How WebP Compression Works

Quick Summary

• WebP uses advanced predictive encoding based on VP8 (lossy) and VP8L (lossless) codecs.
• Offers 25-35% better compression than JPEG and PNG while maintaining similar quality.
• Supports both lossy and lossless compression, plus transparency and animation.
• Ideal for modern web applications and mobile-first designs.

WebP Format Overview

WebP is a modern image format developed by Google that provides superior lossless and lossy compression for images on the web. Using predictive coding, WebP can reduce image file sizes significantly while maintaining high visual quality.

Lossy WebP Compression

Lossy WebP is based on the VP8 video codec and uses block-based predictive encoding. The process works as follows:

• Predictive Encoding: Each block is predicted from already encoded neighboring blocks.
• Transform: The residual (difference between prediction and actual) is transformed using DCT.
• Quantization: Transform coefficients are quantized to reduce precision and file size.
• Entropy Coding: Arithmetic coding efficiently compresses the quantized data.

Lossless WebP Compression

Lossless WebP uses the VP8L codec with several advanced techniques:

• Predictive Coding: Predicts pixel values from nearby pixels using multiple prediction modes.
• Color Cache: Stores recently used colors for efficient encoding of repeated colors.
• Palette: Can use a color palette for images with limited colors.
• Huffman Coding: Uses entropy coding to compress the resulting data stream.

WebP vs JPEG vs PNG

Optimization Techniques

To get the best compression with WebP:

• Choose the Right Mode: Use lossy for photographs and lossless for graphics with text or sharp edges.
• Quality Settings: For lossy WebP, quality 75-85 offers excellent balance of size and visual quality.
• Preprocessing: Consider resizing images to the display size before compression.
• Alpha Channel: For images with transparency, WebP can compress the alpha channel efficiently.

When to Use WebP

WebP is ideal for:

• Modern web applications targeting current browsers
• Mobile-first responsive designs where bandwidth is critical
• E-commerce product images requiring fast loading
• Any scenario where you need both quality and small file sizes
• Images with transparency that don't need to support legacy browsers

Browser Support

WebP is supported by all modern browsers including Chrome (since 2010), Firefox (since 2019), Edge (since 2018), and Safari (since 2020). With over 97% global browser support, WebP is production-ready for most web applications.

For legacy browser support, use the <picture> element with fallbacks:

<picture>
  <source srcset="image.webp" type="image/webp">
  <source srcset="image.jpg" type="image/jpeg">
  <img src="image.jpg" alt="Description">
</picture>