Indicate if changing image mode from RGB to Indexed may modify colors
Environment/Versions
- GIMP version: 2.10.24 revision 3
- Operating System: Windows
Description of the bug
As a user who is concerned both about file size and about image quality, I want to use GIMP to create PNG files that exactly represent the original image but are smaller in size. To do that, I take an RGB image and change its mode to Indexed. There, I select optimal palette. Now if the image has more than 256 colors, I expect a warning that this change of mode is lossy.
This is related to #13 but should be easier to implement since this is not about preventing lossy conversion but only about detecting it.
Reproduction
Is the bug reproducible? Always
Reproduction steps:
- Take an image with more than 256 colors, in RGB mode
- Change the image mode from RGB to Indexed
…
Expected result:
I get a warning that the colors of the image will change. As a bonus, I get a preview showing the areas where the colors will differ. As a bonus, I get a color transition table that shows which colors will be merged and which colors will be changed. In any case, having a Preview checkbox would be nice. Of course, that checkbox only makes sense if the actual conversion has any chance of being lossy.
Actual result:
GIMP silently reduces the number of colors.