Pyside: Separating A Spritesheet / Separating An Image Into Contiguous Regions Of Color

I'm working on a program in which I need to separate spritesheets, or in other words, separate an image into contiguous regions of color. I've never done any image processing befor

Solution 1:

That sounds like something that should be implemented in anything that deals with sprites, but here we will implement our own sprite-spliter.

The first thing we need here is to extract the individual objects. In this situation, it is only a matter of deciding whether a pixel is a background one or not. If we assume the point at origin is a background pixel, then we are done:

from PIL import Image

def sprite_mask(img, bg_point=(0, 0)):
    width, height = img.sizeim= img.load()

    bg = im[bg_point]
    mask_img = Image.new('L', img.size)
    mask = mask_img.load()
    for x in xrange(width):
        for y in xrange(height):
            if im[x, y] != bg:
                mask[x, y] = 255return mask_img, bg

If you save the mask image created above and open it, here is what you would see on it (I added a rectangle inside your empty window):

With the image above, the next thing we need is to fill its holes if we want to join sprites that are inside others (like the rectangle added, see figure above). This is another simple rule: if a point cannot be reached from the point at [0, 0], then it is a hole and it must be filled. All that is left is then separating each sprite in individual images. This is done by connected component labeling. For each component we get its axis-aligned bounding box in order to define the dimensions of the piece, and then we copy from the original image the points that belong to a given component. To keep it short, the following code uses scipy for these tasks:

import sys
import numpy
from scipy.ndimage import label, morphology

defsplit_sprite(img, mask, bg, join_interior=True, basename='sprite_%d.png'):
    im = img.load()

    m = numpy.array(mask, dtype=numpy.uint8)
    if join_interior:
        m = morphology.binary_fill_holes(m)
    lbl, ncc = label(m, numpy.ones((3, 3)))

    for i in xrange(1, ncc + 1):
        px, py = numpy.nonzero(lbl == i)
        xmin, xmax, ymin, ymax = px.min(), px.max(), py.min(), py.max()

        sprite = Image.new(img.mode, (ymax - ymin + 1, xmax - xmin + 1), bg)
        sp = sprite.load()
        for x, y inzip(px, py):
            x, y = int(x), int(y)
            sp[y - int(ymin), x - int(xmin)] = im[y, x]

        name = basename % i
        sprite.save(name)
        print"Wrote %s" % name

sprite = Image.open(sys.argv[1])
mask, bg = sprite_mask(sprite)
split_sprite(sprite, mask, bg)

Now you have all the pieces (sprite_1.png, sprite_2.png, ..., sprite_8.png) exactly as you included in the question.