matProduct=
AlphaTimes(mat1, alpha)
Calculate the product of an image matrix and alpha as would
Screen Alpha
blending: Pointwise multiply and round. Argument 'alpha' may
be either a scaler or the alpha plane. If an alpha plane, it must have
the same x y dimensions of argument 'mat'.
see also:
AlphaSum,
PsychAlphaBlending
Psychtoolbox/PsychAlphaBlending/AlphaTimes.m