关于opencv：使用ctypes将python IplImage对象作为简单结构传递给共享C库

Pass python IplImage object as simple struct to shared C library using ctypes

我正在尝试为用 C/C 编写的应用程序创建一个 python package器，它广泛使用了 OpenCV C API。我想为此使用 ctypes，因为我在以前的程序中成功使用了它。但是当我尝试将 IplImage 从 Python 作为参数传递给 c 库中的函数时遇到了问题。

我创建了一个示例测试库来演示该问题。以下是我想使用的库中的函数：

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// ImageDll.h

#include"opencv2/opencv.hpp"

extern"C" //Tells the compile to use C-linkage for the next scope.
{
// Returns image loaded from location
__declspec(dllexport) IplImage* Load(char* dir);

// Show image
__declspec(dllexport) void Show(IplImage* img);
}

还有一个cpp文件：

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// ImageDll.cpp
// compile with: /EHsc /LD

#include"ImageDll.h"

using namespace std;

extern"C" //Tells the compile to use C-linkage for the next scope.
{
IplImage* Load(char* dir)
{
return cvLoadImage(dir, CV_LOAD_IMAGE_COLOR);
}

void Show(IplImage* img)
{
cvShowImage("image", img);
cvWaitKey(0);
}
}

这是python的初步尝试：

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from time import sleep
from ctypes import *
from modules.acquisition import InitCamera, GetImage
from modules.utils import struct
import cv2.cv as cv

# load DLL containing image functions
print"Loading shared library with genetic algorithm...",
image_lib = cdll.LoadLibrary("OpenCV_test_DLL.dll")
print"Done."
# get function handles
print"Loading functions of library...",
image_load = image_lib.Load
image_show = image_lib.Show
# set return type for functions (because ctypes default is int)
image_load.restype = c_void_p
image_show.restype = None
print"Done."

# initialize source
print"Initializing camera",
source = struct()
InitCamera(source)
print"Done."

# show video
while (1):
# get image as PIL image
img = GetImage(source)
# transform image to OpenCV IplImage
cv_img = cv.CreateImageHeader(img.size, cv.IPL_DEPTH_8U, 3)
cv.SetData(cv_img, img.tostring())
# show image using OpenCV highgui lib
image_show(pointer(cv_img))

如您所见，我从相机获取图像作为 PIL 图像，然后将其转换为 python IplImage。这适用于 100%，因为当我用来自 cv2.cv 模块的 python 绑定替换最后一行 image_show(pointer(cv_img)) 时：

1 2	cv.ShowImage("image", cv_img) cv.WaitKey(20)

然后我得到正确的输出。

所以问题出在 image_show(pointer(cv_img)) 上，它因 TypeError 失败：type must have storage info。这是因为 cv_img 需要是有效的 ctypes IplImage 结构。我试图用 ctypes 模仿它，但收效甚微：

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这是进行转换的函数：

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# convert Python PIL to ctypes Ipl
def PIL2Ipl(input_img):

# mode dictionary:
# (pil_mode : (ipl_depth, ipl_channels)
mode_list = {
"RGB" : (cv.IPL_DEPTH_8U, 3),
"L" : (cv.IPL_DEPTH_8U, 1),
"F" : (cv.IPL_DEPTH_32F, 1)
}

if not mode_list.has_key(input_img.mode):
raise ValueError, 'unknown or unsupported input mode'

result = cIplImage()
result.imageData = c_char_p(input_img.tostring())
result.depth = c_int(mode_list[input_img.mode][0])
result.channels = c_int(mode_list[input_img.mode][1])
result.height = c_int(input_img.size[0])
result.width = c_int(input_img.size[1])

return result
("imageData", c_char_p),
("widthStep", c_int),
("BorderMode", c_int * 4),
("BorderConst", c_int * 4),
("imageDataOrigin", c_char_p)]

视频循环然后变为

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# show video
while (1):
# get image as PIL image
img = GetImage(source)
# transform image to OpenCV IplImage
cv_img = cIplImage()
cv_img = PIL2Ipl(img)
# show image using OpenCV highgui lib
image_show(pointer(cv_img))

通过这种方式，数据被传递到库，但随后它在未知函数中为 OpenCV 错误而哭泣：错误标志(参数或结构字段)(无法识别或不支持的数组类型)。因此创建的 ctypes 结构无效。有谁知道如何正确实施它？当它使我能够将 python IplImage 传递给 c 库时，我什至会接受其他不使用 ctypes 的解决方案。谢谢。

注意：过去 2 天我一直试图找到这个问题的答案，但没有任何成功。有针对 OpenCV 1.0 的解决方案，但最近使用 numpy 数组的 Python 的 OpenCV 绑定几乎不可能使 Python 和 C 应用程序之间的接口正常工作。 :(

我终于找到了解决问题的方法。而不是使用默认的python函数

1 2	cv.CreateImageHeader() cv.SetData()

我使用了从 OpenCV C 库导出的 C 函数。 :) 我什至设法将颜色从 PILs RGB 转换为 IplImage BGR 格式。这是完整的来源：

ImageDll.h

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#include"opencv2/opencv.hpp"

extern"C" //Tells the compile to use C-linkage for the next scope.
{
// Returns image loaded from location
__declspec(dllexport) IplImage* Load(char* dir);

// Show image
__declspec(dllexport) void Show(IplImage* img);

// Auxiliary functions
__declspec(dllexport) void aux_cvSetData(CvArr* arr, void* data, int step);
__declspec(dllexport) IplImage* aux_cvCreateImageHeader(int width, int height, int depth, int channels);
__declspec(dllexport) IplImage* aux_cvCvtColor(const IplImage* src, int code);
__declspec(dllexport) void aux_cvCopy(const CvArr* src, CvArr* dst);
__declspec(dllexport) void aux_cvReleaseImage(IplImage** image);
__declspec(dllexport) void aux_cvReleaseImageHeader(IplImage** image);
}

ImageDll.cpp

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#include"ImageDll.h"

using namespace std;

extern"C" //Tells the compile to use C-linkage for the next scope.
{
IplImage* Load(char* dir)
{
return cvLoadImage(dir, CV_LOAD_IMAGE_COLOR);
}

void Show(IplImage* img)
{
cvShowImage("image", img);
cvWaitKey(5);
}

void aux_cvSetData(CvArr* arr, void* data, int step)
{
cvSetData(arr,data,step);
}

IplImage* aux_cvCreateImageHeader(int width, int height, int depth, int channels)
{
return cvCreateImageHeader(cvSize(width,height), depth, channels);
}

IplImage* aux_cvCvtColor(const IplImage* src, int code)
{
IplImage* dst = cvCreateImage(cvSize(src->width,src->height),src->depth,src->nChannels);
cvCvtColor(src, dst, code);
return dst;
}

void aux_cvCopy(const CvArr* src, CvArr* dst)
{
cvCopy(src, dst, NULL);
}

void aux_cvReleaseImage(IplImage** image)
{
cvReleaseImage(image);
}

void aux_cvReleaseImageHeader(IplImage** image)
{
cvReleaseImageHeader(image);
}
}

run.py

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# This Python file uses the following encoding: utf-8

from time import sleep
from ctypes import *
from modules.acquisition import InitCamera, GetImage
from modules.utils import struct
import cv2.cv as cv
from modules.ipl import *

# load DLL containing image functions
print"Loading shared library with C functions...",
image_lib = cdll.LoadLibrary("OpenCV_test_DLL.dll")
print"Done."
# get function handles
print"Loading functions of library...",
image_load = image_lib.Load
image_show = image_lib.Show
cvReleaseImage = image_lib.aux_cvReleaseImage
# set return type for functions (because ctypes default is int)
image_load.restype = c_void_p
image_show.restype = None
cvReleaseImage.restype = None
print"Done."

# initialize source
print"Initializing camera",
source = struct()
InitCamera(source)
print"Done."

# show video
while (1):
# get image as PIL image
img = GetImage(source)
# transform image to OpenCV IplImage
cv_img = PIL2Ipl(img)
# show image using OpenCV highgui lib
image_show(cv_img)
# release memory
cvReleaseImage(byref(cv_img))

ipl.py

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from ctypes import *
from cv2 import cv

# ctypes IplImage
class cIplImage(Structure):
_fields_ = [("nSize", c_int),
("ID", c_int),
("nChannels", c_int),
("alphaChannel", c_int),
("depth", c_int),
("colorModel", c_char * 4),
("channelSeq", c_char * 4),
("dataOrder", c_int),
("origin", c_int),
("align", c_int),
("width", c_int),
("height", c_int),
("roi", c_void_p),
("maskROI", c_void_p),
("imageID", c_void_p),
("tileInfo", c_void_p),
("imageSize", c_int),
("imageData", POINTER(c_char)),
("widthStep", c_int),
("BorderMode", c_int * 4),
("BorderConst", c_int * 4),
("imageDataOrigin", c_char_p)]

# load DLL containing needed OpenCV functions
libr = cdll.LoadLibrary("OpenCV_test_DLL.dll")
cvSetData = libr.aux_cvSetData
cvCreateImageHeader = libr.aux_cvCreateImageHeader
cvCvtColor = libr.aux_cvCvtColor
cvCopy = libr.aux_cvCopy
cvReleaseImage = libr.aux_cvReleaseImage
cvReleaseImageHeader = libr.aux_cvReleaseImageHeader
# set return types for library functions
cvSetData.restype = None
cvCreateImageHeader.restype = POINTER(cIplImage)
cvCvtColor.restype = POINTER(cIplImage)
cvCopy.restype = None
cvReleaseImage.restype = None
cvReleaseImageHeader.restype = None
#print"auxlib loaded"

# convert Python PIL to ctypes Ipl
def PIL2Ipl(pil_img):
"""Converts a PIL image to the OpenCV/IplImage data format.

Supported input image formats are:
RGB
L
F
"""

# mode dictionary:
# (pil_mode : (ipl_depth, ipl_channels)
mode_list = {
"RGB" : (cv.IPL_DEPTH_8U, 3),
"L" : (cv.IPL_DEPTH_8U, 1),
"F" : (cv.IPL_DEPTH_32F, 1)
}

if not mode_list.has_key(pil_img.mode):
raise ValueError, 'unknown or unsupported input mode'

depth = c_int(mode_list[pil_img.mode][0])
channels = c_int(mode_list[pil_img.mode][1])
height = c_int(pil_img.size[1])
width = c_int(pil_img.size[0])
data = pil_img.tostring()

ipl_img = cvCreateImageHeader(width, height, depth, channels);
cvSetData(ipl_img, create_string_buffer(data,len(data)), c_int(width.value * channels.value))
brg_img = cvCvtColor(ipl_img,cv.CV_RGB2BGR)
cvReleaseImageHeader(byref(ipl_img))
return brg_img

希望对大家有所帮助:)