Apply cbz-style image processing to epub conversion?

[CavemanJoe]

Hey all, vintage ereader user here, intensely appreciative of Calibre's handling of .cbz files and hoping that similar functionality can be applied to non-cbz inputs.

When you use Calibre's built-in PRS-505 profile to import a .cbz (such as a comic) and convert to .epub, Calibre will automatically resize every image to perfectly fit the PRS-505's screen, and also turn the image greyscale to an appropriate number of shades to further reduce file size, with optional sharpening. I believe this feature was originally a plugin that was impressive enough to be merged with the main Calibre project.

I have a stack of ex-display-model PRS-505 ereaders that I'm replacing batteries and handing out to friends, and I'm in the process of writing a guide on how to make new ebook files play nicely with vintage ereaders, to try to keep these machines in use and out of the e-waste stream. Even after removing DRM, these lovely old 600x800 machines frequently choke on the gargantuan chapter heading images inside modern .epub files.

I've had success using a combination of Polish Books (to subset fonts and compress images) and Bulk Image Resizer plugins, but Bulk Image Resizer can't be run on multiple books at once (it requires you to enter the ebook editor window and run on books one at a time), nor does it greyscale any images.

The process I've come up with is a far cry from the excellent one-click .cbz to .epub workflow, and I was initially thinking of writing a plugin that would automatically shrink all images to screen-appropriate sizes and colour depth, but quickly realised this would be a massive duplication of effort given that Calibre already has the ability to resize-and-greyscale all images when converting .cbz to .epub, but doesn't have the same behaviour when importing books in other formats.

Is there a way to do this that I'm missing, should I submit this as a feature request, or am I diving into plugin writing?

Cheers!

[capink]

Originally Posted by CavemanJoe

I've had success using a combination of Polish Books (to subset fonts and compress images) and Bulk Image Resizer plugins, but Bulk Image Resizer can't be run on multiple books at once (it requires you to enter the ebook editor window and run on books one at a time), nor does it greyscale any images.

The process I've come up with is a far cry from the excellent one-click .cbz to .epub workflow, and I was initially thinking of writing a plugin that would automatically shrink all images to screen-appropriate sizes and colour depth, but quickly realised this would be a massive duplication of effort given that Calibre already has the ability to resize-and-greyscale all images when converting .cbz to .epub, but doesn't have the same behaviour when importing books in other formats.

Cheers!

The combination of Editor Chains and Action Chains can process images from multiple books in your library.

Editor chain as an action called "Run Command", which enables you to run a command like ImageMagick convert to process images inside ebooks. More on this in this post.

For more information, consult the documentation of both plugins.

[DNSB]

Have you looked at the Kindle Comic Converter? It will convert images to epub and has quite a few options. See Kindle Comic Converter - Convert comics/manga to MOBI/EPUB

[CavemanJoe]

Originally Posted by DNSB

Have you looked at the Kindle Comic Converter? It will convert images to epub and has quite a few options. See Kindle Comic Converter - Convert comics/manga to MOBI/EPUB

Thanks for the rec but I'm already very happy with how Calibre processes comics, I just want to use that same auto-resize-greyscale-etc functionality on images inside regular .epub files for things like massive chapter heading images, maps, ads for the publisher's other books, author mugshots, that kind of thing.

[CavemanJoe]

Originally Posted by capink

The combination of Editor Chains and Action Chains can process images from multiple books in your library.

Editor chain as an action called "Run Command", which enables you to run a command like ImageMagick convert to process images inside ebooks. More on this in this post.

For more information, consult the documentation of both plugins.

Thanks, if I can't get Calibre to do this with built-in methods I'll take a look at the docs for these two plugins.

[CavemanJoe]

Months later, for those wanting to resize every image inside a book, turns out Calibre already does this but the explanatory text under "EPUB output" in the conversion dialogue is wrong. Where it says "A value of none means use the screen size from the output profile. A value of profile means no maximum size is specified" it should read "A value of profile means use the screen size from the output profile. A value of none means no maximum size is specified."

So just set the "Shrink images larger than:" setting to "profile" and do an epub to epub conversion, and Calibre will resize all the images automatically. No greyscaling or colour reducing but usually a massive file size reduction anyway.

(also, these ereaders that were twenty bucks on eBay five years ago because they couldn't go on the internet, are now two hundred bucks on eBay because they can't go on the internet lol)