/**
 * Returns the image that is generated from the given disjoint set.
 * If the randomColors parameter is true, a random color will be assigned
 * to each segment of the image. If it's false, then the mean color of
 * the pixels in the original image will be assigned to each segment.
 */
func imageFromDisjointSet(set *disjointset.DisjointSet,
	originalimg image.Image, randomColors bool) image.Image {
	resultimg := image.NewNRGBA(originalimg.Bounds())
	width := originalimg.Bounds().Max.X
	height := originalimg.Bounds().Max.Y
	meanColors := make([]ImageColor, width*height, width*height)
	if randomColors {
		for u := 0; u < width*height; u++ {
			meanColors[u] = randomColor()
		}
	} else {
		for y := 0; y < height; y++ {
			for x := 0; x < width; x++ {
				c := set.Find(x + y*width)
				r, g, b, _ := originalimg.At(x, y).RGBA()
				meanColors[c].r += float32(r>>8) / float32(set.Size(c))
				meanColors[c].g += float32(g>>8) / float32(set.Size(c))
				meanColors[c].b += float32(b>>8) / float32(set.Size(c))
			}
		}
	}
	for x := 0; x < width; x++ {
		for y := 0; y < height; y++ {
			resultimg.Set(x, y, &meanColors[set.Find(x+y*width)])
		}
	}
	return resultimg
}
/**
 * Computes the threshold used by the GBS algorithm.
 * T(c) = k/|c|
 */
func threshold(set *disjointset.DisjointSet, k float64, u int) float64 {
	return k / float64(set.Size(u))
}