Image Processing

How to use built-in processors and create custom ones

Nuke features a powerful and efficient image processing infrastructure with multiple built-in processors and an API for creating custom ones. The built-in processors can all be found in the ImageProcessors namespace.

ImageRequest(url: url, processors: [
    .resize(size: imageView.bounds.size)

The screenshot is from the demo project.

ImageProcessors #

Resize #

To resize an image, use ImageProcessors.Resize:

ImageRequest(url: url, processors: [
    .resize(size: imageView.bounds.size)

By default, the target size is in points. When the image is loaded, Nuke will downscale it to fill the target area, maintaining the aspect ratio. To crop the image, set crop to true. For more options, see ImageProcessors.Resize reference.

Use an optional Task Builder package for a more concise API.

 pipeline.image(with: URL(string: "https://..."))
    .resize(width: 320)
    .blur(radius: 10)

Circle #

ImageProcessors.Circle rounds the corners of an image into a circle. It can also add a border.

ImageRequest(url: url, processors: [

RoundedCorners #

ImageProcessors.RoundedCorners rounds the corners of an image to the specified radius.

ImageRequest(url: url, processors: [
    .roundedCorners(radius: 8)

Make sure to resize the image to match the size of the view in which it gets displayed so that the border appears correctly.

GaussianBlur #

ImageProcessors.GaussianBlur blurs the input image using one of the Core Image filters.

CoreImageFilter #

Apply any of the vast number Core Image filters using ImageProcessors.CoreImageFilter:

ImageProcessors.CoreImageFilter(name: "CISepiaTone")

Anonymous #

For simple one-off operations, use ImageProcessors.Anonymous to create a processor with a closure.

ImageProcessors.Anonymous(id: "profile-icon") { image in
    // Perform processing operations...

Custom Processors #

Custom processors need to implement ImageProcessing protocol. For the basic image processing needs, implement process(_:) method and create an identifier that uniquely identifies the processor. For processors with no input parameters, return a static string.

public protocol ImageProcessing {
    func process(image: UIImage) -> UIImage? // NSImage on macOS
    var identifier: String { get }

All processing tasks are executed on a dedicated imageProcessingQueue.

If your processor needs to manipulate image metadata (ImageContainer) or get access to more information via ImageProcessingContext, there is an additional method that you can implement in addition to process(_:).

public protocol ImageProcessing {
    func process(_ image container: ImageContainer,
                 context: ImageProcessingContext) -> ImageContainer?

In addition to var identifier: String, you can implement var hashableIdentifier: AnyHashable to be used by the memory cache where string manipulations would be too slow. By default, this method returns the identifier string. A common approach is to make your processor Hashable and return self from hashableIdentifier.