使用core image

//生成一张毛玻璃图片
- (UIImage *)blur:(UIImage *)theImage
{
    CIContext *context = [CIContextcontextWithOptions:nil];
    CIImage *inputImage = [CIImageimageWithCGImage:theImage.CGImage];
   
    CIFilter *filter = [CIFilterfilterWithName:@"CIGaussianBlur"];
    [filter setValue:inputImageforKey:kCIInputImageKey];
    [filter setValue:[NSNumbernumberWithFloat:15.0]forKey:@"inputRadius"];//其中数值是模糊度（3～30，越大越模糊）
    CIImage *result = [filtervalueForKey:kCIOutputImageKey];
   
    CGImageRef cgImage = [contextcreateCGImage:resultfromRect:[inputImageextent]];
   
    UIImage *returnImage = [UIImageimageWithCGImage:cgImage];
    CGImageRelease(cgImage);
    return returnImage;

}

系统方法，iOS8以上

//方法一：系统方法，iOS8及以上可用
    if (!UIAccessibilityIsReduceTransparencyEnabled()) {
        UIBlurEffect *blurEffect = [UIBlurEffecteffectWithStyle:UIBlurEffectStyleDark];
        UIVisualEffectView *blurEffectView = [[UIVisualEffectViewalloc]initWithEffect:blurEffect];
        blurEffectView.frame = _imageView.bounds;
        [_imageView addSubview:blurEffectView];

    }

上述两种方法可以配合使用，效果可以增加光亮度