Mosaic Filter
An image filter that averages pixel blocks to obscure details in selected regions, commonly used for privacy protection.
A mosaic filter divides a region of an image into a grid of rectangular blocks and replaces all pixels within each block with their average color value, rendering the original detail unrecognizable. Larger block sizes provide stronger concealment, while smaller blocks preserve more of the original contour. Typical block sizes range from 8x8 to 32x32 pixels.
Unlike Gaussian blur, which applies a continuous convolution for smooth defocusing, mosaic processing is discrete and produces a characteristic blocky appearance. This makes it the standard choice for obscuring faces and license plates in broadcast media and street-view imagery.
Implementation involves partitioning the target area into N×N blocks and filling each block with the mean RGB value of its constituent pixels. On the web, the Canvas API or dedicated mosaic tools make it straightforward to apply in real time.