First all, thanks for your suggestion.

What you say is just what I do to get a grayed bitmap form my images.
But if the developer machine has GREEN color for 3d objects, when I copy the screen and paste it on MS-Paint to create the grayed image, it is "GREEN-grayed" and when I use it in a machine with WHITE color for 3d objects, my grayed image IS NOT GRAYED, is GREEN-grayed. Horrible.

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I take a look to some MSDN Library articles and I found some functions of the GDI32 library that can help me with this. But I don't understand everithing. It's talk about ROP, Bitblt, Masks and more...
If you know how it works, please tell me.

Thanks again for your time.
Regards,
Esteban