pub fn rgb_bench_image(width: u32, height: u32) -> RgbImage {
    use std::cmp;
    let mut image = RgbImage::new(width, height);
    for y in 0..image.height() {
        for x in 0..image.width() {
            let r = (x % 7 + y % 6) as u8;
            let g = 255u8 - r;
            let b = cmp::min(r, g);
            image.put_pixel(x, y, Rgb([r, g, b]));
        }
    }
    black_box(image)
}
RGB image to use in benchmarks. See comment on `gray_bench_image`.
src/utils.rs