我正在從 PDFKit 中的 PDFView 拍攝快照以進行流式傳輸（每秒 20 次），并且我使用了這個擴展
extension UIView {
func asImageBackground(viewLayer: CALayer, viewBounds: CGRect) -> UIImage {
let renderer = UIGraphicsImageRenderer(bounds: viewBounds)
return renderer.image { rendererContext in
viewLayer.render(in: rendererContext.cgContext)
}
}
}
但是此擴展的輸出 UIImage 具有高解析度，因此難以流式傳輸。我可以通過這個擴展來減少它
extension UIImage {
func resize(_ max_size: CGFloat) -> UIImage {
// adjust for device pixel density
let max_size_pixels = max_size / UIScreen.main.scale
// work out aspect ratio
let aspectRatio = size.width/size.height
// variables for storing calculated data
var width: CGFloat
var height: CGFloat
var newImage: UIImage
if aspectRatio > 1 {
// landscape
width = max_size_pixels
height = max_size_pixels / aspectRatio
} else {
// portrait
height = max_size_pixels
width = max_size_pixels * aspectRatio
}
// create an image renderer of the correct size
let renderer = UIGraphicsImageRenderer(size: CGSize(width: width, height: height), format: UIGraphicsImageRendererFormat.default())
// render the image
newImage = renderer.image {
(context) in
self.draw(in: CGRect(x: 0, y: 0, width: width, height: height))
}
// return the image
return newImage
}
}
但它增加了額外的作業量，使程序變得更糟。有沒有更好的辦法？
謝謝
uj5u.com熱心網友回復：
您可以使用AppleImageIO推薦的方法對其進行下采樣：
extension UIImage {
func downsample(to resolution: CGSize) -> UIImage? {
let imageSourceOptions = [kCGImageSourceShouldCache: false] as CFDictionary
guard let data = self.jpegData(compressionQuality: 0.75) as? CFData, let imageSource = CGImageSourceCreateWithData(data, imageSourceOptions) else {
return nil
}
let maxDimensionInPixels = Swift.max(resolution.width, resolution.height) * 3
let downsampleOptions = [
kCGImageSourceCreateThumbnailFromImageAlways: true,
kCGImageSourceShouldCacheImmediately: true,
kCGImageSourceCreateThumbnailWithTransform: true,
kCGImageSourceThumbnailMaxPixelSize: maxDimensionInPixels
] as CFDictionary
guard let downsampledImage = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, downsampleOptions) else {
return nil
}
return UIImage(cgImage: downsampledImage)
}
}
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