iOS开发的时候有的时候需要将图片设置模糊，或者通过点击下拉方法，去除模糊。关于图片实现高斯模糊效果有三种方式，CoreImage，GPUImage（第三方开源类库）和vImage。GPUImage没怎么用过，本文就讲两种方式Core Image和vImage。
Core Image
iOS5.0之后就出现了Core Image的API,Core Image的API被放在CoreImage.framework库中,在iOS和OS X平台上，Core Image都提供了大量的滤镜（Filter），在OS X上有120多种Filter，而在iOS上也有90多。首先我们扩展一下UIImage，添加类方法:
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+(UIImage *)coreBlurImage:(UIImage *)image withBlurNumber:(CGFloat)blur
{
CIContext *context = [CIContext contextWithOptions:nil];
CIImage *inputImage=[CIImage imageWithCGImage:image.CGImage];
//设置filter
CIFilter *filter = [CIFilter filterWithName:@"CIGaussianBlur"];
[filter setValue:inputImage forKey:kCIInputImageKey];
[filter setValue:@(blur) forKey: @"inputRadius"];
//模糊图片
CIImage *result=[filter valueForKey:kCIOutputImageKey];
CGImageRef outImage=[context createCGImage:result fromRect:[result extent]];
UIImage *blurImage=[UIImage imageWithCGImage:outImage];
CGImageRelease(outImage);
return blurImage;
}
其中过滤的选项设置为高斯模糊:
vImage 方式
vImage属于Accelerate.Framework，需要导入Accelerate下的Accelerate头文件，Accelerate主要是用来做数字信号处理、图像处理相关的向量、矩阵运算的库。图像可以认为是由向量或者矩阵数据构成的，Accelerate里既然提供了高效的数学运算API，自然就能方便我们对图像做各种各样的处理，模糊算法使用的是vImageBoxConvolve_ARGB8888这个函数。
+(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;
}
图片模糊调用:
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];
参考资料:http://t.cn/RcCyU01
