How to Resize image in Swift?

Question

I am making an app for iOS, using Swift and Parse.com

I am trying to let the user select a picture from an image picker and then resize the selected image to 200x200 pixels before uploading to my backend.

Parse.com have a tutorial for an Instagram copy app called "AnyPic" which gives this code for resizing images, but it is in 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?

And, what is the thumbnailImage function doing?

Answer 1

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

Image resize function in swift as below.

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
}

Use the above function and resize image with 200*200 as below code

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

swift3 updated

 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

For Swift 4.0 and 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
        }
    }

Answer 3

Details

• Xcode 10.2.1 (10E1001), Swift 5

Links

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

Solution

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))
    }
}

Test function

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)
}

Output

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