imghash 2.0.0

Image hashing algorithms for Rust
Documentation 
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use image::{imageops::FilterType, DynamicImage, GenericImageView, GrayImage};

#[derive(Debug, Clone, PartialEq, Eq, Hash, Copy, Default)]
pub enum ColorSpace {
    #[default]
    REC601,
    REC709,
}

/// Converts a given [`DynamicImage`] to grayscale using the specified [`ColorSpace`].
///
/// # Arguments
/// * `img`: A reference to the image to convert
/// * `color_space`: The color space to use for the conversion
///
/// # Returns
/// * The converted dynamic image
fn grayscale(img: &DynamicImage, color_space: ColorSpace) -> DynamicImage {
    let mut buffer = GrayImage::new(img.width(), img.height());

    let coefficients: [f64; 3] = match color_space {
        ColorSpace::REC709 => [0.2126, 0.7152, 0.0722],
        ColorSpace::REC601 => [0.299, 0.587, 0.114],
    };

    buffer.enumerate_pixels_mut().for_each(|(x, y, pixel)| {
        let [r, g, b, _] = img.get_pixel(x, y).0;

        let luma =
            (coefficients[0] * r as f64 + coefficients[1] * g as f64 + coefficients[2] * b as f64)
                .round();

        *pixel = image::Luma([luma as u8]);
    });

    DynamicImage::ImageLuma8(buffer)
}

/// Converts a given [`DynamicImage`] by converting it to grayscale and then resizing it
/// to the specified size.
///
/// # Arguments
/// * `img`: A reference to the image to convert
/// * `width`: The final width of the rescaled image
/// * `height`: The final height of the rescaled image
/// * `color_space`: The color space to use for the conversion
///
/// # Returns
/// * The converted dynamic image
pub(crate) fn convert(
    img: &DynamicImage,
    width: u32,
    height: u32,
    color_space: ColorSpace,
) -> DynamicImage {
    let filter = FilterType::Lanczos3;

    let grayscale_img = grayscale(img, color_space);
    grayscale_img.resize_exact(width, height, filter)
}

#[cfg(test)]
mod tests {
    use super::*;

    use image::ImageReader;
    use std::path::Path;

    const TEST_IMG: &str = "./data/img/test.png";

    const REC_601_IMG: &str = "./data/img/gray-601.png";
    const REC_709_IMG: &str = "./data/img/gray-709.png";

    const REC_601_SCALED_IMG: &str = "./data/img/gray-scaled-601.png";
    const REC_709_SCALED_IMG: &str = "./data/img/gray-scaled-709.png";

    #[test]
    fn test_grayscale_with_601() {
        // Arrange
        let test_img = ImageReader::open(Path::new(TEST_IMG))
            .unwrap()
            .decode()
            .unwrap();

        let grayscale_img = ImageReader::open(Path::new(REC_601_IMG))
            .unwrap()
            .decode()
            .unwrap();

        // Act
        let grayscale = grayscale(&test_img, ColorSpace::REC601);

        // Assert
        assert_eq!(grayscale, grayscale_img);
    }

    #[test]
    fn test_convert_with_rec_601() {
        // Arrange
        let test_img = ImageReader::open(Path::new(TEST_IMG))
            .unwrap()
            .decode()
            .unwrap();

        let converted_img = ImageReader::open(Path::new(REC_601_SCALED_IMG))
            .unwrap()
            .decode()
            .unwrap();

        // Act
        let converted = convert(&test_img, 32, 32, ColorSpace::REC601);

        // Assert
        assert_eq!(converted, converted_img);
    }

    #[test]
    fn test_grayscale_with_709() {
        // Arrange
        let test_img = ImageReader::open(Path::new(TEST_IMG))
            .unwrap()
            .decode()
            .unwrap();

        let grayscale_img = ImageReader::open(Path::new(REC_709_IMG))
            .unwrap()
            .decode()
            .unwrap();

        // Act
        let grayscale = grayscale(&test_img, ColorSpace::REC709);

        // Assert
        assert_eq!(grayscale, grayscale_img);
    }

    #[test]
    fn test_convert_with_rec_709() {
        // Arrange
        let test_img = ImageReader::open(Path::new(TEST_IMG))
            .unwrap()
            .decode()
            .unwrap();

        let converted_img = ImageReader::open(Path::new(REC_709_SCALED_IMG))
            .unwrap()
            .decode()
            .unwrap();

        // Act
        let converted = convert(&test_img, 32, 32, ColorSpace::REC709);

        // Assert
        assert_eq!(converted, converted_img);
    }
}