Calibre error on 'Compress images'

Pachuqismo · 07-17-2026, 07:48 PM

I'm getting the following error on ePubs (also after reinstalling Calibre). I only select to 'Enable lossy compression of JPEG images':

Calibre, version 9.11.0
ERROR: Unexpected error: Failed to compress images, click "Show details" for more information

Traceback (most recent call last):
File "calibre\gui2\tweak_book\polish.py", line 348, in run_compress
File "calibre\ebooks\oeb\polish\images.py", line 172, in compress_images
File "calibre\ebooks\oeb\polish\images.py", line 151, in convert_png_to_format
IndexError: Replacement index 5 out of range for positional args tuple

Any ideas? Cheers!

Comfy.n · 07-17-2026, 08:32 PM

This has been fixed, AFAIK. But we need to wait for next release.

https://github.com/kovidgoyal/calibr...b4fd71030f81e1

Pachuqismo · 07-17-2026, 09:03 PM

Quote:

Originally Posted by Comfy.n

This has been fixed, AFAIK. But we need to wait for next release.

https://github.com/kovidgoyal/calibr...b4fd71030f81e1

Thanks for your response, though the link refers to a bug in converting PNG to JPEG - I'm trying to further reduce JPGs.

I did a 'repair' of my Calibre and may have to do a clean install...

Cheers!

JSWolf · Yesterday, 05:55 AM

If you aren't doing this compression of your JPG in the editor, try the editor. That's where I do it and I’ve not had an error.

PeterT · Yesterday, 09:10 AM

Quote:

Originally Posted by Pachuqismo

Thanks for your response, though the link refers to a bug in converting PNG to JPEG - I'm trying to further reduce JPGs.

I did a 'repair' of my Calibre and may have to do a clean install...

Cheers!

While maybe it does, I sense that this fix will resolve your issue seeing your error occurs in line 151 which is being affected by this change

07-17-2026, 07:48 PM	#1
Pachuqismo Enthusiast Posts: 39 Karma: 10 Join Date: Nov 2009 Device: SM-T820, Galaxy S7	Calibre error on 'Compress images' I'm getting the following error on ePubs (also after reinstalling Calibre). I only select to 'Enable lossy compression of JPEG images': Calibre, version 9.11.0 ERROR: Unexpected error: Failed to compress images, click "Show details" for more information Traceback (most recent call last): File "calibre\gui2\tweak_book\polish.py", line 348, in run_compress File "calibre\ebooks\oeb\polish\images.py", line 172, in compress_images File "calibre\ebooks\oeb\polish\images.py", line 151, in convert_png_to_format IndexError: Replacement index 5 out of range for positional args tuple Any ideas? Cheers!

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07-17-2026, 08:32 PM	#2
Comfy.n want to learn what I want Posts: 2,366 Karma: 7990245 Join Date: Sep 2020 Device: Libra Colour	This has been fixed, AFAIK. But we need to wait for next release. https://github.com/kovidgoyal/calibr...b4fd71030f81e1

Yesterday, 05:55 AM	#4
JSWolf Resident Curmudgeon Posts: 84,204 Karma: 153715495 Join Date: Nov 2006 Location: Roslindale, Massachusetts Device: Kobo Libra 2, Kobo Aura H2O, PRS-650, PRS-T1, nook STR, PW3	If you aren't doing this compression of your JPG in the editor, try the editor. That's where I do it and I’ve not had an error.

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