AttributeError: 'NoneType' object has no attribute 'group' (negative bbox attr)

[skylord123]

	Message: Error from hocr-pdf.exe: [10920] Failed to execute script hocr-pdf
	Traceback (most recent call last):
	  File "hocr-pdf", line 163, in 
	  File "hocr-pdf", line 69, in export_pdf
	  File "hocr-pdf", line 81, in add_text_layer
	AttributeError: 'NoneType' object has no attribute 'group'
	StackTrace: coldfusion.runtime.CustomException: Error from hocr-pdf.exe: [10920] Failed to execute script hocr-pdf
	Traceback (most recent call last):
	  File "hocr-pdf", line 163, in 
	  File "hocr-pdf", line 69, in export_pdf
	  File "hocr-pdf", line 81, in add_text_layer

Looks to have to do with this line not matching negative bounding boxes:
https://github.com/tmbdev/hocr-tools/blob/master/hocr-pdf#L76

I hit this issue on a 60 page PDF around page 14 or so. I don't know why I got negative bounding boxes but It's a thing and caused my code to fail because of it. Updating the above mentioned line to match negative numbers fixes this issue and allows my PDF to be created correctly.

[stweil]

It would be good to have an example for negative bounding boxes. Is it possible to extract the PDF page which causes that and provide it here? Or has someone else an example?

[kba]

How was the input document created? All values of an hocr bbox must be unsigned integers, absolute coordinates on the page. It doesn't make sense to have a bounding box extend beyond the page. Are you creating bounding boxes across double pages?

It is more sensible to fix this upstream in whatever tool created the hocr, e.g. by clipping values to zero.

[skylord123]

I didn't know that about the hocr bbox. I believe the issue may reside in gcv2hocr tool I use to convert google vision responses to hocr. I'm going to do some further testing and report back with my findings. I cannot share the PDF file I am using because it is confidential.

I found another PDF that has 50 pages that is having a similar issue. It is a 50-page scanned document and the issue occurs a couple pages in. The weird thing is the page that has the issue doesn't have any text near the edge of the page. I wonder how I am getting negative values..

I will report back after further tesitng.

[skylord123]

It looks like google vision is giving me negative vertices for one of my pages. I then use gcv2hocr tool to convert the google vision json responses to hocr data. This tool is the one that is converting the mistake from google vision into a negative bbox. Since bbox requires unsigned characters I will be opening a PR on gcv2hocr to fix this.

I just don't know why google vision is giving me negative vertices for this page:

Here is the JSON snippet from the OCR data (search for -5 and you will find the negative values):
https://gist.github.com/skylord123/52a4eb219da687a2f654b080088c56a0#file-page_021-json-L5679

[skylord123]

I've opened a PR at gcv2hocr project. This fixes the error by generating HOCR that is in compliance with the spec (forcing bbox to use unsigned integers or default to 0).

Closing this issue as my problem is resolved. I hope this helps others that run into the same issue.

[stweil]

Thank you for clarifying this issue.