Exporting extremely large images in iOS

Question

I am working on an app that uses a CATiledLayer backed View in a UIScrollView to let the user work on an arbitrarily large canvas. The canvas basically contains a large chart of blocks that the user can color, select, move, etc. I override draw(_ rect: CGRect) to draw on the view.

All of that is working fine - the CATiledLayer works really well to keep memory consumption down while the user is working on their chart. Scrolling and Zooming work great.

What I need to do now is allow the user to export a copy of their chart to the camera roll, but I'm running into memory issues and the app is crashing. I've tried a variety of methods to capture the view to an image. The view isn't completely visible as it's in a UIScrollView

Here is how I am currently generating the image:

// MyView is the view that is used in the scrollView
static func screenshotByDrawingItAgain(_ view: MyView) -> UIImage? {
    var image: UIImage?

    UIGraphicsBeginImageContextWithOptions(view.bounds.size, view.isOpaque, UIScreen.main.scale)

    guard let context = UIGraphicsGetCurrentContext() else {
        return nil
    }
    // This is where my chart data model is stored in memory
    guard let chart = view.chart else {
        return nil
    }

    // drawInRect is also called from MyView's draw(_:) method
    // so all drawing code is in one place
    view.drawInRect(context, with: chart, in: view.bounds, row: 0, col: 0)
    image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return image!
}

Since charts can be any size, this means they can get quite large. I need a way to be able to export large images like this in some fashion. Example error:

BOUNDS (10200.0, 6360.0)
CGBitmapContextInfoCreate: unable to allocate 1037952000 bytes for bitmap data

Most of the posts I've seen deal with how to read in a large image (like a photo) and display it. I haven't been able to find any info on how to do the reverse and get an image of a view out. Is there a way I can generate smaller tiles of the view onto a file and then stitch it together and give them access to the resulting file? Thanks!