将ctypes与tesserac-ocr TessPageIteratorBoundingBox一起使用时出现异常

问题描述

import ctypes
import os
os.putenv("PATH", r'C:\Program Files\Tesseract-OCR')
os.environ["TESSDATA_PREFIX"] = r'C:\Program Files\Tesseract-OCR\tessdata'

liblept = ctypes.cdll.LoadLibrary('liblept-5.dll')
pix = liblept.pixRead('test.png'.encode())
print(pix)

tesseractLib = ctypes.cdll.LoadLibrary('libtesseract-5.dll')

tesseractHandle = tesseractLib.TessBaseAPICreate()

tesseractLib.TessBaseAPIInit3(tesseractHandle, '.', 'eng')

tesseractLib.TessBaseAPISetImage2(tesseractHandle, pix)

# text_out = tesseractLib.TessBaseAPIGetUTF8Text(tesseractHandle)
# print(ctypes.string_at(text_out))

tessPageIterator = tesseractLib.TessResultIteratorGetPageIterator(tesseractHandle)
iteratorLevel = 3  # RIL_BLOCK,  RIL_PARA,  RIL_TEXTLINE,  RIL_WORD,  RIL_SYMBOL
tesseractLib.TessPageIteratorBoundingBox(tessPageIterator, iteratorLevel, ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0))

I有例外：

Traceback (most recent call last):
  File "D:\BaiduYunDownload\programming\Python\CtypesOCR.py", line 25, in <module>
    tesseractLib.TessPageIteratorBoundingBox(tessPageIterator, iteratorLevel, ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0))
OSError: exception: access violation reading 0x00000018

那么怎么了？
该程序的目的是获得每个单词的边界矩形。我知道和

PS在这里指定DLL函数所需的参数类型（函数原型）并不重要。可以不加注释的行，而注释最后三行以对其进行测试。我在之前发布了，对此它已关闭原因

P.S. Specifying the required argument types (function prototypes) for the DLL functions doesn't matter here. One could uncoment the commented lines and comment the last three lines to test it. I posted the question before , and it was closed for this reason

推荐答案

我自己解决了问题

import ctypes
import os
import io
os.putenv("PATH", r'C:\Program Files\Tesseract-OCR')
os.environ["TESSDATA_PREFIX"] = r'C:\Program Files\Tesseract-OCR\tessdata'

liblept = ctypes.cdll.LoadLibrary('liblept-5.dll')
pix = liblept.pixRead(b'test.png')  # 必须encode
print(pix)

tesseractLib = ctypes.cdll.LoadLibrary('libtesseract-5.dll')

tesseractHandle = tesseractLib.TessBaseAPICreate()

tesseractLib.TessBaseAPIInit3(tesseractHandle, b'.', b'eng')  # (TessBaseAPI* handle, const char* datapath,const char* language);

# from PIL import Image
# pixmap = Image.open("test.png")
# image = io.BytesIO()
# pixmap.save(image, 'png')  # 没有什么类型，这里就任意指定个吧；For images created by the library itself (via a factory function, or by running a method on an existing image), this attribute is set to None.
# image.seek(0)  # 要回到开始才行，不然后面requests读的时候会从结尾读，读不到数据

tesseractLib.TessBaseAPISetImage2(tesseractHandle, pix)  # pixmap.tobytes("raw", "RGB")
# text_out = tesseractLib.TessBaseAPIGetUTF8Text(tesseractHandle)
# print(ctypes.string_at(text_out))
tesseractLib.TessBaseAPIRecognize(tesseractHandle, None)  # 必须有，否则下面会出问题
tessResultIterator = tesseractLib.TessBaseAPIGetIterator(tesseractHandle)  # TessResultIteratorGetPageIterator要用

tessPageIterator = tesseractLib.TessResultIteratorGetPageIterator(tessResultIterator)
wordLevel = 3  # RIL_BLOCK,  RIL_PARA,  RIL_TEXTLINE,  RIL_WORD,  RIL_SYMBOL


left = ctypes.c_int(0)  # 这几个是要用来写入数据的，所以要构造出来 可写；byref() argument must be a ctypes instance, not 'int'
top = ctypes.c_int(0)
right = ctypes.c_int(0)
bottom = ctypes.c_int(0)

while True:
    r = tesseractLib.TessPageIteratorBoundingBox(
        tessPageIterator,
        wordLevel,
        ctypes.byref(left),  # byref behaves similar to pointer(obj), but the construction is a lot faster.
        ctypes.byref(top),
        ctypes.byref(right),
        ctypes.byref(bottom)
    )

    text_out = tesseractLib.TessResultIteratorGetUTF8Text(tessPageIterator, wordLevel)
    print(ctypes.string_at(text_out), left.value, top.value, right.value, bottom.value)

    if not tesseractLib.TessPageIteratorNext(tessPageIterator, wordLevel):
        break

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