Get Png Representation of Nsimage in Swift

how to get png representation of an NSImage object in Swift

To help with cross-platform code, I implemented a version ofUIImagePNGRepresentation() that runs on Mac (and uses NSImage):

#if os(macOS)

public func UIImagePNGRepresentation(_ image: NSImage) -> Data? {
    guard let cgImage = image.cgImage(forProposedRect: nil, context: nil, hints: nil)
        else { return nil }
    let imageRep = NSBitmapImageRep(cgImage: cgImage)
    imageRep.size = image.size // display size in points
    return imageRep.representation(using: .png, properties: [:])
}

#endif

get PNG representation of NSImage in swift

The documentation says:

func representationUsingType(_ storageType: NSBitmapImageFileType,
              properties properties: [NSObject : AnyObject]) -> NSData?

So it expects a dictionary, not a nil value. Supply an empty dict like this:

var pngCoverImage = bitmap!.representationUsingType(NSBitmapImageFileType.NSPNGFileType, properties: [:])

Only if an Optional is specified (that is it where [NSObject : AnyObject]?) you could pass a nil value.

How to save PNG file from NSImage (retina issues)

If you have an NSImage and want to save it as an image file to the filesystem, you should never use lockFocus! lockFocus creates a new image which is determined for getting shown an the screen and nothing else. Therefore lockFocus uses the properties of the screen: 72 dpi for normal screens and 144 dpi for retina screens. For what you want I propose the following code:

+ (void)saveImage:(NSImage *)image atPath:(NSString *)path {

   CGImageRef cgRef = [image CGImageForProposedRect:NULL
                                            context:nil
                                              hints:nil];
   NSBitmapImageRep *newRep = [[NSBitmapImageRep alloc] initWithCGImage:cgRef];
   [newRep setSize:[image size]];   // if you want the same resolution
   NSData *pngData = [newRep representationUsingType:NSPNGFileType properties:nil];
   [pngData writeToFile:path atomically:YES];
   [newRep autorelease];
}

NSImage to NSData as PNG Swift

You can use the NSImage property TIFFRepresentation to convert your NSImage to NSData:

let imageData = yourImage.TIFFRepresentation

If you need to save your image data to a PNG file you can use NSBitmapImageRep(data:) and representationUsingType to create an extension to help you convert Data to PNG format:

Update: Xcode 11 • Swift 5.1

extension NSBitmapImageRep {
    var png: Data? { representation(using: .png, properties: [:]) }
}
extension Data {
    var bitmap: NSBitmapImageRep? { NSBitmapImageRep(data: self) }
}
extension NSImage {
    var png: Data? { tiffRepresentation?.bitmap?.png }
}

---

usage

let picture = NSImage(contentsOf: URL(string: "https://i.stack.imgur.com/Xs4RX.jpg")!)!

let imageURL = FileManager.default.urls(for: .desktopDirectory, in: .userDomainMask).first!.appendingPathComponent("image.png")
if let png = picture.png {
    do {
        try png.write(to: imageURL)
        print("PNG image saved")
    } catch {
        print(error)
    }
}

Saving NSImage in Different Formats Locally

You can create a custom method to allow you to specify any image type and also the directory where you would like to save your NSImage. You can also set a default value to the destination directory as the current directory, so if you don't pass the directory url it will save to the current one:

extension NSImage {
    func save(as fileName: String, fileType: NSBitmapImageRep.FileType = .jpeg, at directory: URL = URL(fileURLWithPath: FileManager.default.currentDirectoryPath)) -> Bool {
        guard let tiffRepresentation = tiffRepresentation, directory.isDirectory, !fileName.isEmpty else { return false }
        do {
            try NSBitmapImageRep(data: tiffRepresentation)?
                .representation(using: fileType, properties: [:])?
                .write(to: directory.appendingPathComponent(fileName).appendingPathExtension(fileType.pathExtension))
            return true
        } catch {
            print(error)
            return false
        }
    }
}

---

You will need also to make sure the url passed to your method is a directory url. You can use URL resourceValues method to get the url isDirectoryKey value and check if it is true:

extension URL {
    var isDirectory: Bool {
       return (try? resourceValues(forKeys: [.isDirectoryKey]))?.isDirectory == true
    }
}

---

You can also extend NSBitmapImageRep.FileType to provide the associated file path extension:

extension NSBitmapImageRep.FileType {
    var pathExtension: String {
        switch self {
        case .bmp:
            return "bmp"
        case .gif:
            return "gif"
        case .jpeg:
            return "jpg"
        case .jpeg2000:
            return "jp2"
        case .png:
            return "png"
        case .tiff:
            return "tif"
        }
    }
}

---

Playground Testing:

let desktopDirectory = FileManager.default.urls(for: .desktopDirectory, in: .userDomainMask).first!
// lets change the current directory to the desktop directory
FileManager.default.changeCurrentDirectoryPath(desktopDirectory.path)

// get your nsimage
let picture  = NSImage(contentsOf: URL(string: "https://i.stack.imgur.com/Xs4RX.jpg")!)!

// this will save to the current directory
if picture.save(as: "profile") {
    print("file saved as profile.jpg which is the default type")
}
if picture.save(as: "profile", fileType: .png) {
    print("file saved as profile.png")
}
if picture.save(as: "profile", fileType: .tiff) {
    print("file saved as profile.tif")
}
if picture.save(as: "profile", fileType: .gif) {
    print("file saved as profile.gif")
}
if picture.save(as: "profile", fileType: .jpeg2000) {
    print("file saved as profile.jp2")
}

// you can also chose a choose another directory without the need to change the current directory
let url = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
if picture.save(as: "profile", at: url) {
    print("file saved as profile.jpg at documentDirectory")
}

NSImage missing alpha channel

Set alpha to true in NSBitmapImageRep:

let imageRep = NSBitmapImageRep(data: your_data)
imageRep?.hasAlpha = true

Get Image from CALayer or NSView (swift 3)

Here are some NSView options:

extension NSView {

    /// Get `NSImage` representation of the view.
    ///
    /// - Returns: `NSImage` of view

    func image() -> NSImage {
        let imageRepresentation = bitmapImageRepForCachingDisplay(in: bounds)!
        cacheDisplay(in: bounds, to: imageRepresentation)
        return NSImage(cgImage: imageRepresentation.cgImage!, size: bounds.size)
    }
}

Or

extension NSView {

    /// Get `Data` representation of the view.
    ///
    /// - Parameters:
    ///   - fileType: The format of file. Defaults to PNG.
    ///   - properties: A dictionary that contains key-value pairs specifying image properties.
    /// - Returns: `Data` for image.

    func data(using fileType: NSBitmapImageRep.FileType = .png, properties: [NSBitmapImageRep.PropertyKey: Any] = [:]) -> Data {
        let imageRepresentation = bitmapImageRepForCachingDisplay(in: bounds)!
        cacheDisplay(in: bounds, to: imageRepresentation)
        return imageRepresentation.representation(using: fileType, properties: properties)!
    }
}

---

Some CALayer options:

extension CALayer {

    /// Get `NSImage` representation of the layer.
    ///
    /// - Returns: `NSImage` of the layer.

    func image() -> NSImage {
        let width = Int(bounds.width * contentsScale)
        let height = Int(bounds.height * contentsScale)
        let imageRepresentation = NSBitmapImageRep(bitmapDataPlanes: nil, pixelsWide: width, pixelsHigh: height, bitsPerSample: 8, samplesPerPixel: 4, hasAlpha: true, isPlanar: false, colorSpaceName: .deviceRGB, bytesPerRow: 0, bitsPerPixel: 0)!
        imageRepresentation.size = bounds.size

        let context = NSGraphicsContext(bitmapImageRep: imageRepresentation)!

        render(in: context.cgContext)

        return NSImage(cgImage: imageRepresentation.cgImage!, size: bounds.size)
    }
}

Or

extension CALayer {

    /// Get `Data` representation of the layer.
    ///
    /// - Parameters:
    ///   - fileType: The format of file. Defaults to PNG.
    ///   - properties: A dictionary that contains key-value pairs specifying image properties.
    ///
    /// - Returns: `Data` for image.

    func data(using fileType: NSBitmapImageRep.FileType = .png, properties: [NSBitmapImageRep.PropertyKey: Any] = [:]) -> Data {
        let width = Int(bounds.width * contentsScale)
        let height = Int(bounds.height * contentsScale)
        let imageRepresentation = NSBitmapImageRep(bitmapDataPlanes: nil, pixelsWide: width, pixelsHigh: height, bitsPerSample: 8, samplesPerPixel: 4, hasAlpha: true, isPlanar: false, colorSpaceName: .deviceRGB, bytesPerRow: 0, bitsPerPixel: 0)!
        imageRepresentation.size = bounds.size

        let context = NSGraphicsContext(bitmapImageRep: imageRepresentation)!

        render(in: context.cgContext)

        return imageRepresentation.representation(using: fileType, properties: properties)!
    }
}

MacOS - How to programmatically count bytes for an image in Swift?

As you probably already noticed there is no pngData method for NSImage. You need to first get the image tiffRepresentation, initialize a new NSBitmapImageRep object and get the png storageType representation:

---

let data = NSBitmapImageRep(data: NSImage(imageLiteralResourceName: "toto").tiffRepresentation!)!.representation(using: .png, properties: [:])!
print(data.count)

---

Related Topics