Image Agfa Optima Filter Effect Application

function processImage(originalImg) {
    const canvas = document.createElement('canvas');
    const ctx = canvas.getContext('2d');

    canvas.width = originalImg.naturalWidth;
    canvas.height = originalImg.naturalHeight;

    ctx.drawImage(originalImg, 0, 0, canvas.width, canvas.height);

    const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
    const data = imageData.data;

    // Agfa Optima Filter Effect constants
    // 1. Contrast adjustment
    // The contrast value (-255 to 255). A moderate positive value enhances contrast.
    const contrastValue = 20; // Adjusted for a slightly stronger contrast effect typical of film
    const contrastFactor = (259 * (contrastValue + 255)) / (255 * (259 - contrastValue));

    // 2. Color transformation matrix for Agfa Optima "look"
    // These coefficients aim for warm tones, good red/yellow saturation, and a filmic quality.
    // R' = R*m11 + G*m12 + B*m13
    // G' = R*m21 + G*m22 + B*m23
    // B' = R*m31 + G*m32 + B*m33
    const m11 = 1.05, m12 = 0.15, m13 = -0.10;
    const m21 = 0.05, m22 = 0.95, m23 = 0.05; // Slightly increased G self-term for better greens
    const m31 = -0.05, m32 = 0.10, m33 = 0.90; // Adjusted B for slightly warmer blues, less desaturation


    for (let i = 0; i < data.length; i += 4) {
        let r = data[i];
        let g = data[i + 1];
        let b = data[i + 2];

        // Apply contrast
        let r_c = contrastFactor * (r - 128) + 128;
        let g_c = contrastFactor * (g - 128) + 128;
        let b_c = contrastFactor * (b - 128) + 128;

        // Clamp contrast-adjusted values (though matrix math might handle out-of-range inputs if final clamp is robust)
        r_c = Math.max(0, Math.min(255, r_c));
        g_c = Math.max(0, Math.min(255, g_c));
        b_c = Math.max(0, Math.min(255, b_c));

        // Apply color matrix for Agfa Optima effect
        const finalR = r_c * m11 + g_c * m12 + b_c * m13;
        const finalG = r_c * m21 + g_c * m22 + b_c * m23;
        const finalB = r_c * m31 + g_c * m32 + b_c * m33;

        // Clamp final RGB values to [0, 255]
        data[i]     = Math.max(0, Math.min(255, finalR));
        data[i + 1] = Math.max(0, Math.min(255, finalG));
        data[i + 2] = Math.max(0, Math.min(255, finalB));
        // Alpha channel (data[i + 3]) remains unchanged
    }

    ctx.putImageData(imageData, 0, 0);
    return canvas;
}