How to convert varbinary data (as string) to byte array?

Question

I have a varbinary(BLOB) data as a string (image data)

for example,

std::string ByteStr = "FF-D8-E0-FF-85 ... " ;

I want to convert this string to byte array(or something usefull) then use as cv::Mat format. I get the string from another method. I tried to convert but i get OpenCV error.

Error I get,

OpenCV Error: Assertion failed (size.width>0 && size.height>0) in cv::imshow, >>file ........\opencv\modules\highgui\src\window.cpp

C++ code,

std::string ByteStr = obj->GetBinaryStr();  // this provide varbinary string
std::vector<uchar> vct;
std::string delimiter = "-";

        size_t pos = 0;
        std::string token;

        while ((pos = ByteStr.find(delimiter)) != std::string::npos) {

            token = ByteStr.substr(0, pos);
            vct.push_back((uchar)(token.c_str()));
            ByteStr.erase(0, pos + delimiter.length());

        }          

       cv::Mat img = cv::imdecode(vct,CV_BGR2GRAY );
       cv::namedWindow("MyWindow");
       cv::imshow("MyWindow",img);

How can i convert this string to cv::Mat format. Any advice?

Thanks in advance

Answer 1

cv::imdecode(vct,CV_BGR2GRAY ); doesn't make any sense. Please use something meaningful like cv::imdecode(vct, cv2.IMREAD_GRAYSCALE );.

Also you need to convert the hex string to an integer type. You can use strtol for this.

The code becomes something like:

std::string ByteStr = obj->GetBinaryStr();  // this provide varbinary string
std::vector<uchar> vct;
std::string delimiter = "-";

size_t pos = 0;
std::string token;

while ((pos = ByteStr.find(delimiter)) != std::string::npos) {

    token = ByteStr.substr(0, pos); 
    uchar ucharToken = uchar(strtol(token.c_str(), NULL, 16));
    vct.push_back(ucharToken);
    ByteStr.erase(0, pos + delimiter.length());

}          

cv::Mat img = cv::imdecode(vct, cv::IMREAD_GRAYSCALE);
cv::namedWindow("MyWindow");
cv::imshow("MyWindow",img);