Should I scale an image first, or index it?

I have an image, it’s the Backtrack_5_PitchBlack.jpg found at http://www.backtrack-linux.org/screenshots/, and I’d like to get it down to 640*480 for a Grub4DOS splash screen.
Unfortunately, this also means I need to index it to 14 colors (or less) and save it as an XPM image.

I get that I can crop the whitespace around the edges (so as to avoid needing to scale the image unevenly,) but will I get better results doing the indexing before, or after the scaling?

To summarize:
I need to –

  • Crop the image from 16:10 to 4:3
  • Scale the image so that it’s 480px high
  • index the image to 14 colors

I’m using GIMP, what’s the best order of operations here? I’m most likely going to use the Floyd-Steinburg (normal) dithering, but I also need to know what the best Scaling algorithm for this is. I’d prefer to have it look as if it were vectored straight into that size – edges as smooth as possible.

Answer

You’ll want to scale first. Downsizing the image will compress your palette to some extent in and of itself. Indexing before hand would throw color away that may be helpful in the down-sampling step.

Attribution
Source : Link , Question Author : JamesTheAwesomeDude , Answer Author : plainclothes

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