Converting Photos to Sketches Is Edge Detection Plus Inversion

The pencil sketch effect that photo editors offer is not a neural network or complex algorithm. It is edge detection inverted to white lines on white background. The entire process takes four steps and runs in real time on canvas. The algorithm Step 1: Convert to grayscale. Step 2: Invert the grayscale image. Step 3: Apply Gaussian blur to the inverted image. Step 4: Blend the grayscale and blurred-inverted images using "Color Dodge." function photoToSketch(imageData, blurRadius = 20) { const width = imageData.width; const height = imageData.height; const data = imageData.data; // Step 1: Grayscale const gray = new Uint8Array(width * height); for (let i = 0; i < gray.length; i++) { const idx = i * 4; gray[i] = Math.round(0.299 * data[idx] + 0.587 * data[idx+1] + 0.114 * data[idx+2]); } // Step 2: Invert const inverted = gray.map(v => 255 - v); // Step 3: Blur the inverted image const blurred = gaussianBlur(inverted, width, height, blurRadius); // Step 4: Color Dodge blend for (le