Posterize Photos Online Reduce the number of color levels per channel for a flat, poster-like effect.

The tool works by using the HTML5 Canvas API to manipulate image data. When an image is loaded, it creates a new Image object and sets its source to the uploaded file. Once the image is loaded, it draws the image onto a canvas element using the drawImage method of the 2D drawing context. The getImageData method is then used to retrieve the pixel data from the canvas, which is stored in a Uint8ClampedArray. This array contains four values for each pixel: red, green, blue, and alpha.

The posterization effect is achieved by iterating over this array and applying the formula output = Math.round(Math.floor(input / (256/n)) * (255/(n-1))) to each color channel. This maps 256 input values to n discrete output values evenly distributed across 0-255. The result is a pixelated image with reduced color levels. The putImageData method is then used to draw the modified pixel data back onto the canvas, and the toDataURL method is used to convert the canvas to a PNG image, which can be downloaded by the user.

The tool uses React hooks such as useState and useRef to manage state and references to DOM elements. The useEffect hook is used to revoke the object URL of the uploaded image when it is no longer needed, preventing memory leaks. The useCallback hook is used to memoize functions that are used as event handlers, preventing unnecessary re-renders. The tool also uses TypeScript to ensure type safety and prevent errors at runtime.

The canvas element is used to draw and manipulate the image data in real-time, allowing for fast and efficient processing of images. The range slider and predefined buttons allow users to adjust the number of color levels, which directly affects the level of posterization applied to the image. The tool uses a combination of JavaScript, React, and HTML5 APIs to achieve this functionality, providing a powerful and flexible way to apply posterization effects to images.