Read (custom) EXIF data from png file - ios

Question

For an app I'm trying to parse a vcf-File with all of the colleagues of my firm. Some of them have no real photo and instead automatically get a dummy photo inserted. Now in order to make the app future proof, I don't want to check for a resolution of 500x500 which right now would work. The idea by the department responsible for the vcf generation was to add a comment to the dummy photo base file they always use. I tried reading that in Swift, but have no luck as you can see in my test playground code:
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)")
}
Output:
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
The output of exiftool in Terminal meanwhile shows this on the same image (see especially User Comment and Document Name (Custom Field):
➔ 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
I already tried accessing the User Comment by using kCGImagePropertyExifUserComment, but this returns nil and I guess it would only return some value, if the above code also worked as expected:
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
Do you have any suggestions how to add a comment to the image that is readable with Swift code?

Answer 1

Here is a complete example showing how to create an image, save it as a PNG with metadata, then retrieve that metadata from the file. You should be able to paste this into an iOS Playground.
//: 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
}