If you want to create Pop art in Photoshop, the Threshold filter is the one to use. Place the image in Photoshop then go to the top menu bar and select Image then Adjustments then Threshold. The threshold filter options window will appear. Here you can adjust the image. Enable preview so that you can see live changes to the image. When you have adjusted the image to your preference, click Ok to keep the changes. You will see the image look like a black-and-white pop art image.