JPG to WebP: For major archives like Wikipedia, Kiwix converts most images into WebP format.
Why this works: WebP is roughly 25–35% smaller than a JPG of comparable visual quality. This is how the full English Wikipedia recently dropped from 94 GB to 79 GB—the primary saving came from better image handling, not just text compression.
Lossy vs. Full Quality: Most Kiwix files use a “mobile-optimized” approach where images are slightly downscaled or compressed further than the original desktop versions to keep file sizes manageable for offline use.