@Override
		public PixelEval call() throws Exception {
			for (int row = rs; row < re; row++) {
				for (int col = cs; col < ce; col++) {
					Ray ray = getRay(row, col, dx, dy);
					Color color = scene.getColor(scene.getClosest(ray));
					image.setPixel(col, row, color);
				}
			}
			return this;
		}