GPUImage濾鏡之銳化

　　應用銳化工具可以快速聚焦模糊邊緣，提高圖像中某一部位的清晰度或者焦距程度，使圖像特定區域的色彩更加鮮明。 在應用銳化工具時，若勾選器選項欄中的“對所有圖層取樣”覆選框，則可對所有可見圖層中的圖像進行銳化。但一定要適度。銳化不是萬能的，很容易使東西不真實。

　　在GPUImage中使用GPUImageSharpenFilter類來實現圖像的銳化效果

　　片段著色

 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);
 }

 　　具體應用

+ (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