为什么在设置半径和大小时我的图像质量会下降？

Question

我在 UIImage 扩展中使用以下方法来使用 URL 中的图像并将其显示为 UIBarButtonItem。但是，当我使用以下方法调整角半径和大小时，图像质量明显变差。需要改变什么以防止质量下降？

extension UIImage {

    public func withRoundedCornersAndSetSize(radius: CGFloat? = nil, size: CGSize) -> UIImage? {
        let maxRadius = min(size.width, size.height) / 2
        let cornerRadius: CGFloat
        if let radius = radius, radius > 0 && radius <= maxRadius {
            cornerRadius = radius
        } else {
            cornerRadius = maxRadius
        }
        UIGraphicsBeginImageContextWithOptions(size, false, scale)
        let rect = CGRect(origin: .zero, size: size)
        UIBezierPath(roundedRect: rect, cornerRadius: cornerRadius).addClip()
        draw(in: rect)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }
}

Answer 1

我发现我可以使用以下代码中的 resize() 方法调整 UIImage 的大小而不会降低质量。然后，我只是在我最初询问的 withRoundedCornersAndSetSize() 方法中使用了它。

extension UIImage {
   func withRoundedCornersAndSetSize(radius: CGFloat? = nil, targetSize: CGSize) -> UIImage? {
        let resizedImage = self.resize(targetSize: targetSize)
        
        let maxRadius = min(resizedImage.size.width, resizedImage.size.height) / 2
        let cornerRadius: CGFloat
        if let radius = radius, radius > 0 && radius <= maxRadius {
            cornerRadius = radius
        } else {
            cornerRadius = maxRadius
        }

        UIGraphicsBeginImageContextWithOptions(resizedImage.size, false, resizedImage.scale)
        let rect = CGRect(origin: .zero, size: resizedImage.size)
        UIBezierPath(roundedRect: rect, cornerRadius: cornerRadius).addClip()
        draw(in: rect)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image!
    }
    
    func resize(targetSize: CGSize) -> UIImage {
        return UIGraphicsImageRenderer(size:targetSize).image { _ in
            self.draw(in: CGRect(origin: .zero, size: targetSize))
        }
    }
}

为什么在设置半径和大小时我的图像质量会下降？

Why is my image quality decreasing when setting the radius and size?

ios

swift

xcode

swift3

uiimage