Converting rgb video to grayscale in OpenCV - opencv

Question

I have this program that should convert rgb video to grayscale:
CvCapture* capture = 0;
capture = cvCreateFileCapture( "sample.avi" );
if(!capture)
{
return -1;
}
IplImage *bgr_frame=cvQueryFrame(capture);//Init the video read
double fps = cvGetCaptureProperty (capture,CV_CAP_PROP_FPS);
CvSize size = cvSize((int)cvGetCaptureProperty( capture, CV_CAP_PROP_FRAME_WIDTH),(int)cvGetCaptureProperty( capture, CV_CAP_PROP_FRAME_HEIGHT));
CvVideoWriter *writer = cvCreateVideoWriter("izlaz.avi",CV_FOURCC_DEFAULT,fps,size);
IplImage *grayScaleImage = cvCreateImage(size ,IPL_DEPTH_8U,1);
while( (bgr_frame=cvQueryFrame(capture)) != NULL )
{
cvCvtColor(bgr_frame, grayScaleImage, CV_BGR2GRAY);
cvWriteFrame( writer, grayScaleImage );
}
cvReleaseVideoWriter( &writer );
cvReleaseCapture( &capture );
which is not the case. Can anyone help me to modify it to work exactly that? Thank You :)

Answer 1

I think you will need to choose between fourcc of your codec, CV_FOURCC_DEFAULT didn't work for me. I tried CV_FOURCC('P','I','M,'1') and CV_FOURCC('M','J','P','G'). They both worked for me.
Here is the sample code which I tried.
#include<opencv2\opencv.hpp>
#include<iostream>
using namespace cv;
int main(int argc, char*argv[])
{
char *my_file = "C:\\vid_an2\\Wildlife.wmv";
std::cout<<"Video File "<<my_file<<std::endl;
cv::VideoCapture input_video;
if(input_video.open(my_file))
{
std::cout<<"Video file open "<<std::endl;
}
else
{
std::cout<<"Not able to Video file open "<<std::endl;
}
int fps = input_video.get(CV_CAP_PROP_FPS);
int frameCount = input_video.get(CV_CAP_PROP_FRAME_COUNT);
double fheight = input_video.get(CV_CAP_PROP_FRAME_HEIGHT);
double fwidth = input_video.get(CV_CAP_PROP_FRAME_WIDTH);
CvSize fsize;
fsize.width = fwidth;
fsize.height = fheight;
CvVideoWriter *new_writer = cvCreateVideoWriter("brg_file.avi",CV_FOURCC('M','J','P','G'), fps,fsize, 0);
std::cout<<"Video Frame Rate "<<fps<<std::endl;
std::cout<<"Video Frame Count "<<frameCount<<std::endl;
Mat cap_img;
Mat gry_img;
IplImage new_img;
while(input_video.grab())
{
if(input_video.retrieve(cap_img))
{
cvtColor(cap_img, gry_img, CV_RGB2GRAY);
new_img = gry_img.operator IplImage();
int ret = cvWriteFrame(new_writer, (const IplImage*)&new_img);
std::cout<<"Wrote Frame "<<ret<<std::endl;
}
}
cvReleaseVideoWriter(&new_writer);
return 0;
}