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This is how portrait mode works on your smartphone

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Almost every phone these days is capable of taking photos with a blurred background. But how exactly does this portrait mode on your smartphone work? We’ll explain it to you!

The technology behind the portrait mode on your smartphone

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You probably don’t even think about it: when you take pictures of friends with your smartphone, you habitually tap the portrait mode. Then a nice snapshot automatically rolls out: your friends are sharp, the background is not. However, this requires a lot of technical ingenuity.

Let’s start with a bit of background. When professional photographers shoot a portrait, they usually screw a very bright lens onto their camera. It has an aperture of, for example, f/1.8, f/1.4 or even higher. Yes, higher indeed. It’s a bit confusing, but the smaller the f-number, the more light the lens lets in.

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Portrait mode in action: Mario is in focus, the background is not
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This aperture is also important for depth of field, which is the portion of the photo that is in focus. With an f/1.4 lens, usually only your subject’s face (or part of it) is really sharp, while the background is nicely blurred. This makes your subject seem to jump out of the photo.

Phone cameras nowadays also often have an aperture of f/1.8 or f/1.6. Because the sensor in phones is much smaller than that of real cameras, it unfortunately does not produce the same effect. Even with the brightest smartphone lens, you get a less attractive depth of field than with a ‘real’ camera lens. Too much of the photo is simply in focus.

The solution: depth mapping

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To be able to shoot beautiful portraits with your smartphone, manufacturers have developed the portrait mode. It uses a technique called ‘depth mapping’. With the help of the autofocus, your device determines which part of the photo should be sharp. Anything that doesn’t fall under that will be software-based blurred.

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A not entirely successful portrait photo

So your smartphone looks at the world independently, as it were. That is not easy and therefore errors are still regularly seen in this technique. Especially cheaper devices use less advanced algorithms. Especially in complex situations with a lot of hair, leaves or other small parts, they sometimes get confused. Then your device ‘thinks’ that something belongs to the foreground, while it should actually be background. Or vice versa of course.

Cheaper smartphones such as the Samsung Galaxy A53 sometimes have a separate depth sensor on board that should help you shoot better portrait photos. That’s a bit of a joke. If you tape off this ‘camera’, you usually get exactly the same results. A Time of Flight sensor is more advanced, but in recent years it has not been essential for beautiful portraits. More and more manufacturers are leaving it out. We would therefore not look at the presence of these sensors when purchasing a new smartphone.

Good software is much more important. In our review of the Samsung Galaxy S22 Ultra, we were very pleased with the portrait mode, while this smartphone has no extra sensors on board. The Google Pixel 7 and Pixel 7 Pro are also known for their good portraits. Do you want perfect results? Then you will have to rely on a real camera for the time being.

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A full time tech enthusiast with a passion for writing. Religiously follow everything new happening in the tech world and share my two cents with my audience here.

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