Digital Negative

Digital Negative (DNG) is a patented, open, lossless raw image format developed by Adobe and used for digital photography. Adobe's license allows use without cost on the condition that the licensee prominently displays text saying it is licensed from Adobe in source and documentation, and that the license may be revoked if the licensee brings any patent action against Adobe or its affiliates related to the reading or writing of files that comply with the DNG Specification. It was launched on September 27, 2004. The launch was accompanied by the first version of the DNG specification, 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.
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, and has also stated that there are no known intellectual property encumbrances or license requirements for DNG. Adobe stated that if there were a consensus that DNG should be controlled by a standards body, they were open to the idea. Adobe has submitted DNG to ISO for incorporation into their revision of TIFF/EP.
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.
Objectives.
These objectives are repeatedly emphasized in Adobe documents:
Characteristics.
All of the above objectives are facilitated or enabled by most of these characteristics:
Technical summary.
A DNG file always contains data for one main image, plus metadata, and optionally contains at least one JPEG preview. 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.
DNG is both a raw image format and a format that supports "non-raw", or partly processed, images. The latter (non-raw) format is known as "Linear DNG". Linear DNG is still scene-referred 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 - 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 resultant 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.
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. A few camera manufacturers stated their intention to use DNG at launch. They 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.
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. 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. A DNG converter must therefore 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.
Summary of products that support DNG in some way.
This section summarizes other more comprehensive lists.
Adobe products.
All raw image file handling products from Adobe now support DNG. "Adobe DNG Converter" was utility software 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 and the Apple Macintosh).
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:
Some digital cameras that support DNG:
Apple's iPhones and other iOS devices expose an API for third-party apps such as Halide or Lightroom CC to capture DNG images, but the native Camera app always processes to JPEG or HEIF. The native Photos app does not have proper DNG support either (unlike other RAW formats), displaying DNGs as 1/2-MP previews unless a processed image is embedded into the file.
Some of the Canon cameras can shoot as DNG using additional free software CHDK.
Huawei Android phones using Leica-designed cameras (such as the Mate 9 and Mate 10 Pro) can save raw files to DNG format when shooting in "Pro" mode.
The built-in camera function in the Adobe Lightroom Mobile app saves to DNG format.
Third-party software.
Support by software suppliers varies; there are of the order of 200 software products that use DNG.
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.
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. Each version of the specification describes its compatibility with previous versions.
1.6.0.0, publised December 2020
This version added demosasic information, Semantic Maps and more. 
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: