Retry-gameboy looking image-fx in unity3d

GameboyFX.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

#if UNITY_5_4_OR_NEWER
[ImageEffectAllowedInSceneView]
#endif
[RequireComponent(typeof(Camera)), DisallowMultipleComponent, ExecuteInEditMode]
[AddComponentMenu("Effects/GameboyFX", -1)]
public class GameboyFX : MonoBehaviour {

	private Material _material;
	
	private Material material
	{
		get {
			if (_material == null) 
			{
				_material = new Material( Shader.Find("Hidden/GameboyFX") );
			}
			return _material;
		}
	}
	
	// Postprocess the image
	void OnRenderImage (RenderTexture source, RenderTexture destination)
	{
		Graphics.Blit (source, destination, material);
	}
}

GameboyFX.shader

Shader "Hidden/GameboyFX"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
	}
	SubShader
	{
		// No culling or depth
		Cull Off ZWrite Off ZTest Always

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag

			#include "UnityCG.cginc"

			struct appdata
			{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
			};

			struct v2f
			{
				float2 uv : TEXCOORD0;
				float4 vertex : SV_POSITION;
			};

			v2f vert (appdata v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.uv = v.uv;
				return o;
			}

			sampler2D _MainTex;

			fixed4 frag (v2f i) : SV_Target
			{
				// Size of pixel
				const float pixel_size = 20;
				const float contract = 1.5;
				const float3 tint = float3(1.1, 1.4, 1);

				float2 uv = i.uv;
				float dx = pixel_size * (1.0/_ScreenParams.x);
				float dy = pixel_size * (1.0/_ScreenParams.y);
				float2 tc = float2(dx * floor(uv.x/dx), dy * floor(uv.y/dy));

				float4 color = tex2D(_MainTex, tc);
				color = (color - 0.5) * contract + 0.5;
				float gray = (color.r + color.g + color.b) / 3.0;

				color = float4(gray * tint, color.a);


				return color;
			}
			ENDCG
		}
	}
}