色温调整

色温转rgb

https://github.com/esemeniuc/kelvin_rgb

　　色温色温是表示光源光谱质量最通用的指标。

　　GPUImage中我们通过GPUImageWhiteBalanceFilter来实现

　　顶点着色

      uniform sampler2D inputImageTexture;
      varying highp vec2 textureCoordinate;
      uniform lowp float temperature;
      uniform lowp float tint;
      const lowp vec3 warmFilter = vec3(0.93, 0.54, 0.0);
      const mediump mat3 RGBtoYIQ = mat3(0.299, 0.587, 0.114, 0.596, -0.274, -0.322, 0.212, -0.523, 0.311);
      const mediump mat3 YIQtoRGB = mat3(1.0, 0.956, 0.621, 1.0, -0.272, -0.647, 1.0, -1.105, 1.702);
      void main()
      {
       lowp vec4 source = texture2D(inputImageTexture, textureCoordinate);
       mediump vec3 yiq = RGBtoYIQ * source.rgb; //adjusting tint
       yiq.b = clamp(yiq.b + tint*0.5226*0.1, -0.5226, 0.5226);
       lowp vec3 rgb = YIQtoRGB * yiq;
       lowp vec3 processed = vec3(
       (rgb.r < 0.5 ? (2.0 * rgb.r * warmFilter.r) : (1.0 - 2.0 * (1.0 - rgb.r) * (1.0 - warmFilter.r))), //adjusting temperature
       (rgb.g < 0.5 ? (2.0 * rgb.g * warmFilter.g) : (1.0 - 2.0 * (1.0 - rgb.g) * (1.0 - warmFilter.g))),
       (rgb.b < 0.5 ? (2.0 * rgb.b * warmFilter.b) : (1.0 - 2.0 * (1.0 - rgb.b) * (1.0 - warmFilter.b))));
       gl_FragColor = vec4(mix(rgb, processed, temperature), source.a);
      }
  
 

 色温算法较复杂，它与温度有关

具体应用

      + (UIImage *)changeValueForWhiteBalanceFilter:(float)value image:(UIImage *)image
      {
       GPUImageWhiteBalanceFilter *filter = [[GPUImageWhiteBalanceFilter alloc] init];
       filter.temperature = value;
       filter.tint = 0.0;
       [filter forceProcessingAtSize:image.size];
       GPUImagePicture *pic = [[GPUImagePicture alloc] initWithImage:image];
       [pic addTarget:filter];
       [pic processImage];
       [filter useNextFrameForImageCapture];
       return [filter imageFromCurrentFramebuffer];
      }
  
 

文章来源: blog.csdn.net，作者：网奇，版权归原作者所有，如需转载，请联系作者。

原文链接：blog.csdn.net/jacke121/article/details/108532940