Batch processing EPUB lossy compression

[karlfranz]

I was given several hundred EPUB files that are (needlessly) about 2-300MB in size. I find that I can use Calibre's pub editor to effectively compress each book by 80-90% by using lossy compression set to 60 while still remaining fully readable for my needs. However, it is quite tedious to individually:

1. Open each file in the editor;
2. Select "Tools|Compress images losslessly";
3. Select the two "Enable Lossy Compression" checkboxes;;
4. Click OK;
5. Wait for compression to complete;
6. Click Close on the compression results "Action Report" dialog box;
7. Save the new compressed EPUB and close the editor.

Is there a plugin or action that would allow me to automate this so I can batch process all my files in one go?

[theducks]

That is already a choice of Polish
Select Books: Click the Polish icon: tick the options as desired: OK

[karlfranz]

Originally Posted by theducks

That is already a choice of Polish
Select Books: Click the Polish icon: tick the options as desired: OK

Polish doesn't seem to let me choose a level of lossy compression. I think it only does lossless compression which isn't very effective in reducing file size.

[theducks]

Sorry, misread the request.
Bulk mode Metadata Edit has a spin wheel (Compress Images) near the bottom.

[karlfranz]

Originally Posted by theducks

Sorry, misread the request.
Bulk mode Metadata Edit has a spin wheel (Compress Images) near the bottom.

I'm confused. My Bulk Metadata Edit has a checkbox near the bottom of the "Basic Metadata" tab called "Compress cover images" along with a compression amount spinner. But it's only for the cover image, not all the images in the EPUB.

[JSWolf]

Originally Posted by theducks

Sorry, misread the request.
Bulk mode Metadata Edit has a spin wheel (Compress Images) near the bottom.

That won't work as it's only for compressing the cover.

[karlfranz]

Originally Posted by JSWolf

That won't work as it's only for compressing the cover.

Exactly.

[kovidgoyal]

Do an EPUB to EPUB bulk conversion and in the epub output section specify a max resolution for the images.

[capink]

A combination of Editor Chains and Action Chains lets you perform lossy compression on multiple books.

In Editor Chains, there is a an action called "Compress Images", that enables you to automate this process. You can use the Action Chains to run this for multiple books. (chain in first attachment).

If you want to use an external tool to for lossy compression, e.g. ImageMagick, which can help convert png to jpg, you can use the Run Command action which will iterate over all images in an epub. See this post and screenshots for more details. (chain in second attachment). Note however, that you might need to edit the chain to configure the path to ImageMagick on your system.

To import the attached chains: Action Chains > Add/Modify chains > right click the chains table > import > browse to the zip file.

Note: I have found the ImageMagick approach to be much faster with lossy compression compared to the first approach that uses the editor's "Compress Images". Test with both and see which is more satisfactory.

[JSWolf]

Originally Posted by capink

A combination of Editor Chains and Action Chains lets you perform lossy compression on multiple books, by running ImageMagick commands on the images.

See this post and screenshots for more details.

For how to use both plugins together consult the first post in Editor Chains thread.

Is there a way to do a lossy lossless compression on the images? In the editor, it does the compress of 70 that I specified and then does a lossless compression from there.

[capink]

Originally Posted by JSWolf

Is there a way to do a lossy lossless compression on the images? In the editor, it does the compress of 70 that I specified and then does a lossless compression from there.

It can replicate what the editor does by using the "Compress Images". I updated the post above with example chains.

[karlfranz]

Originally Posted by capink

A combination of Editor Chains and Action Chains lets you perform lossy compression on multiple books.

In Editor Chains, there is a an action called "Compress Images", that enables you to automate this process. You can use the Action Chains to run this for multiple books. (chain in first attachment).

If you want to use an external tool to for lossy compression, e.g. ImageMagick, which can help convert png to jpg, you can use the Run Command action which will iterate over all images in an epub. See this post and screenshots for more details. (chain in second attachment). Note however, that you might need to edit the chain to configure the path to ImageMagick on your system.

To import the attached chains: Action Chains > Add/Modify chains > right click the chains table > import > browse to the zip file.

Note: I have found the ImageMagick approach to be much faster with lossy compression compared to the first approach that uses the editor's "Compress Images". Test with both and see which is more satisfactory.

This worked a treat. THANK YOU!