GNOME Bugzilla – Bug 89022
Brightness & contrast could be improved
Last modified: 2005-01-18 22:41:56 UTC
Increasing BRIGHTNESS (+100) and at the same time decreasing CONTRAST (-100). Output image contains distinctive saturated areas. When decreasing CONTRAST to minimum (-127) then changing BRIGHTNESS has no effect. Pecold
This is exactly the result one would expect from the algorithm used and noone has so far ever complained about the algorithm we use. If you don't get the desired effect from Brightness-Contrast, you probably want to use one of the other color controls (Hue-Saturation, Curves, ...).
Created attachment 10290 [details] test image: brightness=0, contrast=120; saturated areas appear
I am sorry but I don't think algorithm is all right. Some values probably overflow. I attach testing image. Leave brightness 0 and change contrast to -120. Described saturated areas appear. Comparing i.e. Adobe Photoshop your method adjusting contrast gives darker and more saturated results.
Noone claimed that our algorithm is the same as the one that PS or any other application uses. It's just one way to implement Brightness/Contrast adjustments. However I have to admit the some artefacts don't look right so we should probably try to investigate this further. It will however be very difficult to change the algorithm since a lot of scripts out there probably rely on the results of the current implementation. We could only accept a patch that removes an obvious bug in the algorithm, there is no way we could accept a different implementation.
Bug should be revised for 2.0.
Re-changing milestone to Future. Tempted to resolve WONTFIX or NOTABUG. Dave.
Resolving as WONTFIX because that's simply the reality, this is never going to be changed on the basis of the arguments here.