Digital Negative - DNG Conversion

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 software that Pentax supplies with all their dSLR cameras can convert PEF raw image files from Pentax cameras into DNG files.
  • Flexcolor and Phocus from Hasselblad can convert 3FR raw image files from Hasselblad cameras and digital backs into DNG files.
  • Capture One from Phase One is a raw converter that can process not only raw image files from Phase One digital backs, but also raw image files from many other cameras too. Capture One can save images from many of those cameras to DNG.
  • KDE Image Plugin Interface is an API, that can save the images it is processing to DNG. It can be used standalone or with any image processing applications of the KDE desktop environment under Linux and Windows.
  • A number of DNG converters have been developed by "amateurs" to enable raw images from their favored camera or digital back to be processed in a large range of raw converters. These include cases where cameras have been hacked to output raw images that have then been converted to DNG.

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.

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