VSE: Alpha Over + Convert to float changes the color of the top layer #82094
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Reference: blender/blender#82094
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System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: Intel(R) UHD Graphics 600 Intel 4.5.0 - Build 27.20.100.8853
Blender Version
Broken: version: 2.92.0 Alpha
Short description of error
Add two color strips - not black, and change compositing of the top strip to Alpha Over. Toggle 'Convert to float' under color while pressing arrow left/right to update the preview. The top layver will now change color, it's a regression and a bug.
Added subscriber: @tintwotin
#90960 was marked as duplicate of this issue
Added subscriber: @lichtwerk
Changed status from 'Needs Triage' to: 'Needs User Info'
Cannot actually reproduce this one.
I know it is simple, but just to make sure we are on the same page: could you share your .blend file?
Its related to 'Convert to float' under color. Do as described above and toggle that while pressing arrow left/right to update the preview.
VSE: Alpha Over changes the color of the top layerto VSE: Alpha Over + Convert to float changes the color of the top layerChanged status from 'Needs User Info' to: 'Needs Developer To Reproduce'
Added subscriber: @iss
Changed status from 'Needs Developer To Reproduce' to: 'Needs User Info'
I also can't reproduce this.
Can you render image, save it and check the color in external image editor? If the color is OK, then this is most likely openGL issue.
It's actually both Float and Alpha Over individually which causes the color change:
{F9108543, size=full}
Select the top strip, and toggle Convert to Float or switch between Replace and Alpha Over, as show in the gif above.
FloatAlpha.blend
Still cannot reproduce,
Convert to Floatdoes not change anything regarding Display on my end. Have you checked the colors when saved?The rendered image looks correct:
{F9109012,size=full}
Changed status from 'Needs User Info' to: 'Needs Triage'
Added subscriber: @EAW
I can't replicate the issue either. Perhaps this is an issue with the driver 27.20.100.8853. Did you have this issue before 10/19/2020 @tintwotin?
Does this issue appear for you in 2.90, 2.83, ect?
Tested using:
System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 470/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 391.35
Blender Version
2.92.0 Alpha, branch: master, commit date: 2020-10-27 10:45, hash:
4b188bb08cHard to say. I'm not testing this every day.
No problem in 2.90:
{F9111437,size=full}
Changed status from 'Needs Triage' to: 'Needs User Info'
Added subscriber: @fclem
@tintwotin Can you check if switching Preferences > Textures > Image Display Method to 2D Texture or to GLSL make difference?
Looking at blame,
faeaf53255looks to me as possible culprit.@fclem Do you see any obvious bug here, or any info to ask for?
Added subscriber: @ideasman42
Changed status from 'Needs User Info' to: 'Confirmed'
This happens on my systems, caused by
804e90b42dThe texture preference doesn't make any difference.
Added subscriber: @ckerr
I couldn't reproduce this.
System Information
Operating system: Darwin-19.6.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon Pro 5500M OpenGL Engine ATI Technologies Inc. 4.1 ATI-3.10.18
Blender Version
version: 2.93.0 Alpha, branch: master, commit date: 2021-01-22 18:30, hash:
aaa1d58054Added subscriber: @slinkeepie
Removed subscriber: @tintwotin
Changed status from 'Confirmed' to: 'Archived'
As I do not have anymore time or motivation for a continued investment in the Blender project, I'm giving up on this report for now.
Changed status from 'Archived' to: 'Confirmed'
Sorry to hear (thx again reporting). In my opinion we should not sweep this under the carpet (esp. since this already been confirmed), there is still a chance to get this fixed in the future and others might be affected by this issue as well.
I'm not sure if this is the same issue but might be related:
System
Windows 11
RTX 4060 Laptop GPU
Blender
using Version 3.6.0 (2023-06-27)
Steps to reproduce
similar scenario
Using the same ColorSpace in the Strip and Sequencer should prevent color transforms before entering preprocessing. Convert to float will then trigger a call to seq_imbuf_to_sequencer_space within the preprocessing stage.
@Ha_Lo I am not sure what I should expect in "similar scenario". Sequencer template already uses sRGB space for movies and processing.
This report is already confirmed, but I am unable to reproduce, so it could be, that you see the bug, but I don't.
I should have been more specific. By default both Strip and Sequencer are set to sRGB. If you set them to any other combination the colorchange disappears. So I'd guess this has to do with the way the conversion to float interacts with color transformation. At a glance it shouldn't. But somehow does.
The Issue is old and the status history is a little confusing. My conditions to reproduce are slightly differnt form the original so I thought this might help others to reproduce.
Since I can reproduce the bug and I'm going to look at strip preprocessing anyway, I might as well investigate this.
Adding an extened test file.
Timeline automates switches through blend modes
Color blocks on the right are kept in byte buffer, blocks on the left use convert to float
Sections switch color multiplication factor and strip order
@Ha_Lo Playing around with your file on the frame in the screen shot reveals another issue: As far as I can tell, the blending mode is applied to the entire area before cropping, which is why the 2 right side rectangle are different shades.
I would expect it to apply only to the post cropped area of each color strip.
Note to others who may try to reproduce: In the screen shot the frame is 39, in the file it is frame 44.
@EAW I didn't want to dive that deep into the code for a simple start project but looks like I will have to.
There are obviosly differences in the implementation of the byte an float workflow.
Swtiching between the workflows at different points in the stack seems to expose that.
There will obviously always be slight color variations due to math involved. But what we're seeing here ist buggy behaviour.
So either everything needs to be rendered in the same workflow or the workflows need to be matched. Right now, to me this looks like the byte workflow is broken.
Using your example: there should be no color info to process outside of the crop area. Even it there was, the alpha values outside the crop area should prevnet any blending. It works as expected in float and is only broken in certain byte/float combinations.