如何在Swift中调整图像大小？

Question

我正在使用 Swift 和Parse.com

为iOS制作应用

我试图让用户从图像选择器中选择一张图片，然后将所选图像调整为200x200像素，然后再上传到我的后端。

Parse.com有一个名为“AnyPic”的Instagram复制应用程序的教程，该应用程序提供了用于调整图像大小的代码，但它位于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];

如何在Swift中创建所选图片的200x200px版本（然后上传）？

而且，thumbnailImage函数在做什么？

Answer 1

图像调整大小的功能如下所示。

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 = CGSizeMake(size.width * heightRatio, size.height * heightRatio)
    } else {
        newSize = CGSizeMake(size.width * widthRatio,  size.height * widthRatio)
    }

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

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

    return newImage
}

使用上述功能并使用200 * 200调整图像大小，如以下代码

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

有关详细信息，请参阅我的博客文章Resize image in swift and objective C。

swift3已更新

 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!
}

Answer 2

由于@KiritModi的答案是2015年，这是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!
}

Answer 3

适用于Swift 4.0和iOS 10

int ans=0;
int rev(int n)
{
  ans=(ans+(n%10))*10; // using recursive function to reverse a number;
  if(n>9) 
    rev(n/10);
}

int main()
{
  int m=rev(456123); // m=32
  return 0;
}

Answer 4

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

ScriptEngineManager = createObject('java','javax.script.ScriptEngineManager').init();
factory = createObject('java','org.python.jsr223.PyScriptEngineFactory','jython-standalone-2.7.0.jar').init();
ScriptEngineManager.registerEngineName("python", factory);
engine = ScriptEngineManager.getEngineByName("python");

engine.eval("x = 2 + 2");
x = engine.get("x");

writeDump(x);

上一篇文章中的功能给我一个模糊的结果。

Answer 5

对于Swift 4，我只想在引用自己的UIImage上进行扩展。

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!
  }
}

Answer 6

Swift 3版本和扩展程序样式

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!
    }
}

Answer 7

对于Swift 5.0和iOS 12

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

使用：

let image = #imageLiteral(resourceName: "ic_search")
cell!.search.image = image.imageResized(to: cell!.search.frame.size)

Answer 8

Swift 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)!
    }
}

Answer 9

调用resizeimage方法

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

调整图片大小的方法

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!
    }

Answer 10

到目前为止，所有列出的答案似乎都导致图像尺寸减小，但是尺寸不是以像素为单位。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)

Answer 11

@KiritModi答案的Swift 4.2版本

$ext = explode("/",$type);
$filename = './images/'.uniqid(rand(), true) . '.'.$ext[1];
file_put_contents($filename,$portal['image']);
$drawing->setPath($filename);
// make Spreadsheet
unlink($filename);

Answer 12

Swift 4解决方案-

使用此功能

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)

此处28.0是您要设置的像素大小

Answer 13

迅速4，扩展程序版本，边缘没有白线。

似乎没有人提到如果使用非整数值调用pip uninstall wheel ，则生成的图像可能在右侧或底部边缘显示白线伪像。

image.draw()

Answer 14

您可以在 Swift 3 ;

中将其用于合适的图像

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
    }
}

用法;

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

Answer 15

这是一种通用方法（在Swift 5中），用于缩小图像以适合大小。生成的图像可以具有与原始图像相同的宽高比，也可以是目标尺寸，其中原始图像居中。如果图像小于目标尺寸，则不会调整尺寸。

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))
        }
    }
}

Answer 16

将我接受的答案的版本放入此处，即可与Swift 5很好地配合使用。此解决方案不会强制解开生成的图像，从而使其更安全，更干净。

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
        )
        UIGraphicsBeginImageContextWithOptions(new, false, 1.0)
        draw(in: CGRect(origin: .zero, size: new))
        defer { UIGraphicsEndImageContext() }
        return UIGraphicsGetImageFromCurrentImageContext()
    }
}

Answer 17

UIImage Extension 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
    }
}

---

使用： UIImage（）。resize（200，300）

Answer 18

这里有两个简单的UIImage扩展功能：

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
}

Answer 19

详细信息

• Xcode 10.2.1（10E1001），Swift 5

链接

• https://gist.github.com/eugenebokhan/5e62a0155754ae6aa6c3c13cf1744930
• Image Resizing Techniques

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
    }
}

用法

  

获取图像大小

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

Answer 20

示例是将图像最小化为1024或更少

func resizeImage（image：UIImage） - ＆gt; 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
    }

}

Answer 21

关于比例（scaleToFill）和居中图像的 Swift 5 版本：

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))
        }
    }
}

Answer 22

SWIFT 5 - XCODE 12 -- 调整图像大小且无白线

我在上面为 Swift 5 使用了一个很棒的解决方案。我更改了一点以包含术语“地板”，因为我在调整大小的图像周围出现了一条白线。这会将它四舍五入到最近的像素或其他东西，所以它看起来很棒！我还必须在调用函数时更改图像名称周围的语法（最后一行）。

//调整图片大小的方法

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(named: "imagename")

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

Answer 23

带有newImage = UIImage(cgImage: cgImage)的SWIFT 5

func scaleImage(toSize newSize: CGSize) -> UIImage? {
            var newImage: UIImage?
            let newRect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height).integral
            UIGraphicsBeginImageContextWithOptions(newSize, false, 0)
            if let context = UIGraphicsGetCurrentContext(), let cgImage = self.cgImage {
                context.interpolationQuality = .high
                let flipVertical = CGAffineTransform(a: 1, b: 0, c: 0, d: -1, tx: 0, ty: newSize.height)
                context.concatenate(flipVertical)
                context.draw(cgImage, in: newRect)
                newImage = UIImage(cgImage: cgImage)
                UIGraphicsEndImageContext()

            }

            return newImage
   }