Casting Shadows with Photoshop

Compositing one image onto another is a pretty regular task for Photoshop users. The tools Photoshop has make that task quite an easy one to accomplish, but not necessarily one that is accomplished well. 

One of the key elements any Designer or Photographer can use to make a composite image look more true is the images shadows. Get them right and the jobs well on the way, get them wrong and it’s going to be obvious. Miss them out completely and your up for a place in a Photoshop Disasters Blog somewhere. 

In this article I am going to introduce you to a simple yet effective method to add shadows to a composited image. 

Step 1 - Make a Mask

Select the image that is to be composited. Here, I have selected an image of someone running. With the Magnetic Lasso tool, click around the object you want to keep. When done, select Layer > Layer Mask > Reveal Selection or press the Add Layer Mask button. To tidy up the mask, choose Select > Refine Mask (Option-Command-R). Try to make it as neat an edge as possible by changing the Smooth and Feather values.

Step 2 - Create a Composite

Drag the masked image onto the Background image to create a composited image. 

Use Free Transform (Command-T) to size the image to scale. If the image looks too sharp for the background, which it probably will, open the Properties Panel and set the Masks Feather to perhaps 0.2/0.3 px. It should look a little softer.

Step 3 - Match Colors

Next go to Image > Adjustments > Match Color. Use this feature to make the colors of the masked layer better match the Background.

Set the Source: to the original Background file, and the Layer: to Layer 1. Use the Image Options such as Luminance, Color Intensity and Fade to refine the color match until you are satisfied they match, and appear to share the same light source. 

Step 4 - Add a Layer named Shadow

Add a new layer to the Layers Panel (Shift-Command-N) and name it “Shadow”. 

Drag the layer between the background and Mask layers like so. 

Step 5 - Load a Selection from the Mask

Keep the Shadow Layer Selected, hold down the Command key and click on the Mask Thumbnail on the layer above. 

This will re-load the selection that was used to create the mask. 

Step 6 - Fill the Selection

Fill the selection on the Shadows layer (Shift-F5). 

Choose 50% Grey with a Normal Blending Mode and 100% Opacity. Then press Command - D to deselect. 

Step 7 - Distort the Shadow

Choose Edit > Transform > Distort to create the illusion of the shadow being cast. Start by moving the Anchor Point to the position where the shadow meets the subject. In my case thats at the sole of the foot connecting with the ground. 

Drag the position of the upper left and right points of the transformation editor until your shadow fits in with the image. TIP: Use the shadows that are already on the Background as a guide. 

Step 8 - Adjust the Blend Mode

Change the Blend Mode of the Shadow layer to Color Burn. 

Some people prefer Multiply, but I like the Color Burn effect. 

Step 9 - Add some Depth

Shadows are a little denser closer to the subject. We can do the same using the Burn Tool O. Set the Burn Tool to Hardness: 20%, Range: Shadow and Exposure: 50%.

Use the Burn Tool to gently darken the Shadow closer to the subject, making it appear a little denser. 

Step 10 - Blur the Shadow

Lastly, to create a sense of distance, and also to create the illusion of ambient light, apply a gentle Blur effect to the Shadow layer. 

I’ve added a Gaussian Blur set to 1.9 pixels. You might also find that a small adjustment to the Opacity of the Shadow layer helps complete the look. I’ve chosen Opacity 76%. 

And there you have it, a simple yet effective way to create shadows on a composited image.