從png文件中讀取（自定義）EXIF數據

Question

對於一個應用程序，我試圖用我公司的所有同事解析一個vcf文件。其中一些人沒有真正的照片，而是自動地插入一張虛擬照片。現在爲了使應用程序具備未來的可用性，我不想檢查現在可以工作的500x500的分辨率。負責生成vcf的部門的想法是爲他們總是使用的虛擬照片庫文件添加評論。我想讀書，在斯威夫特，但沒有運氣，你可以在我的測試操場代碼中看到：

import UIKit 
import ImageIO 

let photo = UIImage(named: "bild")! 
let photoData = UIImagePNGRepresentation(photo)! 
let base64String = photoData.base64EncodedString() 

let photoSource = CGImageSourceCreateWithData(photoData as CFData, nil)! 
for (key, value) in CGImageSourceCopyPropertiesAtIndex(photoSource, 0, nil) as! [String : Any] { 
    print("\(key): \(value)") 
} 

輸出：

PixelWidth: 500 
Depth: 8 
ProfileName: sRGB IEC61966-2.1 
HasAlpha: 1 
ColorModel: RGB 
{PNG}: { 
    Chromaticities =  (
     "0.3127", 
     "0.329", 
     "0.64", 
     "0.33", 
     "0.3", 
     "0.6000000000000001", 
     "0.15", 
     "0.06" 
    ); 
    Gamma = "0.45455"; 
    InterlaceType = 0; 
    sRGBIntent = 0; 
} 
PixelHeight: 500 

的exiftool在終端的輸出同時顯示了這個在同一圖像上（特別參見User Comment和Document Name（自定義字段）：

➔ exiftool bild.png 
ExifTool Version Number   : 10.50 
File Name      : bild.png 
Directory      : . 
File Size      : 4.2 kB 
File Modification Date/Time  : 2017:05:06 12:51:23+02:00 
File Access Date/Time   : 2017:05:06 12:51:24+02:00 
File Inode Change Date/Time  : 2017:05:06 12:51:23+02:00 
File Permissions    : rw-r--r-- 
File Type      : PNG 
File Type Extension    : png 
MIME Type      : image/png 
Image Width      : 500 
Image Height     : 500 
Bit Depth      : 8 
Color Type      : Palette 
Compression      : Deflate/Inflate 
Filter       : Adaptive 
Interlace      : Noninterlaced 
Palette       : (Binary data 477 bytes, use -b option to extract) 
Transparency     : 0 
Background Color    : 0 
Pixels Per Unit X    : 2835 
Pixels Per Unit Y    : 2835 
Pixel Units      : meters 
Modify Date      : 2017:05:05 08:04:36 
Exif Byte Order     : Big-endian (Motorola, MM) 
Document Name     : dummy 
X Resolution     : 72 
Y Resolution     : 72 
Resolution Unit     : inches 
Y Cb Cr Positioning    : Centered 
Exif Version     : 0231 
Components Configuration  : Y, Cb, Cr, - 
User Comment     : dummy 
Flashpix Version    : 0100 
Color Space      : Uncalibrated 
Image Size      : 500x500 
Megapixels      : 0.250 

我已經嘗試過通過使用kCGImagePropertyExifU訪問用戶評論serComment，但它返回零，我想這將只返回一定的價值，如果上面的代碼也和預期一樣：

let userComment = dict[kCGImagePropertyExifUserComment as String] // User Comment is set --> but this returns nil 
let pixelWidth = dict[kCGImagePropertyPixelWidth as String] // As a reference that this does normally work --> shows 500 as expected 

你有什麼建議，如何添加評論是可讀與圖像SWIFT代碼？

Answer 1

下面是一個完整的示例，展示瞭如何創建一個圖像，將其保存爲帶有元數據的PNG，然後從該文件中檢索該元數據。您應該可以將其粘貼到iOS Playground中。

//: Playground - noun: a place where people can play 

import UIKit 
import ImageIO 
import MobileCoreServices 

var str = "Hello, playground" 

if let image = createImage() { 
    let pngDictionary : NSDictionary =  [ 
     kCGImagePropertyPNGTitle : "Smile for the Camera", 
     kCGImagePropertyPNGAuthor : "Smiles-R-Us", 
     kCGImagePropertyPNGCopyright : "©2017 Smiles-R-Us", 
     kCGImagePropertyPNGCreationTime : String(describing: Date()), 
     kCGImagePropertyPNGDescription : "Have a Nice Day!" 
    ] 

    let imageMetadata : NSDictionary = [ kCGImagePropertyPNGDictionary : pngDictionary ] 

    let tempURL = FileManager.default.temporaryDirectory 
    let filePath = tempURL.appendingPathComponent("Smile.png") as NSURL 

    let imageDestination = CGImageDestinationCreateWithURL(filePath, kUTTypePNG, 1, nil) 
    if let destination = imageDestination { 
     CGImageDestinationAddImage(destination, image.cgImage!, imageMetadata) 
     CGImageDestinationFinalize(destination) 
    } 

    if let imageSource = CGImageSourceCreateWithURL(filePath, nil) { 
    print (CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil)) 
    } 

    print(filePath) 
} 

func createImage() -> UIImage? { 
    let bounds = CGRect(x: 0, y: 0, width: 200, height: 200) 
    UIGraphicsBeginImageContext(bounds.size) 
    if let cgContext = UIGraphicsGetCurrentContext() { 
     let inset = bounds.insetBy(dx: 20, dy: 20) 

     cgContext.clear(bounds) 
     cgContext.saveGState() 
     cgContext.setStrokeColor(UIColor.black.cgColor) 
     cgContext.setFillColor(UIColor.black.cgColor) 
     cgContext.setLineWidth(2.0) 
     cgContext.strokeEllipse(in: inset) 
     let eyeLevel = inset.maxY - (inset.height * 0.618) 
     cgContext.fillEllipse(in: CGRect(x: inset.minX + inset.width * 0.3, 
             y: eyeLevel, width: 10, height: 10)) 
     cgContext.fillEllipse(in: CGRect(x: inset.minX + inset.width * 0.6, 
             y: eyeLevel, width: 10, height: 10)) 
     cgContext.addArc(center: CGPoint(x:inset.midX, y:inset.midY), radius: (inset.width/2.0 - 20), startAngle: 2.61, endAngle: 0.52, clockwise: true) 
     cgContext.strokePath() 
    } 
    let image = UIGraphicsGetImageFromCurrentImageContext() 
    UIGraphicsEndImageContext() 

    return image 
}