three.js/examples/js/shaders/LuminosityHighPassShader.js

/**
 * Luminosity
 * http://en.wikipedia.org/wiki/Luminosity
 */

THREE.LuminosityHighPassShader = {

	shaderID: 'luminosityHighPass',

	uniforms: {

		'tDiffuse': { value: null },
		'luminosityThreshold': { value: 1.0 },
		'smoothWidth': { value: 1.0 },
		'defaultColor': { value: new THREE.Color( 0x000000 ) },
		'defaultOpacity': { value: 0.0 }

	},

	vertexShader: [

		'varying vec2 vUv;',

		'void main() {',

		'	vUv = uv;',

		'	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );',

		'}'

	].join( '\n' ),

	fragmentShader: [

		'uniform sampler2D tDiffuse;',
		'uniform vec3 defaultColor;',
		'uniform float defaultOpacity;',
		'uniform float luminosityThreshold;',
		'uniform float smoothWidth;',

		'varying vec2 vUv;',

		'void main() {',

		'	vec4 texel = texture2D( tDiffuse, vUv );',

		'	vec3 luma = vec3( 0.299, 0.587, 0.114 );',

		'	float v = dot( texel.xyz, luma );',

		'	vec4 outputColor = vec4( defaultColor.rgb, defaultOpacity );',

		'	float alpha = smoothstep( luminosityThreshold, luminosityThreshold + smoothWidth, v );',

		'	gl_FragColor = mix( outputColor, texel, alpha );',

		'}'

	].join( '\n' )

};