The simplest way to resize an UIImage

Question

In my iPhone app  I take a picture with the camera  then I want to resize it to 290 390 pixels  I was using this method to resize the image      UIImage  newImage    image  imageScaledToSize CGSizeMake 290  390                           interpolationQuality 1         It works perfectly  but it s an undocumented function  so I can t use it anymore with iPhone OS4     So    what is the simplest way to resize an UIImage

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Swift 2 0    let image   UIImage named   imageName   let newSize   CGSize width  10  height  10   UIGraphicsBeginImageContextWithOptions newSize  false  0 0  image  drawInRect CGRectMake 0  0  newSize width  newSize height   let imageResized   UIGraphicsGetImageFromCurrentImageContext   UIGraphicsEndImageContext

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The simplest way is to set the frame of your UIImageView and set the contentMode to one of the resizing options   Or you can use this utility method  if you actually need to resize an image      UIImage   imageWithImage  UIImage   image scaledToSize  CGSize newSize         UIGraphicsBeginImageContext newSize          In next line  pass 0 0 to use the current device s pixel scaling factor  and thus account for Retina resolution          Pass 1 0 to force exact pixel size      UIGraphicsBeginImageContextWithOptions newSize  NO  0 0        image drawInRect CGRectMake 0  0  newSize width  newSize height        UIImage  newImage   UIGraphicsGetImageFromCurrentImageContext            UIGraphicsEndImageContext        return newImage      Example usage    import  MYUtil h      UIImage  myIcon    MYUtil imageWithImage myUIImageInstance scaledToSize CGSizeMake 20  20

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Here is a simple way       UIImage   image    UIImage imageNamed   image        CGSize sacleSize   CGSizeMake 10  10       UIGraphicsBeginImageContextWithOptions sacleSize  NO  0 0        image drawInRect CGRectMake 0  0  sacleSize width  sacleSize height        UIImage   resizedImage   UIGraphicsGetImageFromCurrentImageContext        UIGraphicsEndImageContext      resizedImage is a new image

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Here s a modification of the category written by iWasRobbed above  It keeps the aspect ratio of the original image instead of distorting it   -  UIImage  scaleToSizeKeepAspect  CGSize size       UIGraphicsBeginImageContext size        CGFloat ws   size width self size width      CGFloat hs   size height self size height       if  ws  gt  hs            ws   hs ws          hs   1 0        else           hs   ws hs          ws   1 0             CGContextRef context   UIGraphicsGetCurrentContext        CGContextTranslateCTM context  0 0  size height       CGContextScaleCTM context  1 0  -1 0        CGContextDrawImage context  CGRectMake size width 2- size width ws  2          size height 2- size height hs  2  size width ws          size height hs   self CGImage        UIImage  scaledImage   UIGraphicsGetImageFromCurrentImageContext         UIGraphicsEndImageContext         return scaledImage

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Rogerio Chaves answer as a swift extension  func scaledTo size  CGSize  - gt  UIImage      UIGraphicsBeginImageContextWithOptions size  false  0 0       self draw in  CGRect x  0  y  0  width  size width  height  size height       let newImage UIImage   UIGraphicsGetImageFromCurrentImageContext        UIGraphicsEndImageContext       return newImage     And also bonus  func scaledTo height  CGFloat  - gt  UIImage      let width   height self size width self size height     return scaledTo size  CGSize width  width  height  height

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If you just want an image smaller and don t care about exact size       UIImage   imageWithImage  UIImage   image scaledToScale  CGFloat scale       UIGraphicsBeginImageContextWithOptions self size  YES  scale       CGContextRef context   UIGraphicsGetCurrentContext        CGContextSetInterpolationQuality context  kCGInterpolationHigh        self drawInRect CGRectMake 0  0  self size width  self size height        UIImage  newImage   UIGraphicsGetImageFromCurrentImageContext        UIGraphicsEndImageContext        return newImage      Setting scale to 0 25f will give you a 816 by 612 image from a 8MP camera    Here s a category UIImage Scale for those who needs one

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Effective approach without stretching image Swift 4     Method to resize image func resize image  UIImage  toScaleSize CGSize  - gt  UIImage                           UIGraphicsBeginImageContextWithOptions toScaleSize  true  image scale                                          image draw in  CGRect x  0  y  0  width  toScaleSize width  height  toScaleSize height                                           let scaledImage   UIGraphicsGetImageFromCurrentImageContext                                           UIGraphicsEndImageContext                                           return scaledImage                                 Call method      let resizedImage   self resize image  UIImage named   YourImageName     toScaleSize  CGSize width  290  height  390

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For my fellow Xamarians  here is a Xamarin iOS C  version of  Paul Lynch answer   private UIImage ResizeImage UIImage image  CGSize newSize         UIGraphics BeginImageContextWithOptions newSize  false  0 0f       image Draw new CGRect 0  0  newSize Width  newSize Height        UIImage newImage   UIGraphics GetImageFromCurrentImageContext        UIGraphics EndImageContext        return newImage

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Yet another way of resizing an UIImage     Resize to height   100 points  let originalImage   UIImage named   quot MyOriginalImage quot    let resizingFactor   100   originalImage size height let newImage   UIImage cgImage  originalImage cgImage   scale  originalImage scale   resizingFactor  orientation   up

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This is an UIImage extension compatible with Swift 3 and Swift 4 which scales image to given size with an aspect ratio  extension UIImage        func scaledImage withSize size  CGSize  - gt  UIImage           UIGraphicsBeginImageContextWithOptions size  false  0 0          defer   UIGraphicsEndImageContext             draw in  CGRect x  0 0  y  0 0  width  size width  height  size height           return UIGraphicsGetImageFromCurrentImageContext               func scaleImageToFitSize size  CGSize  - gt  UIImage           let aspect   self size width   self size height         if size width   aspect  lt   size height               return scaledImage withSize  CGSize width  size width  height  size width   aspect             else               return scaledImage withSize  CGSize width  size height   aspect  height  size height                        Example usage  let image   UIImage named   apple   let scaledImage   image scaleImageToFitSize size  CGSize width  45 0  height  45 0

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cf Chris  To resize to a desired size   UIImage  after    UIImage imageWithCGImage before CGImage                                      scale CGImageGetHeight before CGImage  DESIREDHEIGHT                                orientation UIImageOrientationUp     or  equivalently  substitute CGImageGetWidth      DESIREDWIDTH

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Swift 4 compatible  iOS 10  and iOS  lt  10 solution  using UIGraphicsImageRenderer if possible  UIGraphicsGetImageFromCurrentImageContext otherwise       Resizes an image         - Parameter newSize  New size     - Returns  Resized image func scaled to newSize  CGSize  - gt  UIImage       let rect   CGRect origin   zero  size  newSize       if  available iOS 10               let renderer   UIGraphicsImageRenderer size  newSize          return renderer image     in             self draw in  rect                  else           UIGraphicsBeginImageContextWithOptions newSize  false  0 0          self draw in  rect          let newImage   UIGraphicsGetImageFromCurrentImageContext           UIGraphicsEndImageContext           return newImage

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I ve discovered that it s difficult to find an answer that you can use out-of-the box in your Swift 3 project  The main problem of other answers that they don t honor the alpha-channel of the image  Here is the technique that I m using in my projects   extension UIImage        func scaledToFit toSize newSize  CGSize  - gt  UIImage           if  size width  lt  newSize width  amp  amp  size height  lt  newSize height                return copy   as  UIImage                    let widthScale   newSize width   size width         let heightScale   newSize height   size height          let scaleFactor   widthScale  lt  heightScale   widthScale   heightScale         let scaledSize   CGSize width  size width   scaleFactor  height  size height   scaleFactor           return self scaled toSize  scaledSize  in  CGRect x  0 0  y  0 0  width  scaledSize width  height  scaledSize height              func scaled toSize newSize  CGSize  in rect  CGRect  - gt  UIImage           if UIScreen main scale    2 0               UIGraphicsBeginImageContextWithOptions newSize   hasAlphaChannel  2 0                    else               UIGraphicsBeginImageContext newSize                     draw in  rect          let newImage   UIGraphicsGetImageFromCurrentImageContext           UIGraphicsEndImageContext            return newImage    UIImage              var hasAlphaChannel  Bool           guard let alpha   cgImage  alphaInfo else               return false                   return alpha    CGImageAlphaInfo first                alpha    CGImageAlphaInfo last                alpha    CGImageAlphaInfo premultipliedFirst                alpha    CGImageAlphaInfo premultipliedLast           Example of usage   override func viewDidLoad         super viewDidLoad        let size   CGSize width  14 0  height  14 0      if let image   UIImage named   barbell    scaledToFit toSize  size            let imageView   UIImageView image  image          imageView center   CGPoint x  100  y  100          view addSubview imageView            This code is a rewrite of Apple s extension with added support for images with and without alpha channel   As a further reading I recommend checking this article for different image resizing techniques  Current approach offers decent performance  it operates high-level APIs and easy to understand  I recommend sticking to it unless you find that image resizing is a bottleneck in your performance

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If you want to make a thumbnail of a UIImage  with proportional resizing or maybe some cropping involved   check out UIImage Resize category that allows you to use concise  ImageMagick-like syntax   UIImage  squareImage          image resizedImageByMagick    320x320

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I ve also seen this done as well  which I use on UIButtons for Normal and Selected state since buttons don t resize to fit    Credit goes to whoever the original author was   First make an empty  h and  m file called UIImageResizing h and UIImageResizing m     Put this in UIImageResizing h  interface UIImage  Resize  -  UIImage  scaleToSize  CGSize size   end     Put this in UIImageResizing m  implementation UIImage  Resize   -  UIImage  scaleToSize  CGSize size   UIGraphicsBeginImageContext size    CGContextRef context   UIGraphicsGetCurrentContext    CGContextTranslateCTM context  0 0  size height   CGContextScaleCTM context  1 0  -1 0    CGContextDrawImage context  CGRectMake 0 0f  0 0f  size width  size height   self CGImage    UIImage  scaledImage   UIGraphicsGetImageFromCurrentImageContext     UIGraphicsEndImageContext     return scaledImage      end   Include that  h file in whatever  m file you re going to use the function in and then call it like this   UIImage  image    UIImage imageNamed   largeImage png    UIImage  smallImage    image scaleToSize CGSizeMake 100 0f 100 0f

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Swift 4 answer   func scaleDown image  UIImage  withSize  CGSize  - gt  UIImage       let scale   UIScreen main scale     UIGraphicsBeginImageContextWithOptions withSize  false  scale      image draw in  CGRect x  0  y  0  width  withSize width  height  withSize height       let newImage   UIGraphicsGetImageFromCurrentImageContext       UIGraphicsEndImageContext       return newImage

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Proper Swift 3 0 for iOS 10  solution  Using ImageRenderer and closure syntax   func imageWith newSize  CGSize  - gt  UIImage       let renderer   UIGraphicsImageRenderer size  newSize      let image   renderer image     in         self draw in  CGRect init origin  CGPoint zero  size  newSize              return image withRenderingMode self renderingMode      And here s the Objective-C version    implementation UIImage  ResizeCategory  -  UIImage   imageWithSize  CGSize newSize       UIGraphicsImageRenderer  renderer     UIGraphicsImageRenderer alloc  initWithSize newSize       UIImage  image    renderer imageWithActions   UIGraphicsImageRendererContext  Nonnull myContext             self drawInRect  CGRect    origin   CGPointZero   size   newSize                return  image imageWithRenderingMode self renderingMode      end

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use this extension  extension UIImage       public func resize size CGSize  completionHandler  resizedImage UIImage  data NSData  - gt               dispatch async dispatch get global queue QOS CLASS USER INITIATED  0        - gt  Void in             let newSize CGSize   size             let rect   CGRectMake 0  0  newSize width  newSize height              UIGraphicsBeginImageContextWithOptions newSize  false  1 0              self drawInRect rect              let newImage   UIGraphicsGetImageFromCurrentImageContext               UIGraphicsEndImageContext               let imageData   UIImageJPEGRepresentation newImage  0 5              dispatch async dispatch get main queue         - gt  Void in                 completionHandler resizedImage  newImage  data imageData

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func resizeImage image  UIImage  newWidth  CGFloat  - gt  UIImage            let scale   newWidth   image size width         let newHeight   image size height   scale         UIGraphicsBeginImageContext CGSizeMake newWidth  newHeight           image drawInRect CGRectMake 0  0  newWidth  newHeight           let newImage   UIGraphicsGetImageFromCurrentImageContext           UIGraphicsEndImageContext           return newImage

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This improvement to Paul s code will give you a sharp high res image on an iPhone with a retina display  Otherwise when scaling down it s blurry      UIImage   imageWithImage  UIImage   image scaledToSize  CGSize newSize   if    UIScreen mainScreen  respondsToSelector  selector scale          if    UIScreen mainScreen  scale     2 0            UIGraphicsBeginImageContextWithOptions newSize  YES  2 0         else           UIGraphicsBeginImageContext newSize           else       UIGraphicsBeginImageContext newSize      image drawInRect CGRectMake 0  0  newSize width  newSize height    UIImage  newImage   UIGraphicsGetImageFromCurrentImageContext        UIGraphicsEndImageContext    return newImage

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Swift 5  func imageWithImage   image  UIImage   scaledToSize newSize  CGSize  - gt  UIImage        UIGraphicsBeginImageContextWithOptions newSize  false  0 0       image  draw in  CGRect x  0 0  y  0 0  width  newSize width  height  newSize height       let newImage  UIImage    UIGraphicsGetImageFromCurrentImageContext       UIGraphicsEndImageContext       return newImage    Usage  let img  UIImage    imageWithImage UIImage named   quot DefaultAvatar quot    scaledToSize CGSize width  20 0  height  20 0

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Use this extension  in case you need to resize width height only with aspect ratio   extension UIImage       func resize to size  CGSize  - gt  UIImage           return UIGraphicsImageRenderer size  size  image     in             draw in  CGRect origin   zero  size  size                       func resize width  CGFloat  - gt  UIImage           return resize to  CGSize width  width  height  width    size width   size height              func resize height  CGFloat  - gt  UIImage           return resize to  CGSize width  height    size width   size height   height  height

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I found a category for UIImage in Apple s own examples which does the same trick  Here s the link  https   developer apple com library ios samplecode sc2273 Listings AirDropSample UIImage Resize m html   You ll just have to change the call   UIGraphicsBeginImageContextWithOptions newSize  YES  2 0     in imageWithImage scaledToSize inRect  with   UIGraphicsBeginImageContextWithOptions newSize  NO  2 0     In order to consider the alpha channel in the image

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Trevor Howard has some UIImage categories that handle resize quite nicely  If nothing else you can use the code as examples    Note  As of iOS 5 1  this answer maybe invalid  See comment below

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Paul Lynch s answer is great  but it would change the image ratio   if you don t want to change the image ratio  and still want the new image fit for new size  try this      UIImage   imageWithImage  UIImage   image scaledToSize  CGSize newSize       calculate a new size which ratio is same to original image CGFloat ratioW   image size width   newSize width  CGFloat ratioH   image size height   newSize height   CGFloat ratio   image size width   image size height   CGSize showSize   CGSizeZero  if  ratioW  gt  1  amp  amp  ratioH  gt  1          if  ratioW  gt  ratioH             showSize width   newSize width          showSize height   showSize width   ratio        else           showSize height   newSize height          showSize width   showSize height   ratio           else if  ratioW  gt  1         showSize width   showSize width      showSize height   showSize width   ratio     else if  ratioH  gt  1         showSize height   showSize height      showSize width   showSize height   ratio        UIGraphicsBeginImageContext newSize      In next line  pass 0 0 to use the current device s pixel scaling factor  and thus account for Retina resolution      Pass 1 0 to force exact pixel size  UIGraphicsBeginImageContextWithOptions showSize  NO  0 0    image drawInRect CGRectMake 0  0  showSize width  showSize height    UIImage  newImage   UIGraphicsGetImageFromCurrentImageContext    UIGraphicsEndImageContext    return newImage

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Why so complicated  I think using system API can achieve the same result   UIImage  largeImage  CGFloat ratio   0 4     you want to get a new image that is 40  the size of large image  UIImage  newImage    UIImage imageWithCGImage largeImage CGImage                                         scale 1 ratio                                   orientation largeImage imageOrientation      notice the second argument  it is 1 ratio  not ratio    The only gotcha is you should pass inverse of target ratio as the second argument  as according to the document the second parameter specifies the ratio of original image compared to the new scaled one

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A more compact version for Swift 4 and iOS 10    extension UIImage       func resized to size  CGSize  - gt  UIImage           return UIGraphicsImageRenderer size  size  image     in             draw in  CGRect origin   zero  size  size                       Usage   let resizedImage   image resized to  CGSize width  50  height  50

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Swift 3 0 with failsafe option  returns the original image in case of error    func resize image  UIImage  toSize size  CGSize  - gt  UIImage      UIGraphicsBeginImageContextWithOptions size false 1 0      image draw in  CGRect x  0  y  0  width  size width  height  size height       if let resizedImage   UIGraphicsGetImageFromCurrentImageContext             UIGraphicsEndImageContext           return resizedImage           UIGraphicsEndImageContext       return image

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For Swift 5  extension UIImage     func resized to newSize  CGSize  - gt  UIImage        UIGraphicsBeginImageContextWithOptions newSize  false  0      defer   UIGraphicsEndImageContext          draw in  CGRect origin   zero  size  newSize       return UIGraphicsGetImageFromCurrentImageContext

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Here my somewhat-verbose Swift code  func scaleImage image UIImage   toSize CGSize  - gt  UIImage       UIGraphicsBeginImageContextWithOptions toSize  false  0 0        let aspectRatioAwareSize   self aspectRatioAwareSize image size  boxSize  toSize  useLetterBox  false        let leftMargin    toSize width - aspectRatioAwareSize width    0 5     let topMargin    toSize height - aspectRatioAwareSize height    0 5       image drawInRect CGRectMake leftMargin  topMargin  aspectRatioAwareSize width   aspectRatioAwareSize height       let retVal   UIGraphicsGetImageFromCurrentImageContext       UIGraphicsEndImageContext       return retVal    func aspectRatioAwareSize imageSize  CGSize  boxSize  CGSize  useLetterBox  Bool  - gt  CGSize          aspect ratio aware size        http   stackoverflow com a 6565988 8047     let imageWidth   imageSize width     let imageHeight   imageSize height     let containerWidth   boxSize width     let containerHeight   boxSize height      let imageAspectRatio   imageWidth imageHeight     let containerAspectRatio   containerWidth containerHeight      let retVal   CGSize        use the else at your own risk  it seems to work  but I don t know         the math     if  useLetterBox            retVal   containerAspectRatio  gt  imageAspectRatio   CGSizeMake imageWidth   containerHeight   imageHeight  containerHeight    CGSizeMake containerWidth  imageHeight   containerWidth   imageWidth        else           retVal   containerAspectRatio  lt  imageAspectRatio   CGSizeMake imageWidth   containerHeight   imageHeight  containerHeight    CGSizeMake containerWidth  imageHeight   containerWidth   imageWidth             return retVal

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Here s a Swift version of Paul Lynch s answer  func imageWithImage image UIImage  scaledToSize newSize CGSize  - gt  UIImage      UIGraphicsBeginImageContextWithOptions newSize  false  0 0       image drawInRect CGRectMake 0  0  newSize width  newSize height       let newImage UIImage   UIGraphicsGetImageFromCurrentImageContext       UIGraphicsEndImageContext       return newImage     And as an extension   public extension UIImage       func copy newSize  CGSize  retina  Bool   true  - gt  UIImage               In next line  pass 0 to use the current device s pixel scaling factor  and thus account for Retina resolution              Pass 1 to force exact pixel size          UIGraphicsBeginImageContextWithOptions                 size     newSize                 opaque     false                 scale     retina   0   1                   defer   UIGraphicsEndImageContext              self draw in  CGRect origin   zero  size  newSize           return UIGraphicsGetImageFromCurrentImageContext

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Swift solution for Stretch Fill  Aspect Fill and Aspect Fit extension UIImage       enum ContentMode           case contentFill         case contentAspectFill         case contentAspectFit                func resize withSize size  CGSize  contentMode  ContentMode    contentAspectFill  - gt  UIImage            let aspectWidth   size width   self size width         let aspectHeight   size height   self size height                  switch contentMode           case  contentFill              return resize withSize  size          case  contentAspectFit              let aspectRatio   min aspectWidth  aspectHeight              return resize withSize  CGSize width  self size width   aspectRatio  height  self size height   aspectRatio           case  contentAspectFill              let aspectRatio   max aspectWidth  aspectHeight              return resize withSize  CGSize width  self size width   aspectRatio  height  self size height   aspectRatio                            private func resize withSize size  CGSize  - gt  UIImage            UIGraphicsBeginImageContextWithOptions size  false  self scale          defer   UIGraphicsEndImageContext             draw in  CGRect x  0 0  y  0 0  width  size width  height  size height           return UIGraphicsGetImageFromCurrentImageContext            and to use you can do the following  let image   UIImage named   quot image png quot    let newImage   image resize withSize  CGSize width  200  height  150   contentMode   contentAspectFill   Thanks to abdullahselek for his original solution

[ios] The simplest way to resize an UIImage?

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