高斯模糊，这个方法很有效

使用方式
需要导入头文件

#import <Accelerate/Accelerate.h>

- (UIImage *)blurryImage:(UIImage *)image withBlurLevel:(CGFloat)blur {
if (blur < 0.f || blur > 1.f) {
    blur = 0.5f;
}
int boxSize = (int)(blur * 100);
boxSize = boxSize - (boxSize % 2) + 1;

CGImageRef img = image.CGImage;

vImage_Buffer inBuffer, outBuffer;
vImage_Error error;

void *pixelBuffer;

CGDataProviderRef inProvider = CGImageGetDataProvider(img);
CFDataRef inBitmapData = CGDataProviderCopyData(inProvider);

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);

// 注意网络上的 这里 是没有被注释掉的，需要注释掉，不然就会多释放一次，出现异常
//    CGColorSpaceRelease(colorSpace);
CGImageRelease(imageRef);

return returnImage;
}