GPUImage中亮度调整的实现——GPUImageBrightnessFilter

亮度brightness其实是对RGB的调整，RGB值越大，效果越亮；反之则越暗。

GPUImage中提供了对图像亮度调整的Filter，其核心代码如下(fragment)：

 1  varying highp vec2 textureCoordinate;
 2  
 3  uniform sampler2D inputImageTexture;
 4  uniform lowp float brightness;
 5  
 6  void main()
 7  {
 8      lowp vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);
 9      
10      gl_FragColor = vec4((textureColor.rgb + vec3(brightness)), textureColor.w);
11  }

其中brightness的取值范围为[-1,1]