C++ 如果图像文件的内容在字符数组中，如何使用 cv::imdecode？
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How to use cv::imdecode, if the contents of an image file are in a char array?
提问by Richard Knop
I have a jpeg image in buffer jpegBuffer. I'm trying to pass it to cv::imdecode function:
我在缓冲区 jpegBuffer 中有一个 jpeg 图像。我试图将它传递给 cv::imdecode 函数：
Mat matrixJprg = imdecode(Mat(jpegBuffer), 1);
I get this error:
我收到此错误：
/home/richard/Desktop/richard/client/src/main.cc:108: error: no matching function for call to ‘cv::Mat::Mat(char*&)'
This is how I fill jpegBuffer:
这就是我填充 jpegBuffer 的方式：
FILE* pFile;
long lSize;
char * jpegBuffer;
pFile = fopen ("img.jpg", "rb");
if (pFile == NULL)
{
exit (1);
}
// obtain file size.
fseek (pFile , 0 , SEEK_END);
lSize = ftell (pFile);
rewind (pFile);
// allocate memory to contain the whole file.
jpegBuffer = (char*) malloc (lSize);
if (jpegBuffer == NULL)
{
exit (2);
}
// copy the file into the buffer.
fread (jpegBuffer, 1, lSize, pFile);
// terminate
fclose (pFile);
回答by ronag
Mat has no constructor that takes a char* argument. Try this instead:
Mat 没有接受 char* 参数的构造函数。试试这个：
std::ifstream file("img.jpg");
std::vector<char> data;
file >> std::noskipws;
std::copy(std::istream_iterator<char>(file), std::istream_iterator<char>(), std::back_inserter(data));
Mat matrixJprg = imdecode(Mat(data), 1);
EDIT:
编辑：
You should also take a look at LoadImageM.
您还应该看看LoadImageM。
If you have your data already in a char* buffer one way is to copy the data into an std::vector.
如果您的数据已经在 char* 缓冲区中，一种方法是将数据复制到 std::vector 中。
std::vector<char> data(buf, buf + size);
回答by Programmer
I had to do the-same thing and my image data was already in chararray format and was arriving from a network and a plugin source. The current answershows how to do this but it requires copying the data into a vector firstwhich is a waste of time and resources.
我不得不做同样的事情，我的图像数据已经是char数组格式，并且来自网络和插件源。当前的答案显示了如何做到这一点，但它需要先将数据复制到向量中，这会浪费时间和资源。
This is possible to do directly without creating a copy of it. You were so close with your imdecode(Mat(jpegBuffer), 1);code in your question.
这可以直接完成而无需创建它的副本。你imdecode(Mat(jpegBuffer), 1);在你的问题中与你的代码非常接近。
You need to use the constructor overload for the Matclass below:
您需要为Mat下面的类使用构造函数重载：
Mat(int rows, int cols, int type, void* data, size_t step=AUTO_STEP);
To create this Mat, pass 1to the rows, the size of the array to the cols, CV_8UC1to the type and the char array itself to the data param. Pass this Matto the cv::imdecodefunction with the mat as the first param and CV_LOAD_IMAGE_UNCHANGEDas the second param.
要创建这个Mat，传递1给行、数组的大小到列、CV_8UC1类型和字符数组本身到数据参数。将此传递Mat给cv::imdecode具有 mat 作为第一个参数和CV_LOAD_IMAGE_UNCHANGED第二个参数的函数。
Basic example:
基本示例：
char *buffer = dataFromNetwork;
int bufferLength = sizeOfDataFromNetwork;
cv::Mat matImg;
matImg = cv::imdecode(cv::Mat(1, bufferLength, CV_8UC1, buffer), CV_LOAD_IMAGE_UNCHANGED);
Complete Example(Reads file named "test.jpg" into char array and uses imdecodeto decode the data from the char array then displays it):
完整示例（将名为“test.jpg”的文件读入字符数组并用于imdecode解码字符数组中的数据然后显示它）：
int main() {
//Open image file to read from
char imgPath[] = "./test.jpg";
ifstream fileImg(imgPath, ios::binary);
fileImg.seekg(0, std::ios::end);
int bufferLength = fileImg.tellg();
fileImg.seekg(0, std::ios::beg);
if (fileImg.fail())
{
cout << "Failed to read image" << endl;
cin.get();
return -1;
}
//Read image data into char array
char *buffer = new char[bufferLength];
fileImg.read(buffer, bufferLength);
//Decode data into Mat
cv::Mat matImg;
matImg = cv::imdecode(cv::Mat(1, bufferLength, CV_8UC1, buffer), CV_LOAD_IMAGE_UNCHANGED);
//Create Window and display it
namedWindow("Image from Char Array", CV_WINDOW_AUTOSIZE);
if (!(matImg.empty()))
{
imshow("Image from Char Array", matImg);
}
waitKey(0);
delete[] buffer;
return 0;
}
