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[操作系统]美图秀秀滤镜之色温(白平衡)


  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];}

 

 

效果

  

          高温度                           低温度