Html color picker from image preview3/16/2024 ![]() ![]() In this forum are some updated images with various gray areas: So my png test image you referenced does show with the color picker exactly the homogenous sRGB values which are given as text information in the png image. I have calibrated and profiled monitors, but my profiles in DT are still all set to default “sRGB (web safe)” for display, softproof and histogram profile. Yes, the display profiles in the “toggle gammut checking” warning triangle (right mouse button) have a strong impact on the color picker. Looking forward to your enlightening comments. This because one white pixel line and one black pixel line do NOT give sRGB=127 as perceived average, but sRGB=188, which is much brighter (50 % instead of 21 %). Especially with fine bright details this is visible. Wrong gamma calculations generally give too dark results. I usually calculate with correct values 188 and 127, but my above figures are not yet updated with this. BTW, depending on calculation and rounding with exponent 2.2 (approximation) or 2.4 (accurate) according to sRGB standard the 50 % gray is 196,187 or 188 and 21 % can be 127 or 128. Decreasing the exposure by −1 EV should give 186 (50 % intensity) and not 127 (21 %). You can try this also with any 255 (100 % intensity) white filled area. The value of 93 is too dark, because sRGB=93 is only about 11 % intensity. And 50 % (−1 EV) intensity decrease of sRGB=186 (50 % intensity) is not sRGB=93, but it is sRGB=137 (25 % intensity). The modification of −1 EV corresponds to 50 % intensity. That is acceptable as arithmetic value, but: The exposure module does the calculation not with linear light. The color picker does show (again left to right = top to down):Īgain, the mean calculation of the second checkerboard value is the “mean” average. ![]() If you decrease with the exposure module in darktable with −1 EV, the result is as follows: Look for the good and famous article of about gamma error in picture scaling. If you zoom such image in a browser or irfanview or most other tools (inclusive darktable), the brightness of the checkerboard will change and deviate strongly from the correct average of 186. The 2nd value of the checkerboard is the arithmetic mean, but not the perceived brightness of 186. The color picker from top to bottom does give the results: With zoom 100 % the background should have the average intensity of 50 % and therefor roughly sRGB=186 (right side area) and not the left side value of sRGB=128. In the foreground are two homogenously filled areas. In the next graphic you see a 50 % checkerboard in the background. Can someone explain to me, why the exposure module and color picker in darktable is doing the calculation not linear and therefor not correct? Please correct me, if I am wrong or do miss something basic with my following interpretation.
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