pub fn luma32f_bench_image(width: u32, height: u32) -> Image<Luma<f32>> {
    use image::DynamicImage;
    let img = gray_bench_image(width, height);
    DynamicImage::ImageLuma8(img).to_luma32f()
}
`Luma<f32>` image to use in benchmarks. See comment on `gray_bench_image`.
src/utils.rs