When I look up the definition for glTexImage2D in the
blue book( OpenGL Reference Manual ) the entry for GL_ALPHA
is as follows.
GL_ALPHA Each element is a single alpha component. It is converted to
floating point and assembled into an RGBA element by
attaching 0.0 for red, green, and blue. Each component is
then multiplied by the signed scale factor GL_c_SCALE,
added to the signed bias GL_c_BIAS, and clamped to the range
[0,1] (see glPixelTransfer).
According to this definition, there is no savings of texture memory
when compared with using GL_RGBA. Is this accurate?
I am especially interested if this is accurate on the Matrox G400 and
Nvidia geForce256 chip sets.