Re: Cross-developing artwork

[Kevin <kevin@hackaday.com>]

On Sunday, November 25, 2012 2:54:00 PM UTC-6, Steve Nickolas wrote:
> On Sun, 25 Nov 2012, BLuRry wrote:
> 
> 
> 
> > Best thing to do is make a custom gimp palette.  Load a sample image 
> 
> > with all 6 colors and then convert it to an indexed color image (if it 
> 
> > isn't already) -- and make sure to limit the size of the palette to 6. 
> 
> > Once you have that, you can go to the palette menu and save it.  It's a 
> 
> > bit tricky to find all the right menu options (the palette management in 
> 
> > Gimp exists but it's not easy to find for some screwy reason -- I think 
> 
> > I had to use an eyedropper and build a custom palette).  You can then 
> 
> > apply this palette to other pictures as needed.  If you're feeling 
> 
> > tricky you can do some optimizations like doing two 4-color palettes 
> 
> > (one with green/purple and one with blue/orange) and interleave the two 
> 
> > resulting images using layers and some creative masking tricks to 
> 
> > alternate so as to avoid the hi/lo color boundaries.  This would help 
> 
> > you simulate the result without having to play guess & check.
> 
> >
> 
> > I am not far away from having a better conversion routine to eliminate 
> 
> > the roundtrip through gimp for color conversion -- except that Java only 
> 
> > has a pattern diffusion and lacks a Floyd-Steinberg implementation (and 
> 
> > the FS dither yields WAY better results when reducing colors.)  I found 
> 
> > some FS java implementations but the code was hard to read and wasn't 
> 
> > using the most optimal Java graphics classes (e.g. drawing points with 
> 
> > Java 2D instead of just touching the framebuffer directly, which is 
> 
> > several times faster.)
> 
> >
> 
> > Anywho, if you're really crafty you can skip using Gimp and use Image 
> 
> > Majick "convert" to do (at least most of) this, but I imagine it may be 
> 
> > more bother than its worth.  The advantage of using convert is that once 
> 
> > you have it, you just reuse the same script and you can apply it to a 
> 
> > stack of images rather quickly.  I used Image Magick to do palette 
> 
> > conversions in the past as well as rescaling and gamma correction and 
> 
> > was very pleased with the results.  I was not pleased that I was writing 
> 
> > a java program that offloaded half its work via a forked process though. 
> 
> > :-)
> 
> 
> 
> Well, I'm actually a fan of ImageMagick and use it a lot. :)
> 
> 
> 
> -uso.

you can use a palette image like
http://www.cheesefactory.us/apple2/apple.xpm

and a imagemagick command like

convert filename.ext -level 0%,70%,1 -dither none -map apple.xpm output.ext

look up the level and dither commands to play around with it