How to call cv::updateMotionHistory() in OpenCV

Question

I'm updating samples/c/motempl.c to OCV 2.3 and I'm a bit puzzled by the cv::updateMotionHistory() method. I create the history following what I've seen in motempl.c:

    history = cv::Mat::zeros(640, 480, CV_32FC1);

Then, I call updateMotionHistory() like so:

cv::Mat diff = cv::Mat::zeros(640, 480, CV_8U);

if(prevFrame.size().width != 0) {
   cv::absdiff(currentFrame, prevFrame, diff);
} else {
   return;
}

cv::updateMotionHistory( diff, history, getElapsedSeconds(), MHI_DURATION);

Seems ok, but it's always throwing the following:

OpenCV Error: Sizes of input arguments do not match () in cvUpdateMotionHistory

Both matrices are the same size,, 640, 480, but just for fun I tried changing history to CV_8U which gets me:

OpenCV Error: Unsupported format or combination of formats () in cvUpdateMotionHistory

Following on the sample, where there's this:

 mhi = cvCreateImage( size, IPL_DEPTH_32F, 1 );

I get why the history needs to be a float image, I'm just not sure how to call this method with matrices rather than IplImage instances. Thanks!

Answer 1

Ok, so I figured this out, right after making this a bounty and I figured I should post the answer, not sure what the etiquette on that is. History needs to be CV_32FC1:

history = cv::Mat::zeros(480, 640, CV_32FC1);

The rows/cols initializing Mat are a little unintuitive too:

cv::Mat diff = cv::Mat::zeros(480, 640, CV_8UC1); // not 640,480

Then:

cv::updateMotionHistory( diff, history, getElapsedSeconds(), MHI_DURATION);