Update globalmatting.md

Author: Nerdyvedi

modules/ximgproc/tutorials/globalmatting.md

@@ -2,7 +2,7 @@
 
 The Global sampling based method uses all known samples(from a trimap), Unlike other sampling based methods
 which collect only nearby samples.<br/>
-It first estimates the foreground and background color and then computes the alpha matte.
+It first estimates the foreground and background color and uses them to compute the alpha matte.
 
 Input to the model is the Image and the trimap, and the output is the alpha matte of the image.