In my limited experience working with BMP, GIMP UI is more intuitive and easy to use in comparison to Photoshop in this particular task, especially when it comes to rearranging colors in the color palette. Also, the image quality after color reduction and shrinking is better effortlessly in my opinion.
Using GIMP
- Open Image: Open your image in GIMP.
- Indexed Mode: Go to Image > Mode > Indexed.
- Set Colors: Choose “Generate optimum palette” and set the Maximum number of colors to 4.
- Reorder Palette: Go to Colors > Map > Rearrange Colormap. Drag and drop the colors into your desired order (Index 0-3).
- Force 8-bit Colormap: Open the Colormap dialog (Windows > Dockable Dialogs > Colormap) and click the ‘+’ button to add colors, ensuring the total is greater than 16, which forces an 8-bit (256 color) palette.
※This is because the index image is reduced to 4 colors, GIMP automatically create a 4-bit (16 colors) map to save space. This will mess up how BMP is displayed in yyCHR. - Export: Go to File > Export As, select BMP.
