Quote:
Originally Posted by k12b5
You're right - Calibre's "compress image" only re-encodes in the current format, and I've never seen a plugin that converts PNG to JPG either. The usual approach is to convert outside Calibre and put the results back in:
1. Extract: EPUBs are just ZIPs, so unzip book.epub -d book/ - the PNGs will be under book/OEBPS/images/.
2. Convert: drop that folder into a batch converter. If you have no qualms about installing, mogrify -format jpg -quality 85 *.png (ImageMagick) does the whole folder at once. If you'd rather not, Handio's PNG to JPG converts all uploaded images in one click with a quality slider and a "download all" button - files are processed in your browser, nothing gets uploaded.
3. Rebuild: swap the converted JPGs back in, then re-zip: cd book && zip -X -r ../book.epub mimetype * (zip the mimetype file first, uncompressed).
Two caveats: only convert photographic images - PNGs containing text or diagrams will look worse as JPG. And keep quality at 85+, since ebook readers stretch images and artifacts show up more than on screen. |
Your wrong. The current version of calibre does support converting PNG to JPG. You have to do this in the editor.