Question

Above is an example image generated by using rand() to get random coordinates and add a constant to the pixel value at those coordinates. This is how it looks from a few thousand iterations. I’m using the rand() from stdlib.h in Mac OS X Lion, giving it time(NULL) as the seed.

You can clearly see the vertical lines, as if the ones with an odd x-coordinate have higher values than those with even x-coordinates.

How would I implement a better algorithm, or where can I find one that doesn’t have many dependencies? (I would prefer a header-only file).

Here’s the code (sorry it took me so long):

void generate(int iterations = 1) {
 for (unsigned int x = 0;x < (area * 4);++x) {
  map[rand() % area] += 1;
 }
 number a = min();
 number b = max();
 for (int i = 0;i < area;++i) {
  map[i] -= a;
  map[i] /= b;
 }
}

Map contains double-floats and is later turned into RGB values.

Answer 1

Have you tried arc4random()? It provides much stronger and more uniform random values than rand().

You could also try SecRandomCopyBytes(), which is part of Security.framework. This basically just reads from /dev/random.