Red shift & slight darkening when cropping
Posted: Mon Nov 16, 2020 5:30 pm
Hi,
not sure if there's already been discussion and/or a bug report about this issue, but here goes.
To reproduce:
1) Add a file with 4:2:0 chroma (such as a Blu-Ray rip from MakeMKV)
2) Set "Scale to" to "No stretch"
3) Find a scene with distinct areas of bright red color
4) Increase "Left crop" one pixel at a time, while keeping a close eye on the red areas
With certain "Left crop" values, I'm seeing two things:
A) the overall brightness of the image decreases slightly
B) there's a horizontal shift to red chroma that doesn't match the rest of the picture
Depending on your container size and other variables, this may happen when "Left crop" is set to eg. 2, 3, 5, 6 or 7. With other values (such as 0, 1, 4 or 8), the problem is less apparent or even nonexistent.
Setting "Scale to" to something else than "No stretch" fixes issue A, but not the more serious issue B.
On the other hand, converting the video file to ProRes 422 HQ before importing to DoM fixes issue B, but not issue A. So it would seem like we're looking at two different bugs...
not sure if there's already been discussion and/or a bug report about this issue, but here goes.
To reproduce:
1) Add a file with 4:2:0 chroma (such as a Blu-Ray rip from MakeMKV)
2) Set "Scale to" to "No stretch"
3) Find a scene with distinct areas of bright red color
4) Increase "Left crop" one pixel at a time, while keeping a close eye on the red areas
With certain "Left crop" values, I'm seeing two things:
A) the overall brightness of the image decreases slightly
B) there's a horizontal shift to red chroma that doesn't match the rest of the picture
Depending on your container size and other variables, this may happen when "Left crop" is set to eg. 2, 3, 5, 6 or 7. With other values (such as 0, 1, 4 or 8), the problem is less apparent or even nonexistent.
Setting "Scale to" to something else than "No stretch" fixes issue A, but not the more serious issue B.
On the other hand, converting the video file to ProRes 422 HQ before importing to DoM fixes issue B, but not issue A. So it would seem like we're looking at two different bugs...