Green Squad Image Tool

function processImage(originalImg, intensity = 100, style = "nightvision") {
    // Create an offscreen canvas
    const canvas = document.createElement('canvas');
    canvas.width = originalImg.width;
    canvas.height = originalImg.height;
    const ctx = canvas.getContext('2d');
    
    // Draw the original image onto the canvas
    ctx.drawImage(originalImg, 0, 0);

    // Fetch pixel data
    const imgData = ctx.getImageData(0, 0, canvas.width, canvas.height);
    const data = imgData.data;

    // Constrain intensity between 0 and 100, then convert to a 0.0 - 1.0 factor
    const factor = Math.max(0, Math.min(100, Number(intensity) || 100)) / 100;
    
    // Constants for vignette calculation in 'nightvision' mode
    const cx = canvas.width / 2;
    const cy = canvas.height / 2;
    const maxDist = Math.sqrt(cx * cx + cy * cy);

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

        // Calculate standard grayscale luminance
        const lum = 0.299 * r + 0.587 * g + 0.114 * b;

        let newR, newG, newB;

        if (style === "camo") {
            // "Camo" Mode: Posterize luminance into 4 classic military camouflage colors
            if (lum < 64) {
                newR = 30; newG = 40; newB = 20; // Black / Dark brown
            } else if (lum < 128) {
                newR = 75; newG = 83; newB = 32; // Dark olive green
            } else if (lum < 192) {
                newR = 120; newG = 134; newB = 59; // Light olive green
            } else {
                newR = 194; newG = 178; newB = 128; // Tan / Sand
            }
        } else {
            // "Night Vision" Mode (Default): High contrast green with scanline, noise, and vignette
            const pixelIndex = i / 4;
            const x = pixelIndex % canvas.width;
            const y = Math.floor(pixelIndex / canvas.width);
            
            // Map luminance mostly to the green channel
            newR = lum * 0.1;
            newG = lum * 1.6;
            newB = lum * 0.1;

            if (newG > 255) newG = 255;

            // Apply horizontal scanline effect (dim every other row slightly)
            if (y % 2 === 0) {
                newG *= 0.85;
            }

            // Apply vignette effect (darker towards the edges)
            const dx = x - cx;
            const dy = y - cy;
            const dist = Math.sqrt(dx * dx + dy * dy);
            const vignette = 1 - (dist / maxDist) * 0.45;

            newR = Math.min(255, newR * vignette);
            newG = Math.min(255, newG * vignette);
            newB = Math.min(255, newB * vignette);
            
            // Add slight random noise to simulate night vision goggles
            const noise = (Math.random() - 0.5) * 30; // Random shift
            newG = Math.max(0, Math.min(255, newG + noise));
        }

        // Apply intensity blending between original image and the green squad effect
        data[i]     = r + (newR - r) * factor;
        data[i + 1] = g + (newG - g) * factor;
        data[i + 2] = b + (newB - b) * factor;
    }

    // Write manipulated pixel data back to the canvas
    ctx.putImageData(imgData, 0, 0);

    return canvas;
}