c# - save a particular area of the scene as screenshot in unity

I need to save a particular part of the scene as screenshot. I have done a sample to show the particular part of the scene.

When I click on the rectangular area the selected area will being shown on the screen on a texture (marked in red rectangle):

But when I save, the whole scene is getting saved but not the selected part:

Here is code:

Texture2D screencap;
Texture2D border;
bool shot=false;
public string path;

void Start () {
     screencap=new Texture2D(300,200,TextureFormat.RGB24,false);
     border=new Texture2D(2,2,TextureFormat.ARGB32,false);

     border.Apply();
}

// Update is called once per frame
void Update () {
    if(Input.GetKeyUp(KeyCode.Mouse0))
    {
        StartCoroutine("Capture");
    }


}
string fileName(int width, int height)
{
    return string.Format("screen_{0}x{1}_{2}.png",
                         width, height,
                         System.DateTime.Now.ToString("yyyy-MM-dd_HH-mm-ss"));
}

void OnGUI()
{

    GUI.DrawTexture(new Rect(200,100,300,2),border,ScaleMode.StretchToFill);
    GUI.DrawTexture(new Rect(200,300,300,2),border,ScaleMode.StretchToFill);
    GUI.DrawTexture(new Rect(195,100,2,200),border,ScaleMode.StretchToFill);
    GUI.DrawTexture(new Rect(500,100,2,201),border,ScaleMode.StretchToFill);

    if(shot)
    {
        GUI.DrawTexture(new Rect(50,10,60,40),screencap,ScaleMode.StretchToFill);
        //Application.CaptureScreenshot(myFolderLocation+myFilename);
    }

}

IEnumerator Capture()
{
    yield return new WaitForEndOfFrame();
    screencap.ReadPixels(new Rect(198,98,298,198),0,0);
    screencap.Apply();
    shot=true;

    byte[] bytes=border.EncodeToPNG();

    string filename=fileName(Convert.ToInt32(screencap.width), Convert.ToInt32(screencap.height));
    Application.CaptureScreenshot("D:"+filename);
}

How can I save only the particular part in unity,can anybody please help me out.

Answer

Your

Application.CaptureScreenshot("D:"+filename);

saves the whole shene on file, you need to save the texture2d to file

Follow the example:

 import System.IO;

  function SaveTextureToFile( texture: Texture2D,fileName)
  {
     var bytes=texture.EncodeToPNG();
     var file = new File.Open(Application.dataPath + "/"+fileName,FileMode.Create);
     var binary= new BinaryWriter(file);
     binary.Write(bytes);
     file.Close();

  }

Call it using:

      SaveTextureToFile( screencap,"picture.png");

EDIT: a variation of SaveTextureToFile can be:

     function SaveTextureToFile(  Texture2D texture ,string fileName)
      {
        byte[] bytes = texture.EncodeToPNG();
         File.WriteAllBytes(filename, bytes);

}