Color space conversion for IplImage

In my application, the color image is captured from my USB webcam.

IplImage* frame = cvQueryFrame( capture ); // depth 8 channel 3
IplImage* blackwhite = cvCreateImage( cvGetSize(frame), frame->depth, 1 ); //depth 8 channel 1
IplImage* differentdepth = cvCreateImage( cvGetSize(frame), IPL_DEPTH_32F, 1); //depth 32 channel 1

cvCvtColor(frame, blackwhite, CV_RGB2GRAY); // to convert greyscale

Reference:

IplImage* cvCreateImage( cvSize, Ipl depth flag, channel number);