Hi Roberto
I changed the source to force pdftoppm to use 300 dpi for all files. This
not only fixes the initial issue that PDF has a worse recognition quality
than JPG, but indeed even improves some details regarding punctuation and
the quality is now even better in the PDF.
I regard this issue as resolved now (for myself), but maybe we can find a
less hacky way for all people? What I did was change line 37 of
/usr/local/lib/python2.7/dist-packages/mayan/apps/converter/backends/python.py
to
pdftoppm = pdftoppm.bake('-jpeg', '-r', '300')
Is there a way to open a bug report for me or how do we proceed? I guess I
could supply you with a test document as well, if needed.
Cheers,
Flo
Am Dienstag, 25. Juli 2017 08:00:51 UTC+2 schrieb Roberto Rosario:
>
> Hello,
>
> I recently published a blog post explaining how the converter works:
> http://www.mayan-edms.org/post/mayan-converter/
> In the case of PDF files, the utility pdftoppm is used to convert the
> pages into images. You can use pdftoppm on the PDF files
> made by img2pdf to see the actual image Mayan is receiving and spot any
> degradation.
>
> As for your questions:
> 1) The OCR doesn't pre process the images before doing the recognition.
> This is some being worked on (already there is a scanline filter to reduce
> pre OCR images to 2 colors), but is not available to the user yet. When
> available, it will be possible to apply a stack of transformations for the
> document images before performing the OCR task.
> 2) Strictly speaking about file types, there is no way to make a
> multi-page JPEG, the format doesn't support it (JPEG 2000 has the JPM and
> JPX extenstions which might do but I don't how good is Pillow's JPEG 2000
> support). Another JPEG format which could be used is MJPG but it is for
> video and it would be hackish attempt to convert the frames to pages. On
> the platform side, you can group images with Mayan already using an Index
> or a SmartLink. All the JPEG uploads need is a unique marker (like a
> metadata value or a filename fragment). This can be accomplished via the UI
> and the API. For example the index template: {{ document.label|slice:":4"
> }} will group all documents with the same 4 first characters in the name.
> To use a different part of the filename for the grouping just change the
> slice argument (
> http://www.diveintopython3.net/native-datatypes.html#slicinglists).
>
> On Monday, July 24, 2017 at 1:57:31 PM UTC-4, Florian Beverborg wrote:
>>
>> Hi all!
>>
>> I'm currently evaluating Mayan as a replacement for my current DMS. The
>> documents are all in the JPG format, multiple pages of the same document
>> per folder, scanned at 300dpi. So far adding JPGs does not allow me to
>> create multi-page documents. I used img2pdf to generate multi-page PDFs for
>> import into Mayan, which mostly works fine. BUT: The OCR-quality for the
>> same page is worse when using the PDF files.
>>
>> I've tried multiple ways to generate the combined PDF and I can see some
>> differences but never managed to get the same recognition quality as using
>> the pure JPG. Since img2pdf (to my knowledge) does not touch the actual JPG
>> data and since I'm using PDF page size fit to image size I don't know
>> what's going wrong here. The PDFs look fine in my PDF viewer and are
>> reported to have correct page sizes. Generating the pages with imagemagick
>> does not improve recognition.
>>
>> This leads me to the conclusion that the PDFs are rendered internally
>> which degrades the quality.
>>
>> I have two questions:
>>
>> 1) What can I do to improve PDF recognition quality, either in generating
>> the PDF or in Mayan settings?
>> 2) Is there another way to make multi-page documents from JPGs? Maybe
>> using the REST-API?
>>
>> Using Mayan version 2.6.2
>>
>> Cheers,
>> Flo
>>
>>
>>
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