dolphin/Data/User/Shaders/posterize.txt

uniform sampler2D samp9;

out vec4 ocol0;
in vec2 uv0;

void main()
{
  float4 c0 = texture(samp9, uv0).rgba;
  float red   = 0.0;
  float green = 0.0;
  float blue  = 0.0;

  if (c0.r > 0.25)
  {
    red = c0.r;
  }

  if (c0.g > 0.25)
  {
    green = c0.g;
  }

  if (c0.b > 0.25)
  {
    blue = c0.b;
  }

  ocol0 = float4(red, green, blue, 1.0);
}