GPUImage滤镜之锐化

　　应用锐化工具可以快速聚焦模糊边缘，提高图像中某一部位的清晰度或者焦距程度，使图像特定区域的色彩更加鲜明。 在应用锐化工具时，若勾选器选项栏中的“对所有图层取样”复选框，则可对所有可见图层中的图像进行锐化。但一定要适度。锐化不是万能的，很容易使东西不真实。

　　在GPUImage中使用GPUImageSharpenFilter类来实现图像的锐化效果

　　片段着色

 precision highp float;

 varying highp vec2 textureCoordinate;
 varying highp vec2 leftTextureCoordinate;
 varying highp vec2 rightTextureCoordinate;
 varying highp vec2 topTextureCoordinate;
 varying highp vec2 bottomTextureCoordinate;

 varying highp float centerMultiplier;
 varying highp float edgeMultiplier;

 uniform sampler2D inputImageTexture;

 void main()
 {
     mediump vec3 textureColor = texture2D(inputImageTexture, textureCoordinate).rgb;
     mediump vec3 leftTextureColor = texture2D(inputImageTexture, leftTextureCoordinate).rgb;
     mediump vec3 rightTextureColor = texture2D(inputImageTexture, rightTextureCoordinate).rgb;
     mediump vec3 topTextureColor = texture2D(inputImageTexture, topTextureCoordinate).rgb;
     mediump vec3 bottomTextureColor = texture2D(inputImageTexture, bottomTextureCoordinate).rgb;

     gl_FragColor = vec4((textureColor * centerMultiplier - (leftTextureColor * edgeMultiplier + rightTextureColor * edgeMultiplier + topTextureColor * edgeMultiplier + bottomTextureColor * edgeMultiplier)), texture2D(inputImageTexture, bottomTextureCoordinate).w);
 }

　　具体应用

+ (UIImage *)changeValueForSharpenilter:(float)value image:(UIImage *)image
{
    GPUImageSharpenFilter *filter = [[GPUImageSharpenFilter alloc] init];
    filter.sharpness = value;
    [filter forceProcessingAtSize:image.size];
    GPUImagePicture *pic = [[GPUImagePicture alloc] initWithImage:image];
    [pic addTarget:filter];

    [pic processImage];
    [filter useNextFrameForImageCapture];
    return [filter imageFromCurrentFramebuffer];
}

　　效果