Python \ OpenCv \ Tesseract stdin

[Aaron A]

I have been unable to find an example where through Python an OpenCv image could be passed to Tesseract via stdin (as opposed to writing the image to a file and then passing tesseract the file path).

Here is the code I have so far but it throws an error.

import cv2
import numpy
import subprocess


frame = cv2.imread("image.jpg", 1)


command = ["tesseract",
           'stdin',
           'stdout']

tesseract_process = subprocess.Popen(command, stdin=subprocess.PIPE, stdout=subprocess.PIPE)


result = tesseract_process.communicate(input=frame.tostring())[0]
result = tesseract_process.stdin.write(frame.tostring())
print(result.decode())

and the error I get is:

Error in fopenReadStream: file not found

$" #! !! && ** ** ** ** ++ *- '* (+ (+ *- #& "$ "$ !# ! " "$ !# ! " " ! ! ! ! ! " " ! " " ! " # " ! !

$" #! !! && ** ** ** ** ++ *- '* (+ (+ *- #& "$ "$ !# ! " "$ !# ! " " ! ! ! ! ! " " ! " " ! " # " ! ! cannot be read!

Error during processing.

ObjectCache(5A2E0A88)::~ObjectCache(): WARNING! LEAK! object 02770A70 still has count 1 (id \Program Files (x86)\Tesseract-OCR\tessdata/eng.traineddatalstm-punc-dawg)

ObjectCache(5A2E0A88)::~ObjectCache(): WARNING! LEAK! object 02752128 still has count 1 (id \Program Files (x86)\Tesseract-OCR\tessdata/eng.traineddatalstm-word-dawg)

ObjectCache(5A2E0A88)::~ObjectCache(): WARNING! LEAK! object 027521D8 still has count 1 (id \Program Files (x86)\Tesseract-OCR\tessdata/eng.traineddatalstm-number-dawg)

ObjectCache(5A2E0A88)::~ObjectCache(): WARNING! LEAK! object 0270BF30 still has count 1 (id \Program Files (x86)\Tesseract-OCR\tessdata/eng.traineddatapunc-dawg)

ObjectCache(5A2E0A88)::~ObjectCache(): WARNING! LEAK! object 035D29A8 still has count 1 (id \Program Files (x86)\Tesseract-OCR\tessdata/eng.traineddataword-dawg)

ObjectCache(5A2E0A88)::~ObjectCache(): WARNING! LEAK! object 02F63088 still has count 1 (id \Program Files (x86)\Tesseract-OCR\tessdata/eng.traineddatanumber-dawg)

ObjectCache(5A2E0A88)::~ObjectCache(): WARNING! LEAK! object 02F67A88 still has count 1 (id \Program Files (x86)\Tesseract-OCR\tessdata/eng.traineddatabigram-dawg)

ObjectCache(5A2E0A88)::~ObjectCache(): WARNING! LEAK! object 02F67B30 still has count 1 (id \Program Files (x86)\Tesseract-OCR\tessdata/eng.traineddatafreq-dawg)

Any help or guidance would be really appreciated. 

I do know that there is a python library https://pypi.python.org/pypi/piltesseract which passes images to tesseract via stdin.

However that library uses PIL and not OpenCv.

I've also tried 

tesseract_process.stdin.write(frame.tostring())
output = tesseract_process.stdout.read()
print output

but this simply hangs and never prints.

Thank you

[John Slade]

Tesseract stdin doesn't accept raw numpy frames, it needs to be encoded in an image format (like png/bmp etc).

This is exactly what the Piltesseract library does using the PIL library:

https://github.com/Digirolamo/PILtesseract/blob/master/piltesseract/tesseractwrapper.py#L131:L143

In opencv you can do the equivalent using cv2.imencode

http://docs.opencv.org/3.0-beta/modules/imgcodecs/doc/reading_and_writing_images.html#imencode

The following code works for me:

import cv2
import subprocess

frame = cv2.imread("image.png", 1)

tesseract_process = subprocess.Popen(
    ["tesseract", 'stdin', 'stdout'],
    stdin=subprocess.PIPE, stdout=subprocess.PIPE)

ret, img = cv2.imencode(".bmp", frame)

result = tesseract_process.communicate(input=img.tostring())[0]
print(result.decode())

John

---

From: tesser...@googlegroups.com <tesser...@googlegroups.com> on behalf of Aaron A <aaron...@gmail.com>
Sent: 09 March 2017 00:54:28
To: tesseract-ocr
Subject: [tesseract-ocr] Python \ OpenCv \ Tesseract stdin

 

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[Aaron A]

thanks so much for the working sample code! perfecto.