Most efficient way to clear an image with C++ interface?

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the equivalent for cvZero you can find it here (that you probably saw). Why do you think that it is slower than the cvZero function? How do you use cvZero and what do you think it does (is there any doc about it?)?

please take another look at setTo(), it does not iterate over pixels, but over planes and consecutive blocks, and then does a memset.

also, a simple memset might be inappropriate for non-continuous data (i.e. a ROI)

thanks, I misread. not sure what blocks are for, though. As a matter of fact, setTo is a lot slower, compared to cvZero. Here is the output of a very basic benchmark I did (image size is Full HD, 8 bit single channel):

1000 x testMat.setTo( cv::Scalar( 0x00 ) ); took 99.3829ms
1000 x testMat = cv::Mat::zeros( testMat.size(), testMat.type() ); took 58.3239ms
1000 x cvZero( im ); took 60.2803ms

Mat::zeros is, however, faster than cvZero. Mat::setTo on the other hand is a lot faster than the old C API's cvSet:

1000 x testMat.setTo( cv::Scalar( 0xff ) ); took 100.06ms
1000 x cvSet( im, cvScalar( 0xff ) ); took 470.597ms

IMHO cv::Mat::zeros is the equivalent to cvZero and cv::Mat::setTo is the equivalent to cvSet. But could you be more explicit about the cvZero( im )? How do you use it? Why would it be a problem if it allocates a new Mat and deallocates the old one? Normally, if you still have some other Mat that use the initial one, you will not arrive in the case of lost pointer, because the Mat is a smart pointer, it will be deallocated only if no-one is using that memory.

Frankly, I don't understand what you're asking - I use cvZero exactly as I wrote above, how else would I use it? cvZero( im ); The reason I am worried about unnecessary memory allocation and deallocation is of course performance, which is traditionally a consideration in most computer vision applications. I don't want to allocate and deallocate hundreds of matrixes each frame. When I use a computer vision library, I really try to use it in the most efficient way and to avoid unnecessary operations.