How use the gray texture by image transform ?

[garfield]

???

please give me help or sample .

In Direct X 9 , i have a gray texture , every frame compare the gray texture pixel , if the pixel >= a compare value , the pixel point's alpha = null , a compare value rise. i set the foreground image pixel point alpha to null . so , the background image show. frame by frame , the gray texture all pixel alpha is null , the transform over. i want to use the stencil buffer , but i do not how to use.

thanks~

mail and msn : garfield.chen@qq.com

the gray texture sample :

http://www.tyohouse.com/image/gray.png