Black squares in Djvu files instead of a text after reflowing

MaxStirner · 01-08-2022, 08:05 PM

Strange thing is that it never happens in the entire document, only every several pages. The pages in between are rendered perfectly fine. I can't find any pattern in this. It is also relatively rare as most djvu files are ok, only one in a dozen seems to be affected. The only way to "solve" the problem is to disable the reflow of a document. What can be the cause of this?

Frenzie · 01-09-2022, 04:26 PM

The watermark option might help.

MaxStirner · 01-11-2022, 05:52 AM

Nope, but does your answer mean that you are aware of the problem? Could you explain it? Is it a bug in Koreader or in Djvu itself?

Frenzie · 01-11-2022, 08:13 AM

No, I mean your description sounds like there's a bit of a smudge on the scan that's detected as content.

(Or a smudge equivalent like a purposeful dot.)

MaxStirner · 01-13-2022, 02:45 PM

The entire text area is black - whole page except margins. When a documemt has this problem it always happens on the same pages in the affected file - no matter how many times and on which device I open it (always with Koreader of course). After dereflowing the page looks completely normal. I have more documents with this issue though not many and can send you some files If you think it'll help. I noticed this many years ago, though I've never reported it since I have always thought that it is a problem with some speciffic small subgroup of files. But it keeps reoccurring time and time again.

Frenzie · 01-14-2022, 02:50 AM

I don't have much time to look at reflow, but chances of it ever being fixed drop significantly without an issue on GH that demonstrates it.

Does it still occur if you extract only one or two pages from the document? (In case they're under copyright; otherwise you can just attach it whole here.)

01-08-2022, 08:05 PM	#1
MaxStirner Connoisseur Posts: 71 Karma: 18500 Join Date: Apr 2013 Device: Kindle Touch, Paperwhite	Black squares in Djvu files instead of a text after reflowing Strange thing is that it never happens in the entire document, only every several pages. The pages in between are rendered perfectly fine. I can't find any pattern in this. It is also relatively rare as most djvu files are ok, only one in a dozen seems to be affected. The only way to "solve" the problem is to disable the reflow of a document. What can be the cause of this? Last edited by MaxStirner; 01-08-2022 at 08:08 PM.

01-13-2022, 02:45 PM	#5
MaxStirner Connoisseur Posts: 71 Karma: 18500 Join Date: Apr 2013 Device: Kindle Touch, Paperwhite	The entire text area is black - whole page except margins. When a documemt has this problem it always happens on the same pages in the affected file - no matter how many times and on which device I open it (always with Koreader of course). After dereflowing the page looks completely normal. I have more documents with this issue though not many and can send you some files If you think it'll help. I noticed this many years ago, though I've never reported it since I have always thought that it is a problem with some speciffic small subgroup of files. But it keeps reoccurring time and time again. Attached Thumbnails Last edited by MaxStirner; 01-13-2022 at 03:31 PM.

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01-09-2022, 04:26 PM	#2
Frenzie Wizard Posts: 1,741 Karma: 730681 Join Date: Oct 2014 Location: Antwerp Device: Kobo Aura H2O	The watermark option might help.

01-11-2022, 05:52 AM	#3
MaxStirner Connoisseur Posts: 71 Karma: 18500 Join Date: Apr 2013 Device: Kindle Touch, Paperwhite	Nope, but does your answer mean that you are aware of the problem? Could you explain it? Is it a bug in Koreader or in Djvu itself?

01-11-2022, 08:13 AM	#4
Frenzie Wizard Posts: 1,741 Karma: 730681 Join Date: Oct 2014 Location: Antwerp Device: Kobo Aura H2O	No, I mean your description sounds like there's a bit of a smudge on the scan that's detected as content. (Or a smudge equivalent like a purposeful dot.)

01-14-2022, 02:50 AM	#6
Frenzie Wizard Posts: 1,741 Karma: 730681 Join Date: Oct 2014 Location: Antwerp Device: Kobo Aura H2O	I don't have much time to look at reflow, but chances of it ever being fixed drop significantly without an issue on GH that demonstrates it. Does it still occur if you extract only one or two pages from the document? (In case they're under copyright; otherwise you can just attach it whole here.)

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