histogram on opencv - opencv

Question

hey i tried to made a histogram that shows frames substraction, the code is running but i got gray window without result.
the message on the command window is:
Compiler did not align stack variables. Libavcodec has been miscompiled
and may be very slow or crash. This is not a bug in libavcodec,
but in the compiler. You may try recompiling using gcc >= 4.2.
Do not report crashes to FFmpeg developers.
OpenCV Error: Assertion failed (images[j].channels() == 1) in unknown function,
file ........\ocv\opencv\src\cv\cvhistogram.cpp, line 137
here is the code someone have an idea?thanks for help.....
int main()
{
int key = 0;
CvCapture* capture = cvCaptureFromAVI( "macroblock.mpg" );
IplImage* frame = cvQueryFrame( capture );
IplImage* currframe = cvCreateImage(cvGetSize(frame),IPL_DEPTH_8U,3);
IplImage* destframe = cvCreateImage(cvGetSize(frame),IPL_DEPTH_8U,3);
IplImage* imgHistogram = 0;
CvHistogram* hist;
if ( !capture )
{
fprintf( stderr, "Cannot open AVI!\n" );
return 1;
}
int fps = ( int )cvGetCaptureProperty( capture, CV_CAP_PROP_FPS );
cvNamedWindow( "dest", CV_WINDOW_AUTOSIZE );
cvNamedWindow( "imgHistogram", CV_WINDOW_AUTOSIZE );
while( key != 'x' )
{
frame = cvQueryFrame( capture );
currframe = cvCloneImage( frame );
frame = cvQueryFrame( capture );
cvSub(frame,currframe,destframe);
int bins = 256;
int hsize[] = {bins};
float max_value = 0, min_value = 0;
float value;
int normalized;
float xranges[] = {0, 256};
float* ranges[] = {xranges};
IplImage* planes[] = {destframe};
hist = cvCreateHist(1, hsize, CV_HIST_ARRAY, ranges,1);
cvCalcHist(planes, hist, 0, NULL);
cvGetMinMaxHistValue(hist, &min_value, &max_value);
// printf("Minimum Histogram Value: %f, Maximum Histogram Value: %f\n", min_value, max_value);
imgHistogram = cvCreateImage(cvSize(bins, 50),IPL_DEPTH_8U,3);
cvRectangle(imgHistogram, cvPoint(0,0), cvPoint(256,50), CV_RGB(255,255,255),-1);
for(int i=0; i < bins; i++){
value = cvQueryHistValue_1D(hist, i);
normalized = cvRound(value*50/max_value);
cvLine(imgHistogram,cvPoint(i,50), cvPoint(i,50-normalized), CV_RGB(0,0,0));
}
if(key==27 )break;
cvShowImage( "dest",destframe);
cvShowImage( "imgHistogram",imgHistogram);
key = cvWaitKey( 1000 / 10 );
}
cvDestroyWindow( "dest" );
cvReleaseCapture( &capture );
return 0;
}

Answer 1

Since you are trying to show a 1D histogram, the histogram plane needs to be in grayscale. So, you need to convert the resulting image from cvSub() to grayscale first. Try
IplImage *gray = NULL;
gray = cvCreateImage(cvGetSize(frame), IPL_DEPTH_8U, 1);
while(key != 'x') {
...
cvSub(frame, currframe, destframe);
cvCvtColor(destframe, gray, CV_BGR2GRAY);
...
IplImage* planes[] = {gray};
..
}
Let me know if it works for you.