Tutorial: Depth of Field Effect with PS

danpen · 06-06-2007, 22:38

On another thread I was asked to explain how Photoshop might be used to create the effect of using a large aperture, there are a number of ways of doing it but I've recently discovered some of what's possible with the Lens Blur Filter and thought I'd write a short tutorial to share with everyone else. This does assume you have a reasonable understanding of the basic operation of PS CS.

As you can see here a lot of the image from front to back is in focus, I used f10. It would have been better to use something like f4 so that only the man at the front was in sharp focus. This is possible to simulate in Photoshop and it's quite simple, although it's a lot more work than using the right aperture to start with

Load your image into Photoshop.
It's not necessary but I usually work on a copy of the background layer so that I can quickly delete it when I go wrong. There are a number of ways to do this, I usually drag the layer onto the New Layer Icon and name it something sensible.

In order for the Lens Blur filter to know which areas to blur and by how much we need a way to tell it how far away from the camera everything is. That's achieved by creating a greyscale image where Black is used to show what's near to the camera, white is things far from the camera and shades of grey represent any distance in between. This is harder to explain than to show, here's the finished version ...

Now I'll explain how I got there.

Go to the Channels Palette and create a new Channel
Make the Channel visible and select it

Ensure the foreground and Background colours are set to Black and White
Select the gradient tool, use it to create a gradient from Black (front) to White (furthest away from the camera). This works well enough for the ground plane which stretches away from the camera, however each runner must be dealt with seperately or they will get progressively more blurred from their feet to their heads which is not the effect we want. (As the mask is shown overlaying the image anything that's Black will actually appear Red)

Click on the foreground colour to get the eyedropper tool, with the channel still selected click near the front runner's feet, this will change the foreground colour to the shade of grey that represents the distance that the man is from the camera. Now use the paintbrush tool to carefully paint over the man.
Repeat with the other runners
When you're happy turn off the Channel Visibility
Now you have the greyscale "Map" it's time to use the Lens Blur Filter, select the layer you created earlier
And open the Lens Blur Filter from the Filter => Blur Menu
Set your Channel to be the Depth Map Source and view the preview

It looks something like this ...

In this instance I could have spent a lot longer on getting the map right to tune the effect, I've also overdone the effect somewhat to make it more obvious but you get the idea.
Finally the real magic of the Lens Blur Filter is that you can choose what distance from the camera should be in focus and it will blur things both nearer and farther from the camera than that plane. Just click on any part of the image to select a different focal distance, here I clicked on the runners in Red.

There are a number of other options in the Lens Blur Filter to play with but they are mostly personal choice.

I hope this quick tutorial has been of some use and if there's anything missing or unclear please ask.

cheers

Dan