如何在 Swift 中调整图像大小？

我正在使用 斯威夫特和 Parse.com 为 iOS 开发一个应用程序

我试图让用户从图像选择器中选择一张图片，然后在上传到我的后端之前将选定的图像调整到200x200像素。

Parse.com 有一个名为“ AnyPic”的 Instagram 复制应用程序教程，它提供了调整图像大小的代码，但是它是在 Objective-C..。

// Resize the image to be square (what is shown in the preview)
UIImage *resizedImage = [anImage resizedImageWithContentMode:UIViewContentModeScaleAspectFit
bounds:CGSizeMake(560.0f, 560.0f)
interpolationQuality:kCGInterpolationHigh];
// Create a thumbnail and add a corner radius for use in table views
UIImage *thumbnailImage = [anImage thumbnailImage:86.0f
transparentBorder:0.0f
cornerRadius:10.0f
interpolationQuality:kCGInterpolationDefault];

How would I create a 200x200px version of the selected picture (to then upload) in Swift?

那么，thumbnailImage 函数在做什么呢？

245744 次浏览
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最佳答案

See my blog post, Resize image in swift and objective C, for further details.

图像调整功能迅速如下。

func resizeImage(image: UIImage, targetSize: CGSize) -> UIImage? {
let size = image.size
    

let widthRatio  = targetSize.width  / size.width
let heightRatio = targetSize.height / size.height
    

// Figure out what our orientation is, and use that to form the rectangle
var newSize: CGSize
if(widthRatio > heightRatio) {
newSize = CGSize(width: size.width * heightRatio, height: size.height * heightRatio)
} else {
newSize = CGSize(width: size.width * widthRatio, height: size.height * widthRatio)
}
    

// This is the rect that we've calculated out and this is what is actually used below
let rect = CGRect(origin: .zero, size: newSize)
    

// Actually do the resizing to the rect using the ImageContext stuff
UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)
image.draw(in: rect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
    

return newImage
}

使用上面的函数，调整图像的大小为200 * 200，如下面的代码

self.resizeImage(UIImage(named: "yourImageName")!, targetSize: CGSizeMake(200.0, 200.0))

Swift 3更新

 func resizeImage(image: UIImage, targetSize: CGSize) -> UIImage {
let size = image.size
    

let widthRatio  = targetSize.width  / size.width
let heightRatio = targetSize.height / size.height
    

// Figure out what our orientation is, and use that to form the rectangle
var newSize: CGSize
if(widthRatio > heightRatio) {
newSize = CGSize(width: size.width * heightRatio, height: size.height * heightRatio)
} else {
newSize = CGSize(width: size.width * widthRatio,  height: size.height * widthRatio)
}
    

// This is the rect that we've calculated out and this is what is actually used below
let rect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)
    

// Actually do the resizing to the rect using the ImageContext stuff
UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)
image.draw(in: rect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
    

return newImage!
}
小开

既然@KiritModi 的回答来自2015年，这就是 Swift 3.0的版本:

func resizeImage(image: UIImage, targetSize: CGSize) -> UIImage {
let size = image.size


let widthRatio  = targetSize.width  / image.size.width
let heightRatio = targetSize.height / image.size.height


// Figure out what our orientation is, and use that to form the rectangle
var newSize: CGSize
if(widthRatio > heightRatio) {
newSize = CGSize(width: size.width * heightRatio, height: size.height * heightRatio)
} else {
newSize = CGSize(width: size.width * widthRatio,  height: size.height * widthRatio)
}


// This is the rect that we've calculated out and this is what is actually used below
let rect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)


// Actually do the resizing to the rect using the ImageContext stuff
UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)
image.draw(in: rect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return newImage!
}
小开

也可以使用 AlamofireImage (https://github.com/Alamofire/AlamofireImage)

let size = CGSize(width: 30.0, height: 30.0)
let aspectScaledToFitImage = image.af_imageAspectScaled(toFit: size)

上一篇文章中的函数给了我一个模糊的结果。

小开

Swift 3 Version and Extension style

这个答案来自“ Kirit Modi”。

extension UIImage {


func resizeImage(targetSize: CGSize) -> UIImage {
let size = self.size


let widthRatio  = targetSize.width  / size.width
let heightRatio = targetSize.height / size.height


// Figure out what our orientation is, and use that to form the rectangle
var newSize: CGSize
if(widthRatio > heightRatio) {
newSize = CGSize(width: size.width * heightRatio, height: size.height * heightRatio)
} else {
newSize = CGSize(width: size.width * widthRatio,  height: size.height * widthRatio)
}


// This is the rect that we've calculated out and this is what is actually used below
let rect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)


// Actually do the resizing to the rect using the ImageContext stuff
UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)
self.draw(in: rect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return newImage!
}
}
小开

这里有两个简单的 UIImage扩展函数:

func scaledWithMaxWidthOrHeightValue(value: CGFloat) -> UIImage? {


let width = self.size.width
let height = self.size.height


let ratio = width/height


var newWidth = value
var newHeight = value


if ratio > 1 {
newWidth = width * (newHeight/height)
} else {
newHeight = height * (newWidth/width)
}


UIGraphicsBeginImageContextWithOptions(CGSize(width: newWidth, height: newHeight), false, 0)


draw(in: CGRect(x: 0, y: 0, width: newWidth, height: newHeight))


let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return image
}


func scaled(withScale scale: CGFloat) -> UIImage? {


let size = CGSize(width: self.size.width * scale, height: self.size.height * scale)


UIGraphicsBeginImageContextWithOptions(size, false, 0)


draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))


let image = UIGraphicsGetImageFromCurrentImageContext()


UIGraphicsEndImageContext()


return image
}
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例如，将图像最小化到1024或更小

func resizeImage(image: UIImage) -> UIImage {

    if image.size.height >= 1024 && image.size.width >= 1024 {


UIGraphicsBeginImageContext(CGSize(width:1024, height:1024))
image.draw(in: CGRect(x:0, y:0, width:1024, height:1024))


let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return newImage!


}
else if image.size.height >= 1024 && image.size.width < 1024
{


UIGraphicsBeginImageContext(CGSize(width:image.size.width, height:1024))
image.draw(in: CGRect(x:0, y:0, width:image.size.width, height:1024))


let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return newImage!


}
else if image.size.width >= 1024 && image.size.height < 1024
{


UIGraphicsBeginImageContext(CGSize(width:1024, height:image.size.height))
image.draw(in: CGRect(x:0, y:0, width:1024, height:image.size.height))


let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return newImage!


}
else
{
return image
}


}
小开

适用于 Swift 4.0和 iOS 10

    extension UIImage {
func resizeImage(_ dimension: CGFloat, opaque: Bool, contentMode: UIViewContentMode = .scaleAspectFit) -> UIImage {
var width: CGFloat
var height: CGFloat
var newImage: UIImage


let size = self.size
let aspectRatio =  size.width/size.height


switch contentMode {
case .scaleAspectFit:
if aspectRatio > 1 {                            // Landscape image
width = dimension
height = dimension / aspectRatio
} else {                                        // Portrait image
height = dimension
width = dimension * aspectRatio
}


default:
fatalError("UIIMage.resizeToFit(): FATAL: Unimplemented ContentMode")
}


if #available(iOS 10.0, *) {
let renderFormat = UIGraphicsImageRendererFormat.default()
renderFormat.opaque = opaque
let renderer = UIGraphicsImageRenderer(size: CGSize(width: width, height: height), format: renderFormat)
newImage = renderer.image {
(context) in
self.draw(in: CGRect(x: 0, y: 0, width: width, height: height))
}
} else {
UIGraphicsBeginImageContextWithOptions(CGSize(width: width, height: height), opaque, 0)
self.draw(in: CGRect(x: 0, y: 0, width: width, height: height))
newImage = UIGraphicsGetImageFromCurrentImageContext()!
UIGraphicsEndImageContext()
}


return newImage
}
}
小开

您可以使用此适合图像在 Swift 3;

extension UIImage {
func resizedImage(newSize: CGSize) -> UIImage {
// Guard newSize is different
guard self.size != newSize else { return self }


UIGraphicsBeginImageContextWithOptions(newSize, false, 0.0);
self.draw(in: CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height))
let newImage: UIImage = UIGraphicsGetImageFromCurrentImageContext()!
UIGraphicsEndImageContext()
return newImage
}


func resizedImageWithinRect(rectSize: CGSize) -> UIImage {
let widthFactor = size.width / rectSize.width
let heightFactor = size.height / rectSize.height


var resizeFactor = widthFactor
if size.height > size.width {
resizeFactor = heightFactor
}


let newSize = CGSize(width: size.width/resizeFactor, height: size.height/resizeFactor)
let resized = resizedImage(newSize: newSize)
return resized
}
}

用途;

let resizedImage = image.resizedImageWithinRect(rectSize: CGSize(width: 1900, height: 1900))
小开

对于 Swift 4，我只是在 UIImage 上做一个引用 self 的扩展。

import UIKit
extension UIImage {
func resizeImage(targetSize: CGSize) -> UIImage {
let size = self.size
let widthRatio  = targetSize.width  / size.width
let heightRatio = targetSize.height / size.height
let newSize = widthRatio > heightRatio ?  CGSize(width: size.width * heightRatio, height: size.height * heightRatio) : CGSize(width: size.width * widthRatio,  height: size.height * widthRatio)
let rect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)


UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)
self.draw(in: rect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return newImage!
}
}
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迅捷4版本

extension UIImage {
func resizeImage(_ newSize: CGSize) -> UIImage? {
func isSameSize(_ newSize: CGSize) -> Bool {
return size == newSize
}


func scaleImage(_ newSize: CGSize) -> UIImage? {
func getScaledRect(_ newSize: CGSize) -> CGRect {
let ratio   = max(newSize.width / size.width, newSize.height / size.height)
let width   = size.width * ratio
let height  = size.height * ratio
return CGRect(x: 0, y: 0, width: width, height: height)
}


func _scaleImage(_ scaledRect: CGRect) -> UIImage? {
UIGraphicsBeginImageContextWithOptions(scaledRect.size, false, 0.0);
draw(in: scaledRect)
let image = UIGraphicsGetImageFromCurrentImageContext() ?? UIImage()
UIGraphicsEndImageContext()
return image
}
return _scaleImage(getScaledRect(newSize))
}


return isSameSize(newSize) ? self : scaleImage(newSize)!
}
}
小开

迅捷4，扩展版，边缘无白线。

似乎没有人提到，如果用非整数值调用 image.draw()，结果图像可能会在右边缘或底部边缘显示一个白线工件。

extension UIImage {


func scaled(with scale: CGFloat) -> UIImage? {
// size has to be integer, otherwise it could get white lines
let size = CGSize(width: floor(self.size.width * scale), height: floor(self.size.height * scale))
UIGraphicsBeginImageContext(size)
draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return image
}
小开

Resizeimage 方法的调用

let image1 = resizeimage(image: myimage.image!, withSize: CGSize(width:200, height: 200))

调整图像大小的方法

func resizeimage(image:UIImage,withSize:CGSize) -> UIImage {
var actualHeight:CGFloat = image.size.height
var actualWidth:CGFloat = image.size.width
let maxHeight:CGFloat = withSize.height
let maxWidth:CGFloat = withSize.width
var imgRatio:CGFloat = actualWidth/actualHeight
let maxRatio:CGFloat = maxWidth/maxHeight
let compressionQuality = 0.5
if (actualHeight>maxHeight||actualWidth>maxWidth) {
if (imgRatio<maxRatio){
//adjust width according to maxHeight
imgRatio = maxHeight/actualHeight
actualWidth = imgRatio * actualWidth
actualHeight = maxHeight
}else if(imgRatio>maxRatio){
// adjust height according to maxWidth
imgRatio = maxWidth/actualWidth
actualHeight = imgRatio * actualHeight
actualWidth = maxWidth
}else{
actualHeight = maxHeight
actualWidth = maxWidth
}
}
let rec:CGRect = CGRect(x:0.0,y:0.0,width:actualWidth,height:actualHeight)
UIGraphicsBeginImageContext(rec.size)
image.draw(in: rec)
let image:UIImage = UIGraphicsGetImageFromCurrentImageContext()!
let imageData = UIImageJPEGRepresentation(image, CGFloat(compressionQuality))
UIGraphicsEndImageContext()
let resizedimage = UIImage(data: imageData!)
return resizedimage!
}
小开

迅捷4解决方案-

使用此函数 

func image(with image: UIImage, scaledTo newSize: CGSize) -> UIImage {
UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)
image.draw(in: CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height))
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
drawingImageView.image = newImage
return newImage ?? UIImage()
}

调用函数:-

image(with: predictionImage, scaledTo: CGSize(width: 28.0, height: 28.0)

这里的28.0是要设置的像素大小

小开

Swift 4.2版本的@KiritModi 问答

func resizeImage(image: UIImage, targetSize: CGSize) -> UIImage {
let size = image.size


let widthRatio  = targetSize.width  / size.width
let heightRatio = targetSize.height / size.height


var newSize: CGSize
if(widthRatio > heightRatio) {
newSize = CGSize(width: size.width * heightRatio, height: size.height * heightRatio)
} else {
newSize = CGSize(width: size.width * widthRatio, height: size.height *      widthRatio)
}


let rect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)


UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)
image.draw(in: rect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return newImage!
}
小开

细节

  • Xcode 10.2.1(10E1001) ，Swift 5

连结

解决方案

import UIKit
import CoreGraphics
import Accelerate


extension UIImage {


public enum ResizeFramework {
case uikit, coreImage, coreGraphics, imageIO, accelerate
}


/// Resize image with ScaleAspectFit mode and given size.
///
/// - Parameter dimension: width or length of the image output.
/// - Parameter resizeFramework: Technique for image resizing: UIKit / CoreImage / CoreGraphics / ImageIO / Accelerate.
/// - Returns: Resized image.


func resizeWithScaleAspectFitMode(to dimension: CGFloat, resizeFramework: ResizeFramework = .coreGraphics) -> UIImage? {


if max(size.width, size.height) <= dimension { return self }


var newSize: CGSize!
let aspectRatio = size.width/size.height


if aspectRatio > 1 {
// Landscape image
newSize = CGSize(width: dimension, height: dimension / aspectRatio)
} else {
// Portrait image
newSize = CGSize(width: dimension * aspectRatio, height: dimension)
}


return resize(to: newSize, with: resizeFramework)
}


/// Resize image from given size.
///
/// - Parameter newSize: Size of the image output.
/// - Parameter resizeFramework: Technique for image resizing: UIKit / CoreImage / CoreGraphics / ImageIO / Accelerate.
/// - Returns: Resized image.
public func resize(to newSize: CGSize, with resizeFramework: ResizeFramework = .coreGraphics) -> UIImage? {
switch resizeFramework {
case .uikit: return resizeWithUIKit(to: newSize)
case .coreGraphics: return resizeWithCoreGraphics(to: newSize)
case .coreImage: return resizeWithCoreImage(to: newSize)
case .imageIO: return resizeWithImageIO(to: newSize)
case .accelerate: return resizeWithAccelerate(to: newSize)
}
}


// MARK: - UIKit


/// Resize image from given size.
///
/// - Parameter newSize: Size of the image output.
/// - Returns: Resized image.
private func resizeWithUIKit(to newSize: CGSize) -> UIImage? {
UIGraphicsBeginImageContextWithOptions(newSize, true, 1.0)
self.draw(in: CGRect(origin: .zero, size: newSize))
defer { UIGraphicsEndImageContext() }
return UIGraphicsGetImageFromCurrentImageContext()
}


// MARK: - CoreImage


/// Resize CI image from given size.
///
/// - Parameter newSize: Size of the image output.
/// - Returns: Resized image.
// https://developer.apple.com/library/archive/documentation/GraphicsImaging/Reference/CoreImageFilterReference/index.html
private func resizeWithCoreImage(to newSize: CGSize) -> UIImage? {
guard let cgImage = cgImage, let filter = CIFilter(name: "CILanczosScaleTransform") else { return nil }


let ciImage = CIImage(cgImage: cgImage)
let scale = (Double)(newSize.width) / (Double)(ciImage.extent.size.width)


filter.setValue(ciImage, forKey: kCIInputImageKey)
filter.setValue(NSNumber(value:scale), forKey: kCIInputScaleKey)
filter.setValue(1.0, forKey: kCIInputAspectRatioKey)
guard let outputImage = filter.value(forKey: kCIOutputImageKey) as? CIImage else { return nil }
let context = CIContext(options: [.useSoftwareRenderer: false])
guard let resultCGImage = context.createCGImage(outputImage, from: outputImage.extent) else { return nil }
return UIImage(cgImage: resultCGImage)
}


// MARK: - CoreGraphics


/// Resize image from given size.
///
/// - Parameter newSize: Size of the image output.
/// - Returns: Resized image.
private func resizeWithCoreGraphics(to newSize: CGSize) -> UIImage? {
guard let cgImage = cgImage, let colorSpace = cgImage.colorSpace else { return nil }


let width = Int(newSize.width)
let height = Int(newSize.height)
let bitsPerComponent = cgImage.bitsPerComponent
let bytesPerRow = cgImage.bytesPerRow
let bitmapInfo = cgImage.bitmapInfo


guard let context = CGContext(data: nil, width: width, height: height,
bitsPerComponent: bitsPerComponent,
bytesPerRow: bytesPerRow, space: colorSpace,
bitmapInfo: bitmapInfo.rawValue) else { return nil }
context.interpolationQuality = .high
let rect = CGRect(origin: CGPoint.zero, size: newSize)
context.draw(cgImage, in: rect)


return context.makeImage().flatMap { UIImage(cgImage: $0) }
}


// MARK: - ImageIO


/// Resize image from given size.
///
/// - Parameter newSize: Size of the image output.
/// - Returns: Resized image.
private func resizeWithImageIO(to newSize: CGSize) -> UIImage? {
var resultImage = self


guard let data = jpegData(compressionQuality: 1.0) else { return resultImage }
let imageCFData = NSData(data: data) as CFData
let options = [
kCGImageSourceCreateThumbnailWithTransform: true,
kCGImageSourceCreateThumbnailFromImageAlways: true,
kCGImageSourceThumbnailMaxPixelSize: max(newSize.width, newSize.height)
] as CFDictionary
guard   let source = CGImageSourceCreateWithData(imageCFData, nil),
let imageReference = CGImageSourceCreateThumbnailAtIndex(source, 0, options) else { return resultImage }
resultImage = UIImage(cgImage: imageReference)


return resultImage
}


// MARK: - Accelerate


/// Resize image from given size.
///
/// - Parameter newSize: Size of the image output.
/// - Returns: Resized image.
private func resizeWithAccelerate(to newSize: CGSize) -> UIImage? {
var resultImage = self


guard let cgImage = cgImage, let colorSpace = cgImage.colorSpace else { return nil }


// create a source buffer
var format = vImage_CGImageFormat(bitsPerComponent: numericCast(cgImage.bitsPerComponent),
bitsPerPixel: numericCast(cgImage.bitsPerPixel),
colorSpace: Unmanaged.passUnretained(colorSpace),
bitmapInfo: cgImage.bitmapInfo,
version: 0,
decode: nil,
renderingIntent: .absoluteColorimetric)
var sourceBuffer = vImage_Buffer()
defer {
sourceBuffer.data.deallocate()
}


var error = vImageBuffer_InitWithCGImage(&sourceBuffer, &format, nil, cgImage, numericCast(kvImageNoFlags))
guard error == kvImageNoError else { return resultImage }


// create a destination buffer
let destWidth = Int(newSize.width)
let destHeight = Int(newSize.height)
let bytesPerPixel = cgImage.bitsPerPixel
let destBytesPerRow = destWidth * bytesPerPixel
let destData = UnsafeMutablePointer<UInt8>.allocate(capacity: destHeight * destBytesPerRow)
defer {
destData.deallocate()
}
var destBuffer = vImage_Buffer(data: destData, height: vImagePixelCount(destHeight), width: vImagePixelCount(destWidth), rowBytes: destBytesPerRow)


// scale the image
error = vImageScale_ARGB8888(&sourceBuffer, &destBuffer, nil, numericCast(kvImageHighQualityResampling))
guard error == kvImageNoError else { return resultImage }


// create a CGImage from vImage_Buffer
let destCGImage = vImageCreateCGImageFromBuffer(&destBuffer, &format, nil, nil, numericCast(kvImageNoFlags), &error)?.takeRetainedValue()
guard error == kvImageNoError else { return resultImage }


// create a UIImage
if let scaledImage = destCGImage.flatMap({ UIImage(cgImage: $0) }) {
resultImage = scaledImage
}


return resultImage
}
}

Usage

Get image size

import UIKit


// https://stackoverflow.com/a/55765409/4488252
extension UIImage {
func getFileSizeInfo(allowedUnits: ByteCountFormatter.Units = .useMB,
countStyle: ByteCountFormatter.CountStyle = .memory,
compressionQuality: CGFloat = 1.0) -> String? {
// https://developer.apple.com/documentation/foundation/bytecountformatter
let formatter = ByteCountFormatter()
formatter.allowedUnits = allowedUnits
formatter.countStyle = countStyle
return getSizeInfo(formatter: formatter, compressionQuality: compressionQuality)
}


func getSizeInfo(formatter: ByteCountFormatter, compressionQuality: CGFloat = 1.0) -> String? {
guard let imageData = jpegData(compressionQuality: compressionQuality) else { return nil }
return formatter.string(fromByteCount: Int64(imageData.count))
}
}

测试功能

private func test() {
guard let img = UIImage(named: "img") else { return }
printInfo(of: img, title: "original image |")
let dimension: CGFloat = 2000


var framework: UIImage.ResizeFramework = .accelerate
var startTime = Date()
if let img = img.resizeWithScaleAspectFitMode(to: dimension, resizeFramework: framework) {
printInfo(of: img, title: "resized image |", with: framework, startedTime: startTime)
}


framework = .coreGraphics
startTime = Date()
if let img = img.resizeWithScaleAspectFitMode(to: dimension, resizeFramework: framework) {
printInfo(of: img, title: "resized image |", with: framework, startedTime: startTime)
}


framework = .coreImage
startTime = Date()
if let img = img.resizeWithScaleAspectFitMode(to: dimension, resizeFramework: framework) {
printInfo(of: img, title: "resized image |", with: framework, startedTime: startTime)
}


framework = .imageIO
startTime = Date()
if let img = img.resizeWithScaleAspectFitMode(to: dimension, resizeFramework: framework) {
printInfo(of: img, title: "resized image |", with: framework, startedTime: startTime)
}


framework = .uikit
startTime = Date()
if let img = img.resizeWithScaleAspectFitMode(to: dimension, resizeFramework: framework) {
printInfo(of: img, title: "resized image |", with: framework, startedTime: startTime)
}
}


private func printInfo(of image: UIImage, title: String, with resizeFramework: UIImage.ResizeFramework? = nil, startedTime: Date? = nil) {
var description = "\(title) \(image.size)"
if let startedTime = startedTime { description += ", execution time: \(Date().timeIntervalSince(startedTime))" }
if let fileSize = image.getFileSizeInfo(compressionQuality: 0.9) { description += ", size: \(fileSize)" }
if let resizeFramework = resizeFramework { description += ", framework: \(resizeFramework)" }
print(description)
}

输出

original image | (5790.0, 8687.0), size: 17.1 MB
resized image | (1333.0, 2000.0), execution time: 0.8192930221557617, size: 1.1 MB, framework: accelerate
resized image | (1333.0, 2000.0), execution time: 0.44696998596191406, size: 1 MB, framework: coreGraphics
resized image | (1334.0, 2000.0), execution time: 54.172922015190125, size: 1.1 MB, framework: coreImage
resized image | (1333.0, 2000.0), execution time: 1.8765920400619507, size: 1.1 MB, framework: imageIO
resized image | (1334.0, 2000.0), execution time: 0.4638739824295044, size: 1 MB, framework: uikit
小开

这里有一个通用的方法(在 Swift 5中)来缩放图像以适应尺寸。得到的图像可以具有与原始图像相同的纵横比，也可以是以原始图像为中心的目标大小。如果图像小于目标大小，则不调整其大小。

extension UIImage {
func scaledDown(into size:CGSize, centered:Bool = false) -> UIImage {
var (targetWidth, targetHeight) = (self.size.width, self.size.height)
var (scaleW, scaleH) = (1 as CGFloat, 1 as CGFloat)
if targetWidth > size.width {
scaleW = size.width/targetWidth
}
if targetHeight > size.height {
scaleH = size.height/targetHeight
}
let scale = min(scaleW,scaleH)
targetWidth *= scale; targetHeight *= scale
let sz = CGSize(width:targetWidth, height:targetHeight)
if !centered {
return UIGraphicsImageRenderer(size:sz).image { _ in
self.draw(in:CGRect(origin:.zero, size:sz))
}
}
let x = (size.width - targetWidth)/2
let y = (size.height - targetHeight)/2
let origin = CGPoint(x:x,y:y)
return UIGraphicsImageRenderer(size:size).image { _ in
self.draw(in:CGRect(origin:origin, size:sz))
}
}
}
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更新了使用最新 UIGraphicsImageRenderer API 的 Swift 5版本。

extension UIImage {
public func resized(to target: CGSize) -> UIImage {
let ratio = min(
target.height / size.height, target.width / size.width
)
let new = CGSize(
width: size.width * ratio, height: size.height * ratio
)
let renderer = UIGraphicsImageRenderer(size: new)
return renderer.image { _ in
self.draw(in: CGRect(origin: .zero, size: new))
}
}
}
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UIImage 扩展 Swift 5

extension UIImage {
func resize(_ width: CGFloat, _ height:CGFloat) -> UIImage? {
let widthRatio  = width / size.width
let heightRatio = height / size.height
let ratio = widthRatio > heightRatio ? heightRatio : widthRatio
let newSize = CGSize(width: size.width * ratio, height: size.height * ratio)
let rect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)
UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)
self.draw(in: rect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return newImage
}
}

用途: UIImage () . resize (200,300)

小开

到目前为止，所有列出的答案似乎都导致图像尺寸缩小，但是尺寸并不是以像素来衡量的。这是 Swift 5，基于像素的调整大小。

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
}
}

用法:

image.resize(500)
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For Swift 5.0 and iOS 12

extension UIImage {
func imageResized(to size: CGSize) -> UIImage {
return UIGraphicsImageRenderer(size: size).image { _ in
draw(in: CGRect(origin: .zero, size: size))
}
}
}

用途:

let image = #imageLiteral(resourceName: "ic_search")
cell!.search.image = image.imageResized(to: cell!.search.frame.size)
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Swift 5版本的比例(scaleTofill)和居中图像:

extension UIImage {
func resized(to newSize: CGSize) -> UIImage {
return UIGraphicsImageRenderer(size: newSize).image { _ in
let hScale = newSize.height / size.height
let vScale = newSize.width / size.width
let scale = max(hScale, vScale) // scaleToFill
let resizeSize = CGSize(width: size.width*scale, height: size.height*scale)
var middle = CGPoint.zero
if resizeSize.width > newSize.width {
middle.x -= (resizeSize.width-newSize.width)/2.0
}
if resizeSize.height > newSize.height {
middle.y -= (resizeSize.height-newSize.height)/2.0
}
            

draw(in: CGRect(origin: middle, size: resizeSize))
}
}
}
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SWIFT 5-XCODE 12——调整图像大小和无白线

I used a wonderful solution above for Swift 5. And I changed one bit to include the term "floor" as I was getting a white line around my resized images. This rounds it to the nearest pixel or something so it looks great! I also had to change the syntax around the image name when the function is called (last line).

//调整图像大小的方法

func resizeimage(image:UIImage,withSize:CGSize) -> UIImage {
var actualHeight:CGFloat = image.size.height
var actualWidth:CGFloat = image.size.width
let maxHeight:CGFloat = withSize.height
let maxWidth:CGFloat = withSize.width
var imgRatio:CGFloat = actualWidth/actualHeight
let maxRatio:CGFloat = maxWidth/maxHeight
let compressionQuality = 0.5
if (actualHeight>maxHeight||actualWidth>maxWidth) {
if (imgRatio<maxRatio){
//adjust width according to maxHeight
imgRatio = maxHeight/actualHeight
actualWidth = floor(imgRatio * actualWidth)
actualHeight = maxHeight
}else if(imgRatio>maxRatio){
// adjust height according to maxWidth
imgRatio = maxWidth/actualWidth
actualHeight = imgRatio * actualHeight
actualWidth = maxWidth
}else{
actualHeight = maxHeight
actualWidth = maxWidth
}
}
let rec:CGRect = CGRect(x:0.0,y:0.0,width:actualWidth,height:actualHeight)
UIGraphicsBeginImageContext(rec.size)
image.draw(in: rec)
let image:UIImage = UIGraphicsGetImageFromCurrentImageContext()!
let imageData = UIImageJPEGRepresentation(image, CGFloat(compressionQuality))
UIGraphicsEndImageContext()
let resizedimage = UIImage(data: imageData!)
return resizedimage!
}

//调用 resizeimage 方法:

Let myimage = UIImage (命名为: “ imagename”)

let image1 = resizeimage(image: myimage!, withSize: CGSize(width:50, height: 50)).withRenderingMode(.alwaysOriginal)


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