With this script, you can extract textures from a Minecraft spritesheet, but with basic Python knowledge, you could easily make adjustments for you case.

There is also a function to recolor opaque pixels.

This is mainly useful for modding.

Usage

1. Download or clone code
2. Adjust values in the example at the bottom of main.py according to your needs.
3. Run main.py with Python
4. Results will be in the output dir

Getting MC textures

From the Wiki:

You can get all spritesheets and coordinates with F3+S in-game (works at least 1.19.4 and above). They get saved into .minecraft/screenshots/debug folder.