For my iPhone 3D apps I am currently using CoreGraphics to load png files that have pre-multiplied alpha. Here are the essentials:

// load a 4-channel rgba png file with pre-multiplied alpha. CGContextRef context =
CGBitmapContextCreate(data, width, height, 8, num_channels * width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

// Draw the image into the context CGRect rect = CGRectMake(0, 0, width, height); CGContextDrawImage(context, rect, image); CGContextRelease(context);

I then go on and use the data as a texture in OpenGL.

My question: By specifying pre-multiplied alpha - kCGImageAlphaPremultipliedLast - am I - inadvertently - telling CoreGraphics to multiply the r g b channels by alpha or - what I have assumed - am I merely indicating that the format of the incoming image has pre-multiplied alpha?

Thanks, Doug