Check the class of objects

[Mael]

> Its important because of how data is aligned.  If the data is not 
Yes, it's obviously linked, but the question is : since each time you want to process an RGB triple in the middle of any row, it won't be necessarily aligned, I don't clearly see where do you save processing time when doing for instance a constant addition to an image ?
I guess there must be reasons linked to image viewing (like screens that like to have their data padded), but I could not find precise references on this