Image Ghosting Persistence Effect Adder

function processImage(originalImg, ghostCount = 5, offsetX = -20, offsetY = 0, scaleStep = 1.0, opacityStart = 0.5, blurAmount = 0, blendMode = "screen") {
    const canvas = document.createElement('canvas');
    const ctx = canvas.getContext('2d');
    
    // Set canvas dimensions to match the original image
    const w = originalImg.width;
    const h = originalImg.height;
    canvas.width = w;
    canvas.height = h;

    // Draw the original base image
    ctx.globalAlpha = 1.0;
    ctx.globalCompositeOperation = 'source-over';
    ctx.drawImage(originalImg, 0, 0, w, h);

    // Parse parameters to guarantee correct types (handles both string/number inputs gracefully)
    const count = Math.max(0, parseInt(ghostCount, 10));
    const dx = parseFloat(offsetX);
    const dy = parseFloat(offsetY);
    const scale = parseFloat(scaleStep);
    const alphaStart = parseFloat(opacityStart);
    const blur = parseFloat(blurAmount);
    
    // Set proper blending mode to get the Ghosting/Persistence aesthetic 
    // Recommended modes: "screen", "lighten", "source-over", "overlay"
    ctx.globalCompositeOperation = String(blendMode);

    // Iteratively draw trailing "ghosts"
    for (let i = 1; i <= count; i++) {
        // Calculate a decaying opacity for each step in the persistence trail
        const currentAlpha = alphaStart * (1 - i / (count + 1));
        
        if (currentAlpha <= 0) break;
        ctx.globalAlpha = currentAlpha;

        if (blur > 0) {
            // Apply progressively increasing blur to simulate fading/motion trail
            ctx.filter = `blur(${blur * i}px)`;
        }

        // Calculate compounded scale and linear translation
        const currentScale = Math.pow(scale, i);
        const currentX = dx * i;
        const currentY = dy * i;

        ctx.save();
        
        // Translate to the middle for scaling from the center, plus the positional offset
        ctx.translate(w / 2 + currentX, h / 2 + currentY);
        ctx.scale(currentScale, currentScale);
        
        // Draw centered relative to the new origin
        ctx.drawImage(originalImg, -w / 2, -h / 2, w, h);
        
        ctx.restore();
    }

    return canvas;
}