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Calibrating colors for DNG processing

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Revision as of 18:53, September 3, 2012 by 89.100.155.170 (Talk)

Note: this page currently refers to using DNG files with Adobe's Camera Raw ("ACR": part of Photoshop, Bridge, and Lightroom), which support the DNG profiles which were introduced in v1.2 of the DNG standard. As information becomes available about other RAW processing software that support DNG profiles, please add information to this page.


DNG files created by CHDK contain a basic color matrix which should generate "normal" colors in RAW processing software. Ever since version 1.2 of the DNG standard (which is supported by ACR 4.5 or later and Lightroom 2.0 and later) we've also been able to use DNG profiles to fine-tune the color processing. Adobe provides a selection of DNG profiles for all the cameras it supports natively, but we can easily install extra profiles. Most photographers who use extra profiles do so in order to get all their cameras producing consistent colours (sometimes including having profiles specific to each individual camera body to cater for the slight differences between bodies of the same model). They can also be used for more esoteric things such as processing RAW files from infrared cameras.

DNG profiles can either apply to a specific lighting condition (more than just a particular white balance, but also the spectrum of light: useful in unusual lighting conditions) or they can be a "dual-illuminant" profile which contains data for both D65 and Standard Illuminant A lighting conditions. If properly defined, these dual-illuminant profiles are suitable for use as generic profiles in most lighting conditions, although custom "single-illuminant" profiles can still be created for unusual lighting conditions. The standard Adobe profiles are dual-illuminant profiles.


Usually when processing DNG files from CHDK cameras no profiles are available from Adobe, and Camera Raw only provides the choice of the psuedo-profile "Embedded" (which is essentially the color matrix embedded by CHDK). By installing our own profiles for these cameras we can improve the color rendering significantly. Note that each DNG profile (usually contained in a .DCP file) is tied to a specific camera model. The profiles can be created/manipulated with Adobe's free DNG Profile Editor (free login required), and with X-Rite's ColorChecker Passport product. Both methods are usually based on taking photos of a ColorChecker target. Some people have instead managed to modify Adobe-provided profiles for several cameras with native RAW support, in order to use them with RAW files from cameras with similar image sensors.


As described in Adobe's documentation, placing the .DCP files in the Adobe/CameraRaw/CameraProfiles folder (the location of which will vary depending on your operating system) and restarting the RAW processing software should be all that's required for installation. If the new profile is still not visible when you're processing files from your camera, this would usually be due to the camera model name in the profile not matching that in the photo's EXIF data (i.e. it's not a profile for your camera).

Once you've found a profile that you're happy with, you can open up a new DNG file from your camera, assign the profile (in the Camera Calibration panel of Camera Raw) and then save those settings as a new Camera Raw Default so that new photos will use that profile by default.


User-provided DNG profiles

This page provides a common reference for DNG profiles for various CHDK-supported cameras, and will hopefully grow over time.

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