Trying to read pixel out of bounds - screenshot of just half the screen

I am trying to take a screenshot of just half the screen. Taking the full screenshot, and sending it to webform works, just like in this example. Each time I try it with just half the screen, I get the fatal error,

"Trying to read pixel out of bounds

UnityEngine.Texture2D:ReadPixels(Rect,Int32,Int32)"

`tex.ReadPixels( Rect(Mathf.Round(width*0.5), 0, width, height), 0, 0 );`

width and height are assigned as floats:

var width = Screen.width;
var height = Screen.height;

You're trying to make the rectangle "Screen.width" wide, but you start reading halfway across the screen. You need to make it as wide as only half the screen.