Image Aura Intensity Enhancer

function processImage(originalImg, auraColor = '255, 255, 255', intensity = 20, threshold = 120) {
    // Sanitize and parse input parameters for robustness
    const safeIntensity = Math.max(0, Number(intensity));
    const safeThreshold = Math.max(0, Math.min(255, Number(threshold)));
    const colorParts = auraColor.split(',').map(s => parseInt(s.trim(), 10));
    const cssColor = (colorParts.length === 3 && colorParts.every(c => !isNaN(c))) 
        ? `rgb(${colorParts[0]}, ${colorParts[1]}, ${colorParts[2]})`
        : 'rgb(255, 255, 255)'; // Default to white on invalid format

    // 1. Setup the main canvas for the final output image
    const canvas = document.createElement('canvas');
    canvas.width = originalImg.naturalWidth;
    canvas.height = originalImg.naturalHeight;
    const ctx = canvas.getContext('2d');

    // 2. Create a silhouette on a temporary, off-screen canvas.
    // This silhouette will be used to cast the "aura" glow effect.
    const silhouetteCanvas = document.createElement('canvas');
    silhouetteCanvas.width = canvas.width;
    silhouetteCanvas.height = canvas.height;
    // Add willReadFrequently hint for performance optimization with getImageData
    const silhouetteCtx = silhouetteCanvas.getContext('2d', { willReadFrequently: true });

    silhouetteCtx.drawImage(originalImg, 0, 0, canvas.width, canvas.height);
    const imageData = silhouetteCtx.getImageData(0, 0, silhouetteCanvas.width, silhouetteCanvas.height);
    const data = imageData.data;

    // Isolate the "bodies" by making everything else transparent.
    // The logic assumes that the subjects ("bodies") are darker than the background.
    for (let i = 0; i < data.length; i += 4) {
        const r = data[i];
        const g = data[i + 1];
        const b = data[i + 2];
        
        // Use the standard luminosity formula for a more accurate perception of brightness
        const brightness = 0.299 * r + 0.587 * g + 0.114 * b;

        if (brightness < safeThreshold) {
            // This pixel is part of the subject. Keep it for the silhouette shape
            // by ensuring its alpha is 255. The actual color doesn't matter for the
            // drop-shadow filter, only the alpha channel.
            data[i + 3] = 255;
        } else {
            // This pixel is part of the background. Make it fully transparent.
            data[i + 3] = 0;
        }
    }
    // Put the modified pixel data back onto the silhouette canvas.
    silhouetteCtx.putImageData(imageData, 0, 0);

    // 3. Draw the aura glow onto the main canvas using the generated silhouette.
    
    // Applying multiple stacked drop-shadows with different radii creates a richer, more intense glow.
    // A wider, more diffuse outer glow is combined with a tighter, brighter inner glow.
    ctx.filter = `drop-shadow(0 0 ${safeIntensity}px ${cssColor}) drop-shadow(0 0 ${Math.floor(safeIntensity / 3)}px ${cssColor})`;

    // Drawing the silhouette source multiple times enhances the opacity and intensity of the glow.
    ctx.drawImage(silhouetteCanvas, 0, 0);
    ctx.drawImage(silhouetteCanvas, 0, 0);
    
    // 4. Draw the original image on top of the generated aura.
    
    // CRITICAL: Reset the filter before drawing the next layer, otherwise the original image
    // will also get a shadow, which is not the desired effect.
    ctx.filter = 'none'; 
    ctx.drawImage(originalImg, 0, 0);

    // 5. Return the final canvas containing the complete image with the aura effect.
    return canvas;
}