![]() ![]() We will conventionally label the patches using four rows (from A to D) and six columns (from 1 to 6). Into the CHT file we will use millimeters as the unit of measure, the coordinate system have the origin (0, 0) into the top-left corner. The chart is sized 140×88 mm, each patch is a square of 18×18 mm and there is a space of 2 mm between the patches. Here you can download an already made file: greywhitebalancecolourcard-2in1.cht. Here we will describe a simple file for the 24 patches color card named The 2 in 1 manufactured by Grey White Balance Colour Cards company. It is not required to add the output color profile module to the image history, just export with the options stated above.Ĭreate a CHT file for the GWBCC Colour CardĪ CHT file ( scan recognition format file) is a text file describing the color chart shape the file format is described in the page Description of the. The exported file will be saved into a darktable_exported subdirectory. Return to the lighttable mode and choose export selected from the right menu, choose PFM (float) format and Lab profile. An photo with shadows and highlights equally distributed, should present an equally distributed histogram, from left to right. In the figures above you can see how the histogram looks like when choosing the wrong or the right color profile. Once selected, verify the history where only two items should exist: 0 - original and 1 - input color profile. Select the most appropriate profile: for a regular JPEG image it should be sRGB, in my case - an image acquired with scanimage from a CanoScan 9000F scanner - it was linear Rec2020 RGB. Still in darkroom mode, on the right menu, expand the input color profile section (you will wish to click the show only active modules button to find it easly). To be on the safe side you should define the input color profile. If you applied some modules on the image, remove them by selecting 0 - original and clicking compress history stack: every module above the one selected will be removed. View the image into the darkroom mode and verify its history (left menu): it should be only 0 - original. Now import the source image into Darktable using import from the left menu. We need to modify the program configuration file, which in my Debian GNU/Linux environment is $HOME/.config/darktable/darktablerc. We will use Darktable to make such conversion, but we need to enable Lab profile export, which is disabled per default. You need to convert the source image into the PFM (float) format and the Lab profile, because this is the format required by darktable-chart. The color card should appear roughly in plane with the camera, possibly non at the edges of the picture to avoid vignetting effect. You need one for each scanning or shooting session made with the same light conditions and the same camera settings (at least as regards white balancing and ISO settings). The source image is an image containing your color card. ![]()
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