How to reduce Color Depth the best way?

[lytron]

Hi,

I'll try to describe my problem as straight-to-the-point as I can:

I ripped an image from a ROM, I can open it with TileMolester and view it correctly with 8bpp linear (hence I presume it has 256 colors). I want to turn it into a number of tiles with 16 colors with various palettes.

So, I expect to have to reduce the number of colors manually, that's not the problem. The question is:

How do I do it the fewest comlicated way?
I guess I have to transfer it in a "regular" graphic data format and edit it with things like GIMP (freeware solutions please, if possible. I'm not into that Warez scene... ) and convert it back. Is there a program that can do it, where I throw in Picture and Palette and it puts out the image?

Thanks for your helping suggestions!

[FAST6191]

What system are you dealing with and/or porting it to (I guess this is the reason, the other big one being more graphics in a given scene/less demand on resources). Depending upon what goes it is less 256 colours as defined by a system and more 256 options for colours on a given image but said colours are using a 16 bit colour format, that the former has its issues as well if you are going to use general image editing.
The latter tends to make it so you might consider going manual when it comes to reducing colours as most automated techniques tend not to do the best with pixel art.
http://docs.gimp.org/2.6/C/gimp-indexed-palette-dialog.html
http://docs.gimp.org/2.6/C/gimp-concepts-palettes.html

As for pixels/tiles I reckon grids and/or guides would work
http://docs.gimp.org/en/gimp-image-configure-grid.html
http://docs.gimp.org/en/script-fu-guide-new.html

With that image -> mode, indexed. Duplicate the original palette of the image (needs to so you can edit it). Delete as many colours as you need to. Convert the original image back to indexed but select your edited palette instead.

[lytron]

What system are you dealing with and/or porting it to (I guess this is the reason, the other big one being more graphics in a given scene/less demand on resources). Depending upon what goes it is less 256 colours as defined by a system and more 256 options for colours on a given image but said colours are using a 16 bit colour format, that the former has its issues as well if you are going to use general image editing.
The latter tends to make it so you might consider going manual when it comes to reducing colours as most automated techniques tend not to do the best with pixel art.
http://docs.gimp.org/2.6/C/gimp-indexed-palette-dialog.html
http://docs.gimp.org/2.6/C/gimp-concepts-palettes.html

As for pixels/tiles I reckon grids and/or guides would work
http://docs.gimp.org/en/gimp-image-configure-grid.html
http://docs.gimp.org/en/script-fu-guide-new.html

With that image -> mode, indexed. Duplicate the original palette of the image (needs to so you can edit it). Delete as many colours as you need to. Convert the original image back to indexed but select your edited palette instead.

I try to transfer some pics from GBA and NDS to SNES, just for testing's sake. Right now I try a GBA title screen with 256 colors, where the "New Game/Load/Options" sprite are added later, and I expect them to use another palette, so I have more than 256 colors on screen.

[TheFireRed]

In GraphicsGale there's a batch conversion tool where you can reduce colour depth. I'm not sure whether you can use your own custom palette, but at least you can throw loads of pictures in one shot. The programme's free of course.