Is HDR bracketing still of any use today?

David Lee

17.12.2019

Translation: machine translated

Capture the same image with different brightness levels and add the individual images together: This is HDR bracketing. It is considered a miracle cure for smartphones when the differences in brightness are too great. But is it also worthwhile with large cameras?

The human eye copes better with large differences in brightness than a photo sensor. Even with backlighting, we can still recognise structures in the shadows. Digicams have trouble with this. The smaller the sensor, the bigger the problem. Even at night, the differences in brightness are often too great for the camera sensors.

There are basically three tricks to achieve an image that allows details to be recognised in both the bright and dark areas.

Under-exposure: When post-processing the photo, the dark areas can be brightened quite easily so that details are revealed. The reverse is not possible: if the image areas are completely white, all image information is missing and nothing can be saved. It is therefore advisable to turn the exposure compensation slightly into the minus range in critical situations.

Shoot in RAW: The above-mentioned correction works much better in RAW format. This is because more colour gradations are stored there. When brightening the shadows, these colour gradations are pulled apart. If there are too few colour gradations, this leads to unsmooth gradients. Or the image processing simply refuses to carry out an extreme correction. In Photoshop or Lightroom, you cannot lighten the shadows of a JPEG as much as those of a RAW image.

Exposure bracketing (HDR bracketing): The third method is to take several shots of the exact same subject with different exposures. For example, three images: A dark one that shows the bright parts correctly, a normal one and a bright one that brings out the dark parts. The images are then combined into a single image. This is called exposure bracketing or HDR bracketing.

The three tricks can be combined as desired. I can bracket RAW photos and tend to underexpose them slightly.

Smartphones versus large cameras

HDR is now standard on smartphones. This happens fully automatically. The device recognises when it needs an exposure bracket and shoots several images in succession. So fast that it even works without a tripod. Smartphone manufacturers have made extreme progress in this area in recent years.

Auto-HDR is very useful for smartphones because, firstly, they have small sensors with low dynamic range and, secondly, nobody wants to edit RAW files with their mobile - if the phone delivers RAW at all.

But what about large cameras, which are always capable of RAW and where it is often used?

The dynamic range of sensors is constantly improving thanks to technological progress. According to dxomark.com, the Sony A7R IV has a dynamic range of 14.8 exposure stops. The ten-year-old Sony Alpha 850 - also a full-frame camera - only achieves 12.2 stops. Today, even compact cameras with 1-inch sensors achieve higher values.

Raw converters such as Lightroom or CaptureOne have not stood still in the last ten years either. Today, they tease more out of an image than before.

This all suggests that HDR bracketing is no longer necessary with the big cameras.

Test shots

I took various shots with backlighting and reflective surfaces, i.e. in conditions with the greatest possible differences in brightness. An exposure series consists of a slightly underexposed image, an image that is 2 or 3 steps darker and an image that is 2 or 3 steps brighter. I put the images together using the HDR function in Lightroom.

In most cases, a single RAW and a moderate underexposure is sufficient. The only important thing is that no crucial areas are overexposed. HDR bracketing will not make it visibly better.

In order to see the difference between bracketing and a single RAW image, you need to be in an extreme lighting situation. Here, for example, I photographed directly into the sun.

In the RAW file, I lighten the shadows and lower the highlights to even out the differences. To do this, the white slider in Lightroom is turned up a little and the black slider is turned down a little. This prevents the image from having an overly artificial "HDR look".

The same image with a RAW exposure bracket. The differences are particularly visible in the basket on the luggage rack at the top of the image.

Since I also saved JPEGs, I can also create an HDR image from them for comparison. The details on the luggage rack are better than in the single RAW, but of course worse than in the composite RAW. However, the colouring is poor and can also be poorly corrected.

Here again the critical area enlarged. Pay attention to the left edge of the basket under the saddle.

Disadvantages of HDR bracketing

In my test shots, I also noticed the disadvantages of the process. As soon as something moves in the image, problems can occur. This is because the images should be absolutely identical except for the exposure. Movements prevent this. Current smartphones such as the Huawei P30 Pro or the Google Pixel 4 are already quite good at cancelling out these differences. But they also produce strange details when there is movement. This is even more the case with large cameras.

From a distance, everything looks okay in this HDR image. [[image:31844120]]

In the enlargement you can see artefacts where a car has driven through (red light) and in the wave movements in the water.

For comparison, the single image RAW: Nothing like this happens.

Depending on the camera, you will encounter further difficulties with exposure bracketing.
My Nikon D7500 only supports automatic bracketing in JPEG format. If I want a RAW bracket, I have to change the settings manually for each image in the bracket. As a result, the images are a few seconds apart, which increases the risk of movement.

The Sony Alpha 6400, which I also experimented with, is capable of RAW bracketing in continuous fire. For example, I can take three shots in one second. But even then, there are still strange artefacts caused by slight movements.

Continuous firing is also useless for night shots with long exposures. But this is precisely where HDR bracketing is needed, because night scenes have extreme differences in brightness. Lamps are almost always overexposed, while unlit areas are far too dark.

Bracketing cannot be combined with the self-timer on the Sony Alpha 6400. The finger must remain on the shutter release. This makes long exposures very blurred, even with a tripod.

Conclusion: mostly unnecessary

HDR bracketing can still bring advantages in certain cases. However, a reasonably good camera with today's technical standards can handle most scenes without bracketing. This is easier and works much better with moving subjects. I would generally not recommend HDR bracketing for night shots.

David Lee

Senior Editor

David.Lee@digitecgalaxus.ch

My interest in IT and writing landed me in tech journalism early on (2000). I want to know how we can use technology without being used. Outside of the office, I’m a keen musician who makes up for lacking talent with excessive enthusiasm.

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