Taking Non Power of Two Resolution Screen Shots

I'm trying to take custom resolution screen shots by first drawing the camera to a render texture, then creating a texture2d and reading the render texture pixels to it, then writing to a png.

The screen shots are coming out as power of two resolutions. For example, if I create a 1920x1080 render texture, the resultant image will be 2048x1024. The Texture2D has the correct 1920x1080 res shown in my debug message, so I believe the problem may be texture formats. I've tried setting the RenderTexure format to various formats such as ARGB32.

What am I missing?

 using UnityEngine;
 using System.Collections;
 using System;
 using System.IO;
 
 public class ScreenCapture : MonoBehaviour
 {
     public Camera camera;
     string filePath = "";
 
     void Start() {
         filePath = Path.Combine(Application.dataPath, "Resources/Notes");
     }
 
     void LateUpdate()
     {
         if (Input.GetKeyDown(KeyCode.L))
         {
             //Application.CaptureScreenshot(filePath);
             StartCoroutine(TakeScreenShot());
         }
     }
 
 
     /// <summary>
     /// Takes a screen shot of the camera render texture
     /// </summary>
     /// <param name="_filePath">complete file path with name</param>
     public void TakeScreenShot(string _filePath) {
         filePath = _filePath;
         StartCoroutine(TakeScreenShot());
     }
 
     public IEnumerator TakeScreenShot()
     {
         yield return new WaitForEndOfFrame();
 
         RenderTexture rt = new RenderTexture(1920, 1080, 0);
         camera.targetTexture = rt;
         Texture2D screenShot = new Texture2D(1920, 1080, TextureFormat.RGB24, false);
         camera.Render();
         RenderTexture currentRT = RenderTexture.active; // remember the active RT
         RenderTexture.active = rt;
 
         Debug.Log(string.Format("Texture2D res, Width - {0} - Height {1}", screenShot.width, screenShot.height));
         screenShot.ReadPixels(new Rect(0, 0, 1920, 1080), 0, 0);
 
         camera.targetTexture = null;
         RenderTexture.active = currentRT;
         Destroy(rt);
 
         byte[] bytes = screenShot.EncodeToPNG();
         string fileName = System.Guid.NewGuid().ToString() + ".png";
         string fullPath = Path.Combine(filePath, fileName);
         System.IO.File.WriteAllBytes(fullPath, bytes);
         Debug.Log(string.Format("Took screenshot to: {0}", fullPath));
     }
 }