Capturing Screenshot of a Rect Transform

hi,
I have an app that need to take screenshot from a specific area of the screen, that covering a Rect Transform. I am using the following code to get screenshot of an area. But i am confused how i can get the pixel rect from the Rect transform that are needed by the below code. Please help.

Code (CSharp):

1. Texture2D tex = new Texture2D (width, height, TextureFormat.RGB24, false);
2.  
3. tex.ReadPixels (new Rect (0,0, width, height), 0, 0);
4.  
5. tex.Apply ();

Thanks in advance