├── demo.playground
    ├── Resources
    │   └── image.jpg
    ├── Contents.swift
    ├── contents.xcplayground
    ├── playground.xcworkspace
    │   ├── contents.xcworkspacedata
    │   └── xcuserdata
    │   │   └── marius.xcuserdatad
    │   │       └── UserInterfaceState.xcuserstate
    ├── timeline.xctimeline
    └── Sources
    │   └── RGBA.swift
└── README.md


/demo.playground/Resources/image.jpg:
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https://raw.githubusercontent.com/mhorga/ImageProcessing/HEAD/demo.playground/Resources/image.jpg


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/README.md:
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1 | # ImageProcessing
2 | 
3 | Repository to accompany the blog post at http://mhorga.org/2015/10/19/image-processing-in-ios-part-3.html
4 | 


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/demo.playground/Contents.swift:
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1 | 
2 | import UIKit
3 | 
4 | let image = UIImage(named: "image.jpg")!
5 | let newImage = contrast(image: image).toUIImage()
6 | image
7 | 
8 | newImage
9 | 


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/demo.playground/contents.xcplayground:
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1 | <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
2 | <playground version='5.0' target-platform='ios'>
3 |     <timeline fileName='timeline.xctimeline'/>
4 | </playground>


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/demo.playground/playground.xcworkspace/contents.xcworkspacedata:
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1 | <?xml version="1.0" encoding="UTF-8"?>
2 | <Workspace
3 |    version = "1.0">
4 |    <FileRef
5 |       location = "self:">
6 |    </FileRef>
7 | </Workspace>
8 | 


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/demo.playground/playground.xcworkspace/xcuserdata/marius.xcuserdatad/UserInterfaceState.xcuserstate:
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https://raw.githubusercontent.com/mhorga/ImageProcessing/HEAD/demo.playground/playground.xcworkspace/xcuserdata/marius.xcuserdatad/UserInterfaceState.xcuserstate


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/demo.playground/timeline.xctimeline:
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 1 | <?xml version="1.0" encoding="UTF-8"?>
 2 | <Timeline
 3 |    version = "3.0">
 4 |    <TimelineItems>
 5 |       <LoggerValueHistoryTimelineItem
 6 |          documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=113&amp;EndingColumnNumber=13&amp;EndingLineNumber=7&amp;StartingColumnNumber=5&amp;StartingLineNumber=7&amp;Timestamp=495797277.68645"
 7 |          selectedRepresentationIndex = "0"
 8 |          shouldTrackSuperviewWidth = "NO">
 9 |       </LoggerValueHistoryTimelineItem>
10 |       <LoggerValueHistoryTimelineItem
11 |          documentLocation = "#CharacterRangeLen=5&amp;CharacterRangeLoc=117&amp;EndingColumnNumber=6&amp;EndingLineNumber=7&amp;StartingColumnNumber=1&amp;StartingLineNumber=7&amp;Timestamp=495797277.686726"
12 |          selectedRepresentationIndex = "0"
13 |          shouldTrackSuperviewWidth = "NO">
14 |       </LoggerValueHistoryTimelineItem>
15 |       <LoggerValueHistoryTimelineItem
16 |          documentLocation = "#CharacterRangeLen=8&amp;CharacterRangeLoc=114&amp;EndingColumnNumber=9&amp;EndingLineNumber=7&amp;StartingColumnNumber=1&amp;StartingLineNumber=7&amp;Timestamp=495797277.686938"
17 |          selectedRepresentationIndex = "0"
18 |          shouldTrackSuperviewWidth = "NO">
19 |       </LoggerValueHistoryTimelineItem>
20 |       <LoggerValueHistoryTimelineItem
21 |          documentLocation = "#CharacterRangeLen=5&amp;CharacterRangeLoc=107&amp;EndingColumnNumber=6&amp;EndingLineNumber=5&amp;StartingColumnNumber=1&amp;StartingLineNumber=5&amp;Timestamp=495797277.687097"
22 |          selectedRepresentationIndex = "0"
23 |          shouldTrackSuperviewWidth = "NO">
24 |       </LoggerValueHistoryTimelineItem>
25 |    </TimelineItems>
26 | </Timeline>
27 | 


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/demo.playground/Sources/RGBA.swift:
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 1 | 
 2 | import UIKit
 3 | 
 4 | struct Pixel {
 5 |     var value: UInt32
 6 |     var red: UInt8 {
 7 |         get { return UInt8(value & 0xFF) }
 8 |         set { value = UInt32(newValue) | (value & 0xFFFFFF00) }
 9 |     }
10 |     var green: UInt8 {
11 |         get { return UInt8((value >> 8) & 0xFF) }
12 |         set { value = (UInt32(newValue) << 8) | (value & 0xFFFF00FF) }
13 |     }
14 |     var blue: UInt8 {
15 |         get { return UInt8((value >> 16) & 0xFF) }
16 |         set { value = (UInt32(newValue) << 16) | (value & 0xFF00FFFF) }
17 |     }
18 |     var alpha: UInt8 {
19 |         get { return UInt8((value >> 24) & 0xFF) }
20 |         set { value = (UInt32(newValue) << 24) | (value & 0x00FFFFFF) }
21 |     }
22 | }
23 | 
24 | public struct RGBA {
25 |     var pixels: UnsafeMutableBufferPointer<Pixel>
26 |     var width: Int
27 |     var height: Int
28 |     
29 |     init?(image: UIImage) {
30 |         guard let cgImage = image.cgImage else { return nil }
31 |         width = Int(image.size.width)
32 |         height = Int(image.size.height)
33 |         let bitsPerComponent = 8
34 |         let bytesPerPixel = 4
35 |         let bytesPerRow = width * bytesPerPixel
36 |         let imageData = UnsafeMutablePointer<Pixel>.allocate(capacity: width * height)
37 |         let colorSpace = CGColorSpaceCreateDeviceRGB()
38 |         var bitmapInfo: UInt32 = CGBitmapInfo.byteOrder32Big.rawValue
39 |         bitmapInfo |= CGImageAlphaInfo.premultipliedLast.rawValue & CGBitmapInfo.alphaInfoMask.rawValue
40 |         guard let imageContext = CGContext(data: imageData, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo) else { return nil }
41 |         imageContext.draw(cgImage, in: CGRect(origin: CGPoint(x: 0,y :0), size: image.size))
42 |         pixels = UnsafeMutableBufferPointer<Pixel>(start: imageData, count: width * height)
43 |     }
44 |     
45 |     public func toUIImage() -> UIImage? {
46 |         let bitsPerComponent = 8
47 |         let bytesPerPixel = 4
48 |         let bytesPerRow = width * bytesPerPixel
49 |         let colorSpace = CGColorSpaceCreateDeviceRGB()
50 |         var bitmapInfo: UInt32 = CGBitmapInfo.byteOrder32Big.rawValue
51 |         bitmapInfo |= CGImageAlphaInfo.premultipliedLast.rawValue & CGBitmapInfo.alphaInfoMask.rawValue
52 |         let imageContext = CGContext(data: pixels.baseAddress, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo, releaseCallback: nil, releaseInfo: nil)
53 |         guard let cgImage = imageContext!.makeImage() else {return nil}
54 |         let image = UIImage(cgImage: cgImage)
55 |         return image
56 |     }
57 | }
58 | 
59 | public func contrast(image: UIImage) -> RGBA {
60 |     let rgba = RGBA(image: image)!
61 |     var totalRed = 0
62 |     var totalGreen = 0
63 |     var totalBlue = 0
64 |     
65 |     for y in 0..<rgba.height {
66 |         for x in 0..<rgba.width {
67 |             let index = y * rgba.width + x
68 |             let pixel = rgba.pixels[index]
69 |             totalRed += Int(pixel.red)
70 |             totalGreen += Int(pixel.green)
71 |             totalBlue += Int(pixel.blue)
72 |         }
73 |     }
74 |     
75 |     let pixelCount = rgba.width * rgba.height
76 |     let avgRed = totalRed / pixelCount
77 |     let avgGreen = totalGreen / pixelCount
78 |     let avgBlue = totalBlue / pixelCount
79 |     
80 |     for y in 0..<rgba.height {
81 |         for x in 0..<rgba.width {
82 |             let index = y * rgba.width + x
83 |             var pixel = rgba.pixels[index]
84 |             let redDelta = Int(pixel.red) - avgRed
85 |             let greenDelta = Int(pixel.green) - avgGreen
86 |             let blueDelta = Int(pixel.blue) - avgBlue
87 |             pixel.red = UInt8(max(min(255, avgRed + 3 * redDelta), 0))
88 |             pixel.green = UInt8(max(min(255, avgGreen + 3 * greenDelta), 0))
89 |             pixel.blue = UInt8(max(min(255, avgBlue + 3 * blueDelta), 0))
90 |             rgba.pixels[index] = pixel
91 |         }
92 |     }
93 |     return rgba
94 | }
95 | 


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