I'm working with Kinect and OpenCV. I already search in this forum but I didn't find anything like my problem. I keep the raw depth data from Kinect (16 bit), I store it in a CvMat* and then I pass it to the cvGetImage to create an IplImage* from it:
CvMat* depthMetersMat = cvCreateMat( 480, 640, CV_16UC1 );
[...]
cvGetImage(depthMetersMat,temp);
But now I need to work on this image in order to do cvThreshdold and find contours. These 2 functions need an 8-bit-depth-image in input. How can I convert the CvMat* depthMetersMat in an 8-bit-depth-CvMat* ?
The answer that @SSteve gave almost did the trick for me, but the call to convertTo
seemed to just chop off the high order byte instead of actually scaling the values to an 8-bit range. Since @Sirnino didn't specify which behavior was wanted, I thought I'd post the code that will do the (linear) scaling, in case anyone else is wanting to do that.
SSteve's original code:
CvMat* depthMetersMat = cvCreateMat( 480, 640, CV_16UC1 );
cv::Mat m2(depthMetersMat, true);
m2.convertTo(m2, CV_8U);
To scale the values, you just need to add the scale factor (1/256, or 0.00390625, for 16-bit to 8-bit scaling) as the third parameter (alpha) to the call to convertTo
m2.convertTo(m2, CV_8U, 0.00390625);
You can also add a fourth parameter (delta) that will be added to each value after it is multiplied by alpha. See the docs for more info.
This should work:
CvMat* depthMetersMat = cvCreateMat( 480, 640, CV_16UC1 );
cv::Mat m2(depthMetersMat, true);
m2.convertTo(m2, CV_8U);
But according to the OpenCV docs, CvMat is obsolete. You should use Mat instead.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With