OpenCV Mat element types and their sizes

Question

I\'m confused by the OpenCV Mat element types. This is from the docs:

There is a limited fixed set of primitive data types the library can operate on.
That i         


        

Answer 1

In short the table you provided is correct. If you want to directly access a pixel, you typecast it to the specifier to the right, for example CV_32S is a signed 32-bit. The S always means a signed integral number (signed char, signed short, signed int) The F always means a floating point number (float, double) The U always means an unsigned integral number.

The enumeration is used only when creating or converting a Mat. It's a way of telling the mat which is the desired type, as I understand it it's the C predecessor to when templates were not used.

I use the C functionality exclusively, and in order to create an image, it would be an error to pass the following:

cvCreateImage(mySize,char, nChannels);

Instead, I pass the following:

cvCreateImage(mySize, IPL_DEPTH_8U, nChannels);

Here, the IPL_DEPTH_8U is a flag that is used by the function. The function itself has a switch-type statement that checks the flag. The actual value of the flag is most often meaningless as it's most often controlled by conditional, not algebraic statements.