GameBoy_007_GameBoyShader_04.shader

Shader "Gameboy"
{
  ...

    sampler2D _MainTex;
    float4 _Darkest, _Dark, _Ligt, _Ligtest;

    float4 frag (v2f i) : SV_Target
    {
      float4 originalColor = tex2D(_MainTex, i.uv);
      float luma = dot(originalColor.rgb, float3(0.2126, 0.7152, 0.0722));
      float posterized = floor(luma * 4) / (4 - 1);
      
      float lumaTimesThree = posterized * 3.0;

      float darkest = saturate(lumaTimesThree);
      float4 color = lerp(_Darkest, _Dark, darkest);

      float light = saturate(lumaTimesThree - 1.0);
      color = lerp(color, _Ligt, light);

      float lightest = saturate(lumaTimesThree - 2.0);
      color = lerp(color, _Ligtest, lightest);

      return color;
    }
  ...
}