Step 4: Increase Image Contrast With Levels

Displacement maps tend to work best when the image you're using as a displacement map has a strong amount of contrast to it, so let's boost the contrast of our new document using Photoshop's Levels command. Use the keyboard shortcut Ctrl+L (Win) / Command+L (Mac) to quickly bring up the Levels dialog box.

In the center of the Levels dialog box, you'll see a large black graph called a histogram which shows us the current tonal range of the image. Below the histogram are three small sliders - a black slider on the bottom left, a white slider on the bottom right, and a gray slider in the middle. Click on the black slider and drag it towards the right until you're just beyond where the left edge of the histogram begins. This will darken the darkest parts of the image. Then, click on the white slider and drag it towards the left until you're just beyond where the right edge of the histogram begins. This will lighten the lightest parts of the image:

Click OK when you're done to exit out of the dialog box. Your image will now appear with stronger contrast:

Step 5: Select The Area Around The Subject

For my image, I want the shadows from the window blinds to bend and wrap around the woman's face, hands and hair, but I don't want the area behind her to be affected by the displacement map. I want the shadows from the blinds to remain perfectly horizontal in those areas, as if the light from the window is shining onto a flat wall behind the woman. To prevent the displacement map from bending the shadows in those areas, I'm going to fill those areas with solid white. To do that, we'll need to select them, so use the selection tool of your choice (Lasso Tool, Pen Tool, etc.) to select everything around the woman. In other words, select everything except for her. Don't worry about selecting around any lose strands of hair, since they won't make a noticeable difference in the effect:

Step 6: Fill The Selection With White

With the area around the woman now selected, go up to the Edit menu at the top of the screen and choose Fill, or use the keyboard shortcut Shift+F5. Either way brings up Photoshop's Fill dialog box. Set the Use option in the top half of the dialog box to White:

Make sure the Mode option is set to Normal and the Opacity option is set to 100%, then click OK to exit out of the dialog box and fill the selection with white:

Press Ctrl+D (Win) / Command+D (Mac) to deselect the selection.

Step 7: Blur The Image With The "Gaussian Blur" Filter

We're almost done preparing our image for use as a displacement map. The only thing left to do is remove any harsh transitions between light and dark areas by applying a small amount of blur to the image. For that, we'll use Photoshop's classic Gaussian Blur filter. Go up to the Filter menu at the top of the screen, choose Blur, and then choose Gaussian Blur. This brings up the Gaussian Blur dialog box. Drag the Radius slider at the bottom of the dialog box to the right to increase the amount of blurring. I'm going to set my Radius value to around 4 pixels, which softens the image nicely. For a higher resolution image, try somewhere around 6-7 pixels:

Click OK to exit out of the dialog box. Here's my image after applying the Gaussian Blur filter:

Step 8: Save The Image As A Photoshop .PSD File

At this point, we're done with our displacement map image. All we need to do now is save it, so press Ctrl+S (Win) / Command+S (Mac) to quickly access Photoshop's Save command. Since this is the first time we're saving the file, Photoshop will pop up the Save As dialog box instead, allowing us to name the file, choose a file type, and decide where we want to save it. I've created a folder on my desktop called "Displacement Maps" so I'm going to save the file in that folder. I'll name it "window-blinds-displace", but of course you can name your file whatever makes sense to you. Finally, make sure you save the file as a Photoshop .PSD file, since those are the only files we can use as displacement maps:

You can close out of the displacement map document once you've saved it, since we no longer need to have it open.