Image Fujifilm ETERNA Motion Picture Film Effect Applicator

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

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

    // Fujifilm ETERNA is known for:
    // 1. Soft contrast (low contrast, lifted blacks, compressed highlights)
    // 2. Desaturated colors (muted palette)
    // 3. Characteristic color response (often slightly greenish/cyan tint, especially in shadows/mid-tones, muted blues)

    const CONTRAST_REDUCTION_FACTOR = 0.85; // Values closer to 1.0 mean less contrast reduction. E.g., 0.85 reduces distance from mid-gray by 15%.
    const DESATURATION_AMOUNT = 0.40;       // 0.0 (no desaturation) to 1.0 (grayscale). Eterna is notably desaturated.
    
    // Eterna-like color tint multipliers. These aim for the characteristic Eterna palette.
    // It often features prominent, slightly desaturated greens and muted blues that can shift towards teal.
    const R_TINT_FACTOR = 0.98; // Slightly reduce red component
    const G_TINT_FACTOR = 1.04; // Boost green component
    const B_TINT_FACTOR = 0.97; // Slightly reduce blue component, helping the green/teal shift

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

        // --- 1. Soft Contrast Adjustment ---
        // This formula brings color values closer to mid-gray (128), effectively reducing contrast.
        // It lifts blacks (e.g., 0 becomes (0-128)*0.85 + 128 = 19.2)
        // And pulls in whites (e.g., 255 becomes (255-128)*0.85 + 128 = 235.95)
        r = (r - 128) * CONTRAST_REDUCTION_FACTOR + 128;
        g = (g - 128) * CONTRAST_REDUCTION_FACTOR + 128;
        b = (b - 128) * CONTRAST_REDUCTION_FACTOR + 128;

        // Clamp after contrast adjustment to prevent issues in next steps
        r = Math.max(0, Math.min(255, r));
        g = Math.max(0, Math.min(255, g));
        b = Math.max(0, Math.min(255, b));

        // --- 2. Desaturation ---
        // Calculate luminance using Rec.709 coefficients (standard for sRGB images)
        const lum = 0.2126 * r + 0.7152 * g + 0.0722 * b;
        
        // The saturation_retain_factor is how much of the original color (difference from luminance) is kept.
        const saturation_retain_factor = 1.0 - DESATURATION_AMOUNT;
        r = lum + saturation_retain_factor * (r - lum);
        g = lum + saturation_retain_factor * (g - lum);
        b = lum + saturation_retain_factor * (b - lum);

        // --- 3. Color Tinting for ETERNA Style ---
        // Apply the characteristic Eterna color shift.
        r = r * R_TINT_FACTOR;
        g = g * G_TINT_FACTOR;
        b = b * B_TINT_FACTOR;

        // --- Final Clamp ---
        // Ensure all color values are within the valid [0, 255] range.
        data[i] = Math.max(0, Math.min(255, r));
        data[i+1] = Math.max(0, Math.min(255, g));
        data[i+2] = Math.max(0, Math.min(255, b));
        // Alpha channel (data[i+3]) remains unchanged
    }

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