565,444, rp8 handling in OpenGL

What is the support that OpenGl renders for 444, 565, rp8 image formats. One of my friend told that GL_RGB4 or GL_RGB5 can be used with glTexImage*() to feed 16 bit textures. Is this the right approach for handling the mentioned formats. I am porting these formats from Glide SDK to OpenGl and hence what are the likely issues involved in this…?

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Thanks Serge