libeffectengine/effects/

kuwahara.rs

use std::{io::Cursor, ops::Range, process::exit};
use wasm_bindgen::prelude::*;

use image::{DynamicImage, GenericImageView, ImageBuffer, ImageFormat, Luma, Rgba};

#[cfg(not(target_arch = "wasm32"))]
use crate::util::subcommand_help_requested;
use crate::util::{get_paths, read_image};

/// Applies an implementation of the Kuwahara filter to the given image.
///
/// The Kuwahara filter is usually used for noise reduction while retaining image
/// quality, but it can be used for artistic purposes because it makes image look
/// "painted". It does this by grabbing small squares from an image, dividing it
/// up into four quadrants, then computing the standard brightness deviation for all
/// pixels inside each quadrant. Whichever quadrant has the lowest deviation then
/// gets used in the next step, where the average color from said quadrant is
/// computed and then applied to the current pixel, which is the center where all
/// four quadrants overlap.
#[wasm_bindgen(js_name = kuwahara)]
pub fn effect() -> Vec<u8> {
    #[cfg(not(target_arch = "wasm32"))]
    {
        if subcommand_help_requested() {
            print_help();
            exit(0);
        }
    }

    let paths = get_paths();
    let image_data = read_image(paths.input_path);

    let image = DynamicImage::ImageRgba8(
        image::load_from_memory(&image_data.data)
            .expect("Failed to decode image from memory")
            .to_rgba8(),
    );
    let luma8_image = image.to_luma8();

    let mut new_image = ImageBuffer::new(image.width(), image.height());

    let window_size: i32 = std::env::args()
        .nth(4)
        .or_else(|| Some(String::from("5")))
        .unwrap()
        .parse()
        .unwrap_or_else(|_| 5);

    if window_size < 5 {
        eprintln!("Window needs to be at least 5 pixels wide.");
        exit(64);
    }

    if window_size % 2 == 0 {
        eprintln!("Window needs to have an odd width.");
    }

    let image_width = image.width() as i32;
    let image_height = image.height() as i32;

    for x in 0..image_width {
        for y in 0..image_height {
            // Offset from the center pixel to the edge of the window
            let offset = window_size / 2;

            // Quadrant A: Top-Left
            let q_a = (
                (x - offset).max(0)..(x + 1).min(image_width),
                (y - offset).max(0)..(y + 1).min(image_height),
            );

            // Quadrant B: Top-Right
            let q_b = (
                x.max(0)..(x + offset + 1).min(image_width),
                (y - offset).max(0)..(y + 1).min(image_height),
            );

            // Quadrant C: Bottom-Left
            let q_c = (
                (x - offset).max(0)..(x + 1).min(image_width),
                y.max(0)..(y + offset + 1).min(image_height),
            );

            // Quadrant D: Bottom-Right
            let q_d = (
                x.max(0)..(x + offset + 1).min(image_width),
                y.max(0)..(y + offset + 1).min(image_height),
            );

            let std_a = get_std_brightness_deviation_for_pixels(&luma8_image, &q_a);
            let std_b = get_std_brightness_deviation_for_pixels(&luma8_image, &q_b);
            let std_c = get_std_brightness_deviation_for_pixels(&luma8_image, &q_c);
            let std_d = get_std_brightness_deviation_for_pixels(&luma8_image, &q_d);

            let min_std = match [(q_a, std_a), (q_b, std_b), (q_c, std_c), (q_d, std_d)]
                .iter()
                .min_by(|a, b| a.1.partial_cmp(&b.1).unwrap())
            {
                Some(x) => x.clone(),
                None => {
                    eprintln!("???");
                    exit(1);
                }
            };

            let mut pixels: Vec<[u8; 4]> = Vec::new();
            for z in min_std.0.0 {
                for w in min_std.0.1.clone() {
                    pixels.push(image.get_pixel(z as u32, w as u32).0);
                }
            }

            let avg = rgba_average(pixels);

            new_image.put_pixel(x as u32, y as u32, Rgba(avg));
        }
    }

    let mut cursor = Cursor::new(Vec::new());

    if image_data.format == ImageFormat::Jpeg {
        let rgb_image = DynamicImage::ImageRgba8(new_image).into_rgb8();
        rgb_image
            .write_to(&mut cursor, image_data.format)
            .expect("Failed to encode JPEG");
    } else {
        new_image
            .write_to(&mut cursor, image_data.format)
            .expect("Failed to encode image");
    }

    return cursor.into_inner();
}

/// Calculates the standard deviation for pixels from an image
/// within a given square.
fn get_std_brightness_deviation_for_pixels(
    image: &ImageBuffer<Luma<u8>, Vec<u8>>,
    ranges: &(Range<i32>, Range<i32>),
) -> u32 {
    let mut brightnesses: Vec<u32> = Vec::new();

    let x_range = ranges.0.clone();
    let y_range = ranges.1.clone();

    for x in x_range {
        for y in y_range.clone() {
            brightnesses.push(image.get_pixel(x as u32, y as u32).0[0] as u32);
        }
    }

    calculate_std_deviation(&brightnesses)
}

/// Calculates the average RGB color from the given colors.
fn rgba_average(colors: Vec<[u8; 4]>) -> [u8; 4] {
    let folded: [u32; 4] = colors.iter().fold([0, 0, 0, 0], |mut acc, color| {
        acc[0] += color[0] as u32;
        acc[1] += color[1] as u32;
        acc[2] += color[2] as u32;
        acc[3] += color[3] as u32;

        acc
    });

    return [
        (folded[0] / colors.len() as u32) as u8,
        (folded[1] / colors.len() as u32) as u8,
        (folded[2] / colors.len() as u32) as u8,
        (folded[3] / colors.len() as u32) as u8,
    ];
}

/// Calculates the variance for a vector of numbers.
fn calculate_variance(data: &Vec<u32>) -> u32 {
    let mean: u32 = data.iter().sum::<u32>() / data.len() as u32;
    let variance = data
        .iter()
        .map(|val| {
            let diff = mean as i32 - (*val as i32);
            (diff * diff) as u32
        })
        .sum::<u32>()
        / data.len() as u32;

    variance
}

/// Calculates the standard deviation for a vector of numbers.
fn calculate_std_deviation(data: &Vec<u32>) -> u32 {
    let variance = calculate_variance(data);
    variance.isqrt()
}

/// Prints the help text for this effect.
#[cfg(not(target_arch = "wasm32"))]
fn print_help() {
    println!(
        r#"
Kuwahara Filter Effect
Applies a filter usually used for noise reduction which makes images look
like they were painted.

USAGE:
  effectengine-cli kuwahara <INPUT_PATH> <OUTPUT_PATH> [WINDOW_SIZE]

ARGUMENTS:
  <INPUT_PATH>     The path to an input image that should be processed.
  <OUTPUT_PATH>    The path where the resulting image should be saved.
                   Needs to include the filename.
  [WINDOW_SIZE]    Optional. How big the various "paint strokes" should
                   appear. Bigger numbers will mean bigger strokes and
                   less detail. (Default: 5)
  "#
    );
}