Easily strip alpha channel from images in Mathematica

What 开发者_开发技巧is the simplest way to strip the alpha channel (and possible convert images to greyscale) in Mathematica?

I would like to use ImageAssemble, but some of the images come with and some without an alpha channel. Is there a simpler built-in way than manipulating the ImageData directly?

The RemoveAlphaChannel function will do this.

For Mathematica 7, I believe this works:

ColorCombine@Most@ColorSeparate@# &

It's not robust at this point, but type checking could be added.

Your second question (not sure it is) conversion to grayscale, is done with:

ColorConvert[image, "Grayscale"]