iOS開發的時候有的時候需要將圖片設置模糊，或者通過點擊下拉方法，去除模糊。關于圖片實現高斯模糊效果有三種方式，CoreImage，GPUImage（第三方開源類庫）和vImage。GPUImage沒怎么用過，本文就講兩種方式Core Image和vImage。

Core Image

iOS5.0之后就出現了Core Image的API,Core Image的API被放在CoreImage.framework庫中,在iOS和OS X平臺上，Core Image都提供了大量的濾鏡（Filter），在OS X上有120多種Filter，而在iOS上也有90多。首先我們擴展一下UIImage，添加類方法:

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+(UIImage *)coreBlurImage:(UIImage *)image withBlurNumber:(CGFloat)blur
 {
    CIContext *context = [CIContext contextWithOptions:nil];
    CIImage *inputImage=[CIImage imageWithCGImage:image.CGImage];
    //設置filter
    CIFilter *filter = [CIFilter filterWithName:@"CIGaussianBlur"];
    [filter setValue:inputImage forKey:kCIInputImageKey];
    [filter setValue:@(blur) forKey: @"inputRadius"];
    //模糊圖片
    CIImage *result=[filter valueForKey:kCIOutputImageKey];
    CGImageRef outImage=[context createCGImage:result fromRect:[result extent]];
    UIImage *blurImage=[UIImage imageWithCGImage:outImage];
    CGImageRelease(outImage);
    return blurImage;
}

其中過濾的選項設置為高斯模糊:

vImage 方式

vImage屬于Accelerate.Framework，需要導入Accelerate下的Accelerate頭文件，Accelerate主要是用來做數字信號處理、圖像處理相關的向量、矩陣運算的庫。圖像可以認為是由向量或者矩陣數據構成的，Accelerate里既然提供了高效的數學運算API，自然就能方便我們對圖像做各種各樣的處理，模糊算法使用的是vImageBoxConvolve_ARGB8888這個函數。

+(UIImage *)boxblurImage:(UIImage *)image withBlurNumber:(CGFloat)blur {
    if (blur < 0.f || blur > 1.f) {
        blur = 0.5f;
    }
    int boxSize = (int)(blur * 40);
    boxSize = boxSize - (boxSize % 2) + 1;
     
    CGImageRef img = image.CGImage;
     
    vImage_Buffer inBuffer, outBuffer;
    vImage_Error error;
     
    void *pixelBuffer;
    //從CGImage中獲取數據
    CGDataProviderRef inProvider = CGImageGetDataProvider(img);
    CFDataRef inBitmapData = CGDataProviderCopyData(inProvider);
    //設置從CGImage獲取對象的屬性
    inBuffer.width = CGImageGetWidth(img);
    inBuffer.height = CGImageGetHeight(img);
    inBuffer.rowBytes = CGImageGetBytesPerRow(img);
     
    inBuffer.data = (void*)CFDataGetBytePtr(inBitmapData);
     
    pixelBuffer = malloc(CGImageGetBytesPerRow(img) *
                         CGImageGetHeight(img));
     
    if(pixelBuffer == NULL)
        NSLog(@"No pixelbuffer");
     
    outBuffer.data = pixelBuffer;
    outBuffer.width = CGImageGetWidth(img);
    outBuffer.height = CGImageGetHeight(img);
    outBuffer.rowBytes = CGImageGetBytesPerRow(img);
     
    error = vImageBoxConvolve_ARGB8888(&inBuffer, &outBuffer, NULL, 0, 0, boxSize, boxSize, NULL, kvImageEdgeExtend);
     
    if (error) {
        NSLog(@"error from convolution %ld", error);
    }
     
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef ctx = CGBitmapContextCreate(
                                             outBuffer.data,
                                             outBuffer.width,
                                             outBuffer.height,
                                             8,
                                             outBuffer.rowBytes,
                                             colorSpace,
                                             kCGImageAlphaNoneSkipLast);
    CGImageRef imageRef = CGBitmapContextCreateImage (ctx);
    UIImage *returnImage = [UIImage imageWithCGImage:imageRef];
     
    //clean up
    CGContextRelease(ctx);
    CGColorSpaceRelease(colorSpace);
     
    free(pixelBuffer);
    CFRelease(inBitmapData);
     
    CGColorSpaceRelease(colorSpace);
    CGImageRelease(imageRef);
     
    return returnImage;
}

圖片模糊調用:

self.imageView=[[UIImageView alloc]initWithFrame:CGRectMake(0, 300, SCREENWIDTH, 100)];
self.imageView.contentMode=UIViewContentModeScaleAspectFill;
self.imageView.image=[UIImage boxblurImage:self.image withBlurNumber:0.5];
self.imageView.clipsToBounds=YES;
[self.view addSubview:self.imageView];

參考資料:http://t.cn/RcCyU01