Hi, I have the following in OpenCV 3.4.2
cv::Mat3b a(cv::Size(30511, 26060));
cout << a.isContinuous() << endl;
and the result is 0 (false), which I think is not correct looking at the step size in a.step[0]. Is this a bug or some quirk with large arrays? Thanks
First, the step defines the data layout of the array a. It shouldn't be used for element access. a.step[0] gives you the number of bytes needed to store a line (first dimension); a.step[1] for a pixel (second dimension), a.step[2] for the third dimension (channel).
Images don't have to be continuous. Large images can be split up to better fit in the memory. Lines are always stored in a continuous memory block (step[0] bytes).
As a general rule, it's better to consider matrices as non-continuous and use the ptr function to get the address of a line. To access an element (x,y), you should use (considering that you have an element size of 1):
a.ptr(y)+x
instead of
a.data()+y*a.cols()+x
Sorry, my bad. step[0] is the line size (2nd dimension), step[1] is the 3rd dimension - i.e. the number of channels or the number of planes.
OTOH I checked your code, and I always get 1 (true) for the continuity - even on 32 bit 3 channel images. It takes about 2GB of memory, but it's always continuous on my computer. I use OpenCV 3.4.1 on Ubuntu 64bit.
Asked: 2018-07-19 05:14:23 -0600
Seen: 493 times
Last updated: Jul 19 '18
