Pixelate images in less than 50 lines of code

pixie.rs

//! # pixie
//!
//! Pixelate images. This file provides the code demonstrated
//! in this video: <https://youtu.be/Q18vAySAiHc>
//! 
//! Uses image 0.24.0 <https://docs.rs/image/0.24.6/image/>

use image::io::Reader as ImageReader;
use image::{GenericImageView, DynamicImage, ImageBuffer, Rgba};

type Image = ImageBuffer<Rgba<u8>, Vec<u8>>;

fn resize(img: &Image, new_dims: (u32, u32)) -> Image {
    let (old_width, old_height) = img.dimensions();
    let (new_width, new_height) = new_dims;

    let mut resized = ImageBuffer::new(new_width, new_height);

    for (new_x, new_y, pixel) in resized.enumerate_pixels_mut() {
        let old_x = (new_x as f32 * (old_width  as f32 / new_width  as f32)) as u32;
        let old_y = (new_y as f32 * (old_height  as f32 / new_height  as f32)) as u32;

        if let Some(old_pixel) = img.get_pixel_checked(old_x, old_y) {
            *pixel = *old_pixel;
        } else {
            println!("({old_x} -> {new_x}, {old_y} -> {new_y})");
        }
    }

    resized
}

fn pixelate(img: &DynamicImage, new_dims: (u32, u32)) -> Image {
    let old_dims = img.dimensions();

    let img = img.to_rgba8();

    let small = resize(&img, ((old_dims.0 / new_dims.0), (old_dims.1 / new_dims.1)));
    small.save("debug-small.png").unwrap();


    let pixelated = resize(&small, old_dims);
    pixelated.save("debug-pixelated.png").unwrap();
    pixelated
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let img = ImageReader::open("starlings.jpg")?
        .decode()?;
    let img_ = pixelate(&img, (50, 50));

    let _ = img_.save("pixelated.png");
    Ok(())
}