blueish artifacts when using opencl
#3 Updated by Ulrich Pegelow over 7 years ago
I can confirm your findings with the image submitted. I suspect a problem in handling of out-of-bound a and b values in Lab, which we seem to handle differently on CPU and GPU. Will need to dig deeper into this problem.
As a short term remedy you can switch to "standard matrix" as input profile.
#9 Updated by Ulrich Pegelow over 7 years ago
I think the last reported topic is not a DT bug. It's in the nature of sharpen to enhance structure including noise. If you reduce sharpen amount to zero, and look close you still see that some weak magenta colored noise is there.
I assume this is based on different clipping values of camera in an overexposure situation. As this is only visible under very close pixel inspection, I do not regard this as a major issue. You might check different raw converters. If you can convince us that other converters deal much better with this situation we might consider to investigate it later.
#12 Updated by supermaz - over 7 years ago
I still think that darktable shouldn't create these blue pixels when sharpening. Both other programs don't do it, though RawTherapee gives some other colors on default settings.
After all I really like darktable, you are doing a great work!
#13 Updated by Ulrich Pegelow over 7 years ago
- Status changed from In Progress to Fixed
Obviously all raw converters struggle to deliver a realistic reconstruction of this over-exposed situation. All of them produce artifacts and I would not call one more "correct" than the other. There simply is no standard way of solving this.
As the biggest influence in this special case seems to come from the input profile, I suggest that you select within DT the best suited one for you by trial and error. Either enhanced or standard matrix or a profile supplied by Canon. In some cases these manufacturer profiles deliver better results than the matrix approach.
I will mark this issue as solved. The real artifact has been fixed. Thanks again for reporting!