iOS几种高斯模糊效果的实现与比较

iOS的模糊效果实现方法有好几种，基本分为两种方式，一种是将图片进行模糊，一种是将模糊的控件放在UI界面上，使控件覆盖的区域达到模糊的效果。每种方式我各选了2种方法，下面介绍一下它们的实现方式以及对比一下它们的优缺点。

屏幕快照 2016-07-29 上午10.10.32.png

coreImage

该方法实现的模糊效果较好，模糊程度的可调范围很大，可以根据实际的需求随意调试。缺点就是耗时，我在模拟器上跑需要1-2秒的时间，所有该方法需要放在子线程中执行。

dispatch_async(dispatch_get_global_queue(0, 0), ^{
        CIContext *context = [CIContext contextWithOptions:nil];
        CIImage *ciImage = [CIImage imageWithCGImage:image.CGImage];
        CIFilter *filter = [CIFilter filterWithName:@"CIGaussianBlur"];
        [filter setValue:ciImage forKey:kCIInputImageKey];
        //设置模糊程度
        [filter setValue:@30.0f forKey: @"inputRadius"];
        CIImage *result = [filter valueForKey:kCIOutputImageKey];
        CGRect frame = [ciImage extent];
        NSLog(@"%f,%f,%f,%f",frame.origin.x,frame.origin.y,frame.size.width,frame.size.height);
        CGImageRef outImage = [context createCGImage: result fromRect:ciImage.extent];
        UIImage * blurImage = [UIImage imageWithCGImage:outImage];
        dispatch_async(dispatch_get_main_queue(), ^{
            coreImgv.image = blurImage;
        });
    });

vImage

该方法效率高，但是模糊程度最大只能达到上图展示的程度，而且我在使用它对网络加载的图片进行模糊时，整个图片会变红。

//使用前需要导入头文件
#import <Accelerate/Accelerate.h>
+ (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;
    //从CGImage中获取数据
    CGDataProviderRef inProvider = CGImageGetDataProvider(img);
    CFDataRef inBitmapData = CGDataProviderCopyData(inProvider);
    //设置从CGImage获取对象的属性
    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;
}

下面两种方法实现起来都很简单，但是只有几种系统提供的样式可选。
BlurEffect是在iOS8之后才出现的，它和toolbar实现的效果基本一样，比toolbar多了一种颜色更深的样式，如上面大图所示。

BlurEffect

UIImageView *blurImgv = [[UIImageView alloc]initWithFrame:CGRectMake(50, 500, 150, 150)];
blurImgv.image = image;
[self.view addSubview:blurImgv];
UIBlurEffect *beffect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleLight];
UIVisualEffectView *view = [[UIVisualEffectView alloc]initWithEffect:beffect];
view.frame = blurImgv.frame;
[self.view addSubview:view];

toolbar

UIImageView *toolImgv = [[UIImageView alloc]initWithFrame:CGRectMake(210, 500, 150, 150)];
toolImgv.image = image;
[self.view addSubview:toolImgv];
UIToolbar *toolBar = [[UIToolbar alloc]initWithFrame:CGRectMake(210, 500, 150, 150)];
toolBar.barStyle = UIBarStyleDefault;
[self.view addSubview:toolBar];

上面介绍了四种实现模糊效果的方法，同时也进行了简单的比较。具体的使用还是要根据项目的需求选择最合适的方法。