How to get pixel data from a UIImage Cocoa Touch or CGImage Core Graphics

Question

I have a UIImage  Cocoa Touch   From that  I m happy to get a CGImage or anything else you d like that s available  I d like to write this function   -  int getRGBAFromImage  UIImage   image atX  int xx andY  int yy                   What do I want to read about to help      me fill in this bit  here                int result    red  lt  lt  24     green  lt  lt  16     blue  lt  lt  8    alpha    return result

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Couldn t believe that there is not one single correct answer here  No need to allocate pointers  and the unmultiplied values still need to be normalized  To cut to the chase  here is the correct version for Swift 4  For UIImage just use  cgImage   extension CGImage       func colors at   CGPoint   - gt   UIColor             let colorSpace   CGColorSpaceCreateDeviceRGB           let bytesPerPixel   4         let bytesPerRow   bytesPerPixel   width         let bitsPerComponent   8         let bitmapInfo  UInt32   CGImageAlphaInfo premultipliedLast rawValue   CGBitmapInfo byteOrder32Big rawValue          guard let context   CGContext data  nil  width  width  height  height  bitsPerComponent  bitsPerComponent  bytesPerRow  bytesPerRow  space  colorSpace  bitmapInfo  bitmapInfo               let ptr   context data  assumingMemoryBound to  UInt8 self  else               return nil                    context draw self  in  CGRect x  0  y  0  width  width  height  height            return at map   p in             let i   bytesPerRow   Int p y    bytesPerPixel   Int p x               let a   CGFloat ptr i   3     255 0             let r    CGFloat ptr i     a    255 0             let g    CGFloat ptr i   1     a    255 0             let b    CGFloat ptr i   2     a    255 0              return UIColor red  r  green  g  blue  b  alpha  a                      The reason you have to draw convert the image first into a buffer is because images can have several different formats  This step is required to convert it to a consistent format you can read

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One way of doing it is to draw the image to a bitmap context that is backed by a given buffer for a given colorspace  in this case it is RGB    note that this will copy the image data to that buffer  so you do want to cache it instead of doing this operation every time you need to get pixel values   See below as a sample      First get the image into your data buffer CGImageRef image    myUIImage CGImage   NSUInteger width   CGImageGetWidth image   NSUInteger height   CGImageGetHeight image   CGColorSpaceRef colorSpace   CGColorSpaceCreateDeviceRGB    unsigned char  rawData   malloc height   width   4   NSUInteger bytesPerPixel   4  NSUInteger bytesPerRow   bytesPerPixel   width  NSUInteger bitsPerComponent   8  CGContextRef context   CGBitmapContextCreate rawData  width  height  bitsPerComponent  bytesPerRow  colorSpace  kCGImageAlphaPremultipliedLast   kCGBitmapByteOrder32Big   CGColorSpaceRelease colorSpace    CGContextDrawImage context  CGRectMake 0  0  width  height    CGContextRelease context       Now your rawData contains the image data in the RGBA8888 pixel format  int byteIndex    bytesPerRow   yy    xx   bytesPerPixel  red   rawData byteIndex   green   rawData byteIndex   1   blue   rawData byteIndex   2   alpha   rawData byteIndex   3

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UIImage is a wrapper the bytes are CGImage or CIImage  According the the Apple Reference on UIImage the object is immutable and you have no access to the backing bytes  While it is true that you can access the CGImage data if you populated the UIImage with a CGImage  explicitly or implicitly   it will return NULL if the UIImage is backed by a CIImage and vice-versa      Image objects not provide direct access to their underlying image   data  However  you can retrieve the image data in other formats for   use in your app  Specifically  you can use the cgImage and ciImage   properties to retrieve versions of the image that are compatible with   Core Graphics and Core Image  respectively  You can also use the   UIImagePNGRepresentation    and UIImageJPEGRepresentation        functions to generate an NSData object containing the image data in   either the PNG or JPEG format    Common tricks to getting around this issue  As stated your options are   UIImagePNGRepresentation or JPEG Determine if image has CGImage or CIImage backing data and get it there   Neither of these are particularly good tricks if you want output that isn t ARGB  PNG  or JPEG data and the data isn t already backed by CIImage   My recommendation  try CIImage  While developing your project it might make more sense for you to avoid UIImage altogether and pick something else  UIImage  as a Obj-C image wrapper  is often backed by CGImage to the point where we take it for granted  CIImage tends to be a better wrapper format in that you can use a CIContext to get out the format you desire without needing to know how it was created  In your case  getting the bitmap would be a matter of calling   - render toBitmap rowBytes bounds format colorSpace   As an added bonus you can start doing nice manipulations to the image by chaining filters onto the image  This solves a lot of the issues where the image is upside down or needs to be rotated scaled etc

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FYI  I combined Keremk s answer with my original outline  cleaned-up the typos  generalized it to return an array of colors and got the whole thing to compile   Here is the result      NSArray  getRGBAsFromImage  UIImage  image atX  int x andY  int y count  int count       NSMutableArray  result    NSMutableArray arrayWithCapacity count           First get the image into your data buffer     CGImageRef imageRef    image CGImage       NSUInteger width   CGImageGetWidth imageRef       NSUInteger height   CGImageGetHeight imageRef       CGColorSpaceRef colorSpace   CGColorSpaceCreateDeviceRGB        unsigned char  rawData    unsigned char   calloc height   width   4  sizeof unsigned char        NSUInteger bytesPerPixel   4      NSUInteger bytesPerRow   bytesPerPixel   width      NSUInteger bitsPerComponent   8      CGContextRef context   CGBitmapContextCreate rawData  width  height                      bitsPerComponent  bytesPerRow  colorSpace                      kCGImageAlphaPremultipliedLast   kCGBitmapByteOrder32Big       CGColorSpaceRelease colorSpace        CGContextDrawImage context  CGRectMake 0  0  width  height   imageRef       CGContextRelease context           Now your rawData contains the image data in the RGBA8888 pixel format      NSUInteger byteIndex    bytesPerRow   y    x   bytesPerPixel      for  int i   0   i  lt  count     i                CGFloat alpha     CGFloat  rawData byteIndex   3      255 0f          CGFloat red       CGFloat  rawData byteIndex          alpha          CGFloat green     CGFloat  rawData byteIndex   1      alpha          CGFloat blue      CGFloat  rawData byteIndex   2      alpha          byteIndex    bytesPerPixel           UIColor  acolor    UIColor colorWithRed red green green blue blue alpha alpha            result addObject acolor            free rawData      return result

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One way of doing it is to draw the image to a bitmap context that is backed by a given buffer for a given colorspace  in this case it is RGB    note that this will copy the image data to that buffer  so you do want to cache it instead of doing this operation every time you need to get pixel values   See below as a sample      First get the image into your data buffer CGImageRef image    myUIImage CGImage   NSUInteger width   CGImageGetWidth image   NSUInteger height   CGImageGetHeight image   CGColorSpaceRef colorSpace   CGColorSpaceCreateDeviceRGB    unsigned char  rawData   malloc height   width   4   NSUInteger bytesPerPixel   4  NSUInteger bytesPerRow   bytesPerPixel   width  NSUInteger bitsPerComponent   8  CGContextRef context   CGBitmapContextCreate rawData  width  height  bitsPerComponent  bytesPerRow  colorSpace  kCGImageAlphaPremultipliedLast   kCGBitmapByteOrder32Big   CGColorSpaceRelease colorSpace    CGContextDrawImage context  CGRectMake 0  0  width  height    CGContextRelease context       Now your rawData contains the image data in the RGBA8888 pixel format  int byteIndex    bytesPerRow   yy    xx   bytesPerPixel  red   rawData byteIndex   green   rawData byteIndex   1   blue   rawData byteIndex   2   alpha   rawData byteIndex   3

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Swift 5 version  The answers given here are either outdated or incorrect because they don t take into account the following    The pixel size of the image can differ from its point size that is returned by image size width image size height  There can be various layouts used by pixel components in the image  such as BGRA  ABGR  ARGB etc  or may not have an alpha component at all  such as BGR and RGB  For example  UIView drawHierarchy in afterScreenUpdates   method can produce BGRA images  Color components can be premultiplied by the alpha for all pixels in the image and need to be divided by alpha in order to restore the original color  For memory optimization used by CGImage  the size of a pixel row in bytes can be greater than the mere multiplication of the pixel width by 4    The code below is to provide a universal Swift 5 solution to get the UIColor of a pixel for all such special cases  The code is optimized for usability and clarity  not for performance   public extension UIImage        var pixelWidth  Int           return cgImage  width    0            var pixelHeight  Int           return cgImage  height    0            func pixelColor x  Int  y  Int  - gt  UIColor           assert              0   lt pixelWidth    x  amp  amp  0   lt pixelHeight    y               Pixel coordinates are out of bounds            guard             let cgImage   cgImage              let data   cgImage dataProvider  data              let dataPtr   CFDataGetBytePtr data               let colorSpaceModel   cgImage colorSpace  model              let componentLayout   cgImage bitmapInfo componentLayout         else               assertionFailure  Could not get a pixel of an image               return  clear                    assert              colorSpaceModel     rgb               The only supported color space model is RGB           assert              cgImage bitsPerPixel    32    cgImage bitsPerPixel    24               A pixel is expected to be either 4 or 3 bytes in size            let bytesPerRow   cgImage bytesPerRow         let bytesPerPixel   cgImage bitsPerPixel 8         let pixelOffset   y bytesPerRow   x bytesPerPixel          if componentLayout count    4               let components                     dataPtr pixelOffset   0                   dataPtr pixelOffset   1                   dataPtr pixelOffset   2                   dataPtr pixelOffset   3                             var alpha  UInt8   0             var red  UInt8   0             var green  UInt8   0             var blue  UInt8   0              switch componentLayout               case  bgra                  alpha   components 3                 red   components 2                 green   components 1                 blue   components 0             case  abgr                  alpha   components 0                 red   components 3                 green   components 2                 blue   components 1             case  argb                  alpha   components 0                 red   components 1                 green   components 2                 blue   components 3             case  rgba                  alpha   components 3                 red   components 0                 green   components 1                 blue   components 2             default                  return  clear                               If chroma components are premultiplied by alpha and the alpha is  0                  keep the chroma components to their current values              if cgImage bitmapInfo chromaIsPremultipliedByAlpha  amp  amp  alpha    0                   let invUnitAlpha   255 CGFloat alpha                  red   UInt8  CGFloat red  invUnitAlpha  rounded                    green   UInt8  CGFloat green  invUnitAlpha  rounded                    blue   UInt8  CGFloat blue  invUnitAlpha  rounded                               return  init red  red  green  green  blue  blue  alpha  alpha             else if componentLayout count    3               let components                     dataPtr pixelOffset   0                   dataPtr pixelOffset   1                   dataPtr pixelOffset   2                             var red  UInt8   0             var green  UInt8   0             var blue  UInt8   0              switch componentLayout               case  bgr                  red   components 2                 green   components 1                 blue   components 0             case  rgb                  red   components 0                 green   components 1                 blue   components 2             default                  return  clear                            return  init red  red  green  green  blue  blue  alpha  UInt8 255              else               assertionFailure  Unsupported number of pixel components               return  clear                     public extension UIColor        convenience init red  UInt8  green  UInt8  blue  UInt8  alpha  UInt8            self init              red  CGFloat red  255              green  CGFloat green  255              blue  CGFloat blue  255              alpha  CGFloat alpha  255            public extension CGBitmapInfo        enum ComponentLayout            case bgra         case abgr         case argb         case rgba         case bgr         case rgb          var count  Int               switch self               case  bgr   rgb  return 3             default  return 4                                     var componentLayout  ComponentLayout            guard let alphaInfo   CGImageAlphaInfo rawValue  rawValue  amp  Self alphaInfoMask rawValue  else   return nil           let isLittleEndian   contains  byteOrder32Little           if alphaInfo     none               return isLittleEndian    bgr    rgb                   let alphaIsFirst   alphaInfo     premultipliedFirst    alphaInfo     first    alphaInfo     noneSkipFirst          if isLittleEndian               return alphaIsFirst    bgra    abgr           else               return alphaIsFirst    argb    rgba                      var chromaIsPremultipliedByAlpha  Bool           let alphaInfo   CGImageAlphaInfo rawValue  rawValue  amp  Self alphaInfoMask rawValue          return alphaInfo     premultipliedFirst    alphaInfo     premultipliedLast

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To access the raw RGB values of an UIImage in Swift 5 use the underlying CGImage and its dataProvider   import UIKit  let image   UIImage named   example png     guard let cgImage   image cgImage      let data   cgImage dataProvider  data      let bytes   CFDataGetBytePtr data  else       fatalError  Couldn t access image data     assert cgImage colorSpace  model     rgb   let bytesPerPixel   cgImage bitsPerPixel   cgImage bitsPerComponent for y in 0    lt  cgImage height       for x in 0    lt  cgImage width           let offset    y   cgImage bytesPerRow     x   bytesPerPixel          let components    r  bytes offset   g  bytes offset   1   b  bytes offset   2           print   x   x   y   y     components              print  ---       https   www ralfebert de ios examples image-processing uiimage-raw-pixels

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Based on different answers but mainly on this  this works for what I need   UIImage  image1           The image from where you want a pixel data int pixelX           The X coordinate of the pixel you want to retrieve int pixelY           The Y coordinate of the pixel you want to retrieve  uint32 t pixel1     Where the pixel data is to be stored CGContextRef context1   CGBitmapContextCreate  amp pixel1  1  1  8  4  CGColorSpaceCreateDeviceRGB    kCGImageAlphaNoneSkipFirst   CGContextDrawImage context1  CGRectMake -pixelX  -pixelY  CGImageGetWidth image1 CGImage   CGImageGetHeight image1 CGImage    image1 CGImage   CGContextRelease context1     As a result of this lines  you will have a pixel in AARRGGBB format with alpha always set to FF in the 4 byte unsigned integer pixel1

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Apple s Technical Q amp A QA1509 shows the following simple approach    CFDataRef CopyImagePixels CGImageRef inImage        return CGDataProviderCopyData CGImageGetDataProvider inImage        Use CFDataGetBytePtr to get to the actual bytes  and various CGImageGet  methods to understand how to interpret them

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Based on different answers but mainly on this  this works for what I need   UIImage  image1           The image from where you want a pixel data int pixelX           The X coordinate of the pixel you want to retrieve int pixelY           The Y coordinate of the pixel you want to retrieve  uint32 t pixel1     Where the pixel data is to be stored CGContextRef context1   CGBitmapContextCreate  amp pixel1  1  1  8  4  CGColorSpaceCreateDeviceRGB    kCGImageAlphaNoneSkipFirst   CGContextDrawImage context1  CGRectMake -pixelX  -pixelY  CGImageGetWidth image1 CGImage   CGImageGetHeight image1 CGImage    image1 CGImage   CGContextRelease context1     As a result of this lines  you will have a pixel in AARRGGBB format with alpha always set to FF in the 4 byte unsigned integer pixel1

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Building on Olie and Algal s answer  here is an updated answer for Swift 3   public func getRGBAs fromImage image  UIImage  x  Int  y  Int  count  Int  - gt   UIColor     var result    UIColor        First get the image into your data buffer guard let cgImage   image cgImage else       print  CGContext creation failed       return       let width   cgImage width let height   cgImage height let colorSpace   CGColorSpaceCreateDeviceRGB   let rawdata   calloc height width 4  MemoryLayout lt CUnsignedChar gt  size  let bytesPerPixel   4 let bytesPerRow   bytesPerPixel   width let bitsPerComponent   8 let bitmapInfo  UInt32   CGImageAlphaInfo premultipliedLast rawValue   CGBitmapInfo byteOrder32Big rawValue  guard let context   CGContext data  rawdata  width  width  height  height  bitsPerComponent  bitsPerComponent  bytesPerRow  bytesPerRow  space  colorSpace  bitmapInfo  bitmapInfo  else       print  CGContext creation failed       return result    context draw cgImage  in  CGRect x  0  y  0  width  width  height  height       Now your rawData contains the image data in the RGBA8888 pixel format  var byteIndex   bytesPerRow   y   bytesPerPixel   x  for   in 0   lt count       let alpha   CGFloat rawdata  load fromByteOffset  byteIndex   3  as  UInt8 self     255 0     let red   CGFloat rawdata  load fromByteOffset  byteIndex  as  UInt8 self     alpha     let green   CGFloat rawdata  load fromByteOffset  byteIndex   1  as  UInt8 self     alpha     let blue   CGFloat rawdata  load fromByteOffset  byteIndex   2  as  UInt8 self     alpha     byteIndex    bytesPerPixel      let aColor   UIColor red  red  green  green  blue  blue  alpha  alpha      result append aColor     free rawdata   return result     swift

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Couldn t believe that there is not one single correct answer here  No need to allocate pointers  and the unmultiplied values still need to be normalized  To cut to the chase  here is the correct version for Swift 4  For UIImage just use  cgImage   extension CGImage       func colors at   CGPoint   - gt   UIColor             let colorSpace   CGColorSpaceCreateDeviceRGB           let bytesPerPixel   4         let bytesPerRow   bytesPerPixel   width         let bitsPerComponent   8         let bitmapInfo  UInt32   CGImageAlphaInfo premultipliedLast rawValue   CGBitmapInfo byteOrder32Big rawValue          guard let context   CGContext data  nil  width  width  height  height  bitsPerComponent  bitsPerComponent  bytesPerRow  bytesPerRow  space  colorSpace  bitmapInfo  bitmapInfo               let ptr   context data  assumingMemoryBound to  UInt8 self  else               return nil                    context draw self  in  CGRect x  0  y  0  width  width  height  height            return at map   p in             let i   bytesPerRow   Int p y    bytesPerPixel   Int p x               let a   CGFloat ptr i   3     255 0             let r    CGFloat ptr i     a    255 0             let g    CGFloat ptr i   1     a    255 0             let b    CGFloat ptr i   2     a    255 0              return UIColor red  r  green  g  blue  b  alpha  a                      The reason you have to draw convert the image first into a buffer is because images can have several different formats  This step is required to convert it to a consistent format you can read

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NSString   path     NSBundle mainBundle  pathForResource   filename  ofType   jpg    UIImage   img     UIImage alloc initWithContentsOfFile path   CGImageRef image    img CGImage   CFDataRef data   CGDataProviderCopyData CGImageGetDataProvider image    const unsigned char   buffer    CFDataGetBytePtr data

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To access the raw RGB values of an UIImage in Swift 5 use the underlying CGImage and its dataProvider   import UIKit  let image   UIImage named   example png     guard let cgImage   image cgImage      let data   cgImage dataProvider  data      let bytes   CFDataGetBytePtr data  else       fatalError  Couldn t access image data     assert cgImage colorSpace  model     rgb   let bytesPerPixel   cgImage bitsPerPixel   cgImage bitsPerComponent for y in 0    lt  cgImage height       for x in 0    lt  cgImage width           let offset    y   cgImage bytesPerRow     x   bytesPerPixel          let components    r  bytes offset   g  bytes offset   1   b  bytes offset   2           print   x   x   y   y     components              print  ---       https   www ralfebert de ios examples image-processing uiimage-raw-pixels

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FYI  I combined Keremk s answer with my original outline  cleaned-up the typos  generalized it to return an array of colors and got the whole thing to compile   Here is the result      NSArray  getRGBAsFromImage  UIImage  image atX  int x andY  int y count  int count       NSMutableArray  result    NSMutableArray arrayWithCapacity count           First get the image into your data buffer     CGImageRef imageRef    image CGImage       NSUInteger width   CGImageGetWidth imageRef       NSUInteger height   CGImageGetHeight imageRef       CGColorSpaceRef colorSpace   CGColorSpaceCreateDeviceRGB        unsigned char  rawData    unsigned char   calloc height   width   4  sizeof unsigned char        NSUInteger bytesPerPixel   4      NSUInteger bytesPerRow   bytesPerPixel   width      NSUInteger bitsPerComponent   8      CGContextRef context   CGBitmapContextCreate rawData  width  height                      bitsPerComponent  bytesPerRow  colorSpace                      kCGImageAlphaPremultipliedLast   kCGBitmapByteOrder32Big       CGColorSpaceRelease colorSpace        CGContextDrawImage context  CGRectMake 0  0  width  height   imageRef       CGContextRelease context           Now your rawData contains the image data in the RGBA8888 pixel format      NSUInteger byteIndex    bytesPerRow   y    x   bytesPerPixel      for  int i   0   i  lt  count     i                CGFloat alpha     CGFloat  rawData byteIndex   3      255 0f          CGFloat red       CGFloat  rawData byteIndex          alpha          CGFloat green     CGFloat  rawData byteIndex   1      alpha          CGFloat blue      CGFloat  rawData byteIndex   2      alpha          byteIndex    bytesPerPixel           UIColor  acolor    UIColor colorWithRed red green green blue blue alpha alpha            result addObject acolor            free rawData      return result

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One way of doing it is to draw the image to a bitmap context that is backed by a given buffer for a given colorspace  in this case it is RGB    note that this will copy the image data to that buffer  so you do want to cache it instead of doing this operation every time you need to get pixel values   See below as a sample      First get the image into your data buffer CGImageRef image    myUIImage CGImage   NSUInteger width   CGImageGetWidth image   NSUInteger height   CGImageGetHeight image   CGColorSpaceRef colorSpace   CGColorSpaceCreateDeviceRGB    unsigned char  rawData   malloc height   width   4   NSUInteger bytesPerPixel   4  NSUInteger bytesPerRow   bytesPerPixel   width  NSUInteger bitsPerComponent   8  CGContextRef context   CGBitmapContextCreate rawData  width  height  bitsPerComponent  bytesPerRow  colorSpace  kCGImageAlphaPremultipliedLast   kCGBitmapByteOrder32Big   CGColorSpaceRelease colorSpace    CGContextDrawImage context  CGRectMake 0  0  width  height    CGContextRelease context       Now your rawData contains the image data in the RGBA8888 pixel format  int byteIndex    bytesPerRow   yy    xx   bytesPerPixel  red   rawData byteIndex   green   rawData byteIndex   1   blue   rawData byteIndex   2   alpha   rawData byteIndex   3

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One way of doing it is to draw the image to a bitmap context that is backed by a given buffer for a given colorspace  in this case it is RGB    note that this will copy the image data to that buffer  so you do want to cache it instead of doing this operation every time you need to get pixel values   See below as a sample      First get the image into your data buffer CGImageRef image    myUIImage CGImage   NSUInteger width   CGImageGetWidth image   NSUInteger height   CGImageGetHeight image   CGColorSpaceRef colorSpace   CGColorSpaceCreateDeviceRGB    unsigned char  rawData   malloc height   width   4   NSUInteger bytesPerPixel   4  NSUInteger bytesPerRow   bytesPerPixel   width  NSUInteger bitsPerComponent   8  CGContextRef context   CGBitmapContextCreate rawData  width  height  bitsPerComponent  bytesPerRow  colorSpace  kCGImageAlphaPremultipliedLast   kCGBitmapByteOrder32Big   CGColorSpaceRelease colorSpace    CGContextDrawImage context  CGRectMake 0  0  width  height    CGContextRelease context       Now your rawData contains the image data in the RGBA8888 pixel format  int byteIndex    bytesPerRow   yy    xx   bytesPerPixel  red   rawData byteIndex   green   rawData byteIndex   1   blue   rawData byteIndex   2   alpha   rawData byteIndex   3

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Building on Olie and Algal s answer  here is an updated answer for Swift 3   public func getRGBAs fromImage image  UIImage  x  Int  y  Int  count  Int  - gt   UIColor     var result    UIColor        First get the image into your data buffer guard let cgImage   image cgImage else       print  CGContext creation failed       return       let width   cgImage width let height   cgImage height let colorSpace   CGColorSpaceCreateDeviceRGB   let rawdata   calloc height width 4  MemoryLayout lt CUnsignedChar gt  size  let bytesPerPixel   4 let bytesPerRow   bytesPerPixel   width let bitsPerComponent   8 let bitmapInfo  UInt32   CGImageAlphaInfo premultipliedLast rawValue   CGBitmapInfo byteOrder32Big rawValue  guard let context   CGContext data  rawdata  width  width  height  height  bitsPerComponent  bitsPerComponent  bytesPerRow  bytesPerRow  space  colorSpace  bitmapInfo  bitmapInfo  else       print  CGContext creation failed       return result    context draw cgImage  in  CGRect x  0  y  0  width  width  height  height       Now your rawData contains the image data in the RGBA8888 pixel format  var byteIndex   bytesPerRow   y   bytesPerPixel   x  for   in 0   lt count       let alpha   CGFloat rawdata  load fromByteOffset  byteIndex   3  as  UInt8 self     255 0     let red   CGFloat rawdata  load fromByteOffset  byteIndex  as  UInt8 self     alpha     let green   CGFloat rawdata  load fromByteOffset  byteIndex   1  as  UInt8 self     alpha     let blue   CGFloat rawdata  load fromByteOffset  byteIndex   2  as  UInt8 self     alpha     byteIndex    bytesPerPixel      let aColor   UIColor red  red  green  green  blue  blue  alpha  alpha      result append aColor     free rawdata   return result     swift

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Apple s Technical Q amp A QA1509 shows the following simple approach    CFDataRef CopyImagePixels CGImageRef inImage        return CGDataProviderCopyData CGImageGetDataProvider inImage        Use CFDataGetBytePtr to get to the actual bytes  and various CGImageGet  methods to understand how to interpret them

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NSString   path     NSBundle mainBundle  pathForResource   filename  ofType   jpg    UIImage   img     UIImage alloc initWithContentsOfFile path   CGImageRef image    img CGImage   CFDataRef data   CGDataProviderCopyData CGImageGetDataProvider image    const unsigned char   buffer    CFDataGetBytePtr data

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Here is a SO thread where  Matt renders only the desired pixel into a 1x1 context by displacing the image so that the desired pixel aligns with the one pixel in the context

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Here is a SO thread where  Matt renders only the desired pixel into a 1x1 context by displacing the image so that the desired pixel aligns with the one pixel in the context

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Swift 5 version  The answers given here are either outdated or incorrect because they don t take into account the following    The pixel size of the image can differ from its point size that is returned by image size width image size height  There can be various layouts used by pixel components in the image  such as BGRA  ABGR  ARGB etc  or may not have an alpha component at all  such as BGR and RGB  For example  UIView drawHierarchy in afterScreenUpdates   method can produce BGRA images  Color components can be premultiplied by the alpha for all pixels in the image and need to be divided by alpha in order to restore the original color  For memory optimization used by CGImage  the size of a pixel row in bytes can be greater than the mere multiplication of the pixel width by 4    The code below is to provide a universal Swift 5 solution to get the UIColor of a pixel for all such special cases  The code is optimized for usability and clarity  not for performance   public extension UIImage        var pixelWidth  Int           return cgImage  width    0            var pixelHeight  Int           return cgImage  height    0            func pixelColor x  Int  y  Int  - gt  UIColor           assert              0   lt pixelWidth    x  amp  amp  0   lt pixelHeight    y               Pixel coordinates are out of bounds            guard             let cgImage   cgImage              let data   cgImage dataProvider  data              let dataPtr   CFDataGetBytePtr data               let colorSpaceModel   cgImage colorSpace  model              let componentLayout   cgImage bitmapInfo componentLayout         else               assertionFailure  Could not get a pixel of an image               return  clear                    assert              colorSpaceModel     rgb               The only supported color space model is RGB           assert              cgImage bitsPerPixel    32    cgImage bitsPerPixel    24               A pixel is expected to be either 4 or 3 bytes in size            let bytesPerRow   cgImage bytesPerRow         let bytesPerPixel   cgImage bitsPerPixel 8         let pixelOffset   y bytesPerRow   x bytesPerPixel          if componentLayout count    4               let components                     dataPtr pixelOffset   0                   dataPtr pixelOffset   1                   dataPtr pixelOffset   2                   dataPtr pixelOffset   3                             var alpha  UInt8   0             var red  UInt8   0             var green  UInt8   0             var blue  UInt8   0              switch componentLayout               case  bgra                  alpha   components 3                 red   components 2                 green   components 1                 blue   components 0             case  abgr                  alpha   components 0                 red   components 3                 green   components 2                 blue   components 1             case  argb                  alpha   components 0                 red   components 1                 green   components 2                 blue   components 3             case  rgba                  alpha   components 3                 red   components 0                 green   components 1                 blue   components 2             default                  return  clear                               If chroma components are premultiplied by alpha and the alpha is  0                  keep the chroma components to their current values              if cgImage bitmapInfo chromaIsPremultipliedByAlpha  amp  amp  alpha    0                   let invUnitAlpha   255 CGFloat alpha                  red   UInt8  CGFloat red  invUnitAlpha  rounded                    green   UInt8  CGFloat green  invUnitAlpha  rounded                    blue   UInt8  CGFloat blue  invUnitAlpha  rounded                               return  init red  red  green  green  blue  blue  alpha  alpha             else if componentLayout count    3               let components                     dataPtr pixelOffset   0                   dataPtr pixelOffset   1                   dataPtr pixelOffset   2                             var red  UInt8   0             var green  UInt8   0             var blue  UInt8   0              switch componentLayout               case  bgr                  red   components 2                 green   components 1                 blue   components 0             case  rgb                  red   components 0                 green   components 1                 blue   components 2             default                  return  clear                            return  init red  red  green  green  blue  blue  alpha  UInt8 255              else               assertionFailure  Unsupported number of pixel components               return  clear                     public extension UIColor        convenience init red  UInt8  green  UInt8  blue  UInt8  alpha  UInt8            self init              red  CGFloat red  255              green  CGFloat green  255              blue  CGFloat blue  255              alpha  CGFloat alpha  255            public extension CGBitmapInfo        enum ComponentLayout            case bgra         case abgr         case argb         case rgba         case bgr         case rgb          var count  Int               switch self               case  bgr   rgb  return 3             default  return 4                                     var componentLayout  ComponentLayout            guard let alphaInfo   CGImageAlphaInfo rawValue  rawValue  amp  Self alphaInfoMask rawValue  else   return nil           let isLittleEndian   contains  byteOrder32Little           if alphaInfo     none               return isLittleEndian    bgr    rgb                   let alphaIsFirst   alphaInfo     premultipliedFirst    alphaInfo     first    alphaInfo     noneSkipFirst          if isLittleEndian               return alphaIsFirst    bgra    abgr           else               return alphaIsFirst    argb    rgba                      var chromaIsPremultipliedByAlpha  Bool           let alphaInfo   CGImageAlphaInfo rawValue  rawValue  amp  Self alphaInfoMask rawValue          return alphaInfo     premultipliedFirst    alphaInfo     premultipliedLast

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UIImage is a wrapper the bytes are CGImage or CIImage  According the the Apple Reference on UIImage the object is immutable and you have no access to the backing bytes  While it is true that you can access the CGImage data if you populated the UIImage with a CGImage  explicitly or implicitly   it will return NULL if the UIImage is backed by a CIImage and vice-versa      Image objects not provide direct access to their underlying image   data  However  you can retrieve the image data in other formats for   use in your app  Specifically  you can use the cgImage and ciImage   properties to retrieve versions of the image that are compatible with   Core Graphics and Core Image  respectively  You can also use the   UIImagePNGRepresentation    and UIImageJPEGRepresentation        functions to generate an NSData object containing the image data in   either the PNG or JPEG format    Common tricks to getting around this issue  As stated your options are   UIImagePNGRepresentation or JPEG Determine if image has CGImage or CIImage backing data and get it there   Neither of these are particularly good tricks if you want output that isn t ARGB  PNG  or JPEG data and the data isn t already backed by CIImage   My recommendation  try CIImage  While developing your project it might make more sense for you to avoid UIImage altogether and pick something else  UIImage  as a Obj-C image wrapper  is often backed by CGImage to the point where we take it for granted  CIImage tends to be a better wrapper format in that you can use a CIContext to get out the format you desire without needing to know how it was created  In your case  getting the bitmap would be a matter of calling   - render toBitmap rowBytes bounds format colorSpace   As an added bonus you can start doing nice manipulations to the image by chaining filters onto the image  This solves a lot of the issues where the image is upside down or needs to be rotated scaled etc

[cocoa] How to get pixel data from a UIImage (Cocoa Touch) or CGImage (Core Graphics)?

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