compression - Compressing IplImage to JPEG using libjpeg in OpenCV

Question

So I have this problem. I have an IplImage that i want to compress to JPEG and do something with it. I use libjpeg. I found a lot of answers "read through examples and docs" and such and did that. And successfully written a function for that.

FILE* convert2jpeg(IplImage* frame) 
{
FILE* outstream = NULL;
outstream=malloc(frame->imageSize*frame->nChannels*sizeof(char))

unsigned char *outdata = (uchar *) frame->imageData;
struct jpeg_error_mgr jerr;
struct jpeg_compress_struct cinfo;
int row_stride;
JSAMPROW row_ptr[1];

jpeg_create_compress(&cinfo);
jpeg_stdio_dest(&cinfo, outstream);

cinfo.image_width = frame->width;
cinfo.image_height = frame->height;
cinfo.input_components = frame->nChannels;
cinfo.in_color_space = JCS_RGB;

jpeg_set_defaults(&cinfo);
jpeg_start_compress(&cinfo, TRUE);
row_stride = frame->width * frame->nChannels;

while (cinfo.next_scanline < cinfo.image_height) {
    row_ptr[0] = &outdata[cinfo.next_scanline * row_stride];
    jpeg_write_scanlines(&cinfo, row_ptr, 1);
}

jpeg_finish_compress(&cinfo);
jpeg_destroy_compress(&cinfo);

return outstream;
}

Now this function is straight from the examples (except the part of allocating memory, but i need that since i'm not writnig to a file), but it still doesn't work. It dies on jpeg_start_compress(&cinfo, TRUE); part?

Can anybody help?

Answer 1

I've been able to found a solution using the latest jpeglib available on their website. New methods in : jpeg_mem_dest(&cinfo, outbuffer, outlen);

bool ipl2jpeg(IplImage *frame, unsigned char **outbuffer, long unsigned int *outlen) {
unsigned char *outdata = (uchar *) frame->imageData;
struct jpeg_compress_struct cinfo = {0};
struct jpeg_error_mgr jerr;
JSAMPROW row_ptr[1];
int row_stride;

*outbuffer = NULL;
*outlen = 0;

cinfo.err = jpeg_std_error(&jerr);
jpeg_create_compress(&cinfo);
jpeg_mem_dest(&cinfo, outbuffer, outlen);

cinfo.image_width = frame->width;
cinfo.image_height = frame->height;
cinfo.input_components = frame->nChannels;
cinfo.in_color_space = JCS_RGB;

jpeg_set_defaults(&cinfo);
jpeg_start_compress(&cinfo, TRUE);
row_stride = frame->width * frame->nChannels;

while (cinfo.next_scanline < cinfo.image_height) {
    row_ptr[0] = &outdata[cinfo.next_scanline * row_stride];
    jpeg_write_scanlines(&cinfo, row_ptr, 1);
}

jpeg_finish_compress(&cinfo);
jpeg_destroy_compress(&cinfo);

return true;

}