Calculated the Mandelbrot Set and Julia Set in blocks

Mandelbrot Set and Julia Set never have islands of color (pixels not in the set) within the black (pixels in the set)... at least as far as Jason Woofenden knows. So Jason's Fractal Generator has an optimization where, instead of checking every pixel, it checks the pixels that border square areas of the screen (and some rectangles at the edge) and if every pixel around the edge of that square is black, it assumes the whole inside is black too. This speeds up the program a lot, because the black pixels take the longest to check.