Shallow depth of field capabilities on any mobile device is heart wrenching at best. People mistake the f/2.0 aperture of a mobile device camera for getting great 'bokeh' effects only to be disappointed by its inability to render any creamy blurs often found on full frame camera lenses. The disappointment is warranted of course, but you need to know a smidgen of physics to know that shallow depth of field is not possible on such small devices.
There are exceptions to the rule of impossibility. Get purpose made bokeh rendering apps to do your bidding. Of course you could wait for the new generation of smartphones with dual camera lenses and sensors to come out at the end of the year so I will leave this up to you. But if you want to get Bokeh now, then read on.
Shopped till they Dropped
These days, Photoshopping isn't a term that is confined to desktop image editing. Back in its day, anyone with good image editing skills could easily render those shallow depth of field effects with Adobe Photoshop but that meant owning a PC or Mac. Today, some of most used features are available on mobile apps.
Today, mobile apps can render bokeh or Gaussian blur, but this is a post production process and not a 'live' process. A live process is one that lets you shoot and compose a bokeh in camera. Basically, I do believe this is possible but at this stage, just that the megapixel race has foreshadowed the process.
If you had a 5 megapixel image, there is a good chance that an image detection algorithm can distinguish a foreground subject from a background. But once you have a 16 megapixel image, then there is too much data to process and it defeats the purpose of having an in-camera depth of field processing engine.
Right now, there are several apps that give you tilt-shift blurring but these are either too basic or difficult to use. When researching my book on smartphone photography, I tested busloads of them and I found them misleading at best.
So my take here is based on two apps, Tadaa SLR for iOS only and AfterFocus for both Android and iOS. These are paid apps.
Tadaa SLR iOS App
How do you mimic a shallow depth of field process on mobile photography? Tadaa SLR is the first app I tried on iOS and basically it works to a point. I came across the app while using their free version, called Tadaa Classic. This is a photo sharing community which I think has some ways to go before it gets more traction but it's a good start.
Tadaa has an edge detection algorithm built into both apps—allowing you to paint over the foreground subject. You then select the type of blurring you want, which is either radial or linear. The linear blur gives you a tilt-shift effect.
|Paint over the Focus Area with your fingers like so|
To fake a bokeh, you need to determine the focus and out of focus areas. This is quite tricky as you need to think in 3D to select the areas. For this picture, you can see that we want to see the face and his thumb in focus. and part of it includes the belly and his foot and all the way down to base.
|Apply Radial Blur|
You can vary the range of the blur the intensity of the blur with aperture and range settings.
|The final effect|
Once it is complete, there isn't much you can fine tune unless you can visually see this area being highlighted in the masking mode. I must say that the effect is satisfactory. Look closely at the thumb and you'd notice that the area surrounding it is not properly edged out. This is one of the weaknesses of the edge detection algorithm of Tadaa SLR.
|The original image|
I have tried it on several other images and found that Tadaa SLR's blurring feature is both a miss and hit affair. It is very difficult for the algorithm to edge detect areas that have a messy background. To mimic a good bokeh, you need to isolate an area of focus and not just give it a blur stamp of approval.
Tadaa has its own photo sharing community so if you want to join up, you'd be given a chance to share your bokehlicious experiences with them.