# When we compute the complexity of a given algorithm related to image processing does the N refers to the number of Pixels in the image?

When we compute the complexity of an image processing algorithm, we get an $O(N)$.

does the $N$ refers to the number of pixels in the image or to the height/width of the image, I mean it is computed related to $O(nm)$ with $n\times m$ the size of the image ?

Whether any given paper follows this observation is of course a different matter, but if nothing different is specified, I would assume that $N$ is the number of pixels indeed.