three.js/examples/js/shaders/BrightnessContrastShader.js

/**
 * Brightness and contrast adjustment
 * https://github.com/evanw/glfx.js
 * brightness: -1 to 1 (-1 is solid black, 0 is no change, and 1 is solid white)
 * contrast: -1 to 1 (-1 is solid gray, 0 is no change, and 1 is maximum contrast)
 */

THREE.BrightnessContrastShader = {

	uniforms: {

		'tDiffuse': { value: null },
		'brightness': { value: 0 },
		'contrast': { value: 0 }

	},

	vertexShader: [

		'varying vec2 vUv;',

		'void main() {',

		'	vUv = uv;',

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

		'}'

	].join( '\n' ),

	fragmentShader: [

		'uniform sampler2D tDiffuse;',
		'uniform float brightness;',
		'uniform float contrast;',

		'varying vec2 vUv;',

		'void main() {',

		'	gl_FragColor = texture2D( tDiffuse, vUv );',

		'	gl_FragColor.rgb += brightness;',

		'	if (contrast > 0.0) {',
		'		gl_FragColor.rgb = (gl_FragColor.rgb - 0.5) / (1.0 - contrast) + 0.5;',
		'	} else {',
		'		gl_FragColor.rgb = (gl_FragColor.rgb - 0.5) * (1.0 + contrast) + 0.5;',
		'	}',

		'}'

	].join( '\n' )

};