Vignette shader hard edges

[maxxa05]

When I tried the vignette effect, it gave me the hard edges you can see in the picture below. I gave a shot at doing my own shader for it, and even if I’m able to make them more sublte, it isn’t quite as smooth as I’d like. I know it’s due to the gap between the 256 levels of grayscale, but i’d like to know if there’s any workaround for this.

The screenshot below is the camera facing a gray plane. I included my shader code below.

	Shader "test/VignettingShader" {
	
	Properties {
		_MainTex ("Base", 2D) = "white" {}
	}
	
	CGINCLUDE
	
	#include "UnityCG.cginc"
	

	ENDCG 
	
Subshader {
 Pass {
	  ZTest Always Cull Off ZWrite Off
	  Fog { Mode off }      

      CGPROGRAM
      #pragma fragmentoption ARB_precision_hint_fastest 
      #pragma vertex vert
      #pragma fragment frag
      
      	struct v2f {
		float4 pos : POSITION;
		float2 uv : TEXCOORD0;
	};
	
	sampler2D _MainTex;

		
	v2f vert( appdata_img v ) {
		v2f o;
		o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
		o.uv = v.texcoord.xy;
		return o;
	} 
	
	half4 frag(v2f i) : COLOR {

		
		
		  float2 texCoord=i.uv;

  // Take texture color
  half4 color = tex2D (_MainTex, i.uv);
  
  //vignette effect
  texCoord -= 0.5;
	float vignette = 1.0 - pow(dot(texCoord, texCoord),1);

	vignette = pow(vignette,5);//determine vignette amount

color*=vignette;


  return color;
		
		
	}
      
      ENDCG
  }
}

Fallback off	
}

[ScroodgeM]

these hard edges are not shader or calculations limit. this is a screen limit. 99% of world screens works with 32bit color, 8 bit per color channel. so you can’t increase this 1/256 color level step.

but… you can do something 8)

replace

return color;

with

return color + float4(0, 0.0013, 0.0026, 0);

this will smooth color step

(50,50,50) -> (51,51,51)

to something like

(50,50,50) -> (51,50,50) -> (51,51,50) -> (51,51,51)

some type of fake, but looks triple smoothly 8)