如何提高UIImageView的渲染图像质量？

Question

我有一个uiimageView contentmode = .aspectFit。我在ImageView中有一个图像，哪个维度大于ImageView的大小。用户可以绘制一些线条并将其保存为Sublayer。之后，我需要保存编辑的图像。但是保存图像的质量比我加载的图像质量差。 我在做什么错？我试图使用变换，但它不起作用。

import UIKit

extension UIImageView {
    
    var contentClippingRect: CGRect {
        let imgViewSize = self.frame.size
        let imgSize = self.image?.size ?? .zero
        let scaleW = imgViewSize.width / imgSize.width
        let scaleH = imgViewSize.height / imgSize.height
        let aspect = fmin(scaleW, scaleH)
        
        let width = imgSize.width * aspect
        let height = imgSize.height * aspect
        
        let imageRect = CGRect(x: (imgViewSize.width-width)/2 + self.frame.origin.x, y: (imgViewSize.height-height)/2 + self.frame.origin.y, width: width, height: height)
        return imageRect
    }
    
    func asImage() -> UIImage {
        let imageRect = self.contentClippingRect
        let renderer = UIGraphicsImageRenderer(bounds: imageRect)
        let renderedImage = renderer.image { rendererContext in
            layer.render(in: rendererContext.cgContext)
        }

        return renderedImage
    }
}

Answer 1

您可以使用uigraphicsimagerendererformat（）。缩放它将增加渲染图像的质量。

import UIKit

extension UIImageView {

var contentClippingRect: CGRect {
    let imgViewSize = self.frame.size
    let imgSize = self.image?.size ?? .zero
    let scaleW = imgViewSize.width / imgSize.width
    let scaleH = imgViewSize.height / imgSize.height
    let aspect = fmin(scaleW, scaleH)
    
    let width = imgSize.width * aspect
    let height = imgSize.height * aspect
    
    let imageRect = CGRect(x: (imgViewSize.width-width)/2 + self.frame.origin.x, y: (imgViewSize.height-height)/2 + self.frame.origin.y, width: width, height: height)
    return imageRect
}

func asImage() -> UIImage {
    let imageRect = self.contentClippingRect
    
    //add this
    let format = UIGraphicsImageRendererFormat()
    format.scale = 2

    let renderer = UIGraphicsImageRenderer(bounds: imageRect, format: format)
    let renderedImage = renderer.image { rendererContext in
        layer.render(in: rendererContext.cgContext)
    }

    return renderedImage
}
}