Written By Steve Patterson

In this Adobe Photoshop tutorial, we're going to learn how to create the illusion that light is being cast on to the subject of your photo through window blinds, using a displacement map to bend and wrap the shadows of the blinds around the subject in a realistic 3D fashion. We'll also be using a Color Balance adjustment layer to create a more convincing light source.

Here's the image I'll be working with in this tutorial:

And here's how it will look when we're done:

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Let's get started!

Step 1: Convert The Image Into The Lab Color Mode

As I mentioned, we'll be using Photoshop's Displacement Map feature to wrap the shadows from the blinds around the natural curves of the woman's face, hands and hair, so the first thing we need to do is create our displacement map. A displacement map is nothing more than a black and white image which Photoshop uses to determine how to move and reposition pixels. I like to think of it as Photoshop moving pixels from "dis place" to "dis place". The first thing we need to do then is create a black and white version of our image. There's lots of different ways to do that, but one of my favorite ways is to use Photoshop's Lab color mode, which conveniently separates the luminosity (lightness) values of the image from the color.

To convert the image to Lab color, go up to the Image menu at the top of the screen, choose Mode, and then choose Lab Color from the list:

Step 2: Select The "Lightness" Channel

When you convert your image to the Lab color mode, nothing will seem to have happened to it in your document window, but something has most definitely happened. We've now separated the lightness values from the color in the image, and to see exactly what's happened, switch over to your Channels palette, which you'll find grouped in beside the Layers palette. You'll see four channels listed - "Lab", "Lightness", "a", and "b". The "Lightness" channel contains all of the lightness values in the image, while the colors have been separated into the "a" and "b" channels. The top "Lab" channel isn't really a channel at all. It's just the composite of the Lightness and color channels.

Click on the "Lightness" channel to select it:

As soon as you select the "Lightness" channel, you'll see your image in the document window change to black and white:

Step 3: Create A New Document From The "Lightness" Channel

We need our displacement map to be a separate document from our original image, so Right-click (Win) / Control-click (Mac) directly on the "Lightness" channel in the Channels palette and select Duplicate Channel from the menu that appears:

This brings up Photoshop's Duplicate Channel dialog box. Change the Document option to New so we create a new document from the channel rather than simply duplicating the channel in the same document, then click OK to exit out of the dialog box:

You'll now have two documents open on your screen, one containing the original image and one containing the duplicate "Lightness" channel. We're going to work on the duplicate "Lightness" channel document for a few minutes to prepare it for use as our displacement map.