如何将文件作为流从python发送到C库

Question

我正试图在python中使用Leptonica（C库）。该库有一个pixRead方法，该方法将图像文件的绝对路径作为参数。目前，我成功地从python调用了这个：

leptonica = ctypes.cdll.LoadLibrary("/path/to/lept.so")
pix_image = leptonica.pixRead("/path/to/image.jgp")

但是，我想调用方法pixReadStream，它将文件流作为输入参数。在我的python程序中，我可以使用OpenCV以numpy数组的形式访问图像。

问题

有没有任何方法可以将我在Python程序中作为numpy数组的图像传递给leptopnica C库中的pixReadStream方法，该方法将文件流作为输入参数？

roi #OpenCV image numpy array
leptonica = ctypes.cdll.LoadLibrary("/path/to/lept.so")
pix_image = leptonica.pixReadStream(##any way to pass roi here?##)

Answer 1

从Numpy数组创建Leptonica PIX结构可以在不将数据编码为用于存储的图像格式的情况下完成，并以某种方式通过内核将其作为文件在同一进程中传输。将OpenCV中的数组数据转换为RGBA数据，并从Leptonica中包装足够的数据，以创建适当大小的空PIX结构，然后将数组中的数据复制到PIX中。

以下是一个小示例，说明如何使用OpenCV加载图像，将其转换为包裹PIX结构的Python对象，并使用Leponica将图像数据再次保存到文件中：

#!/usr/bin/env python
# coding: utf8
from __future__ import absolute_import, division, print_function
from ctypes import c_char_p, c_uint32, c_void_p, CDLL, memmove, pointer, POINTER
from ctypes.util import find_library
import cv2

LEPTONICA = CDLL(find_library('lept'))
_pix_create = LEPTONICA.pixCreate
_pix_create.argtypes = [c_uint32, c_uint32, c_uint32]
_pix_create.restype = c_void_p
_pix_destroy = LEPTONICA.pixDestroy
_pix_destroy.argtypes = [POINTER(c_void_p)]
_pix_destroy.restype = None
_pix_get_data = LEPTONICA.pixGetData
_pix_get_data.argtypes = [c_void_p]
_pix_get_data.restype = POINTER(c_uint32)
_pix_endian_byte_swap = LEPTONICA.pixEndianByteSwap
_pix_endian_byte_swap.argtypes = [c_void_p]
_pix_endian_byte_swap.restype = c_uint32
_pix_write_implied_format = LEPTONICA.pixWriteImpliedFormat
_pix_write_implied_format.argtypes = [c_char_p, c_void_p, c_uint32, c_uint32]
_pix_write_implied_format.restype = c_uint32

class Pix(object):
    def __init__(self, width, height, depth):
        self._as_parameter_ = _pix_create(width, height, depth)
        self._pointer = pointer
        self._pix_destroy = _pix_destroy
    def __del__(self):
        pix_pointer = self._pointer(c_void_p(self._as_parameter_))
        self._pix_destroy(pix_pointer)
        assert pix_pointer[0] is None
    @property
    def data(self):
        return _pix_get_data(self)
    def endian_byte_swap(self):
        _pix_endian_byte_swap(self)
    def save(self, filename, quality=0, progessive=False):
        _pix_write_implied_format(filename, self, quality, progessive)
    @classmethod
    def from_rgba(cls, array):
        width, height, depth = array.shape
        if depth != 4 and array.itemsize != 1:
            raise ValueError('array has wrong format')
        result = cls(width, height, 32)
        memmove(result.data, array.ctypes.data, array.size * array.itemsize)
        result.endian_byte_swap()
        return result

def main():
    image = cv2.imread('test.jpg')
    image = cv2.cvtColor(image, cv2.cv.CV_BGR2RGBA)
    pix = Pix.from_rgba(image)
    pix.save('test.png')

if __name__ == '__main__':
    main()

Answer 2

这可能对您有帮助吗？

给出的答案是"您可以从中使用PyFile_AsFile。"

Answer 3

1. 对于转换，您可以使用numpy.load函数。。。http://docs.scipy.org/doc/numpy-1.10.1/reference/generated/numpy.load.html

https://github.com/numpy/numpy/blob/v1.10.1/numpy/lib/npyio.py#L257-L419

2. 为了与c沟通，你可以有ctypes或cffi

https://kogs-www.informatik.uni-hamburg.de/~seppke/content/taching/wise1314/20131107_pridoehl-cffi.pdf