Warning. Invalid resolution 0 dpi. Using 70 instead.

[JILeXanDR]

command tesseract https://image.ibb.co/eibzaT/test.png result

Current Behavior:

Warning. Invalid resolution 0 dpi. Using 70 instead.
Estimating resolution as 161
Estimating resolution as 161

version

tesseract 4.0.0-beta.2-313-g29f2
 leptonica-1.76.0
  libgif 5.1.4 : libjpeg 8d (libjpeg-turbo 1.4.2) : libpng 1.2.54 : libtiff 4.0.6 : zlib 1.2.8 : libwebp 0.4.4 : libopenjp2 2.1.0
 Found AVX
 Found SSE

original image https://image.ibb.co/eibzaT/test.png

[amitdo]

It means your image does not contain a resolution info in its metadata, so Tesseract warns you about this issue in the image and it tries to estimate the resolution by itself.

[JILeXanDR]

@amitdo In which way?

[amitdo]

tesseract/src/ccmain/pagesegmain.cpp

Line 313 in 2645f72

int res = IntCastRounded(to_block->line_size * kResolutionEstimationFactor);

By measuring lines height.

[ghost]

@zdenop I think, you can close this topic

[lloiodice]

Tesseract uses Leptonica which uses libpng to read the input image source resolution.
If the input png does not have the correct metadata info, it will generate the warning referred in
this issue. I also seen this to cause tesseract to return slightly different text results for certain images.
The code above adds metadata to the PNG

[lloiodice]

To test if an image has the correct header you can use
magick identify -verbose filename or equivalent tools

and make sure these 2 values are set
Resolution: 118.11x118.11
Units: PixelsPerCentimeter
Above is for a 300 dpi PNG

[15013605249]

@lloiodice The version I am using is 3.05.02 and I can't find the function you said.

[stweil]

tesseract https://image.ibb.co/eibzaT/test.png result

How did you manage that Tesseract could read the input image from a URL?

[bhasinnaik]

Hello team,

I am trying to extract text from text using tesseract but every time it returns warning .
Warning: Invalid resolution 0 dpi. Using 70 instead.
Estimating resolution as 463
Empty page!!
Estimating resolution as 463
Empty page!!

[stweil]

There is an undocumented command line option. Try using --dpi 300 (or the correct value for your image).

[zdenop]

@bhasinnaik : your input image has no information about dpi. If you want to avoid warning, you should fix it.

[maky-hnou]

@zdenop , any idea how to fix the photo's DPI when it is 0?
I tried using different methods (pyexiv2, imagemagick,..) but I still get the same error when I use tesseract...

[zdenop]

What did you try with imagemagick? Show your command ;-)

[maky-hnou]

mogrify -set density 300 image.jpg I found this on a post in Stackoverflow.

[zdenop]

Just very easy and short internet search suggest this modification:
mogrify -set units PixelsPerInch -density 300 image.jpg

[maky-hnou]

Thank you. I already tried that :-D , but still get the same tesseract error. Probably it is because of my image.
I'll try to find a workaround.
Thank you again :-)

[zdenop]

I tried it and it works for my image.jpg. If you are using tesseract >=4 you can use --dpi option of tesseract executable.

[jbreiden]

Try 300x300 with the mogrify command.

…

On Fri, Oct 18, 2019, 10:02 AM zdenop ***@***.***> wrote: I tried it and it works for my image.jpg. If you are using tesseract >=4 you can use --dpi option of tesseract executable. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#1702?email_source=notifications&email_token=ABF3NJXAR7FBSXBYDSVQN7LQPHT3JA5CNFSM4FGUSYKKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEBVEZZI#issuecomment-543837413>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABF3NJUPTPMR4QZWDNUIDGTQPHT3JANCNFSM4FGUSYKA> .

[lloiodice]

FYI

In my test of tesseract 4.1 (trying to upgrade from 4.0) .. I get this warning often and
using 70 dpi instead of the correct dpi affects the efficacy of results especially when
running script detection.

In 4.0 setting the metadata in the PNG as described in my post above allowed the correct
resolution to be used by tesseract. That does not work anymore so something has changed
in 4.1 (maybe in the dependencies ... libpng? ... not sure).

If anybody knows what PNG metadata fields are necessary to avoid the warning please
let me know ... using the tesseract dpi setting is a complication that would be good to avoid
when processing arbitrary images.

[zdenop]

so you have png that does not produce dpi warning with tesseact 4.0, but it produces warning in 4.1?

[lloiodice]

It appears to be a problem with script detection

tesseract dpi_issue.png out --psm 0
Tesseract Open Source OCR Engine v4.1.0 with Leptonica
Warning. Invalid resolution 0 dpi. Using 70 instead.

File:
https://www.dropbox.com/s/y7yb49ew04kj72q/dpi_issue.png?dl=0

When using 300 dpi or with 4.0 I get detected script Han. In 4.1 I get Latin.

[zdenop]

interesting: I see file has dpi (118x118 in IrfanView). Even when I specify dpi for tesseract, I see warning message:

tesseract dpi_issue.png - --dpi 300 --psm 0
Warning. Invalid resolution 0 dpi. Using 70 instead.
Page number: 0
Orientation in degrees: 0
Rotate: 0
Orientation confidence: 7.89
Script: Latin
Script confidence: 0.09

BTW:

identify -format '%x,%y' dpi_issue.png
'46.460000000000001,46.460000000000001'

so it seems like problem with generating your png(?)

[stweil]

That's a bug in Tesseract. Tesseract internally creates a new image for that png file, but does not copy the resolution from the original image. Fixed now in commit a209a6b.

[zdenop]

@stweil : Thanks for looking into this. Funny that problem was with psm 0 only. Others psm works as expected.

[OmarJabri7]

I am using pytesseract and there are some images that work with the image_to_osd, but other images do not and the program gives me the following error:
"raise TesseractError(proc.returncode, get_errors(error_string))
pytesseract.pytesseract.TesseractError: (1, 'Tesseract Open Source OCR Engine v4.1.0-bibtag19 with Leptonica Warning. Invalid resolution 0 dpi. Using 70 instead. Too few characters. Skipping this page Error during processing.')"
I am using Python 3.7 anaconda distribution and tesseract >=4.0.0 with pytesseract as a tool.
Please help.

[stweil]

Please use the user forum for questions.

[PrashantDixit0]

After having an image of 300dpi , then also same error is coming mention below

TesseractError: (3221225501, "read_params_file: Can't open txt Tesseract Open Source OCR Engine v4.1.1 with Leptonica Warning: Invalid resolution 0 dpi. Using 70 instead. Estimating resolution as 711")

[anilbb23]

I am using pytesseract and there are some images that work with the image_to_osd, but other images do not and the program gives me the following error:
"raise TesseractError(proc.returncode, get_errors(error_string))
pytesseract.pytesseract.TesseractError: (1, 'Tesseract Open Source OCR Engine v4.1.0-bibtag19 with Leptonica Warning. Invalid resolution 0 dpi. Using 70 instead. Too few characters. Skipping this page Error during processing.')"
I am using Python 3.7 anaconda distribution and tesseract >=4.0.0 with pytesseract as a tool.
Please help.

Hi @OmarJabri7,
I am getting the same error. How did you resolve it? Please share the solution / sample code.

I am rotating the image with OpenCV and then passing it to pytesseract.image_to_osd()
TesseractError: (1, 'Tesseract Open Source OCR Engine v5.0.0-alpha.20201127 with Leptonica Warning: Invalid resolution 0 dpi. Using 70 instead. Estimating resolution as 179 Warning. Invalid resolution 0 dpi. Using 70 instead. Too few characters. Skipping this page Error during processing.')

[esraa-abdelmaksoud]

I've been using Tesseract for a while and got the same error. I just want to confirm that it is never about the metadata. I got the error while using image_to_osd for photos captured using the same device and this happened to only 3 of 50 images. I've checked the image details and the dpi already exists.

I've been trying to see if the error disappears when I crop the background around the objects in the image, and I saw that the error disappeared for 2 of them, not all of them. I still don't really know the reason, but if it was the metadata, the third one would have worked.

However, I believe that it has something related to the number of characters. The images that resulted in the error that disappeared after cropping were somewhat rotated. The text angle was around 30-40. Tesseract was giving me rotations of 90,180, and 270 only for the images that worked. When it comes to the image that gave error in both cases, it already has a low number of characters. This is why it would be interesting if more people try this so we can figure out if it's really the reason.

[amitdo]

Run this command on the original image:
identify -verbose imagename.jpg

[zdenop]

Please respect guidelines for posting issue: we do not provide support for 3rd party projects (I assume you use pytesseract based on image_to_osd). Also provide information about tesseract and leptonica version.
Provide test case to reproduce problem with resent version of tesseract executable - otherwise you are alone with your thoughts and believes.

[dzg]

Is there any way to set a default resolution in the event of Invalid resolution ? I would like to force --dpi 72 but only when no DPI detected.

[stweil]

That is not directly supported by Tesseract, but could be implemented by a wrapper script.

The current Tesseract release 5.0.0 tries to guess the correct resolution if there is no explicit information from the image file.

[dzg]

That is not directly supported by Tesseract, but could be implemented by a wrapper script.

The current Tesseract release 5.0.0 tries to guess the correct resolution if there is no explicit information from the image file.

Most of the images I need to process are macOS screenshots – which are all PNG @ 144 DPI – and none of which tesseract recgonizes as having a DPI. Bummer. (Furthermore, to process well I have to set --dpi 72)

[stweil]

I tested some macOS screenshots, and Tesseract 5.0.0 worked well without the need to give a resolution. But you are free to add --dpi 72 if that helps for your screenshots.