Arithmetics operations between 2 images (mix or Blend) using hardware acceleration.

Well. My question is very simple :
I would like to do « arithmetics » operations between 2 images, of any size, with OpenGL.
But, i don’t want to do “Logicals Operations” but “Arithmetics Operations”.

The “Arithmetic Operator” can to be an add/soustract/divide/multiplicate… operation.
So, how to do this by using OpenGL, in order to use the hardware acceleration ? ! (here, time is critical).
Yes, i don’t want to do a “software” procedure, but a “hardware” procedure (using the 3D cards).

Perhaps with textures (blending of 2 textures), but the problem is the SIZE : it must to be a multiple of two, not any size.

Anybody has got an idea ? !