#version 300 es
precision mediump float;
in vec2 v_texcoord;
uniform sampler2D tex;
out vec4 FragColor;


// Values obtained from: http://en.wikipedia.org/wiki/Grayscale#Luma_coding_in_video_systems
vec3 LumaFactors = vec3(0.299, 0.587, 0.114);

void main() {
  vec4 c = texture(tex, v_texcoord);

  // average brightness
  float luma = dot(vec3(c.r, c.g, c.b), LumaFactors);

  if (c.r < c.b) {
    FragColor = vec4(luma, luma, c.b, c.a);
  } else {
    FragColor = vec4(c.r, luma, luma, c.a);
  }
  // FragColor = vec4(c.r, luma, c.b, c.a);
}