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Load-Save TGA wiping alpha channel #2629
Description
Activity
Sorry, library version is 3.1.1
The image descriptor byte in the file header of the provided image is 0. Usually bits 0-3 indicate designated as alpha channel bits.
Since the descriptor is 0, the decoder assumes there is no alpha channel.That is the reason it is lost when decoding and encoding again.
I still believe the provided image does not follow the spec with omitting the image descriptor, when there is alpha data.
Other decoders have problems with it too, like irfanview:
edit: not sure why this image renders so weird in github, looks different when you click on it.
I think one solution in handling this is to assume true color images with 32 bits per pixel to always have a alpha channel with 8 bit. @JimBobSquarePants What do you think about this? Would anyone write a 32 bits per pixel image without a alpha channel?
Reacted by James Jackson-SouthYeah @brianpopow good idea! I think that’s a safe assumption and it’s non-destructive. We should add it to the v3.1.x branch and then main.
@AN3Orik can I use the image you have provided in a unit test?
We should add it to the v3.1.x branch
@JimBobSquarePants I have opened a PR for this Issue. I am not sure how the procedure is to add it to the v3.1.x, I think, it would be better if you do that, so I dont break stuff. Also I am not totally sure this should go into a hotfix, since the image is not following the spec correctly and this PR only adds a workaround to deal with those kind of images.
I’m happy to skip adding to 3.1.x I’ve only been doing so because v4 is so far away.
closing this now with #2643 merged
Reacted by Anton Lasevich
Prerequisites
DEBUGandRELEASEmodeImageSharp version
3.0.0
Other ImageSharp packages and versions
3.0.0
Environment (Operating system, version and so on)
Windows 10
.NET Framework version
.NET 8
Description
Loading 32bit RGBA TGA and saving after wiping Alpha channel to white (255) color.
Steps to Reproduce
Before:
After:
Images
test.zip