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

User · Answer

Swift 4 Version  extension UIImage       func resizeImage   newSize  CGSize  - gt  UIImage            func isSameSize   newSize  CGSize  - gt  Bool               return size    newSize                    func scaleImage   newSize  CGSize  - gt  UIImage                func getScaledRect   newSize  CGSize  - gt  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  - gt  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

User · Answer

You can use this for fit image at Swift 3   extension UIImage       func resizedImage newSize  CGSize  - gt  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  - gt  UIImage           let widthFactor   size width   rectSize width         let heightFactor   size height   rectSize height          var resizeFactor   widthFactor         if size height  gt  size width               resizeFactor   heightFactor                    let newSize   CGSize width  size width resizeFactor  height  size height resizeFactor          let resized   resizedImage newSize  newSize          return resized           Usage   let resizedImage   image resizedImageWithinRect rectSize  CGSize width  1900  height  1900

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calling of resizeimage method  let image1   resizeimage image  myimage image   withSize  CGSize width 200  height  200     method for resizeing image  func resizeimage image UIImage withSize CGSize  - gt  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 gt maxHeight  actualWidth gt maxWidth                if  imgRatio lt maxRatio                     adjust width according to maxHeight                 imgRatio   maxHeight actualHeight                 actualWidth   imgRatio   actualWidth                 actualHeight   maxHeight              else if imgRatio gt 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

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Swift 4  extension version  NO WHITE LINE ON EDGES   Nobody seems to be mentioning that if image draw   is called with non-integer values  resulting image could show a white line artifact at the right or bottom edge   extension UIImage        func scaled with scale  CGFloat  - gt  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

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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  - gt  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  gt  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     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  - gt  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  gt  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

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For Swift 4 I would just make an extension on UIImage with referencing to self   import UIKit extension UIImage     func resizeImage targetSize  CGSize  - gt  UIImage       let size   self size     let widthRatio    targetSize width    size width     let heightRatio   targetSize height   size height     let newSize   widthRatio  gt  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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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  - gt  UIImage             if max size width  size height   lt   dimension   return self            var newSize  CGSize          let aspectRatio   size width size height          if aspectRatio  gt  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  - gt  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  - gt  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  - gt  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  - gt  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  - gt  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  - gt  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  amp sourceBuffer   amp 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 lt UInt8 gt  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  amp sourceBuffer   amp destBuffer  nil  numericCast kvImageHighQualityResampling           guard error    kvImageNoError else   return resultImage               create a CGImage from vImage Buffer         let destCGImage   vImageCreateCGImageFromBuffer  amp destBuffer   amp format  nil  nil  numericCast kvImageNoFlags    amp 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  - gt  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  - gt  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

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SWIFT 5 with newImage   UIImage cgImage  cgImage   func scaleImage toSize newSize  CGSize  - gt  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

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For Swift 4 0 and iOS 10      extension UIImage           func resizeImage   dimension  CGFloat  opaque  Bool  contentMode  UIViewContentMode    scaleAspectFit  - gt  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  gt  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

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UIImage Extension Swift 5  extension UIImage       func resize   width  CGFloat    height CGFloat  - gt  UIImage            let widthRatio    width   size width         let heightRatio   height   size height         let ratio   widthRatio  gt  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              Use   UIImage   resize 200  300

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Swift 4 2 version of  KiritModi answer  func resizeImage image  UIImage  targetSize  CGSize  - gt  UIImage       let size   image size      let widthRatio    targetSize width    size width     let heightRatio   targetSize height   size height      var newSize  CGSize     if widthRatio  gt  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

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Swift 3 Version and Extension style  This answer come from  Kirit Modi   extension UIImage        func resizeImage targetSize  CGSize  - gt  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  gt  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

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Example is for image minimize to 1024 and less   func resizeImage image  UIImage  -  UIImage        if image size height  gt   1024  amp  amp  image size width  gt   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  gt   1024  amp  amp  image size width  lt  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  gt   1024  amp  amp  image size height  lt  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

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Here you have two simple functions of UIImage extension   func scaledWithMaxWidthOrHeightValue value  CGFloat  - gt  UIImage         let width   self size width     let height   self size height      let ratio   width height      var newWidth   value     var newHeight   value      if ratio  gt  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  - gt  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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Throwing in here my version of the accepted answer to work nicely with Swift 5  This solution does not force unwrap the resulting image making it a bit safer and overall cleaner solution   extension UIImage       public func resized to target  CGSize  - gt  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

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Swift 5 version respecting ratio  scaleToFill  and centering image  extension UIImage       func resized to newSize  CGSize  - gt  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  gt  newSize width                   middle x -   resizeSize width-newSize width  2 0                           if resizeSize height  gt  newSize height                   middle y -   resizeSize height-newSize height  2 0                                        draw in  CGRect origin  middle  size  resizeSize

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For Swift 5 0 and iOS 12 extension UIImage       func imageResized to size  CGSize  - gt  UIImage           return UIGraphicsImageRenderer size  size  image     in             draw in  CGRect origin   zero  size  size                      use  let image    imageLiteral resourceName   quot ic search quot   cell  search image   image imageResized to  cell  search frame size

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All of the listed answers so far seem to result in an image of a reduced size  however the size isn t measured in pixels  Here s a Swift 5  pixel-based resize   extension UIImage       func resize   max size  CGFloat  - gt  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  gt  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            Usage   image resize 500

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It s also possible to use AlamofireImage  https   github com Alamofire AlamofireImage   let size   CGSize width  30 0  height  30 0  let aspectScaledToFitImage   image af imageAspectScaled toFit  size    The function in the previous post gave me a blurry result

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Here s a general method  in Swift 5  for downscaling an image to fit a size  The resulting image can have the same aspect ratio as the original  or it can be the target size with the original image centered in it  If the image is smaller than the target size  it is not resized   extension UIImage       func scaledDown into size CGSize  centered Bool   false  - gt  UIImage           var  targetWidth  targetHeight     self size width  self size height          var  scaleW  scaleH     1 as CGFloat  1 as CGFloat          if targetWidth  gt  size width               scaleW   size width targetWidth                   if targetHeight  gt  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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Since  KiritModi  s answer is from 2015  this is the Swift 3 0 s version   func resizeImage image  UIImage  targetSize  CGSize  - gt  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  gt  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

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Swift 4 Solution-   Use this function           func image with image  UIImage  scaledTo newSize  CGSize  - gt  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       Calling a function -  image with  predictionImage  scaledTo  CGSize width  28 0  height  28 0    here 28 0 is the pixel size that you want to set

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