How to easily resize optimize an image size with iOS

Question

My application is downloading a set of image files from the network  and saving them to the local iPhone disk  Some of those images are pretty big in size  widths larger than 500 pixels  for instance   Since the iPhone doesn t even have a big enough display to show the image in its original size  I m planning on resizing the image to something a bit smaller to save on space performance   Also  some of those images are JPEGs and they are not saved as the usual 60  quality setting   How can I resize a picture with the iPhone SDK  and how can I change the quality setting of a JPEG image

User · Answer

Best way to scale images without losing the aspect ratio (i.e. without stretching the imgage) is to use this method:

//to scale images without changing aspect ratio
+ (UIImage *)scaleImage:(UIImage *)image toSize:(CGSize)newSize {

    float width = newSize.width;
    float height = newSize.height;

    UIGraphicsBeginImageContext(newSize);
    CGRect rect = CGRectMake(0, 0, width, height);

    float widthRatio = image.size.width / width;
    float heightRatio = image.size.height / height;
    float divisor = widthRatio > heightRatio ? widthRatio : heightRatio;

    width = image.size.width / divisor;
    height = image.size.height / divisor;

    rect.size.width  = width;
    rect.size.height = height;

    //indent in case of width or height difference
    float offset = (width - height) / 2;
    if (offset > 0) {
        rect.origin.y = offset;
    }
    else {
        rect.origin.x = -offset;
    }

    [image drawInRect: rect];

    UIImage *smallImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return smallImage;

}

Add this method to your Utility class so you can use it throughout your project, and access it like so:

xyzImageView.image = [Utility scaleImage:yourUIImage toSize:xyzImageView.frame.size];

This method takes care of scaling while maintaining aspect ratio. It also adds indents to the image in case the scaled down image has more width than height (or vice versa).

User · Answer

you can use this code to scale image in required size      UIImage   scaleImage  UIImage   image toSize  CGSize newSize       CGSize actSize   image size      float scale   actSize width actSize height       if  scale  lt  1            newSize height   newSize width scale             else           newSize width   newSize height scale             UIGraphicsBeginImageContext newSize        image drawInRect CGRectMake 0  0  newSize width  newSize height        UIImage  newImage   UIGraphicsGetImageFromCurrentImageContext        UIGraphicsEndImageContext         return newImage

User · Answer

I developed an ultimate solution for image scaling in Swift   You can use it to resize image to fill  aspect fill or aspect fit specified size    You can align image to center or any of four edges and four corners   And also you can trim extra space which is added if aspect ratios of original image and target size are not equal   enum UIImageAlignment       case Center  Left  Top  Right  Bottom  TopLeft  BottomRight  BottomLeft  TopRight    enum UIImageScaleMode       case Fill      AspectFill      AspectFit UIImageAlignment     extension UIImage       func scaleImage width width  CGFloat    nil  height  CGFloat    nil  scaleMode  UIImageScaleMode    AspectFit  Center   trim  Bool   false  - gt  UIImage           let preWidthScale   width map    0   size width           let preHeightScale   height map    0   size height           var widthScale   preWidthScale    preHeightScale    1         var heightScale   preHeightScale    widthScale         switch scaleMode           case  AspectFit                 let scale   min widthScale  heightScale              widthScale   scale             heightScale   scale         case  AspectFill              let scale   max widthScale  heightScale              widthScale   scale             heightScale   scale         default              break                   let newWidth   size width   widthScale         let newHeight   size height   heightScale         let canvasWidth   trim   newWidth    width    newWidth          let canvasHeight   trim   newHeight    height    newHeight          UIGraphicsBeginImageContextWithOptions CGSizeMake canvasWidth  canvasHeight   false  0           var originX  CGFloat   0         var originY  CGFloat   0         switch scaleMode           case  AspectFit let alignment               switch alignment               case  Center                  originX    canvasWidth - newWidth    2                 originY    canvasHeight - newHeight    2             case  Top                  originX    canvasWidth - newWidth    2             case  Left                  originY    canvasHeight - newHeight    2             case  Bottom                  originX    canvasWidth - newWidth    2                 originY   canvasHeight - newHeight             case  Right                  originX   canvasWidth - newWidth                 originY    canvasHeight - newHeight    2             case  TopLeft                  break             case  TopRight                  originX   canvasWidth - newWidth             case  BottomLeft                  originY   canvasHeight - newHeight             case  BottomRight                  originX   canvasWidth - newWidth                 originY   canvasHeight - newHeight                       default              break                   self drawInRect CGRectMake originX  originY  newWidth  newHeight           let image   UIGraphicsGetImageFromCurrentImageContext           UIGraphicsEndImageContext           return image           There are examples of applying this solution below   Gray rectangle is target site image will be resized to  Blue circles in light blue rectangle is the image  I used circles because it s easy to see when it s scaled without preserving aspect   Light orange color marks areas that will be trimmed if you pass trim  true   Aspect fit before and after scaling      Another example of aspect fit      Aspect fit with top alignment      Aspect fill      Fill      I used upscaling in my examples because it s simpler to demonstrate but solution also works for downscaling as in question   For JPEG compression you should use this    let compressionQuality  CGFloat   0 75    adjust to change JPEG quality if let data   UIImageJPEGRepresentation image  compressionQuality                 You can check out my gist with Xcode playground

User · Answer

The above methods work well for small images  but when you try to resize a very large image  you will quickly run out of memory and crash the app  A much better way is to use CGImageSourceCreateThumbnailAtIndexto resize the image without completely decoding it first    If you have the path to the image you want to resize  you can use this    -  void resizeImageAtPath  NSString   imagePath          Create the image source  from path      CGImageSourceRef src   CGImageSourceCreateWithURL    bridge CFURLRef   NSURL fileURLWithPath imagePath   NULL           To create image source from UIImage  use this        NSData  pngData    UIImagePNGRepresentation image          CGImageSourceRef src   CGImageSourceCreateWithData  CFDataRef pngData  NULL           Create thumbnail options     CFDictionaryRef options      bridge CFDictionaryRef                  id  kCGImageSourceCreateThumbnailWithTransform    YES               id  kCGImageSourceCreateThumbnailFromImageAlways    YES               id  kCGImageSourceThumbnailMaxPixelSize     640                Generate the thumbnail     CGImageRef thumbnail   CGImageSourceCreateThumbnailAtIndex src  0  options        CFRelease src          Write the thumbnail at path     CGImageWriteToFile thumbnail  imagePath       More details here

User · Answer

The easiest and most straightforward way to resize your images would be this  float actualHeight   image size height  float actualWidth   image size width  float imgRatio   actualWidth actualHeight  float maxRatio   320 0 480 0   if imgRatio  maxRatio       if imgRatio  lt  maxRatio           imgRatio   480 0   actualHeight          actualWidth   imgRatio   actualWidth          actualHeight   480 0            else          imgRatio   320 0   actualWidth          actualHeight   imgRatio   actualHeight          actualWidth   320 0          CGRect rect   CGRectMake 0 0  0 0  actualWidth  actualHeight   UIGraphicsBeginImageContext rect size    image drawInRect rect   UIImage  img   UIGraphicsGetImageFromCurrentImageContext    UIGraphicsEndImageContext

User · Answer

According to this session  iOS Memory Deep Dive  we had better use ImageIO to downscale images    The bad of using UIImage downscale images     Will decompress original image into memory Internal coordinate space transforms are expensive   Use ImageIO   ImageIO can read image sizes and metadata information without dirtying memory  ImageIO can resize images at cost of resized image only    About Image in memory    Memory use is related to the dimensions of the images  not the file size  UIGraphicsBeginImageContextWithOptions always uses SRGB rendering-format  which use 4 bytes per pixel  A image have load - gt  decode - gt  render 3 phases  UIImage is expensive for sizing and to resizing   For the following image  if you use UIGraphicsBeginImageContextWithOptions we only need 590KB to load a image  while we need 2048 pixels x 1536 pixels x 4 bytes per pixel   10MB when decoding     while UIGraphicsImageRenderer  introduced in iOS 10  will automatically pick the best graphic format in iOS12  It means  you may save 75  of memory by replacing UIGraphicsBeginImageContextWithOptions with UIGraphicsImageRenderer if you don t need SRGB   This is my article about iOS images in memory  func resize url  NSURL  maxPixelSize  Int  - gt  CGImage        let imgSource   CGImageSourceCreateWithURL url  nil      guard let imageSource   imgSource else           return nil            var scaledImage  CGImage      let options   NSString  Any                     The maximum width and height in pixels of a thumbnail              kCGImageSourceThumbnailMaxPixelSize  maxPixelSize              kCGImageSourceCreateThumbnailFromImageAlways  true                 Should include kCGImageSourceCreateThumbnailWithTransform  true in the options dictionary  Otherwise  the image result will appear rotated when an image is taken from camera in the portrait orientation              kCGImageSourceCreateThumbnailWithTransform  true           scaledImage   CGImageSourceCreateThumbnailAtIndex imageSource  0  options as CFDictionary       return scaledImage     let filePath   Bundle main path forResource  large leaves 70mp   ofType   jpg    let url   NSURL fileURLWithPath  filePath         let image   resize url  url  maxPixelSize  600     or      Downsampling large images for display at smaller size func downsample imageAt imageURL  URL  to pointSize  CGSize  scale  CGFloat  - gt  UIImage       let imageSourceOptions    kCGImageSourceShouldCache  false  as CFDictionary     let imageSource   CGImageSourceCreateWithURL imageURL as CFURL  imageSourceOptions       let maxDimensionInPixels   max pointSize width  pointSize height    scale     let downsampleOptions            kCGImageSourceCreateThumbnailFromImageAlways  true          kCGImageSourceShouldCacheImmediately  true             Should include kCGImageSourceCreateThumbnailWithTransform  true in the options dictionary  Otherwise  the image result will appear rotated when an image is taken from camera in the portrait orientation          kCGImageSourceCreateThumbnailWithTransform  true          kCGImageSourceThumbnailMaxPixelSize  maxDimensionInPixels  as CFDictionary     let downsampledImage           CGImageSourceCreateThumbnailAtIndex imageSource  0  downsampleOptions       return UIImage cgImage  downsampledImage

User · Answer

To resize an image I have better  graphical  results by using this function in stead of DrawInRect   -  UIImage   reduceImageSize  UIImage   pImage newwidth  float  pWidth       float lScale   pWidth   pImage size width      CGImageRef cgImage   pImage CGImage      UIImage    lResult    UIImage imageWithCGImage cgImage scale lScale                             orientation UIImageOrientationRight       return lResult      Aspect ratio is taken care for automatically

User · Answer

Adding to the slew of answers here  but I have gone for a solution which resizes by file size  rather than dimensions    This will both reduce the dimensions and quality of the image until it reaches your given size   func compressTo toSizeInMB size  Double  - gt  UIImage        let bytes   size   1024   1024     let sizeInBytes   Int bytes      var needCompress Bool   true     var imgData Data      var compressingValue CGFloat   1 0      while  needCompress             if let resizedImage   scaleImage byMultiplicationFactorOf  compressingValue   let data  Data   UIImageJPEGRepresentation resizedImage  compressingValue                 if data count  lt  sizeInBytes    compressingValue  lt  0 1                   needCompress   false                 imgData   data               else                   compressingValue -  0 1                                    if let data   imgData           print  Finished with compression value of    compressingValue            return UIImage data  data            return nil    private func scaleImage byMultiplicationFactorOf factor  CGFloat  - gt  UIImage        let size   CGSize width  self size width factor  height  self size height factor      UIGraphicsBeginImageContext size      draw in  CGRect x  0  y  0  width  size width  height  size height       if let newImage  UIImage   UIGraphicsGetImageFromCurrentImageContext             UIGraphicsEndImageContext           return newImage            return nil     Credit for scaling by size answer

User · Answer

If you image is in document directory  Add this URL extension   extension URL       func compressedImageURL quality  CGFloat   0 3  throws - gt  URL            let imageData   try Data contentsOf  self          debugPrint  Image file size before compression    imageData count  bytes            let compressedURL   NSURL fileURL withPath  NSTemporaryDirectory     NSUUID   uuidString     jpg            guard let actualImage   UIImage data  imageData  else   return nil           guard let compressedImageData   UIImageJPEGRepresentation actualImage  quality  else               return nil                   debugPrint  Image file size after compression    compressedImageData count  bytes            do               try compressedImageData write to  compressedURL              return compressedURL           catch               return nil                     Usage   guard let localImageURL   URL string    lt  LocalImagePath jpg  gt    else       return      Here you will get URL of compressed image guard let compressedImageURL   try localImageURL compressedImageURL   else       return    debugPrint  compressedImageURL    compressedImageURL absoluteString      Note - Change  lt  LocalImagePath jpg   with your local jpg image path

User · Answer

Swift Version  func resizeImage image  UIImage  newWidth  CGFloat  - gt  UIImage         let scale   newWidth   image size width     let newHeight   CGFloat 200 0      UIGraphicsBeginImageContext CGSize width  newWidth  height  newHeight       image draw in  CGRect x  0  y  0  width  newWidth  height  newHeight        let newImage   UIGraphicsGetImageFromCurrentImageContext       UIGraphicsEndImageContext        return newImage

User · Answer

A problem that might occur on retina displays is that the scale of the image is set by ImageCapture or so  The resize functions above will not change that  In these cases the resize will work not properly   In the code below  the scale is set to 1  not scaled  and the returned image has the size that you would expect  This is done in the UIGraphicsBeginImageContextWithOptions call   - UIImage   resizeImage   UIImage   theImage   CGSize theNewSize       UIGraphicsBeginImageContextWithOptions theNewSize  NO  1 0        theImage drawInRect CGRectMake 0  0  theNewSize width  theNewSize height        UIImage  newImage   UIGraphicsGetImageFromCurrentImageContext        UIGraphicsEndImageContext        return newImage

User · Answer

If anyone still looking for better option  - UIImage   scaleImage  UIImage   image toSize  CGSize targetSize         UIImage  sourceImage   image      UIImage  newImage   nil       CGSize imageSize   sourceImage size      CGFloat width   imageSize width      CGFloat height   imageSize height       CGFloat targetWidth   targetSize width      CGFloat targetHeight   targetSize height       CGFloat scaleFactor   0 0      CGFloat scaledWidth   targetWidth      CGFloat scaledHeight   targetHeight       CGPoint thumbnailPoint   CGPointMake 0 0 0 0        if  CGSizeEqualToSize imageSize  targetSize     NO             CGFloat widthFactor   targetWidth   width          CGFloat heightFactor   targetHeight   height           if  widthFactor  lt  heightFactor              scaleFactor   widthFactor          else             scaleFactor   heightFactor           scaledWidth    width   scaleFactor          scaledHeight   height   scaleFactor              center the image           if  widthFactor  lt  heightFactor                thumbnailPoint y    targetHeight - scaledHeight    0 5            else if  widthFactor  gt  heightFactor                thumbnailPoint x    targetWidth - scaledWidth    0 5                           this is actually the interesting part       UIGraphicsBeginImageContext targetSize        CGRect thumbnailRect   CGRectZero      thumbnailRect origin   thumbnailPoint      thumbnailRect size width    scaledWidth      thumbnailRect size height   scaledHeight        sourceImage drawInRect thumbnailRect        newImage   UIGraphicsGetImageFromCurrentImageContext        UIGraphicsEndImageContext         if newImage    nil  NSLog   could not scale image          return newImage

User · Answer

-  UIImage   resizeImage  UIImage  image newSize  CGSize newSize       CGRect newRect   CGRectIntegral CGRectMake 0  0  newSize width  newSize height        CGImageRef imageRef   image CGImage       UIGraphicsBeginImageContextWithOptions newSize  NO  0       CGContextRef context   UIGraphicsGetCurrentContext         CGContextSetInterpolationQuality context  kCGInterpolationHigh       CGAffineTransform flipVertical   CGAffineTransformMake 1  0  0  -1  0  newSize height        CGContextConcatCTM context  flipVertical       CGContextDrawImage context  newRect  imageRef        CGImageRef newImageRef   CGBitmapContextCreateImage context       UIImage  newImage    UIImage imageWithCGImage newImageRef        CGImageRelease newImageRef       UIGraphicsEndImageContext         return newImage

User · Answer

A couple of suggestions are provided as answers to this question   I had suggested the technique described in this post  with the relevant code      UIImage  imageWithImage  UIImage  image                 scaledToSize  CGSize newSize       UIGraphicsBeginImageContext  newSize        image drawInRect CGRectMake 0 0 newSize width newSize height       UIImage  newImage   UIGraphicsGetImageFromCurrentImageContext       UIGraphicsEndImageContext        return newImage      As far as storage of the image  the fastest image format to use with the iPhone is PNG  because it has optimizations for that format   However  if you want to store these images as JPEGs  you can take your UIImage and do the following   NSData  dataForJPEGFile   UIImageJPEGRepresentation theImage  0 6     This creates an NSData instance containing the raw bytes for a JPEG image at a 60  quality setting   The contents of that NSData instance can then be written to disk or cached in memory

User · Answer

For Swift 3  the below code scales the image keeping the aspect ratio  You can read more about the ImageContext in Apple s documentation   extension UIImage       class func resizeImage image  UIImage  newHeight  CGFloat  - gt  UIImage           let scale   newHeight   image size height         let newWidth   image size width   scale         UIGraphicsBeginImageContext CGSize width  newWidth  height  newHeight           image draw in  CGRect x  0  y  0  width  newWidth  height  newHeight           let newImage   UIGraphicsGetImageFromCurrentImageContext           UIGraphicsEndImageContext           return newImage            To use it  call resizeImage   method   UIImage resizeImage image  yourImageName  newHeight  yourImageNewHeight

User · Answer

I ended up using Brads technique to create a scaleToFitWidth method in UIImage Extensions if that s useful to anyone     - UIImage   scaleToFitWidth  CGFloat width       CGFloat ratio   width   self size width      CGFloat height   self size height   ratio       NSLog   W  f H  f  width height        UIGraphicsBeginImageContext CGSizeMake width  height         self drawInRect CGRectMake 0 0f 0 0f width height        UIImage  newImage   UIGraphicsGetImageFromCurrentImageContext        UIGraphicsEndImageContext         return newImage      then wherever you like   import  UIImage Extensions h   UIImage  newImage    image scaleToFitWidth 100 0f    Also worth noting you could move this further down into a UIView Extensions class if you want to render images from a UIView

User · Answer

If you have control over the server  I would strongly recommend resizing the images server side with ImageMagik  Downloading large images and resizing them on the phone is a waste of many precious resources - bandwidth  battery and memory  All of which are scarce on phones

User · Answer

I just wanted to answer that question for Cocoa Swift programmers  This function returns NSImage with new size  You can use that function like this             let sizeChangedImage   changeImageSize image  ratio  2            changes image size      func changeImageSize  image  NSImage  ratio  CGFloat  - gt  NSImage             getting the current image size     let w   image size width     let h   image size height         calculating new size     let w new   w   ratio      let h new   h   ratio          creating size constant     let newSize   CGSizeMake w new  h new         creating rect     let rect    NSMakeRect 0  0  w new  h new          creating a image context with new size     let newImage   NSImage init size newSize         newImage lockFocus               drawing image with new size in context         image drawInRect rect       newImage unlockFocus         return newImage

[ios] How to easily resize/optimize an image size with iOS?

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