Can you create digital bokeh, and is it as good as the real thing?

If you want the short answer, it’s yes and no. Yes, you can create digital bokeh, and no, it’s not as good as the real thing. You can, however, create a reasonably convincing bokeh ‘look’.

But let’s clarify one thing early on. Lots of people (and lots of software programs) use the word ‘bokeh’ to mean shallow depth of field. They’re not the same thing at all.

Shallow depth of field means foreground or background blur in front of or behind the plane of sharp focus. ‘Bokeh’ is actually the appearance of out of focus areas. For purists, there’s ‘good’ bokeh and ‘bad’ bokeh, perfect disk-shaped highlights versus nasty distorted, diaphragm-shaped or ‘onion skin’ bokeh.

So this guide isn’t about good bokeh versus bad bokeh, but how to simulated shallow depth of field in software. And it’s a lot harder than you might think, largely because you’re trying to separate objects in three dimensions when they’ve already been flattened into two.

Here’s an example. This fairground truck makes a striking composition, but the background is as sharp as the front of the truck and makes the picture look muddled and messy. But what if I could keep the front of the truck sharp and blur the background. Should be easy enough, right?

Let’s see. I’m using Exposure X7, which has some of the best bokeh/blur tools around (they all work in much the same way).

1. A vertical ellipse

My first attempt uses Exposure’s elliptical bokeh too, which I’ve sized and positioned vertically over this truck’s grille. Inside the center part of the ellipse the image is completely sharp, between the center and the outer edge the sharpness fades away, and beyond the outer edge the image is blurred.

So this has achieved a nice, progressive blur effect that works quite well, but any photographer will immediately see the flaw – with ‘real’ background blur, the full width of the front of the truck would be sharp and not blurred at the edges.

2. A horizontal ellipse

So here I’ve swapped the ellipse round so that it’s horizontal and the headlamps are sharp, Now, though, the top of the grille is blurred. I could enlarge the blur marquee to include the top of the grille too, but then it would be so large that only. the corners of the image would be blurred.

This is an example of how you have to compromise with ‘digital bokeh’, or ‘digital depth of field’. You have to settle for an image that simply has an effective look, because you’re not going to get technical accuracy.

But let’s keep going anyway.

3. Linear blur

Here, I’ve swapped to Exposure X’s linear blur tool, given that the front of the truck is more or less a horizontal subject. This linear blur tool is very effective at creating a miniature ‘diorama’ effect, but only when you’re subject is on a receding plane at an angle to the camera – not when it’s completely front-on, as here.

4. Manual masking

So what about masking the area manually? The software can’t work out the 3D depth in the picture but we can do it by eye. Here, I’ve used the polygon selection tool in Exposure X7 to manually select the background area for blurring. It takes a little longer to do, so is it worth the effort?

5. Manual mask refinement

Well, it’s worked up to a point. The trouble with manual selections is that they produce a hard edge, so that when you apply a blur effect, the transition from sharp to blurred looks completely unnatural. So I’ve had to go in with the mask Erase tool set to a medium flow value and low hardness to paint away at the edges of the mask to blend it in more gently. I’ve also had to reduce the blur value to make it look anywhere near natural.

After all that, there’s still one more problem. Once you’ve made a selection or a mask, only that area will be blurred. HOWEVER, the blur is generated using areas both inside and outside the mask. This means that some of the bright metalwork in the truck radiator finds its way into the blur effect around its edges.

Digital bokeh is a ‘look’ not a simulation

If you want shallow depth of field, use a longer focal length or a wider lens aperture. It’s an effect you can ONLY achieve optically at the moment of capturing a 3D scene.

You CAN, however, achieve something of the ‘look’ of shallow depth of field digitally, and it can be quite evocative and satisfying in its own way. But you should accept that it’s never going to be technically correct, and if you try to get that through more sophisticated masking, feathering and blurring techniques you’re just going to disappear down a rabbit hole.

I do quite like digital bokeh/blur effects, but I long ago accepted that it’s all about the overall ‘look’, and chasing a technically accurate simulation of shallow depth of field is pointless.

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