Image Kodak Ektar 100 Film Filter Effect

function processImage(originalImg) {
    const canvas = document.createElement('canvas');
    
    // Ensure the originalImg is a loaded image with valid dimensions
    if (!originalImg || typeof originalImg.width === 'undefined' || originalImg.width === 0 || typeof originalImg.height === 'undefined' || originalImg.height === 0) {
        console.error("Provided originalImg is not valid or not loaded.");
        // Return an empty canvas or handle as an error appropriately
        canvas.width = 1; // Minimal canvas
        canvas.height = 1;
        return canvas;
    }

    canvas.width = originalImg.width;
    canvas.height = originalImg.height;

    const ctx = canvas.getContext('2d', { willReadFrequently: true });

    if (!ctx) {
        console.error("Could not get 2D rendering context.");
        // Fallback: return the canvas, which might be empty or not properly initialized
        return canvas;
    }

    try {
        ctx.drawImage(originalImg, 0, 0, canvas.width, canvas.height);
    } catch (e) {
        console.error("Error drawing image to canvas: ", e);
        // Return canvas, possibly empty or with partial draw if error occurred
        return canvas;
    }

    let imageData;
    try {
        imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
    } catch (e) {
        console.error("Error getting ImageData (e.g., canvas tainted from cross-origin image): ", e);
        // If canvas is tainted, pixel manipulation is not possible.
        // Return the canvas with the original image drawn.
        return canvas;
    }
    
    const data = imageData.data;

    // Kodak Ektar 100 Film Effect Parameters. These values are tuned to approximate
    // the known characteristics of Ektar 100 film (high saturation, fine grain,
    // punchy reds/blues, good contrast, slight warmth).
    const CONTRAST_FACTOR = 1.15;       // Increases contrast for a "punchier" image.
    const SATURATION_FACTOR = 1.30;     // Ektar is known for its vivid, saturated colors.
    
    // Channel-specific multipliers to adjust the color palette.
    const RED_CHANNEL_MULTIPLIER = 1.10;  // Enhances reds, making them more vibrant.
    const GREEN_CHANNEL_MULTIPLIER = 0.97;// Slightly subdues or shifts greens. Ektar greens are often described as natural but not overly dominant.
    const BLUE_CHANNEL_MULTIPLIER = 1.08; // Deepens and enriches blues.

    // Additive warmth to introduce a subtle warm color cast.
    const WARMTH_ADD_R = 6; // Adds warmth via the red channel.
    const WARMTH_ADD_G = 3; // Adds a smaller amount of warmth via the green channel.
                               // Blue channel is not warmed to maintain clarity of cool tones.

    // Standard luminance coefficients for saturation calculation.
    const R_LUM_COEFF = 0.299;
    const G_LUM_COEFF = 0.587;
    const B_LUM_COEFF = 0.114;

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

        // 1. Apply Contrast
        // Pixel values are normalized to [0,1], adjusted around the 0.5 midpoint, then scaled back.
        r = (r / 255.0 - 0.5) * CONTRAST_FACTOR + 0.5;
        g = (g / 255.0 - 0.5) * CONTRAST_FACTOR + 0.5;
        b = (b / 255.0 - 0.5) * CONTRAST_FACTOR + 0.5;
        
        // Convert back to 0-255 range and clamp
        r = Math.max(0, Math.min(1.0, r)) * 255.0;
        g = Math.max(0, Math.min(1.0, g)) * 255.0;
        b = Math.max(0, Math.min(1.0, b)) * 255.0;

        // 2. Apply Saturation
        // Calculates luminance, then adjusts color components away from or towards this gray value.
        const lum = R_LUM_COEFF * r + G_LUM_COEFF * g + B_LUM_COEFF * b;
        r = lum + SATURATION_FACTOR * (r - lum);
        g = lum + SATURATION_FACTOR * (g - lum);
        b = lum + SATURATION_FACTOR * (b - lum);
        
        // Clamp values after saturation
        r = Math.max(0, Math.min(255.0, r));
        g = Math.max(0, Math.min(255.0, g));
        b = Math.max(0, Math.min(255.0, b));

        // 3. Apply Ektar Color Signature (Channel Multipliers and Warmth)
        r *= RED_CHANNEL_MULTIPLIER;
        g *= GREEN_CHANNEL_MULTIPLIER;
        b *= BLUE_CHANNEL_MULTIPLIER;
        
        // Add warmth
        r += WARMTH_ADD_R;
        g += WARMTH_ADD_G;
        // b is intentionally not increased by WARMTH_ADD to preserve cool blue tones.

        // Final clamp and assignment
        // Values are rounded to the nearest integer for pixel data.
        data[i]   = Math.max(0, Math.min(255, Math.round(r)));
        data[i+1] = Math.max(0, Math.min(255, Math.round(g)));
        data[i+2] = Math.max(0, Math.min(255, Math.round(b)));
        // Alpha channel (data[i+3]) is preserved.
    }

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