GIMP-Python script for dithering pixel art

Here's a Python script for GIMP that takes an indexed color image and replaces every other color with a checkerboard dithering of its neighbors. The intended use was to create grayscale 4 color images with this style of dithering, by first creating a hand-tuned 7 color image, then applying the script. After it runs, you can delete the in-between tones from the palette. It should work for any odd number of colors, n>=3.

Having scripted Gimp in both Python and Scheme, I definitely found Python more pleasant.

This is the kind of silly thing I used to do, to pass the time:

#!/usr/bin/env python

# Pixel art dither script for GIMP
# Author: ahefner@gmail.com

import math
from gimpfu import *
from array import array

def python_8bit_dither(img, srclayer):

    try:
        pdb.gimp_message("Running...")
        pdb.gimp_image_undo_group_start(img)

        layer = srclayer.copy()
        img.add_layer(layer, 0) 
        width = layer.width
        height = layer.height

        rgn = layer.get_pixel_rgn(0, 0, width, height, TRUE, FALSE)
        src_pixels = array("B", rgn[0:width, 0:height])

#        cmbytes, cmdata = pdb.gimp_image_get_colormap(img)
#        colors = cmbytes / 3
#        pdb.gimp_message(str(cmdata))

        i = 0
        ph = 0
        for y in range(height):
            ph = y & 1
            for x in range(width):
                c = src_pixels[i]
                if (c & 1):
                    c = c-1 if (ph == 0) else c+1
                src_pixels[i] = c
                ph = ph ^ 1
                i = i + 1

        rgn[0:width, 0:height] = src_pixels.tostring()

        layer.flush()
#        layer.merge_shadow()
        layer.update(0,0,width,height)
        pdb.gimp_image_undo_group_end(img)
        pdb.gimp_message("Finished!")

    except Exception, err:
        pdb.gimp_message("ERR: " + str(err))
        pdb.gimp_image_undo_group_end(img)

register(
        "python_fu_dither",
        "Dither odd colors in an indexed-color image",
        "Dither odd colors in an indexed-color image",
        "Andy Hefner",
        "Andy Hefner",
        "2010",
        "/Filters/Mine/8-Bit Dither Helper",
        "INDEXED",
        [],
        [],
        python_8bit_dither)

main()