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Overview

Most of an EPUB’s size comes from its images. Compresto compresses the JPEG, PNG, and WebP images inside the book and leaves the text, styles, and fonts untouched, so the book reads exactly as before, only smaller. Opening an EPUB in Finder still opens it in your reader. To compress one, add it to Compresto.

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Quick Start

1
Click on the selection panel to select EPUB files, or drag and drop them into it
2
Choose an EPUB quality level
3
Press Compress to start
4
View compression results and open files in Finder

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Quality Options

Images are only scaled down, never up. Each image keeps its format and file name, so links inside the book keep working.

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What gets compressed

  • Compressed: JPEG, PNG, and WebP images
  • Left unchanged: text, CSS, fonts, GIF and SVG images, and everything else in the book
Compresto never makes a book bigger. An image is only replaced if the compressed version is smaller, and if the whole book doesn’t get smaller, the original is kept.

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Copy-protected books

Books protected with DRM have encrypted images, which can’t be compressed. Compresto leaves these files unchanged and shows a message explaining why. Books that only encrypt their fonts (common with font obfuscation) are not treated as copy-protected and can still be compressed.

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Where EPUB compression is available

Folder monitoring doesn’t support EPUB files.

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Tips for Best Results

  • For comics and photo books: Start with High to keep artwork sharp
  • For text-heavy novels: Balance or Low works well; the savings come from cover and inline images
  • For sending by email: Use Low for the smallest file
  • If a book barely shrinks: It likely has few images, or they’re already well compressed