UGUI-图片黑白Shader

Shader：

// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

Shader "UI/Default Grey"     
{     
    Properties     
    {     
        [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}     
        _Color ("Tint", Color) = (1,1,1,1)  
    }     

    SubShader     
    {     
        Tags     
        {      
            "Queue"="Transparent"      
            "IgnoreProjector"="True"      
            "RenderType"="Transparent"      
            "PreviewType"="Plane"     
            "CanUseSpriteAtlas"="True"     
        }     
        // 源rgba*源a + 背景rgba*(1-源A值)   
        Blend SrcAlpha OneMinusSrcAlpha  

        Pass     
        {     
            CGPROGRAM     
            #pragma vertex vert     
            #pragma fragment frag     
            #include "UnityCG.cginc"     

            struct appdata_t     
            {     
                float4 vertex   : POSITION;     
                float4 color    : COLOR;     
                float2 texcoord : TEXCOORD0;     
            };     

            struct v2f     
            {     
                float4 vertex   : SV_POSITION;     
                fixed4 color    : COLOR;     
                half2 texcoord  : TEXCOORD0;     
            };     

            sampler2D _MainTex;       
            fixed4 _Color;     

            v2f vert(appdata_t IN)     
            {     
                v2f OUT;     
                OUT.vertex = UnityObjectToClipPos(IN.vertex);     
                OUT.texcoord = IN.texcoord;     
#ifdef UNITY_HALF_TEXEL_OFFSET     
                OUT.vertex.xy -= (_ScreenParams.zw-1.0);     
#endif     
                OUT.color = IN.color * _Color;     
                return OUT;  
            }  

            fixed4 frag(v2f IN) : SV_Target     
            {     
                half4 color = tex2D(_MainTex, IN.texcoord) * IN.color;     
                float grey = dot(color.rgb, fixed3(0.22, 0.707, 0.071));   
                return half4(grey,grey,grey,color.a);     
            }     
            ENDCG     
        }     
    }     
}

效果图：