GrayscaleLayers.cs

using System;
using UnityEngine;

// Grayscale effect, with added ExcludeLayer option
// Usage: Attach this script to camera, Select excludeLayers, Set your excluded objects to that layer


#if !UNITY_5_3_OR_NEWER
namespace UnityStandardAssets.ImageEffects
{

    [ExecuteInEditMode]
    [AddComponentMenu("Image Effects/Color Adjustments/Grayscale")]
    public class GrayscaleLayers : ImageEffectBase
    {
        public Texture textureRamp;
        public LayerMask excludeLayers = 0;

        private GameObject tmpCam = null;
        private Camera _camera;

        [Range(-1.0f, 1.0f)]
        public float rampOffset;

        // Called by camera to apply image effect
        void OnRenderImage(RenderTexture source, RenderTexture destination)
        {
            material.SetTexture("_RampTex", textureRamp);
            material.SetFloat("_RampOffset", rampOffset);
            Graphics.Blit(source, destination, material);

            // exclude layers
            Camera cam = null;
            if (excludeLayers.value != 0) cam = GetTmpCam();

            if (cam && excludeLayers.value != 0)
            {
                cam.targetTexture = destination;
                cam.cullingMask = excludeLayers;
                cam.Render();
            }
        }


        // taken from CameraMotionBlur.cs
        Camera GetTmpCam()
        {
            if (tmpCam == null)
            {
                if (_camera == null) _camera = GetComponent<Camera>();

                string name = "_" + _camera.name + "_GrayScaleTmpCam";
                GameObject go = GameObject.Find(name);

                if (null == go) // couldn't find, recreate
                {
                    tmpCam = new GameObject(name, typeof(Camera));
                } else
                {
                    tmpCam = go;
                }
            }

            tmpCam.hideFlags = HideFlags.DontSave;
            tmpCam.transform.position = _camera.transform.position;
            tmpCam.transform.rotation = _camera.transform.rotation;
            tmpCam.transform.localScale = _camera.transform.localScale;
            tmpCam.GetComponent<Camera>().CopyFrom(_camera);

            tmpCam.GetComponent<Camera>().enabled = false;
            tmpCam.GetComponent<Camera>().depthTextureMode = DepthTextureMode.None;
            tmpCam.GetComponent<Camera>().clearFlags = CameraClearFlags.Nothing;

            return tmpCam.GetComponent<Camera>();
        }
    }
}
#endif