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ColorMatch ========== ColorMatch allows you to create an ICC standard color profile based on the color transform your camera firmware uses to create JPG files. This profile can then be applied to your RAW files using RAW editing software. Keep in mind that ColorMatch should be considered as highly experimental and requires meticulous application of the procedures below in order to be successful. WARNING: Keep in mind that ColorMatch comes with no warranty whatsoever, use at your own peril. Target ====== To be able to use ColorMatch you need the following target: * Wolf Faust C1 DIN A4 IT8 Camera Target (http://www.targets.coloraid.de/) Software ======== To be able to use ColorMatch you need the following software: * bash (4.3) * argyll (1.6.3) * shared-color-targets (0.1.0) * exiv2 (0.23) Camera Configuration ==================== Properly configuring your camera is absolutely critical for ColorMatch to succeed, please consult your camera manual for instructions on how the achieve the settings below: * Disable Nikon Active D-Light * Disable Canon Auto Lighting Optimizer * Disable Canon Highlight Tone Priority * Disable Sony Dynamic Range Optimizer * Disable Olympus Shadow Adjustment Technology * Disable Panasonic Intelligent D-Range * Disable Samsung Smart Range * Disable Pentax D-Range * Disable Pentax Multi Auto White Balance * Disable Lens correction, if possible * Set camera to Adobe RGB colorspace * Set camera to 1/3EV exposure increments * Set camera to base ISO (usually 100 or 200) * Set camera to RAW+JPG (Full Resolution, Super Fine) * Lower camera applied sharpening Shooting The Target =================== Shoot the IT8 target preferably in direct sunlight as close to midday as possible. Have the target fill out most of the frame. matrix metered camera exposure should be mostly right (probably +1/3EV), however it's recommended to do extensive bracketing to make sure you have a wide range of exposures to select the right one from later on. You may need to shoot the target at a slight angle to prevent glare. It's probably best not to use exotic glass to shoot the target, a 50 mm prime is likely ideal, if unavailable, any kit-lens should suffice. To prevent vignetting from affecting the procedure, it's recommended to close down the aperture a few stops from its maximum value. So you'll likely end up shooting at f/8 or f/11. Selecting The Right Exposure ============================ Open a candidate JPG in GIMP and verify there is no dust or glare in the image. Then open the color picker, set sample average, use info window and get HSV values. When you sample the white GS0 patch, you should see a value of about 97%, and 3% for the black GS23 patch. Then proceed to measure the four grey outer corners of the chart, the value difference between the darkest and brightest corners should be well below 5%. If all of the above requirements have been satisfied, crop the chart, so only the chart remains visible, including cropping off the text. Save the resulting image as a 8-bit TIFF (without compression). Processing The RAW ================== Open the respective RAW in your favorite RAW processing software, and disable all possible processing. Set linear gamma (1.0) and set input and output profile to the same profile, and rendering intent to absolute colorimetric if possible, effectively creating a color management pass-through. Then apply cropping, and lens distortion correction if needed, be careful not to apply lens vignetting correction. Then save to a 16-bit TIFF (again without compression). Particularly for Darktable, make sure camera white balance is unchanged, disable basecurve, disable sharpen, set a linear rec2020 for input and output color profile. Make sure not to override the output color profile while exporting. Particularly for UFRaw, make sure camera white balance is unchanged, restore details for negative EV: clip, clip highlights for positive EV: digital linear, load Argyll's ClayRGB1998.icm both as camera and output profile, with an absolute colorimetric rendering intent. Set output bit depth to 16-bit. Set gamma 1,00 and linearity 0,000. Also make sure Embed exif data in output is enabled. Particularly for DCRaw, you can use the following command: # dcraw -v -w -M -H 0 -o 0 -6 -W -g 1 1 -f -m 1 -T ../_MG_1234.CR2 Running ColorMatch ================== The ColorMatch script takes three arguments, first the camera processed image, second the linear RAW processed by your RAW converter, and optionally a style name to be included into the profile description. # colormatch CAMERA.TIF _MG_1234.TIF Standard At the end of the script, you should see a plot, which should be a fairly smooth curve, with in most cases a notch at the lower right side. Note that colormatch expects all ArgyllCMS utilities to be available in your system path, if not, you will have to adapt the script to whatever your situation is. Using The Profile ================= Particularly for Darktable, copy the resulting ICC color profile into Darktable's input color profile directory, like so: # mkdir -p ~/.config/darktable/color/in # cp my.icc ~/.config/darktable/color/in Then select the profile in the input color profile module, in Darkroom mode. Make sure basecurve is disabled. Particularly for UFRaw, copy the resulting ICC color profile to a location that's convenient for you. Then load the ICC file from UFRaw GUI as the camera profile, make sure gamma is set to 1,00 and linearity is set to 0,000. Particularly for DCRaw, you can use the following command: # dcraw -v -w -H 0 -o 1 -p my.icc -W -g 1 1 -f -m 1 -T _MG_1234.CR2 Testing The Profile =================== There is no definitive way to test a generated profile, it may work marvellously on one image and fail horribly on another. Most typical problems will likely occur in the highlights and shadows. So testing a profile with overexposed and underexposed images is a good way to start. Other good test cases are portraits, images with clouds, high-key, low-key, etc. Thanks ====== A lot of people on the ArgyllCMS mailing have been very helpful, but one person in particular helped me in tricking ArgyllCMS into producing these camera emulation profiles: Klaus Karcher. Without his help, ColorMatch may never have existed. Donate ====== ColorMatch critically hinges on tools provided free of charge by ArgyllCMS, so if ColorMatch has been useful for you, please seriously consider donating to ArgyllCMS' author: http://www.argyllcms.com/ Frequently Asked Questions ========================== Q: My camera does not support RAW+JPG A: RAW files have a lower-quality embedded thumbnail, which you extract using Exiv2: # exiv2 -ep3 IMG_1234.CR2 This embedded thumbnail might however be in sRGB colorspace (regardless of camera configuration). Q: My camera does not support AdobeRGB A: sRGB could work too, but you'll have to modify the script accordingly. Q: My camera does not support 1/3EV increments A: You really need this precision to easily get the right shot, presumably you could do without, but be prepared to do a huge amount of trial and error. It won't be fun. Q: Can ColorMatch work with other targets A: In theory, yes, practically no. I've done testing with several charts, where Wolf Faust's IT8 charts are both most suitable and most affordable. I have no interest whatsoever in adapting ColorMatch for other types of charts. Q: Why no TIFF compression A: Depending on your version of ArgyllCMS it may or may not have been linked against a version of libtiff with deflate support. Disabling compression means you can be sure your TIFFs will be compatible. Q: Can profiles be used interchangeably between RAW converters A: Since RAW files aren't self-descriptive, decoding a RAW, requires RAW converters to apply arbitrary parameters to be able to make sense of the data. This may vary between different RAW converters; it may match for some camera models, and it might differ for others. Q: Will there be a repository of generated profiles A: I currently have no desire nor time to curate a repository of camera profiles. These resulting profiles should be considered a personal-use item. Q: My distro does not have shared-color-targets A: You merely need to download R080505.it8 manually, and modify the script accordingly. In this particular use-case it typically won't have to match the text on your actual target.