNG uses DNG for each frame of a movie clip. There are additional tags specifically for movies: TimeCodes and FrameRate.[53] It is not clear whether these tags will be added to a later version of the DNG specification, or will remain separately described only in the CinemaDNG specification.

Standardization

DNG is not (yet) a standard format, but is based on several open formats or standards and is being used by ISO in its revision of TIFF/EP. A timeline:

See also

References

  1. 1 2 3 "Adobe Unifies Raw Photo Formats with Introduction of Digital Negative Specification" (Press release). Adobe Systems. September 27, 2004.
  2. 1 2 3 4 5 6 7 8 9 "Specification" (PDF), DNG (PDF), Adobe.
  3. 1 2 Pearson, Barry, Adobe products that support DNG, UK.
  4. 1 2 "Specification Patent License", Digital Negative (DNG), Adobe.
  5. 1 2 "File Format", CinemaDNG, Adobe Labs.
  6. 1 2 3 4 "Adobe's Kevin Connor Speaks on Adobe's DNG Specification", Digital Media Designer (Digital Media net).
  7. 1 2 dpreview staff (May 15, 2008), "Adobe seeks International recognition for DNG", DPReview, retrieved December 11, 2014, Adobe is submitting its DNG 'universal RAW' format to the International Standard's Organization (ISO), in a move aimed at increasing acceptance and usage. The format is being proposed as part of ISO's TIFF/EP (electronic photography), standard..
  8. ↑ universal photographic digital imaging guidelines (UPDIG): File formats - the raw file issue
  9. ↑ Archaeology Data Service / Digital Antiquity: Guides to Good Practice - Section 3 Archiving Raster Images - File Formats
  10. ↑ University of Connecticut: "Raw as Archival Still Image Format: A Consideration" by Michael J. Bennett and F. Barry Wheeler
  11. ↑ Inter-University Consortium for Political and Social Research: Obsolescence - File Formats and Software
  12. ↑ JISC Digital Media - Still Images: Choosing a File Format for Digital Still Images - File formats for master archive
  13. ↑ International Digital Enterprise Alliance, Digital Image Submission Criteria (DISC) Guidelines & Specifications 2007 (PDF)
  14. ↑ The J. Paul Getty Museum - Department of Photographs: Rapid Capture Backlog Project - Presentation
  15. ↑ American Institute for Conservation - Electronic Media Group: Digital Image File Formats
  16. ↑ Archives Association of British Columbia: Born Digital Photographs: Acquisition and Preservation Strategies (Rosaleen Hill)
  17. 1 2 Adobe: Digital Negative (DNG) - The public, archival format for digital camera raw data
  18. ↑ Adobe: Introducing the Digital Negative Specification: Information for manufacturers
  19. ↑ Planning for US Library of Congress Collections: Sustainability Factors
  20. ↑ Planning for US Library of Congress Collections: Preferences in Summary
  21. ↑ dpBestflow: Raw File Formats
  22. 1 2 Barry Pearson: Support via DNG but not native raws
  23. 1 2 3 Barry Pearson: Products from Camera Manufacturers that support DNG in some way.
  24. 1 2 3 Barry Pearson: A brief history of DNG
  25. ↑ Planning for US Library of Congress Collections: Adobe Digital Negative (DNG), Version 1.1
  26. ↑ The Luminous Landscape: The RAW Flaw by Michael Reichmann and Juergen Specht
  27. 1 2 Barry Pearson: DNG's relationship to standards
  28. 1 2 Adobe: DNG Specification (Section 4)
  29. 1 2 Barry Pearson: Version control in DNG files
  30. ↑ Adobe: Adobe DNG Software Development Kit (SDK)
  31. ↑ Adobe
  32. ↑ Lossy DNG comparison
  33. ↑ Barry Pearson: Linear DNG
  34. ↑ CIE: "Scene-referred": image state, scene-referred
  35. ↑ http://www.adobe.com/content/dam/Adobe/en/products/photoshop/pdfs/dng_spec_1.4.0.0.pdf
  36. ↑ Seitz Phototechnik: Roundshot D3 with Seitz D3 digital scan back
  37. ↑ Seitz Phototechnik: Seitz 6x17 Digital with Seitz D3 digital scan back
  38. ↑ Ikonoskop: Ikonoskop A-cam dII
  39. ↑ Zeiss: PhotoScope 85 T* FL
  40. ↑ Ricoh: Ricoh GXR
  41. ↑ Ikonoskop: Ikonoskop A-cam3D
  42. ↑ Wadleigh, John (Oct 30, 2009). "Competition does not accept DNG". Retrieved 3 January 2015.
  43. ↑ Adobe-hosted User Forum: Reconvert with new DNG Converter?
  44. ↑ DPReview Forum: PROGRESS: version 0.9.0.0 now supports PEF files
  45. 1 2 Adobe: DNG hardware and software support
  46. ↑ Barry Pearson: Products that support DNG in some way
  47. ↑ "MS Windows product download", DNG converter, Adobe.
  48. ↑ "Apple Mac product download", DNG converter, Adobe.
  49. ↑ "Ricoh GXR", DPReview (quick review).
  50. ↑ Round shot, CH.
  51. ↑ Barry Pearson: Software products that support DNG in some way
  52. ↑ Barry Pearson: Products without explicit DNG support
  53. ↑ Adobe Labs: CinemaDNG - Image Data Format Specification (Version 1.0.0.0) (PDF)
  54. ↑ A member of the ISO TC42 (technical committee for photography) working group 18 (electronic imaging) standards group (26 April 2007), Digikam-devel (archive) (mailing list).
  55. ↑ "ISO 12234 Part 2 – TIFF/EP", Eye on standards (working group report) (I3A (International Imaging Industry Association)), October 2008, down a bit.
  56. ↑ Minutes of ISO/TC 130/WG2, 39th Meeting (PDF), Peking, China: NPES, September 2009, 14f.
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