Best way to downsize a palette to 256 colors

[Monsieur OUXX]

My process is the following :
1) I make my background in true-color (let's say 32-bit colors)
2) I use the "downgrade colors to 256 colors" feature of my favorite image editing program (Photoshop, whatever...)

One could say I should directly draw in 256 colors, but I don't like it.

My question is : Do you know of a more optimized way to do that, to preserve the best possible color quality?

For example :

1) Do YOU use a specific drawing technique involving "main" color tones, thus avoiding the need of too many "transition" colors between color tone A (e.g. redish colors) and color tone B (e.g. blueish colors)?

2) Do you know a program that has a palette downgrade algorithm far superior to other programs? (for example, it is a fact that some algorithms to scale down images are better than others. I suppose it's the same with color downgrading).

etc.

Any tip is welcome.

[CaptainD]

I find the Posterize filter in GIMP to be pretty good, but I'm afraid I wouldn't know whether it's any better or worse than any other programs. 

[Scavenger]

I use this thing:

http://www.compuphase.com/software_palettemaker.htm

It's a little tricky to set up, but it's way good for making suitable colour palettes. Just make sure you increase the canvas of your background over 200% so you can crop out the watermark. I also tend to reduce the amount of colours in photoshop first to 256 BEFORE doing the AGS palette reduction, with diffusion dithering, or pattern depending on what kind of picture it is.

By importing your AGS palette into PaletteMaker and locking those entries, you can have a background that uses all 256 colours while still taking advantage of the other slots!
Once you've done that, just paint over all the weird dithering colours (sometimes they creep into a picture) using your favorite 256 colour painting program.

What do you want to use these 8 bit images for?

[Shane 'ProgZmax' Stevens]

If you want an image to be x colors there's just no real substitute for drawing the image in x colors to begin with.  Anything else is going to yield middling results by dithering to compensate for lost colors or erasing chunks of color entirely.  If the image doesn't have too many varied colors, photoshop's color reduce tends to work acceptably but you'll still have to deal with some kind of dither pattern which may or may not be to your liking.

Learning to draw effectively with limited colors is one of the great challenges of artwork and it can teach you many tricks about substituting one color for another and improve your understanding and appreciation of color usage in general so I recommend it.

[Monsieur OUXX]

Learning to draw effectively with limited colors is one of the great challenges of artwork and it can teach you many tricks about substituting one color for another and improve your understanding and appreciation of color usage in general so I recommend it.

I drew with Deluxe Paint II for over 10 years but nowadays I'm too lazy. Starting with hi-res and finishing low-res is the best compromise for me, "effort versus result"-wise (not everybody has this super intuition of pixel-art that you have, ProgZ)

I think I'll do as follows :
- I'll draw in hi-color
- I'll reduce to 256
- I'll use a 256-colors editor to check that my antialisaing is OK everywhere and correct it where needed
- I'll use a 256-colors editor to manually replace the broken gradients with the relevant dithering patterns.

[Armageddon]

I just index the colours in GIMP.

[Blount]

I use Jasc Paint Shop Pro 9 on the Decrease Color Depth window you choose between:
Three palettes: Optimized Median Cut, Optimized Octree & Windows.
And three reduction methods: Nearest color, Ordered dither & Error difusion.
Changing palettes and reduction methods gives you HUGELY different results, i suggest you try different combinations.

[Shane 'ProgZmax' Stevens]

(not everybody has this super intuition of pixel-art that you have, ProgZ)

Which I developed by practicing in exactly the way I suggested above, it just takes some effort and patience.