8000 Transparent images lose alpha channel · Issue #1365 · k4yt3x/video2x · GitHub
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Transparent images lose alpha channel #1365

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zhanghai opened this issue Apr 7, 2025 · 6 comments
Open

Transparent images lose alpha channel #1365

zhanghai opened this issue Apr 7, 2025 · 6 comments
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state:Backlog This issue will be worked on in the future type:Bug Something isn't working

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@zhanghai
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zhanghai commented Apr 7, 2025 •
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Describe the bug

video2x works fine on upscaling plain BMP files, but drops the alpha channel for PNG files with alpha channel.

To Reproduce

Steps to reproduce the behavior:

  1. Use real-esrgan to upscale a PNG file with alpha channel.
  2. Observe that the alpha channel is lost after upscaling.

Expected behavior

The alpha channel is kept and upscaled in the output PNG.

Actual behavior

The alpha channel is lost in the output PNG.

Screenshots

Image Image

Environment:

  • OS: Windows 10 22H2
  • GPU: NVIDIA GeForce RTX 3080
  • Video2X Version: 6.4.0

Full command

.\video2x.exe -i PNG_transparency_demonstration_1.png -o PNG_transparency_demonstration_1.3x.png -p realesrgan -c png --pix-fmt rgba -s 3

Additional context

I tried specifying --pix-fmt rgba as in #457 (which was for waifu2x back in 2021), but it didn't work either, probably because it's for output instead of input.
@zhanghai zhanghai added the type:Bug Something isn't working label Apr 7, 2025
@github-actions github-actions bot added the state:Backlog This issue will be worked on in the future label Apr 7, 2025
@k4yt3x
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k4yt3x commented Apr 8, 2025 •
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This is because the current models take and output RGB24 images. This is just not possible AFAIK.

@k4yt3x
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k4yt3x commented Apr 8, 2025

Specifically here:

video2x/src/conversions.cpp

Line 90 in 6bf0ee5

ncnn::Mat ncnn_image = ncnn::Mat(width, height, static_cast<size_t>(3), 3);

I needed BGR24 to create the ncnn::Mat. I don't think it's possible to preserve the alpha channel here.

@zhanghai
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zhanghai commented Apr 8, 2025

Thanks for the reply!

For other people with this problem, I ended up using xinntao/Real-ESRGAN-ncnn-vulkan directly with the models included in this project and it handled the alpha channel well.

I wanted to check if it's easy to support the same thing in this project, but given that it's not possible I'll just close this issue.

@zhanghai zhanghai closed this as completed Apr 8, 2025
@github-actions github-actions bot added state:Done This issue has been resolved/dismissed and removed state:Backlog This issue will be worked on in the future labels Apr 8, 2025
@k4yt3x
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k4yt3x commented Apr 8, 2025

I think it could be possible if I end up using libtorch instead of ncnn. It's something I can look out for down the road.

@zhanghai
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zhanghai commented Apr 8, 2025

I think it could be possible if I end up using libtorch instead of ncnn.

Is ncnn the problem here though? Asking because I was able to use xinntao/Real-ESRGAN-ncnn-vulkan directly and it did handle alpha channel properly.

@k4yt3x
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k4yt3x commented Apr 8, 2025

Hmm maybe I missed something here? Can you please reopen the issue? I'll take a look when I have time.

@zhanghai zhanghai reopened this Apr 9, 2025
@github-actions github-actions bot added state:Backlog This issue will be worked on in the future and removed state:Done This issue has been resolved/dismissed labels Apr 9, 2025
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