KuwaharaFilter.osl

// KuwaharaFilter.osl by DizzyQuarkArt
// This file is licensed under Apache 2.0 license

shader kuwahara_filter(
    string fileName = "" [[string widget="filename", string page = "Image" ]],
    string fileColorSpace = "" [[string label = "Colorspace", string page = "Color Space Conversion", string widget = "colorspace"]],

    float Radius = 0.003,
    output color Output = color(0.0))

{
    int radSteps = int(Radius * 1000); // Convert radius to integer steps
    if (radSteps < 1)
        radSteps = 1;

    color mean[4] = {color(0), color(0), color(0), color(0)};
    float variance[4] = {0.0, 0.0, 0.0, 0.0};

    // Offset directions for the four neighborhoods
    int offset_x[4] = {-1, 1, -1, 1};
    int offset_y[4] = {-1, -1, 1, 1};

    // Get the base UV coordinates
    vector uv = vector(u, -v, 0);

    // Loop through the four neighborhoods
    for (int n = 0; n < 4; n++) {
        color sum = color(0.0);
        float sum_sq = 0.0;
        int count = 0;

        // Sample the neighborhood
        for (int x = 0; x <= radSteps; x++) {
            for (int y = 0; y <= radSteps; y++) {
                // Compute texture coordinates with offsets
                float u_offset = offset_x[n] * x * Radius;
                float v_offset = offset_y[n] * y * Radius;
                float u_new = uv[0] + u_offset;
                float v_new = uv[1] + v_offset;

                // Wrap UV coordinates to stay within 0 to 1
                u_new = u_new - floor(u_new);
                v_new = v_new - floor(v_new);

                // Sample texture at offset
                color sample = texture(fileName, u_new, v_new);
                sum += sample;
                sum_sq += dot(sample, sample);
                count++;
            }
        }

        // Calculate mean and variance for the neighborhood
        mean[n] = sum / count;
        variance[n] = (sum_sq / count) - dot(mean[n], mean[n]);
    }

    // Find the neighborhood with the minimum variance
    int min_index = 0;
    float min_variance = variance[0];
    for (int i = 1; i < 4; i++) {
        if (variance[i] < min_variance) {
            min_variance = variance[i];
            min_index = i;
        }
    }

    // Set the output color to the mean of the selected neighborhood
    color output_mean = mean[min_index];

    color textureSampleRAW = transformc("ACEScg", "scene-linear Rec.709-sRGB", output_mean);
    color outColor = transformc(fileColorSpace, "ACEScg", textureSampleRAW);

    Output = outColor;
}