Lossy Compression
Lossy Compression (Perceptual Data Reduction)
Lossy compression achieves much smaller file sizes by permanently discarding image data that is less perceptible to human vision. JPEG, WebP lossy, and AVIF use this approach to achieve 10:1 to 50:1 compression ratios.
技术细节
JPEG lossy compression applies DCT to 8x8 pixel blocks, then quantizes frequency coefficients based on quality settings. Higher quantization discards more high-frequency detail, reducing file size but introducing visible artifacts.
示例
```javascript
// Image compression via Canvas
canvas.toBlob(
blob => console.log(`Size: ${(blob.size/1024).toFixed(0)} KB`),
'image/jpeg',
0.8 // quality: 0.0 (smallest) to 1.0 (best)
);
// WebP output (25-34% smaller than JPEG)
canvas.toBlob(cb, 'image/webp', 0.8);
```