Cropping an UIImage

Question

I ve got some code that resizes an image so I can get a scaled chunk of the center of the image - I use this to take a UIImage and return a small  square representation of an image  similar to what s seen in the album view of the Photos app   I know I could use a UIImageView and adjust the crop mode to achieve the same results  but these images are sometimes displayed in UIWebViews    I ve started to notice some crashes in this code and I m a bit stumped  I ve got two different theories and I m wondering if either is on-base   Theory 1  I achieve the cropping by drawing into an offscreen image context of my target size  Since I want the center portion of the image  I set the CGRect argument passed to drawInRect to something that s larger than the bounds of my image context  I was hoping this was Kosher  but am I instead attempting to draw over other memory that I shouldn t be touching   Theory 2  I m doing all of this in a background thread  I know there are portions of UIKit that are restricted to the main thread  I was assuming   hoping that drawing to an offscreen view wasn t one of these  Am I wrong    Oh  how I miss NSImage s drawInRect fromRect operation fraction  method

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None of the answers here handle all of the scale and rotation issues 100  correctly  Here s a synthesis of everything said so far  up-to-date as of iOS7 8  It s meant to be included as a method in a category on UIImage   -  UIImage   croppedImageInRect  CGRect rect       double   rad  double      double deg            return deg   180 0   M PI              CGAffineTransform rectTransform      switch  self imageOrientation            case UIImageOrientationLeft              rectTransform   CGAffineTransformTranslate CGAffineTransformMakeRotation rad 90    0  -self size height               break          case UIImageOrientationRight              rectTransform   CGAffineTransformTranslate CGAffineTransformMakeRotation rad -90    -self size width  0               break          case UIImageOrientationDown              rectTransform   CGAffineTransformTranslate CGAffineTransformMakeRotation rad -180    -self size width  -self size height               break          default              rectTransform   CGAffineTransformIdentity             rectTransform   CGAffineTransformScale rectTransform  self scale  self scale        CGImageRef imageRef   CGImageCreateWithImageInRect  self CGImage   CGRectApplyAffineTransform rect  rectTransform        UIImage  result    UIImage imageWithCGImage imageRef scale self scale orientation self imageOrientation       CGImageRelease imageRef        return result

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Heads up  all these answers assume a CGImage-backed image object   image CGImage can return nil  if the UIImage is backed by a CIImage  which would be the case if you created this image using a CIFilter    In that case  you might have to draw the image in a new context  and return that image  slow    UIImage  crop UIImage  image  rect        UIGraphicsBeginImageContextWithOptions rect size  false   image scale         image drawAtPoint CGPointMake -rect origin x  -rect origin y        cropped image   UIGraphicsGetImageFromCurrentImageContext        UIGraphicsEndImageContext        return cropped image

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I use the method below     - UIImage   getNeedImageFrom  UIImage  image cropRect  CGRect rect         CGSize cropSize   rect size      CGFloat widthScale         image size width self imageViewOriginal bounds size width      CGFloat heightScale        image size height self imageViewOriginal bounds size height      cropSize   CGSizeMake rect size width widthScale        rect size height heightScale       CGPoint  pointCrop   CGPointMake rect origin x widthScale       rect origin y heightScale       rect   CGRectMake pointCrop x  pointCrop y  cropSize width       cropSize height       CGImageRef subImage   CGImageCreateWithImageInRect image CGImage  rect       UIImage  croppedImage    UIImage imageWithCGImage subImage       CGImageRelease subImage       return croppedImage

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To crop retina images while keeping the same scale and orientation  use the following method in a UIImage category  iOS 4 0 and above    -  UIImage   crop  CGRect rect       if  self scale  gt  1 0f            rect   CGRectMake rect origin x   self scale                            rect origin y   self scale                            rect size width   self scale                            rect size height   self scale              CGImageRef imageRef   CGImageCreateWithImageInRect self CGImage  rect       UIImage  result    UIImage imageWithCGImage imageRef scale self scale orientation self imageOrientation       CGImageRelease imageRef       return result

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Swift Extension  extension UIImage       func crop var rect  CGRect  - gt  UIImage           rect origin x  self scale         rect origin y  self scale         rect size width  self scale         rect size height  self scale          let imageRef   CGImageCreateWithImageInRect self CGImage  rect          let image   UIImage CGImage  imageRef  scale  self scale  orientation  self imageOrientation           return image

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Swift 3 version func cropImage imageToCrop UIImage  toRect rect CGRect  - gt  UIImage           let imageRef CGImage   imageToCrop cgImage  cropping to  rect       let cropped UIImage   UIImage cgImage imageRef      return cropped     let imageTop UIImage    UIImage named  quot one jpg quot       add validation   with help of this bridge function CGRectMake - gt  CGRect  credits to this answer answered by  rob mayoff    func CGRectMake   x  CGFloat    y  CGFloat    width  CGFloat    height  CGFloat  - gt  CGRect       return CGRect x  x  y  y  width  width  height  height     The usage is  if var image UIImage    UIImage named  quot one jpg quot       let  croppedImage   cropImage imageToCrop  image  toRect  CGRectMake          image size width 4          0          image size width 2          image size height           Output

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Look at https   github com vvbogdan BVCropPhoto   -  UIImage   croppedImage       CGFloat scale   self sourceImage size width   self scrollView contentSize width       UIImage  finalImage   nil      CGRect targetFrame   CGRectMake  self scrollView contentInset left   self scrollView contentOffset x    scale               self scrollView contentInset top   self scrollView contentOffset y    scale              self cropSize width   scale              self cropSize height   scale        CGImageRef contextImage   CGImageCreateWithImageInRect   self imageWithRotation self sourceImage  CGImage   targetFrame        if  contextImage    NULL            finalImage    UIImage imageWithCGImage contextImage                                          scale self sourceImage scale                                    orientation UIImageOrientationUp            CGImageRelease contextImage              return finalImage      -  UIImage   imageWithRotation  UIImage   image         if  image imageOrientation    UIImageOrientationUp  return image      CGAffineTransform transform   CGAffineTransformIdentity       switch  image imageOrientation            case UIImageOrientationDown          case UIImageOrientationDownMirrored              transform   CGAffineTransformTranslate transform  image size width  image size height               transform   CGAffineTransformRotate transform  M PI               break           case UIImageOrientationLeft          case UIImageOrientationLeftMirrored              transform   CGAffineTransformTranslate transform  image size width  0               transform   CGAffineTransformRotate transform  M PI 2               break           case UIImageOrientationRight          case UIImageOrientationRightMirrored              transform   CGAffineTransformTranslate transform  0  image size height               transform   CGAffineTransformRotate transform  -M PI 2               break          case UIImageOrientationUp          case UIImageOrientationUpMirrored              break             switch  image imageOrientation            case UIImageOrientationUpMirrored          case UIImageOrientationDownMirrored              transform   CGAffineTransformTranslate transform  image size width  0               transform   CGAffineTransformScale transform  -1  1               break           case UIImageOrientationLeftMirrored          case UIImageOrientationRightMirrored              transform   CGAffineTransformTranslate transform  image size height  0               transform   CGAffineTransformScale transform  -1  1               break          case UIImageOrientationUp          case UIImageOrientationDown          case UIImageOrientationLeft          case UIImageOrientationRight              break                Now we draw the underlying CGImage into a new context  applying the transform        calculated above      CGContextRef ctx   CGBitmapContextCreate NULL  image size width  image size height              CGImageGetBitsPerComponent image CGImage   0              CGImageGetColorSpace image CGImage               CGImageGetBitmapInfo image CGImage        CGContextConcatCTM ctx  transform       switch  image imageOrientation            case UIImageOrientationLeft          case UIImageOrientationLeftMirrored          case UIImageOrientationRight          case UIImageOrientationRightMirrored                 Grr                CGContextDrawImage ctx  CGRectMake 0  0  image size height  image size width   image CGImage               break           default              CGContextDrawImage ctx  CGRectMake 0  0  image size width  image size height   image CGImage               break                And now we just create a new UIImage from the drawing context     CGImageRef cgimg   CGBitmapContextCreateImage ctx       UIImage  img    UIImage imageWithCGImage cgimg       CGContextRelease ctx       CGImageRelease cgimg       return img

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Swift 5   extension UIImage       func cropped rect  CGRect  - gt  UIImage            guard let cgImage   cgImage else   return nil            UIGraphicsBeginImageContextWithOptions rect size  false  0          let context   UIGraphicsGetCurrentContext            context  translateBy x  0 0  y  self size height          context  scaleBy x  1 0  y  -1 0          context  draw cgImage  in  CGRect x  rect minX  y  rect minY  width  self size width  height  self size height   byTiling  false            let croppedImage   UIGraphicsGetImageFromCurrentImageContext           UIGraphicsEndImageContext            return croppedImage

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Here is my UIImage crop implementation which obeys the imageOrientation property  All orientations were thoroughly tested   inline double rad double deg        return deg   180 0   M PI     UIImage  UIImageCrop UIImage  img  CGRect rect        CGAffineTransform rectTransform      switch  img imageOrientation                case UIImageOrientationLeft              rectTransform   CGAffineTransformTranslate CGAffineTransformMakeRotation rad 90    0  -img size height               break          case UIImageOrientationRight              rectTransform   CGAffineTransformTranslate CGAffineTransformMakeRotation rad -90    -img size width  0               break          case UIImageOrientationDown              rectTransform   CGAffineTransformTranslate CGAffineTransformMakeRotation rad -180    -img size width  -img size height               break          default              rectTransform   CGAffineTransformIdentity             rectTransform   CGAffineTransformScale rectTransform  img scale  img scale        CGImageRef imageRef   CGImageCreateWithImageInRect  img CGImage   CGRectApplyAffineTransform rect  rectTransform        UIImage  result    UIImage imageWithCGImage imageRef scale img scale orientation img imageOrientation       CGImageRelease imageRef       return result

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swift3  extension UIImage       func crop rect  CGRect  - gt  UIImage            var scaledRect   rect         scaledRect origin x    scale         scaledRect origin y    scale         scaledRect size width    scale         scaledRect size height    scale         guard let imageRef  CGImage   cgImage  cropping to  scaledRect  else               return nil                   return UIImage cgImage  imageRef  scale  scale  orientation  imageOrientation

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Swift 2 0 Update  CIImage compatibility   Expanding off of Maxim s Answer but works if your image is CIImage based  as well   public extension UIImage       func imageByCroppingToRect rect  CGRect  - gt  UIImage            if let image   CGImageCreateWithImageInRect self CGImage  rect                return UIImage CGImage  image            else if let image    self CIImage   imageByCroppingToRect rect                return UIImage CIImage  image                   return nil

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Here s an updated Swift 3 version based on Noodles answer  func cropping to rect  CGRect  - gt  UIImage         if let cgCrop   cgImage  cropping to  rect            return UIImage cgImage  cgCrop            else if let ciCrop   ciImage  cropping to  rect            return UIImage ciImage  ciCrop             return nil

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Follow Answer of  Arne  I Just fixing to Category function  put it in Category of UIImage   - UIImage  cropImage  CGRect rect       UIGraphicsBeginImageContextWithOptions rect size  false   self scale         self drawAtPoint CGPointMake -rect origin x  -rect origin y        UIImage  cropped image   UIGraphicsGetImageFromCurrentImageContext        UIGraphicsEndImageContext        return cropped image

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Best solution for cropping an UIImage in Swift  in term of precision  pixels scaling       private func squareCropImageToSideLength let sourceImage  UIImage      let sideLength  CGFloat  - gt  UIImage              input size comes from image         let inputSize  CGSize   sourceImage size             round up side length to avoid fractional output size         let sideLength  CGFloat   ceil sideLength              output size has sideLength for both dimensions         let outputSize  CGSize   CGSizeMake sideLength  sideLength              calculate scale so that smaller dimension fits sideLength         let scale  CGFloat   max sideLength   inputSize width              sideLength   inputSize height              scaling the image with this scale results in this output size         let scaledInputSize  CGSize   CGSizeMake inputSize width   scale              inputSize height   scale              determine point in center of  canvas          let center  CGPoint   CGPointMake outputSize width 2 0              outputSize height 2 0              calculate drawing rect relative to output Size         let outputRect  CGRect   CGRectMake center x - scaledInputSize width 2 0              center y - scaledInputSize height 2 0              scaledInputSize width              scaledInputSize height              begin a new bitmap context  scale 0 takes display scale         UIGraphicsBeginImageContextWithOptions outputSize  true  0              optional  set the interpolation quality             For this you need to grab the underlying CGContext         let ctx  CGContextRef   UIGraphicsGetCurrentContext           CGContextSetInterpolationQuality ctx  kCGInterpolationHigh              draw the source image into the calculated rect         sourceImage drawInRect outputRect              create new image from bitmap context         let outImage  UIImage   UIGraphicsGetImageFromCurrentImageContext               clean up         UIGraphicsEndImageContext               pass back new image         return outImage     Instructions used to call this function   let image  UIImage   UIImage named   Image jpg    let squareImage  UIImage   self squareCropImageToSideLength image  sideLength  320  self myUIImageView image   squareImage   Note  the initial source code inspiration written in Objective-C has been found on  Cocoanetics  blog

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-  UIImage   getSubImage  CGRect  rect      CGImageRef subImageRef   CGImageCreateWithImageInRect self CGImage  rect       CGRect smallBounds   CGRectMake rect origin x  rect origin y  CGImageGetWidth subImageRef   CGImageGetHeight subImageRef         UIGraphicsBeginImageContext smallBounds size       CGContextRef context   UIGraphicsGetCurrentContext        CGContextDrawImage context  smallBounds  subImageRef       UIImage  smallImg    UIImage imageWithCGImage subImageRef       UIGraphicsEndImageContext         return smallImg

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On iOS9 2SDK  I use below method to convert frame from UIView to  UIImage   - UIImage   getNeedImageFrom  UIImage  image cropRect  CGRect rect     CGSize cropSize   rect size    CGFloat widthScale   image size width self imageViewOriginal bounds size width    CGFloat heightScale   image size height self imageViewOriginal bounds size height    cropSize   CGSizeMake rect size width widthScale                 rect size height heightScale     CGPoint pointCrop   CGPointMake rect origin x widthScale               rect origin y heightScale     rect   CGRectMake pointCrop x  pointCrop y  cropSize width  cropSize height     CGImageRef subImage   CGImageCreateWithImageInRect image CGImage  rect     UIImage  croppedImage    UIImage imageWithCGImage subImage     CGImageRelease subImage      return croppedImage

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Update 2014-05-28  I wrote this when iOS 3 or so was the hot new thing  I m certain there are better ways to do this by now  possibly built-in  As many people have mentioned  this method doesn t take rotation into account  read some additional answers and spread some upvote love around to keep the responses to this question helpful for everyone   Original response   I m going to copy paste my response to the same question elsewhere   There isn t a simple class method to do this  but there is a function that you can use to get the desired results  CGImageCreateWithImageInRect CGImageRef  CGRect  will help you out   Here s a short example using it   CGImageRef imageRef   CGImageCreateWithImageInRect  largeImage CGImage   cropRect      or use the UIImage wherever you like  UIImageView setImage  UIImage imageWithCGImage imageRef     CGImageRelease imageRef

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I wasn t satisfied with other solutions because they either draw several time  using more power than necessary  or have problems with orientation  Here is what I used for a scaled square croppedImage from a UIImage   image   CGFloat minimumSide   fminf image size width  image size height   CGFloat finalSquareSize   600      create new drawing context for right size CGRect rect   CGRectMake 0  0  finalSquareSize  finalSquareSize   CGFloat scalingRatio   640 0 minimumSide  UIGraphicsBeginImageContext rect size      draw  image drawInRect CGRectMake  minimumSide - photo size width  scalingRatio 2    minimumSide - photo size height  scalingRatio 2   photo size width scalingRatio  photo size height scalingRatio     UIImage  croppedImage   UIGraphicsGetImageFromCurrentImageContext     UIGraphicsEndImageContext

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UIImage   squareImageWithImage  UIImage   image scaledToSize  CGSize newSize       double ratio      double delta      CGPoint offset         make a new square size  that is the resized imaged width     CGSize sz   CGSizeMake newSize width  newSize width          figure out if the picture is landscape or portrait  then       calculate scale factor and offset     if  image size width  gt  image size height            ratio   newSize width   image size width          delta    ratio image size width - ratio image size height           offset   CGPointMake delta 2  0         else           ratio   newSize width   image size height          delta    ratio image size height - ratio image size width           offset   CGPointMake 0  delta 2                make the final clipping rect based on the calculated values     CGRect clipRect   CGRectMake -offset x  -offset y                                    ratio   image size width    delta                                    ratio   image size height    delta           start a new context  with scale factor 0 0 so retina displays get       high quality image     if    UIScreen mainScreen  respondsToSelector  selector scale              UIGraphicsBeginImageContextWithOptions sz  YES  0 0         else           UIGraphicsBeginImageContext sz             UIRectClip clipRect        image drawInRect clipRect       UIImage  newImage   UIGraphicsGetImageFromCurrentImageContext        UIGraphicsEndImageContext         return newImage

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CGSize size    originalImage size   int padding   20  int pictureSize   300  int startCroppingPosition   100  if  size height  gt  size width        pictureSize   size width -  2 0   padding       startCroppingPosition    size height - pictureSize    2 0     else       pictureSize   size height -  2 0   padding       startCroppingPosition    size width - pictureSize    2 0       WTF  Don t forget that the CGImageCreateWithImageInRect believes that     the image is 180 rotated  so x and y are inverted  same for height and width  CGRect cropRect   CGRectMake startCroppingPosition  padding  pictureSize  pictureSize   CGImageRef imageRef   CGImageCreateWithImageInRect  originalImage CGImage   cropRect   UIImage  newImage    UIImage imageWithCGImage imageRef scale 1 0 orientation originalImage imageOrientation    m photoView setImage newImage   CGImageRelease imageRef     Most of the responses I ve seen only deals with a position of  0  0  for  x  y   Ok that s one case but I d like my cropping operation to be centered  What took me a while to figure out is the line following the WTF comment   Let s take the case of an image captured with a portrait orientation    The original image height is higher than its width  Woo  no surprise so far   The image that the CGImageCreateWithImageInRect method imagines in its own world is not really a portrait though but a landscape  That is also why if you don t use the orientation argument in the imageWithCGImage constructor  it will show up as 180 rotated   So  you should kind of imagine that it is a landscape  the  0  0  position being the top right corner of the image     Hope it makes sense  If it does not  try different values you ll see that the logic is inverted when it comes to choosing the right x  y  width  and height for your cropRect

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Looks a little bit strange but works great and takes into consideration image orientation   var image UIImage        let img   CIImage image  image   imageByCroppingToRect rect  image   UIImage CIImage  img  scale  1  orientation  image imageOrientation

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You can make a UIImage category and use it wherever you need  Based on HitScans response and comments bellow it     implementation UIImage  Crop   -  UIImage   crop  CGRect rect        rect   CGRectMake rect origin x self scale                         rect origin y self scale                         rect size width self scale                         rect size height self scale               CGImageRef imageRef   CGImageCreateWithImageInRect  self CGImage   rect       UIImage  result    UIImage imageWithCGImage imageRef                                            scale self scale                                      orientation self imageOrientation        CGImageRelease imageRef       return result      end   You can use it this way   UIImage  imageToCrop    lt yourImageToCrop gt   CGRect cropRect    lt areaYouWantToCrop gt         for example   CGRectMake 0  40  320  100    UIImage  croppedImage    imageToCrop crop cropRect

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Swift version of awolf s answer  which worked for me   public extension UIImage       func croppedImage inRect rect  CGRect  - gt  UIImage           let rad   Double  - gt  CGFloat     deg in             return CGFloat deg   180 0    pi                    var rectTransform  CGAffineTransform         switch imageOrientation           case  left              let rotation   CGAffineTransform rotationAngle  rad 90               rectTransform   rotation translatedBy x  0  y  -size height          case  right              let rotation   CGAffineTransform rotationAngle  rad -90               rectTransform   rotation translatedBy x  -size width  y  0          case  down              let rotation   CGAffineTransform rotationAngle  rad -180               rectTransform   rotation translatedBy x  -size width  y  -size height          default              rectTransform    identity                   rectTransform   rectTransform scaledBy x  scale  y  scale          let transformedRect   rect applying rectTransform          let imageRef   cgImage  cropping to  transformedRect           let result   UIImage cgImage  imageRef  scale  scale  orientation  imageOrientation          return result

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Below code snippet might help   import UIKit  extension UIImage       func cropImage toRect rect  CGRect  - gt  UIImage            if let imageRef   self cgImage  cropping to  rect                return UIImage cgImage  imageRef                    return nil

[ios] Cropping an UIImage

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