ImageEffectGradientMap

Shader "Hidden/GradientMap"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _GradientMap("Gradient Map", 2D) = "white" {}
        _Intensity("Intensity", Range(0,10)) = 1
    }
    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, _GradientMap;
            float _Intensity;

            fixed4 frag (v2f i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.uv);

        // take the 3 color channels and average them out to create a grayscale version
        float grayscale = (col.r + col.g + col.b) / 3;
        // control the intensity
        grayscale *= _Intensity;
        // project the gradient map over the grayscale
        fixed4 gradient = tex2D(_GradientMap, grayscale);
        // get the transparency
        gradient *= gradient.a;
        // add original camera view back where the gradient is transparent
        gradient += (1 - gradient.a) * col;

                return gradient;
            }
            ENDCG
        }
    }
}