ImageDecoder

Image decoder in Swift using Image I/O. This implementation is based on WebKit (WebCore ImageDecoderCG class) and you can expect similar to how Safari handles images.

This pacakge is handy if you need to:

• Incrementally load an image;
• Decode animated images.

ImageDecoder supports animated images in GIF, APNG, and HEICS formats.

Usage

Use Swift Package Manager integration in Xcode to install ImageDecoder.

If you have the complete image data you can create ImageDecoder object and set it, allDataReceived indicates if the image data is complete:

let imageDecoder = ImageDecoder()
imageDecoder.setData(data, allDataReceived: true)

Use this approach if you read the image data from a file or downloaded from network using URLSessionDataTask:

let task = urlSession.dataTask(with: url) { data, _, _ in
    guard let data = data else {
        return
    }
                    
    let imageDecoder = ImageDecoder()
    imageDecoder.setData(data, allDataReceived: true)
                    
    guard let uiImage = imageDecoder.uiImage else {
        return
    }
                    
    DispatchQueue.main.async {
        self.uiImage = uiImage
    }
}
            
task.resume()

When you incrementally loading an image create the image data object for accumulating the image data. Pass the partial image data to ImageDecoder and the complete image data when loading completes. This example uses URLSessionDelegate:

let imageDecoder = ImageDecoder()

var imageData = Data()

func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
    imageData.append(data)
    imageDecoder.setData(imageData, allDataReceived: false)
}

func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
    imageDecoder.setData(imageData, allDataReceived: true)
}

Decoding an image

ImageDecoder can create animated or static images. Use createFrameImage(at index: Int, subsamplingLevel: SubsamplingLevel = .default, decodingOptions: DecodingOptions = .default) -> CGImage?.

Creating static image:

let cgImage = imageDecoder.createFrameImage(at: 0)

Animated image has multiple frames:

for i in 0..<imageDecoder.frameCount {
    let cgImage = imageDecoder.createFrameImage(at: i)
    let duration = imageDecoder.frameDuration(at: i)
}

For convenience you can use ImageDecoder+UIKit extension:

extension ImageDecoder {

    /// Creates static or animated image depending on `frameCount`.
    public var uiImage: UIImage?
    
    /// Creates animated image if there is more than one frame.
    public var animatedUIImage: UIImage?
    
    /// Creates static image from the first frame.
    public var staticUIImage: UIImage?
}

Displaying animated images with UIKit and SwiftUI

UIImageView can display animated images. In SwiftUI Image is static. Wrap UIImageView in UIViewRepresentable to display animated images:

struct AnimatedImage: UIViewRepresentable {
    
    let image: UIImage
    
    func updateUIView(_ uiView: UIImageView, context: UIViewRepresentableContext<AnimatedImage>) {
        uiView.image = image
    }
    

    func makeUIView(context: UIViewRepresentableContext<AnimatedImage>) -> UIImageView {
        let imageView = UIImageView(image: image)
        imageView.startAnimating()
        
        return imageView
    }
}

Performance

Decoding an animated image can sometimes be slow because each frame must be decoded. Use background queue to decode animated image and make sure you use DecodingOptions.Mode.asynchronous. This is the default decoding mode. If you decode images on the main queue use DecodingOptions.Mode.synchronous.

Misc

If you found a bug, have a feature request, or want to contribute - please open an issue.

Make sure to check out URLImage package if you need to dowload and display an image in SwiftUI. For updates on this and other packages follow me on Twitter: dmytroanokhin.