This example shows how you can apply a dot screen filter to an image.
let filter = DotScreen()
//change filter settings
img.apply(filter)
let image = Image("chop")!
image.constrainsProportions = true
image.width = canvas.width
canvas.add(image)
var filter = DotScreen()
filter.center = canvas.center
filter.width = 5
filter.sharpness = 100
image.apply(filter)