Image Archaeological Find Filter Effect Tool

function processImage(originalImg, sepiaLevel = 0.7, noiseStrength = 20, brightnessAdj = -15, contrastMul = 0.9, vignetteIntensity = 0.5) {
    // Ensure parameters are numbers and clamp them to sensible ranges
    sepiaLevel = Math.max(0, Math.min(1, Number(sepiaLevel)));
    noiseStrength = Math.max(0, Math.min(100, Number(noiseStrength))); // Max 100 for noise is quite high
    brightnessAdj = Math.max(-255, Math.min(255, Number(brightnessAdj)));
    contrastMul = Math.max(0, Math.min(5, Number(contrastMul))); // Contrast factor
    vignetteIntensity = Math.max(0, Math.min(1, Number(vignetteIntensity)));

    const canvas = document.createElement('canvas');
    const ctx = canvas.getContext('2d');

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

    // If image is not loaded or has no dimensions, return an empty canvas of correct size (or draw nothing)
    if (width === 0 || height === 0) {
        // Optionally fill with a placeholder color if desired, or just return
        // ctx.fillStyle = 'grey'; 
        // ctx.fillRect(0,0,width,height);
        return canvas;
    }

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

    const centerX = width / 2;
    const centerY = height / 2;
    // Max distance from center to a corner, for vignette calculations
    const maxDistCorner = (width > 0 && height > 0) ? Math.sqrt(centerX * centerX + centerY * centerY) : 0;

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

        // 1. Apply Sepia
        if (sepiaLevel > 0) {
            // Standard sepia weights
            const sr = (r_orig * 0.393) + (g_orig * 0.769) + (b_orig * 0.189);
            const sg = (r_orig * 0.349) + (g_orig * 0.686) + (b_orig * 0.168);
            const sb = (r_orig * 0.272) + (g_orig * 0.534) + (b_orig * 0.131);
            
            // Blend original with sepia based on sepiaLevel
            r = r_orig * (1 - sepiaLevel) + sr * sepiaLevel;
            g = g_orig * (1 - sepiaLevel) + sg * sepiaLevel;
            b = b_orig * (1 - sepiaLevel) + sb * sepiaLevel;
        }

        // 2. Apply Brightness Adjustment
        r += brightnessAdj;
        g += brightnessAdj;
        b += brightnessAdj;

        // 3. Apply Contrast Adjustment
        // Adjust contrast by stretching/compressing values around midpoint (128)
        r = (r - 128) * contrastMul + 128;
        g = (g - 128) * contrastMul + 128;
        b = (b - 128) * contrastMul + 128;
        
        // Intermediate clamping after tonal adjustments
        r = Math.max(0, Math.min(255, r));
        g = Math.max(0, Math.min(255, g));
        b = Math.max(0, Math.min(255, b));

        // 4. Apply Noise
        if (noiseStrength > 0) {
            // Generate noise between -noiseStrength and +noiseStrength
            const noise = (Math.random() - 0.5) * 2 * noiseStrength;
            r += noise;
            g += noise;
            b += noise;
        }
        
        // Clamp again after noise
        r = Math.max(0, Math.min(255, r));
        g = Math.max(0, Math.min(255, g));
        b = Math.max(0, Math.min(255, b));

        // 5. Apply Vignette
        if (vignetteIntensity > 0 && maxDistCorner > 0) {
            const currentX = (i / 4) % width;
            const currentY = Math.floor((i / 4) / width);
            
            const dx = currentX - centerX;
            const dy = currentY - centerY;
            const dist = Math.sqrt(dx * dx + dy * dy);
            
            // vignetteFactor goes from 1 (center) to (1 - vignetteIntensity) at corners
            let vignetteFactor = 1.0 - (dist / maxDistCorner) * vignetteIntensity;
            vignetteFactor = Math.max(0, Math.min(1, vignetteFactor)); // Ensure factor is [0, 1]
            
            r *= vignetteFactor;
            g *= vignetteFactor;
            b *= vignetteFactor;
        }

        // Final Clamp for all combined effects
        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;
}