Add image tinting about imageproc

[theotherphil]

I couldn't make sense of the ImageMagick code, but I guess we're after something like the following:

use image::{
    GrayImage,
    Luma,
    Pixel,
    Rgb,
    RgbImage
};

use definitions::Clamp;

pub fn tint_image(image: &GrayImage, tint_color: Rgb<u8>) -> RgbImage {
    let (width, height) = image.dimensions();
    let mut out = RgbImage::new(width, height);

    for y in 0..height {
        for x in 0..width {
            let tinted = tint(*image.get_pixel(x, y), tint_color);
            out.put_pixel(x, y, tinted);
        }
    }

    out
}

/// Tint a grayscale value with the given color.
pub fn tint(gray: Luma<u8>, color: Rgb<u8>) -> Rgb<u8> {
    let dist_from_mid = (gray[0] as f32 - 128f32).abs();
    let scale_factor = 1f32 - 4f32 * dist_from_mid * dist_from_mid;
    Rgb([gray[0]; 3])
        .map2(&color, |p, q| {
            Clamp::clamp(p as f32 + scale_factor * q as f32)
        })
}

#[cfg(test)]
mod test {

    use super::{
        tint_image
    };
    use utils::{
        load_image_or_panic
    };
    use image::Rgb;
    use test;
    use std::path::Path;

    #[test]
    fn test_tint() {
      let ip = Path::new("./tests/data/elephant.png");
      let tp = Path::new("./tests/data/truth/tintyphant.png");
      let image = load_image_or_panic(&ip).to_luma();
      let eq = tint_image(&image, Rgb([0u8, 0u8, 255u8]));
      let _ = eq.save(&Path::new(tp)).unwrap();
    }
}

[theotherphil]

@softprops: is this roughly what you were after? I'll tidy this up before committing anyway (it was bodged together in a few minutes, and has some odd artefacts), but I'll wait and see if this is actually what's wanted first.

[softprops]

Damn you guys are fast! I'm out to town today but I'll give it a spin when i get hone tonight. I think this is perfect for tinting but what I was looking for was something slightly different.

The duotone effect looks something like that but parameterized with 2 colors that form a gradient that could be color mapped to the grayscale pixels.

Here's some visual examples

https://www.google.com/search?q=duotone&client=ms-android-verizon&biw=360&bih=264&prmd=isvn&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjXjaz_lqDKAhWCKj4KHb2hAgYQ_AUIBigB

[softprops]

There's a bit more info under the image magic docs about the technique. http://www.imagemagick.org/Usage/color_mods/#duotone

[theotherphil]

Cool, thanks. I missed that somehow. I'll add that in the next couple of days.

[softprops]

Man. You guys set a high bar for oss friendliness and turnarounds. Keep it up

[theotherphil]

Thanks! Sadly the tint function above is rubbish, but I'll add a fixed version tomorrow

[softprops]

I'm not sure how compatible it is typewise with this crate but I thought this may be of use http://www.piston.rs/image/image/imageops/colorops/fn.index_colors.html

[theotherphil]

imageproc is based on that image crate (the small overlap between this crate and image::imagops will be removed eventually). So the traits and concrete types used are identical. However, it doesn't look like that function gains us too much - implementing our own ColorMap impl for either tinting or duotone would be the same amount of work as writing the functions directly.

[theotherphil]

Ok, I may have been a little optimistic when I claimed I'd get this done in a couple of days. Getting aesthetically pleasing results looks like it will require a lot of flexibility in the tinting/blending functions, and writing something decent for this would take a lot longer than I have free this week (and to get the brightness of the tinted image to match the input image we'll need HSL support, which isn't currently available).

In the meantime, I've written a prototype implementation of tint and colour blending and pushed to a branch of my repo: theotherphil@0d9eccb.

Example tinting output:

Example blending output:

Hopefully this at least gives you a starting point to play around with. I wouldn't count on anything in this area getting released soon, but I'm happy to help with any problems you have getting this to work for your use cases.

[theotherphil]

One obvious problem with the current code is that we do non-trivial work for every pixel. So if you need this to be fast we can tweak the code to use a LUT as you suggested.

[softprops]

@theotherphil you are a magician! That looks great

[theotherphil]

Glad you like it. I've added an example with these colour effects in 1667547, so will close this issue now. (Bonus of this code over that in theotherphil/imageproc/effects is that it actually produces the output shown above, instead of getting the colour gradient wrong.)

cargo run --example color_effects <your_file_here>

It'll create a tinted.png and gradient.png file in the same directory as the input file you provide.