precision highp float;

varying vec2 textureCoordinate;

uniform sampler2D inputImageTexture;

const highp vec3 W = vec3(0.2125, 0.7154, 0.0721);

void main(){
    lowp vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);
    float luminance = dot(textureColor.rgb, W);
    gl_FragColor = vec4(vec3(luminance), textureColor.a);
}