G-Major 22 Image Effect Generator

function processImage(originalImg, effectIntensity = "100") {
    const canvas = document.createElement('canvas');
    const ctx = canvas.getContext('2d');
    
    canvas.width = originalImg.width;
    canvas.height = originalImg.height;

    // Draw the original image onto the canvas
    ctx.drawImage(originalImg, 0, 0);

    const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
    const data = imageData.data;
    
    // Parse the intensity parameter and map it from 0-100 to 0.0-1.0
    const intensity = Math.min(100, Math.max(0, Number(effectIntensity))) / 100;

    // Contrast adjustment factor (to make it look more harsh/creepy like the meme effects)
    const contrastLevel = 60; // Adjust between 0 to 255
    const contrastFactor = (259 * (contrastLevel + 255)) / (255 * (259 - contrastLevel));

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

        // 1. Invert colors (Base of standard G-Major effects)
        let ir = 255 - r;
        let ig = 255 - g;
        let ib = 255 - b;

        // 2. Channel Swapping / Hue shifting (Typically G-Major has shifted RGB channels)
        // For distinct visual flair often found in variant effects like G-Major 22:
        let outR = ir;
        let outG = ib; // Swap Green and Blue channels
        let outB = ig;

        // 3. Apply contrast boost
        outR = contrastFactor * (outR - 128) + 128;
        outG = contrastFactor * (outG - 128) + 128;
        outB = contrastFactor * (outB - 128) + 128;

        // 4. Clamp colors and apply the blending intensity
        data[i]     = r + (Math.max(0, Math.min(255, outR)) - r) * intensity; // Red
        data[i + 1] = g + (Math.max(0, Math.min(255, outG)) - g) * intensity; // Green
        data[i + 2] = b + (Math.max(0, Math.min(255, outB)) - b) * intensity; // Blue
        // Alpha channel (data[i + 3]) remains untouched
    }

    // Put the processed pixel data back onto the canvas
    ctx.putImageData(imageData, 0, 0);
    
    return canvas;
}