Setting images to indexed mode on Gimp 2.10 is completely broken.

[GIMP Devil]

I really need help this is really stressing and frustrating me.

I have been on Windows 7 for the longest time and using Gimp 2.8 with no hassle and it was very easy and comfortable, I now recently "upgraded" to Linux Mint Cinnamon 22.1 and installed Gimp 2.10.36 from the Software Manager on it.

Now I like drawing sprite art on a transparent background and when it's done I index the sprite art because it makes it to a very small filesize which makes me happy, on Windows 7 Gimp 2.8 this was super easy I would just select the indexed mode and apply it and bam it would index the image with no issue at all.


Now on Linux Mint Cinnamon 22.1 and Gimp 2.10 (I don't know if Linux is causing this problem or Gimp is) when I try to index an image with transparency it completely messes up the saved image!

This is just an example of an indexed image I happen to have it's of a Charizard sprite, as you can see the original indexed image from Gimp 2.8 on Win7 is completely fine and has its transparency and is a super low filesize.
[attachment=13873]

Now when I open that image in Gimp 2.10 and do absolutely no changes except export it as a new image look at what happens to it!
[attachment=13874]


Now here's the weird thing, if I add a solid color background (like white for example) to the original image then export it the colors don't get corrupted, but the filesize is still massive! [attachment=13875]
I'm at a loss for what to do.. did gimp 2.10 just completely break indexed mode or maybe it's the version of gimp on the Linux Mint Software Manager?

Somebody please help

[Ofnuts]

I don't see your attachments.

Other tan this, 2.10 has been around since 2018 and I didn't see many problems reported against its indexed mode.

[GIMP Devil]

(09-06-2025, 06:14 AM)Ofnuts Wrote: I don't see your attachments.

Other tan this, 2.10 has been around since 2018 and I didn't see many problems reported against its indexed mode.

I'm trying to upload the attachments, I don't know why they didn't show up... let me try uploading them to imgur as well in case it glitches again and doesn't put the image here

https://imgur.com/a/ihNNKxY

that is a link to imgur it shows all the images, but I will try it here too


This is the indexed image edited on Gimp 2.8 on Windows 7, you can see it has a low filesize of 1.1 kb and no problems


This is the same indexed image as one edited on Gimp 2.8 on Win7, but I exported on Linux Mint Cinnamon 22.1 with Gimp 2.10 (didn't change anything at all just exported the texture)


This is the same indexed image as one edited on Gimp 2.8 on Win7, but I exported on Linux Mint Cinnamon 22.1 with Gimp 2.10 and I added a white background and for some reason the colors don't get corrupted? But the file size is still bloated unlike the original it's 5.3kb instead of 1.1kb and that's without transparency!


These are the settings for the above exported textures on Linux Mint Cinnamon 22.1 on Gimp 2.10 (they are all default, I didn't change anything)

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It has to be a problem with either Linux version of Gimp 2.10 or Gimp 2.10 itself! I just installed Gimp 2.8.22 from my backup HDD and I run it through Wine even though it's so horribly laggy and choppy, but when I exported this same image I showed of the original Charizard as an indexed image it had no problem like the Gimp 2.10 Linux native version did!

See this is the image I exported and it still maintains the transparency, but it was still bloated to 1.2kb instead of 1.1kb, but much better than what Gimp 2.10 did.
I really hope I can be guided to fix this problem or install native version of Gimp 2.8.22 for Linux then I can see if that is indexed mode works or maybe the indexed mode is just broken for all versions of native linux gimps on Linux Mint ;-;

This is the charizard I exported in Gimp 2.8.22 windows version installed with Wine on Linux Mint Cinnamon 22.1 it's how I expected the image to be!
   

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I did some more testing and I changed the settings because after reinstalling Windows gimp 2.8.22 I realized there was a lot of strange settings on gimp 2.10 that are enabled by default, and after changing some my image is no longer getting corrupted when I export it! As seen here with these settings the Charizard image did not get corrupted colors when exported

   

   

But unfortunately it seems gimp 2.10 is just inferior when it comes to smaller file size from indexed images? As instead of 1.1kb original image and the exported 2.8.22 gimp run with wine who exported same image to 1.2kb the settings  exported this charizard image to 2.4kb this is more than 2x size compared to gimp 2.8.22!

I think there is no fixing it unless you have an idea to lower the filesize more? Maybe there is a setting I missed as I never used gimp 2.10 till moving to Linux Mint 2 weeks ago

If it's not possible then I really hope somebody can guide me to install gimp 2.8.22 linux native version to see if that one has proper indexed like the windows version because the gimp 2.8.22 run with wine is SUPER laggy, but if I have no choice I guess I will have to use it

[CmykStudent]

Just FYI, the issue is exporting indexed sprites with alpha as PNGs in GIMP 2.10.36, not the index mode as a whole. You shouldn't have issues with exporting as an indexed GIF for example. The PNG bug was fixed in 2.10.38: https://www.gimp.org/news/2024/05/05/gim...ther-fixes

The file size issue may be because you're exporting as 8BPC RGBA, rather than an indexed sprite.

[GIMP Devil]

(09-06-2025, 03:58 PM)CmykStudent Wrote: Just FYI, the issue is exporting indexed sprites with alpha as PNGs in GIMP 2.10.36, not the index mode as a whole. You shouldn't have issues with exporting as an indexed GIF for example. The PNG bug was fixed in 2.10.38: https://www.gimp.org/news/2024/05/05/gim...ther-fixes

The file size issue may be because you're exporting as 8BPC RGBA, rather than an indexed sprite.

Ah, that is so unfortunate that the version of Gimp on the Software Manager for Linux Mint is one that is has such a horrible bug
I don't know if there is an easy way to update to that version seeing as Gimp 2.10 itself is probably outdated as 3.0 is the latest supported Gimp..

I did not see any option to export an image as an "indexed sprite" on Gimp 2.10, unfortunately. It defaults to "automatic pixelformat" which was giving corrupted image, so I used that 8BPC RGBA which did not seem to be corrupted but still bigger file size.
   

[CmykStudent]

That makes sense - 8BPC RGBA (as I understand it) is regular RGBA colors rather than indexed, so you're not saving it as an indexed image - thus the larger file size. The bug was specifically exporting an indexed PNG with transparency. You could try to get a flatpak of 2.10.38.

[GIMP Devil]

Thank you everybody, I installed the Gimp 2.10.38 appimage from here
https://www.gimp-forum.net/Thread-new-gi...1#pid39451
and it works the indexed image is now small like original and not corrupted, thank you all for your help!