G-Major 74 Image Effect Generator

function processImage(originalImg, hueShift = "180", invertLevel = "100", contrastLevel = "300", saturateLevel = "500", rgbSplit = "8", mirrorEffect = "1", useScanlines = "1") {
    // Create canvas to process the image
    const canvas = document.createElement("canvas");
    const ctx = canvas.getContext("2d");
    const w = originalImg.width;
    const h = originalImg.height;
    canvas.width = w;
    canvas.height = h;

    // 1. Initial pass: Apply classic "G-Major" meme effects (Extreme saturation, color inversion, hue shift, harsh contrast)
    ctx.filter = `invert(${parseFloat(invertLevel)}%) hue-rotate(${parseFloat(hueShift)}deg) saturate(${parseFloat(saturateLevel)}%) contrast(${parseFloat(contrastLevel)}%)`;
    ctx.drawImage(originalImg, 0, 0, w, h);

    // Parse additional FX parameters
    const offset = parseInt(rgbSplit, 10);
    const isMirror = parseInt(mirrorEffect, 10) === 1;
    const hasScanlines = parseInt(useScanlines, 10) === 1;

    // 2. Pixel manipulation pass: Chromatic aberration, symmetrical mirroring, and retro TV scanlines
    if (offset !== 0 || isMirror || hasScanlines) {
        const imageData = ctx.getImageData(0, 0, w, h);
        const data = imageData.data;
        const outputData = ctx.createImageData(w, h);
        const out = outputData.data;

        for (let y = 0; y < h; y++) {
            // Darken every 3rd line slightly to emulate CRT/VCR scanline distortion often found in creepy video effects
            const scanlineMultiplier = (hasScanlines && y % 3 === 0) ? 0.7 : 1.0;

            for (let x = 0; x < w; x++) {
                const outIdx = (y * w + x) * 4;

                // Calculate source X for mirror effect (reflecting the left half over the right half)
                let srcX = x;
                if (isMirror && x > w / 2) {
                    srcX = w - 1 - x;
                }

                // Calculate X offsets for chromatic aberration (RGB Channel Split)
                const rX = Math.max(0, srcX - offset);
                const bX = Math.min(w - 1, srcX + offset);
                const gX = srcX;

                // Get array indices
                const rIdx = (y * w + rX) * 4;
                const gIdx = (y * w + gX) * 4;
                const bIdx = (y * w + bX) * 4;

                // Assign to the output array with chromatic shifts and dark lines applied
                out[outIdx] = data[rIdx] * scanlineMultiplier;       // Red
                out[outIdx + 1] = data[gIdx + 1] * scanlineMultiplier; // Green
                out[outIdx + 2] = data[bIdx + 2] * scanlineMultiplier; // Blue
                out[outIdx + 3] = data[gIdx + 3];                      // Alpha (kept intact)
            }
        }
        // Draw the modified pixels back to the canvas
        ctx.putImageData(outputData, 0, 0);
    }

    return canvas;
}