iOS 圖像處理 － 模糊圖像 – iPhone手機開發技術文章 iPhone軟體開發教學課程

解決問題：將圖像模糊

前提：添加 CoreGraphics.framework

源碼：

- (UIImage*) blur:(UIImage*)theImage
{
    // create our blurred image
    CIContext *context = [CIContext contextWithOptions:nil];
    CIImage *inputImage = [CIImage imageWithCGImage:theImage.CGImage];
    
    // setting up Gaussian Blur (could use one of many filters offered by Core Image)
    CIFilter *blurFilter = [CIFilter filterWithName:@"CIGaussianBlur"];
    [blurFilter setValue:inputImage forKey:kCIInputImageKey];
    [blurFilter setValue:[NSNumber numberWithFloat:10.0f] forKey:@"inputRadius"];
    CIImage *result = [blurFilter valueForKey:kCIOutputImageKey];
    
    // CIGaussianBlur has a tendency to shrink the image a little,
    // this ensures it matches up exactly to the bounds of our original image
    CGImageRef cgImage = [context createCGImage:result fromRect:[inputImage extent]];
    
    UIImage *returnImage = [UIImage imageWithCGImage:cgImage];
    //create a UIImage for this function to "return" so that ARC can manage the memory of the blur...
    //ARC can't manage CGImageRefs so we need to release it before this function "returns" and ends.
    CGImageRelease(cgImage);//release CGImageRef because ARC doesn't manage this on its own.
    
    return returnImage;
}

出現問題：因為在模糊的時候，邊緣會變成半透明的狀態，所以理想狀況是可以對原圖像進行適當放大，選擇使用CIAffineClamp在模糊之前對圖像進行處理。

源碼：

- (UIImage*) blur:(UIImage*)theImage
{
    // create our blurred image
    CIContext *context = [CIContext contextWithOptions:nil];
    CIImage *inputImage = [CIImage imageWithCGImage:theImage.CGImage];
    
    CIFilter *affineClampFilter = [CIFilter filterWithName:@"CIAffineClamp"];
    CGAffineTransform xform = CGAffineTransformMakeScale(1.0, 1.0);
    [affineClampFilter setValue:inputImage forKey:kCIInputImageKey];
    [affineClampFilter setValue:[NSValue valueWithBytes:&xform
                                               objCType:@encode(CGAffineTransform)]
                                                 forKey:@"inputTransform"];
    
    CIImage *extendedImage = [affineClampFilter valueForKey:kCIOutputImageKey];
    
    // setting up Gaussian Blur (could use one of many filters offered by Core Image)
    CIFilter *blurFilter = [CIFilter filterWithName:@"CIGaussianBlur"];
    [blurFilter setValue:extendedImage forKey:kCIInputImageKey];
    [blurFilter setValue:[NSNumber numberWithFloat:10.0f] forKey:@"inputRadius"];
    CIImage *result = [blurFilter valueForKey:kCIOutputImageKey];
    
    // CIGaussianBlur has a tendency to shrink the image a little,
    // this ensures it matches up exactly to the bounds of our original image
    CGImageRef cgImage = [context createCGImage:result fromRect:[inputImage extent]];
    
    UIImage *returnImage = [UIImage imageWithCGImage:cgImage];
    //create a UIImage for this function to "return" so that ARC can manage the memory of the blur...
    //ARC can't manage CGImageRefs so we need to release it before this function "returns" and ends.
    CGImageRelease(cgImage);//release CGImageRef because ARC doesn't manage this on its own.
    
    return returnImage;
}

參考：（網上資源，部分鏈接已丟失）

https://stackoverflow.com/questions/12839729/correct-crop-of-cigaussianblur