Faking Narrow Depth of Field

Posted on: April 11th, 2010 0

Creating the illusion of a narrow DoF photo is super-easy. So easy in fact, I didn’t even go through the trouble of recording a screencast of it! Yup, this is a simple step-by-step tutorial. If you have a photo that was shot with an aperture of, say, f/22, and you want to make it look like it was shot at f/2.5 (or whatever), you can do so in about 1 minute!

Here we have 2 photos; one shot at f/22 and the other at f/3.5. You can see how the background in the f/3.5 shot is much more blurry:

Here are the steps:

  1. Open the image in Photoshop. (duh)
  2. Copy the ‘Background’ layer by dragging it down to the Create New Layer icon, simply hit Command-J (mac) Control-J (pc).
  3. Rename this new layer “blur”.
  4. Go to Filter/Blur/Gaussian Blur. Adjust the amount of blur so the background looks the way you want it to. The entire image on this layer will blur as well. No worries, we’ll fix that in the next steps.
  5. Add a Layer Mask to this ‘blur’ layer by clicking the Add Layer Mask icon at the bottom of the Layer panel. A new layer mask appears to the right of the image icon, and it is automatically selected (you can tell because it will have a thin black frame around it).
  6. Hit the “D” key on your keyboard to reset the foreground and background colors to default black and white.
  7. Activate the Gradient Tool from the Tools panel, and in the Options bar, make sure ‘Foreground to Background’ and ‘Linear Gradient’ are selected.
  8. Here is where we combine the blur layer with the background layer to create the illusion of a narrow DoF. Since the foreground color is set to black, start at the upper left corner of the image and drag diagonally to the right. You should see a diagonal linear gradient appear in the mask of the ‘blur’ layer. If you saw the gradient appear in the main image, that means you did not have the LAYER MASK selected. Undo the gradient fill, click on the layer mask icon in the ‘blur’ layer, and repeat dragging diagonally across the image.

Here is the result. Compare it to the image shot at f/3.5 above:

Let’s take an image that presents a slightly more complicated scenario:

The problem here is that the elements in this photo don’t line up neatly across the scene in such a way that simply applying a gradient fill layer mask on the blurred layer won’t give us what we need. No problemo! We simply follow the exact same steps as before, but after we create the gradient fill on our mask, we can paint on the mask with either black or white (depending on whether we are revealing or concealing -“white reveals, black conceals”). Here is the result:

And here is what the layer mask looks like:

You can view a layer mask in the main image window in Photoshop by holding down the OPTION(mac) ALT(pc) key and click on the mask. To return to the image, just repeat. You can see that I painted in areas where I needed to reveal the original sharp layer, and white where I needed blur. By changing the opacity of the brush in the Options bar, I was able to adjust how much of each layer I needed to reveal/conceal. Painting on a layer mask and adjusting the opacity of the brush provides a huge degree of flexibility here.

You will occasionally encounter an image that won’t easily lend itself to this technique. Should that happen, you can create selections of the elements that need to remain sharp and save them in Alpha Channels (From the main menu, choose Select/Save Selection…). Then call them up as active selections after you’ve done the Gradient Fill step and fill them with black to conceal them on the ‘blur’ layer.

It so happens that in my 2 examples a diagonal orientation for the gradient fill seemed to work best. I don’t think I need to tell you that you will adjust the angle of the gradient based on the needs of the image you are working on do I?

Unfortunately, doing the opposite, faking a LONG DoF isn’t possible. As powerful as Photoshop is, sharpening a blurry background ain’t gonna happen.

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