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Getting component coordinates with python from tesseract C-API   

posledná zmena: 8. December 2013

back to tesseract-ocr-en

Tesseract-ocr C-API brought an option to use tesseract API within python via ctype. Simple example is included in tessseract source (in contrib directory) already.

With ctypes in python you can face several difficulties e.g. when you should pass file object to C library. For this issue there is the example tesseract-ocr C-API with file via ctypes in python on

Other task could be handling of result structures and defining C enums. Here is the example how these can be solved. This example is based on C++ tesseract API example. It shows how to get information (position, size) about image component (in this case line – but can be easily modified for paragraph, words , symbols by replacing of ‘RIL_TEXTLINE’ with other page level iterator). This example use leptonica library via ctype too (there is also python wrapper for leptonica call pylepthonica)

  # * coding: utf-8 *

# Copyright 2013 Zdenko Podobný # Author: Zdenko Podobný # # Licensed under the Apache License, Version 2.0 (the “License”); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an “AS IS” BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. “”“ This is python version of C++ example: It demonstrate how to use tesseract-ocr 3.02 c-api and leptonica to get info about image components. Tested on openSUSE 13.1 64bit with tesseract 3.03 (r918), leptonica 1.69 “”“ #pylint: disable-msg=C0103, R0903 import os import ctypes # Demo variables lang = “eng” filename = “../phototest.tif” TESSDATA_PREFIX = os.environ.get(‘TESSDATA_PREFIX’) if not TESSDATA_PREFIX: TESSDATA_PREFIX = “../” (L_INSERT, L_COPY, L_CLONE, L_COPY_CLONE) = map(ctypes.c_int, xrange(4)) # Define Page Iterator Levels (RIL_BLOCK, RIL_PARA, RIL_TEXTLINE, RIL_WORD, RIL_SYMBOL) = \ map(ctypes.c_int, xrange(5)) # Define Page Segmentation Modes (PSM_OSD_ONLY, PSM_AUTO_OSD, PSM_AUTO_ONLY, PSM_AUTO, PSM_SINGLE_COLUMN, PSM_SINGLE_BLOCK_VERT_TEXT, PSM_SINGLE_BLOCK, PSM_SINGLE_LINE, PSM_SINGLE_WORD, PSM_CIRCLE_WORD, PSM_SINGLE_CHAR, PSM_SPARSE_TEXT, PSM_SPARSE_TEXT_OSD, PSM_COUNT) = map(ctypes.c_int, xrange(14)) class BOX: “”“Leptonica box structure “”“ fields = [ (“x”, ctypes.c_int32), (“y”, ctypes.c_int32), (“w”, ctypes.c_int32), (“h”, ctypes.c_int32), (“refcount”, ctypes.c_uint32) ] libname = “” leptlib = “” try: tesseract = ctypes.cdll.LoadLibrary(libname) except OSError, error: print “Loading of ‘%s failed…” % libname print error exit(1) try: leptonica = ctypes.cdll.LoadLibrary(leptlib) except OSError, error: print “Loading of ‘%s failed…” % leptlib print error exit(1) tesseract.TessVersion.restype = ctypes.c_char_p tesseract_version = tesseract.TessVersion()[:4] # We need to check library version because is symlink # and can point to other version than 3.02 if float(tesseract_version) < 3.02: print “Found tesseract-ocr library version %s.” % tesseract_version print “C-API is present only in version 3.02!” exit(2) # Read image with leptonica => create PIX structure and report image size info pix_image = leptonica.pixRead(filename) print “image width:”, leptonica.pixGetWidth(pix_image) print “image height:”, leptonica.pixGetHeight(pix_image) # Create tesseract api api = tesseract.TessBaseAPICreate() rc = tesseract.TessBaseAPIInit3(api, TESSDATA_PREFIX, lang) if (rc): tesseract.TessBaseAPIDelete(api) print(“Could not initialize tesseract.\n”) exit(3) tesseract.TessBaseAPISetPageSegMode(api, PSM_AUTO_OSD) # Set PIX structure to tesseract api tesseract.TessBaseAPISetImage2(api, pix_image) # Get info(BOXA structure) about lines(RIL_TEXTLINE) from image in api boxa = tesseract.TessBaseAPIGetComponentImages(api, RIL_TEXTLINE, 1, None, None) # Get info about number of items on image n_items = leptonica.boxaGetCount(boxa) print “Found %d textline image components.” % n_items # Set up result type (BOX structure) for leptonica function boxaGetBox BOX_Ptr_t = ctypes.POINTER leptonica.boxaGetBox.restype = BOX_Ptr_t # Shut up tesseract – there is a lot of unwanted messages for RIL_TEXTLINE tesseract.TessBaseAPISetVariable(api, “debug_file”, “/dev/null”) # print info about items for item in range(0, n_items): BOX = leptonica.boxaGetBox(boxa, item, L_CLONE) box = BOX.contents tesseract.TessBaseAPISetRectangle(api, box.x, box.y, box.w, box.h) ocr_result = tesseract.TessBaseAPIGetUTF8Text(api) result_text = ctypes.string_at(ocr_result) conf = tesseract.TessBaseAPIMeanTextConf(api) print “Box[%d]: x=%d, y=%d, w=%d, h=%d, confidence: %d, text: %s” % \ (item, box.x, box.y, box.w, box.h, conf, result_text.strip())

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