What Is a WEBP File? Architecture, Lossy vs Lossless, and Browser Support

WEBP is a raster image file format developed by Google in 2010 to accelerate webpage load times. Built upon the intra-frame prediction algorithms of the VP8 video codec and packaged inside a Resource Interchange File Format (RIFF) container, WEBP provides both lossy compression (replacing JPEG) and lossless compression (replacing PNG) in a single unified specification.

Every WEBP file begins with a 12-byte RIFF header. The first 4 bytes are ASCII "RIFF", followed by a 4-byte little-endian file length, and the 4-byte FourCC code "WEBP". Subsequent chunks specify either VP8 (lossy), VP8L (lossless), or VP8X (extended features such as alpha channel, EXIF metadata, and animations).

• Magic Bytes (Hex): 52 49 46 46 [Length] 57 45 42 50
• MIME Content-Type: image/webp
• Standard Extension: .webp
• Payload Chunks: VP8 (lossy DCT), VP8L (lossless spatial prediction), VP8X (canvas & alpha headers)

WEBP features two completely distinct compression engines depending on whether lossless fidelity or maximum size reduction is required:

• Lossy WEBP (VP8): Uses block prediction based on neighboring sub-blocks before computing discrete cosine transforms, reducing quantization noise in photographic scenes.
• Lossless WEBP (VP8L): Uses spatial transforms, color subtraction, local color cache indices, and Huffman entropy coding to achieve 26% higher density than optimized PNG files.
• Alpha Channel Transparency: Supports 8-bit alpha transparency with both lossy and lossless color payloads — a feature legacy JPEG cannot perform.