Image Dreamy Glow Filter

function processImage(originalImg, blurAmount = 8, glowBrightness = 1.2, glowOpacity = 0.6) {
    // Ensure numeric types for parameters, coercing if they are strings
    const numBlurAmount = Number(blurAmount);
    const numGlowBrightness = Number(glowBrightness);
    const numGlowOpacity = Number(glowOpacity);

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

    // Use naturalWidth/Height for intrinsic dimensions of the image
    const width = originalImg.naturalWidth || originalImg.width;
    const height = originalImg.naturalHeight || originalImg.height;

    canvas.width = width;
    canvas.height = height;

    // 1. Create a temporary canvas for the glow layer
    const glowCanvas = document.createElement('canvas');
    glowCanvas.width = width;
    glowCanvas.height = height;
    const glowCtx = glowCanvas.getContext('2d');

    // 2. Prepare the glow layer:
    //    Apply blur and brightness filters. The filter is applied when drawImage is called.
    glowCtx.filter = `blur(${numBlurAmount}px) brightness(${numGlowBrightness})`;
    glowCtx.drawImage(originalImg, 0, 0, width, height);
    
    // It's good practice to reset filter on the context if it were to be used for other drawings,
    // though for this single-use temporary canvas, it's not strictly necessary.
    // glowCtx.filter = 'none';

    // 3. Draw the original image onto the main canvas
    ctx.drawImage(originalImg, 0, 0, width, height);

    // 4. Blend the glow layer onto the main canvas
    //    'screen' blend mode is effective for glow effects as it brightens.
    //    'lighter' (same as 'add' in some software) could also be used for a more intense glow.
    ctx.globalAlpha = numGlowOpacity;
    ctx.globalCompositeOperation = 'screen'; 
    ctx.drawImage(glowCanvas, 0, 0, width, height);

    // 5. Reset main canvas context properties to defaults
    ctx.globalAlpha = 1.0;
    ctx.globalCompositeOperation = 'source-over';
    ctx.filter = 'none';

    return canvas;
}