Dropbox 針對 JPEG 圖片再次「無損壓縮」的 Lepton

Dropbox 針對 JPEG 圖片再次無損壓縮所發展出來的 Lepton:「Lepton image compression: saving 22% losslessly from images at 15MB/s」。

直接用傳統壓縮方式對 JPEG 檔壓縮是沒有用的,他們針對 JPEG 裡的內容分析後再次無損壓縮,並且可以還原成原來的 JPEG:

Lepton achieves a 22% savings reduction for existing JPEG images, by predicting coefficients in JPEG blocks and feeding those predictions as context into an arithmetic coder. Lepton preserves the original file bit-for-bit perfectly.

當檔案夠大時的壓縮率大約就是 22%:

很可觀的數字... 另外 Dropbox 也透漏了至少有 160 億張 JPEG 圖片:

We have used Lepton to encode 16 billion images saved to Dropbox, and are rapidly recoding our older images.

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