Capturing 360 Image causes to darken the image and show ghosting and artifacts

I made a code to capture 360 image using render texture, When I capture image to render texture it appears fine but when I Encode it to PNG or JPG the problem occurs. .

The image darkens and artifacts / ghosting is very visible.

Here's the image encoded to PNG using code. https://imgur.com/KJDHsWw

Here's a photoshopped version of the image to increase lighting. https://imgur.com/VmUPNaz

and Here's a zoomed images of the artifact https://imgur.com/sSVocSV https://imgur.com/SZlVo9O

below is my code:

 public class PanoramaCapture : MonoBehaviour
 {
     public Camera targetCamera;
     public RenderTexture cubemapLeft;
     public RenderTexture equirectRT;
     public string fileName;
     public int captureInstance;
     public int imageWidth = 4096;
     private void Start()
     {
         if (fileName == null)
         {
             fileName = "KitchenCombinations_";
         }
         captureInstance = 1;
     }
     private void Update()
     {
         if (Input.GetKeyDown(KeyCode.Return))
         {
             Capture();
         }
     }
     void Capture()
     {
         targetCamera.stereoSeparation = 0f;
         targetCamera.RenderToCubemap(cubemapLeft);
         cubemapLeft.ConvertToEquirect(equirectRT);
         Save(equirectRT);
         captureInstance += 1;
     }
 
     public void Save(RenderTexture rt)
     {
         Texture2D tex = new Texture2D(rt.width, rt.height);
 
         RenderTexture.active = rt;
         tex.ReadPixels(new Rect(0, 0, rt.width, rt.height), 0, 0);
         RenderTexture.active = null;
 
         byte[] bytes = tex.EncodeToPNG();
 
         //data path could be in the game folder or database but we have to figure that out
         string path = Application.dataPath + "/" + fileName + captureInstance.ToString() + ".png";
 
         System.IO.File.WriteAllBytes(path, bytes);
 
     }