Swift. How to extract the individual sub images from an HEIC image - swift

Question

I need to be able to load an heic image and extract and output all of the sub images as pngs similar to how preview does it. For example, if you open a dynamic heic wallpaper in preview, it shows all the images in the sidebar with their names:
How do you do this? I've tried to use NSImage like below. But that only outputs a single image:
let image = NSImage(byReferencing: url)
image.writePNG(toURL: newUrl)

Answer 1

You need to load the HEIC data, get its CGImageSource and its count. Then create a loop from 0 to count-1 and get each image at the corresponding index. You can create an array with those CGImages in memory or write them to disk (preferred). Note that this will take a while to be executed because of the size of the HEIC file 186MB. Each image extracted will be from 19MB to 28MB.
func extractHeicImages(from url: URL) throws {
let data = try Data(contentsOf: url)
let location = url.deletingLastPathComponent()
let pathExtension = url.pathExtension
let fileName = url.deletingPathExtension().lastPathComponent
let destinationFolder = location.appendingPathComponent(fileName)
guard pathExtension == "heic", let imageSource = CGImageSourceCreateWithData(data as CFData, nil) else { return }
let count = CGImageSourceGetCount(imageSource)
try FileManager.default.createDirectory(at: destinationFolder, withIntermediateDirectories: false, attributes: nil)
for index in 0..<count {
try autoreleasepool {
if let cgImage = CGImageSourceCreateImageAtIndex(imageSource, index, nil) {
let number = String(format: "#%05d", index)
let destinationURL = destinationFolder
.appendingPathComponent(fileName+number)
.appendingPathExtension(pathExtension)
try NSImage(cgImage: cgImage, size: .init(width: cgImage.width, height: cgImage.height))
.heic?
.write(to: destinationURL)
print("saved image " + number)
}
}
}
}
You will need these helpers as well to extract the cgimate from your image and also to get a HEIC data representation from them:
extension NSImage {
var heic: Data? { heic() }
var cgImage: CGImage? {
var rect = NSRect(origin: .zero, size: size)
return cgImage(forProposedRect: &rect, context: .current, hints: nil)
}
func heic(compressionQuality: CGFloat = 1) -> Data? {
guard
let mutableData = CFDataCreateMutable(nil, 0),
let destination = CGImageDestinationCreateWithData(mutableData, "public.heic" as CFString, 1, nil),
let cgImage = cgImage
else { return nil }
CGImageDestinationAddImage(destination, cgImage, [kCGImageDestinationLossyCompressionQuality: compressionQuality] as CFDictionary)
guard CGImageDestinationFinalize(destination) else { return nil }
return mutableData as Data
}
}
Playground testing. This assumes the "Catalina.heic" is located at your desktop.
let catalinaURL = FileManager.default.urls(for: .desktopDirectory, in: .userDomainMask).first!.appendingPathComponent("Catalina.heic")
do {
try extractHeicImages(from: catalinaURL)
} catch {
print(error)
}

Answer 2

Each subimage is represented by a NSBitmapImageRep. Loop the image reps, convert to png and save:
let imageReps = image.representations
for imageIndex in 0..<imageReps.count {
if let imageRep = imageReps[imageIndex] as? NSBitmapImageRep {
if let data = imageRep.representation(using: .png, properties: [:]) {
do {
let url = folderURL.appendingPathComponent("image \(imageIndex).png", isDirectory: false)
try data.write(to: url, options:[])
} catch {
print("Unexpected error: \(error).")
}
}
}
}
The conversion to png takes some time. Running the conversions in parallel is faster but I'm not sure if it's save:
DispatchQueue.concurrentPerform(iterations: imageReps.count) { iteration in
if let imageRep = imageReps[iteration] as? NSBitmapImageRep {
if let data = imageRep.representation(using: .png, properties: [:]) {
do {
let url = folderURL.appendingPathComponent("image \(iteration).png", isDirectory: false)
try data.write(to: url, options:[])
} catch {
print("Unexpected error: \(error).")
}
}
}
}