c++ - OpenCV to use in memory buffers or file pointers

Question

The two functions in openCV cvLoadImage and cvSaveImage accept file path's as arguments.

For example, when saving a image it's cvSaveImage("/tmp/output.jpg", dstIpl) and it writes on the disk.

Is there any way to feed this a buffer already in memory? So instead of a disk write, the output image will be in memory.

I would also like to know this for both cvSaveImage and cvLoadImage (read and write to memory buffers). Thanks!

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My goal is to store the Encoded (jpeg) version of the file in Memory. Same goes to cvLoadImage, I want to load a jpeg that's in memory in to the IplImage format.

Answer 1

This worked for me

// decode jpg (or other image from a pointer)
// imageBuf contains the jpg image
    cv::Mat imgbuf = cv::Mat(480, 640, CV_8U, imageBuf);
    cv::Mat imgMat = cv::imdecode(imgbuf, CV_LOAD_IMAGE_COLOR);
// imgMat is the decoded image

// encode image into jpg
    cv::vector<uchar> buf;
    cv::imencode(".jpg", imgMat, buf, std::vector<int>() );
// encoded image is now in buf (a vector)
    imageBuf = (unsigned char *) realloc(imageBuf, buf.size());
    memcpy(imageBuf, &buf[0], buf.size());
//  size of imageBuf is buf.size();

I was asked about a C version instead of C++:

#include <opencv/cv.h>
#include <opencv/highgui.h>

int
main(int argc, char **argv)
{
    char *cvwin = "camimg";

    cvNamedWindow(cvwin, CV_WINDOW_AUTOSIZE);

    // setup code, initialization, etc ...
    [ ... ]

    while (1) {      
        // getImage was my routine for getting a jpeg from a camera
        char *img = getImage(fp);
        CvMat mat;

   // substitute 640/480 with your image width, height 
        cvInitMatHeader(&mat, 640, 480, CV_8UC3, img, 0);
        IplImage *cvImg = cvDecodeImage(&mat, CV_LOAD_IMAGE_COLOR);
        cvShowImage(cvwin, cvImg);
        cvReleaseImage(&cvImg);
        if (27 == cvWaitKey(1))         // exit when user hits 'ESC' key
        break;
    }

    cvDestroyWindow(cvwin);
}