The Differences Among SDR, HDR and Fake HDR Illustrated by Three Pictures

The HDR technology has become popular in recent years, but it has actually been misused in many contexts. Here we have HDR for photo taking, for photography, for video shooting, and even for display. Do all these HDRs refer to the same technology? Actually, the answer is No.

HDR, the abbreviation of High Dynamic Range imaging, is now a prevalent function on both iOS and Android. Contrary to taking mere one photo, HDR mode enables your cellphone camera to capture several photos at different exposures so as to incorporate them together and highlight the best sections of each photo with the aid of algorithm. However, this kind of HDR feature is actually still a Multi-frame synthesis technology, which might cause the image correctness to go wild and unnatural contrast ratio. Therefore, this type of HDR should also be categorized as SDR (Standard Dynamic Range) in the strict sense.

So here comes the questions: What is real HDR? And what's the difference between HDR and SDR? All of them can be illustrated by the three pictures posted below.

The Differences between SDR and HDR

SDR

HDR

Compared to SDR, the core advantage of HDR is that it allows you to see more details. As illustrated in the above pictures, the curve of SDR image is connected by a few points with the intervals as 1 in X-axis and the maximum as 100 in Y-axis. By contrast, the curve of HDR image is connected by quite a number of points with the intervals far less than 1 in X-axis and the maximum over 1000 in Y-axis. That is why you can see more details and colors in scenes with a high dynamic range. HDR does not mean the simple elevation of brightness, but bring about more subtle changes made by the variation of light-and-shade levels.

It also explains why the HDR scene is more difficult to be made in video games than in photography. Our reality space boasts more details than what HDR required. It's easy to achieve the HDR effect with powerful devices. While details in video games are produced by developers, and it calls for more parameters and the later debugging and operation in order to achieve the same HDR effect.

Be Careful of the Fake HDR

Fake HDR

The above picture shows the fake HDR. Instead of providing more details, the fake HDR draws the picture parameters of SDR to the dynamic range of HDR level forcibly, and raises the minimum of brightness at the same time. For example, A shadow may contain 10 levels of brightness in HDR, ranging from 0 to 1000. While in SDR, it may have only three different brightness levels, ranging from 0 to 100. But the fake HDR is to force the range to be raised from 100 to 1000, with the three brightness levels remained the same. As a result, what we finally see are those overexposed whiteness.

Besides, there exists another damage that the fake HDR might causes. Most parameters of television cannot be adjusted while receiving real HDR signals. However, the television would be deceived by the fake HDR signal labeled with HDR. That means you neither receive the detailed images presented by the real HDR signal, nor enjoy the picture improvement obtained by the adjustment of television parameters.