Implement gaussian_blur

[edgarriba]

Implement Gaussian Blur using separable filters -> imgproc::filters::gaussian_filter2d_separable

Links of interest:

• https://github.com/kornia/kornia/blob/main/kornia/filters/gaussian.py
• https://github.com/kornia/kornia/blob/main/kornia/filters/filter.py#L140

Reference implementation (need to be adjusted for gaussian):

fn box_blur(input: &[f32], width: usize, height: usize, radius: usize) -> Vec<f32> {
    let mut output = input.to_vec();

    for _ in 0..3 { // Repeat 3 iterations for Gaussian approximation
        output = horizontal_box_blur(&output, width, height, radius);
        output = vertical_box_blur(&output, width, height, radius);
    }

    output
}

fn horizontal_box_blur(input: &[f32], width: usize, height: usize, radius: usize) -> Vec<f32> {
    let mut output = vec![0.0; input.len()];

    for y in 0..height {
        for x in 0..width {
            let mut sum = 0.0;
            let mut count = 0;

            for k in -(radius as isize)..=(radius as isize) {
                let nx = x as isize + k;
                if nx >= 0 && nx < width as isize {
                    sum += input[y * width + nx as usize];
                    count += 1;
                }
            }

            output[y * width + x] = sum / count as f32;
        }
    }

    output
}

fn vertical_box_blur(input: &[f32], width: usize, height: usize, radius: usize) -> Vec<f32> {
    let mut output = vec![0.0; input.len()];

    for x in 0..width {
        for y in 0..height {
            let mut sum = 0.0;
            let mut count = 0;

            for k in -(radius as isize)..=(radius as isize) {
                let ny = y as isize + k;
                if ny >= 0 && ny < height as isize {
                    sum += input[ny as usize * width + x];
                    count += 1;
                }
            }

            output[y * width + x] = sum / count as f32;
        }
    }

    output
}

fn main() {
    let input = vec![
        1.0, 2.0, 3.0, 4.0, 5.0,
        6.0, 7.0, 8.0, 9.0, 10.0,
        11.0, 12.0, 13.0, 14.0, 15.0,
        16.0, 17.0, 18.0, 19.0, 20.0,
        21.0, 22.0, 23.0, 24.0, 25.0,
    ];
    let width = 5;
    let height = 5;
    let radius = 1;

    let blurred = box_blur(&input, width, height, radius);

    for y in 0..height {
        for x in 0..width {
            print!("{:.2} ", blurred[y * width + x]);
        }
        println!();
    }
}