If you have hexagonal pixels, what do you do at the edges? Have half hexagons or jagged edges?
Also, what interpolation method would you use? With square or rectangular pixels, bilinear or bicubic interpolation makes sense. With hexagons, will you have tri-linear or tri-cubic interpolation? If so, this is something that you'll have to implement yourself. In fact, you'll ave to implement all the image processing functions, since as Metioche says in his/her answer, everything is based on orthogonal grids.
