OpenCV C++ Convert Byte array to Mat - opencv

Question

How can I convert byte array to Mat which is received from socket ?.
My client application will send color image data like this
Mat frame; //colour image
int imgSize = frame.total()*frame.elemSize();
int bytes = send(clientSock, frame.data, imgSize, 0));//write to the socket
And the server will receives the data like
char sockData[imgSize];
Mat img;
for (int i = 0; i < imgSize; i += bytes) {
bytes = recv(connectSock, sockData +i, imgSize - i, 0));
}
// Write to mat
for (int i = 0; i < img.rows; i++) {
for (int j = 0; j < img.cols; j++) {
(img.row(i)).col(j) = (uchar)sockData[((img.cols)*i)+j];
}
}
I am getting distorted image at the receiver. Is there any problem in my code ?
Thanks in advance.......

Answer 1

If you have colour image you may read it in a math with 3 channels of uchar so change this piece of code:
for (int i = 0; i < img.rows; i++) {
for (int j = 0; j < img.cols; j++) {
(img.row(i)).col(j) = (uchar)sockData[((img.cols)*i)+j];
}
}
with this:
int baseIndex = 0;
for (int i = 0; i < img.rows; i++) {
for (int j = 0; j < img.cols; j++) {
img.at<cv::Vec3b>(i,j) = cv::Vec3b(sockData[baseIndex + 0],
sockData[baseIndex + 1],
sockData[baseIndex + 2]);
baseIndex = baseIndex + 3;
}
}
Maybe this should work.

Answer 2

Doesn't this work?
cv::Mat frame(img.rows, img.cols, CV_8UC3, sockData);
Just replace CV_8UC3 with the correct image format:
CV_<bit-depth>{U|S|F}C(<number_of_channels>)
see https://docs.opencv.org/2.4/modules/core/doc/basic_structures.html
Edit: There is a 5th additional field which can be useful. The number of bytes per row (in case there are a few padding bytes). In working with V4L2 today, I successfully used this cv::Mat constructor:
v4l2_format camera_format = ...; // see https://linuxtv.org/downloads/v4l-dvb-apis/uapi/v4l/vidioc-g-fmt.html#description
cv::Mat mat(camera_format.fmt.pix.height,
camera_format.fmt.pix.width,
CV_8UC3,
raw_data_ptr,
camera_format.fmt.pix.bytesperline);

Answer 3

I solved the problem using below code.
int ptr=0;
for (int i = 0; i < img.rows; i++) {
for (int j = 0; j < img.cols; j++) {
img.at<cv::Vec3b>(i,j) = cv::Vec3b(sockData[ptr+0],sockData[ptr+1],sockData[ptr+2]);
ptr=ptr+3;
}
}

Answer 4

Adding to Michele answer, one can also use the MatIterator to solve this.
cv::Mat m;
m.create(10, 10, CV_32FC3);
// This is the socket data.
float *array = (float *)malloc( 3*sizeof(float)*10*10 );
cv::MatIterator_<cv::Vec3f> it = m.begin<cv::Vec3f>();
for (unsigned i = 0; it != m.end<cv::Vec3f>(); it++ ) {
for ( unsigned j = 0; j < 3; j++ ) {
(*it)[j] = *(array + i );
i++;
}
}
Now you have a float cv::Mat. In case of 8 bit, simply change float to uchar and Vec3f to Vec3b and CV_32FC3 to CV_8UC3