Question

I was browsing over some code in the OpenCV page when it came to accessing Pixel Data

IplImage* img=cvCreateImage(cvSize(640,480),IPL_DEPTH_32F,3);
CvScalar s;
s=cvGet2D(img,i,j); // get the (i,j) pixel value
printf("B=%f, G=%f, R=%f\n",s.val[0],s.val[1],s.val[2]);
s.val[0]=111;
s.val[1]=111;
s.val[2]=111;
cvSet2D(img,i,j,s); // set the (i,j) pixel value

I had done something similar, but I used the Template Class provided to access pixel data……anyways Im not sure I understand the part s.val[0]=111….etc?
if s.val[0] contains the B value, what exactly is s.val[0]=111 doing? is it setting it to black?……..I dont understand exactly what it’s supposed to be?

Im used to CVscalars and such but I dont understand this format? Specifically what 111 means?

thanks

Answer 1

The cvSet2D(img, i, j, s) functions to not access the (i,j)th pixel. It accesses the (j,i)th pixel. That is because images are stored as a matrix – you need to specify the row first (the Y coordinate) and then the column (the X coordinate).

Instead of using the cvGet/Set functions, did you try using pointers to access data within an image?