CIGaussianBlur的正确裁剪 [英] Correct crop of CIGaussianBlur

问题描述

正如我注意到的那样，当将CIGaussianBlur应用于图像时，图像的角变得模糊，因此看起来比原始图像要小.因此，我发现我需要正确裁剪它，以免图像出现透明边缘.但是如何根据模糊量来计算需要裁剪多少呢?

As I noticed when CIGaussianBlur is applied to image, image's corners gets blurred so that it looks like being smaller than original. So I figured out that I need to crop it correctly to avoid having transparent edges of image. But how to calculate how much I need to crop in dependence of blur amount?

示例:

原始图片:

Original image:

CIGaussianBlur输入半径为50的图像(蓝色是所有内容的背景):

Image with 50 inputRadius of CIGaussianBlur (blue color is background of everything):

推荐答案

以下面的代码为例...

Take the following code as an example...

CIContext *context = [CIContext contextWithOptions:nil];

CIImage *inputImage = [[CIImage alloc] initWithImage:image];

CIFilter *filter = [CIFilter filterWithName:@"CIGaussianBlur"];

[filter setValue:inputImage forKey:kCIInputImageKey];

[filter setValue:[NSNumber numberWithFloat:5.0f] forKey:@"inputRadius"];

CIImage *result = [filter valueForKey:kCIOutputImageKey];

CGImageRef cgImage = [context createCGImage:result fromRect:[result extent]];

这将产生您上面提供的图像.但是，如果我改用原始图像rect来根据上下文创建CGImage，则结果图像将为所需大小.

This results in the images you provided above. But if I instead use the original images rect to create the CGImage off of the context the resulting image is the desired size.

CGImageRef cgImage = [context createCGImage:result fromRect:[inputImage extent]];

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