Step 4: Use The Threshold Adjustment To Remove The Detail From The Main Subject

Next we need to convert the main subject to black and white and remove most of the detail, and we can do that easily using Photoshop's Threshold adjustment. First, click back on the "threshold" layer to select it in the Layers palette. Then, go up to the Image menu at the top of the screen, select Adjustments, and then select Threshold. This brings up the Threshold dialog box:

Drag the slider at the bottom of the Threshold dialog box (circled in red above) until you've removed most of the details from the image, leaving just enough to still be able to make out the main areas. In my case, I've left just enough detail to still be able to make out the girl's eyes, nose, mouth, and so on, yet the majority of the image detail is now gone:

Click OK when you're done to exit out of the Threshold adjustment.

Step 5: Select The First Area Of Your Subject To Colorize And Copy It To Its Own Layer

In order to create the pop art effect, we need to be able to colorize the different areas of our main subject separately from each other, and in order to do that, we need to select each area and place it on its own layer. Again, using the Lasso tool or the selection tool of your choice, draw a selection around the first area of your main subject that you want to colorize. I'm going to start with the girl's hair:

Next, with her hair selected, I'm going to copy her hair onto its own layer, using the same keyboard shortcut as before, Ctrl+Alt+J (Win) / Command+Option+J (Mac), which brings up the New Layer dialog box once again. Give this layer a descriptive name. I'm going to name mine "hair":

Click OK, and Photoshop adds the selection onto its own layer above the "threshold" layer: