How can the culling mask be used?

I have put different gameobjects in different layers and set the camera culling mask, but what i have seen seems unreasonable. The objects have changed into the which culling mask covers, but i cannot see the object in the scene. Could you help me find the reason for that?

         //the culling mask of unicam is 2 and -1 of maincam
         //this function is called with index decreased from objlist.Count to zero
     private void saveScene(int index){
         print ("getS");
         string filename = savepath + System.DateTime.Now.ToString ("yyyy-MM-dd_HH-mm-ss");
         //if it is for the whole view
         if (index == objlist.Count) {
             MakeCameraImg (filename,mainCam);
             objlist [objlist.Count - 1].layer = 1;
             return;
         }
         //get the classification
         GameObject gb = objlist [index];
         string typename = gb.name.Split ('_') [1];
         //check if it falls
         if (gb.transform.position.y < -0.5) {
             return;
         }
         MakeCameraImg (filename + "_" + typename+index.ToString(),uniCam);
             objlist[index].layer=0;
         if (index > 0)
             objlist [index - 1].layer = 1;
     }

 
     private void MakeCameraImg(string filename,Camera mCam){
         RenderTexture rt = new RenderTexture (width, height, 2);
         mCam.pixelRect = new Rect (0, 0, width, height);
         mCam.targetTexture = rt;
         Texture2D screenShot = new Texture2D ((int)(width), (int)(height), TextureFormat.RGB24, false);
         mCam.Render ();
         RenderTexture.active = rt;
         screenShot.ReadPixels (new Rect (0, 0,width,height),0,0);
         mCam.targetTexture = null;
         RenderTexture.active = null;
         UnityEngine.Object.Destroy (rt);
         byte[] bytes = screenShot.EncodeToJPG ();
         System.IO.File.WriteAllBytes (filename+".jpg", bytes);
     }