Handling High Dynamic Range in Photography
Handling High Dynamic Range in Photography
Recently, Adobe released Photoshop 23 and ACR 15 (Adobe Camera RAW). Whilst both have some great new features, it’s the High Dynamic Range feature in ACR 15 that has me excited (almost). Later in this article, I’ll share more about to use this, but first, let’s look at why we might need this.
The High Dynamic Range Problem and Solutions
For a long time, photographers and especially landscape photographers, have struggled with excessive dynamic range. Often the range between the brightest and darkest areas of a scene is so great, the camera can’t record it. When this happens, areas of the image will record as pure black or pure white. This loses detail in the image which the camera can’t capture.
Back in the days of film, this was a particular problem for anyone shooting slide film. Negative films however tend to have a much greater latitude for recording high dynamic range scenes. At times, it makes you wonder why many people stopped using it.
Slide film however was notorious for having a limited dynamic range of around 6 stops. And when the dynamic range was exceeded, those areas would quickly turn white or black. The effect was extremely ugly as there wasn’t a soft transition.
To address this issue, photographers have developed a range of solutions over time.
Using Neutral Density Graduated Filters
The solution for anyone shooting slide film in these conditions was to use graduated neutral density filters. These would typically be attached to the front of the lens with the dark part of the filter placed over a bright sky. This would help to reduce the brightness and balance the exposure with the ground.
This technique remains valid today and can be used with digital cameras. It’s also one that I use much of the time to capture images at sunset and sunrise.
In this sunset scene, I use a 3 stop reverse neutral density graduated filter over the sky. It reduced the dynamic range in the scene to something my camera could record.
Exposure Blending Techniques
Another popular technique to overcome the limited dynamic range problem is exposure blending. This involves capturing two frames for a scene. One image is exposure correctly for the brightest areas whilst the other for the darkest. The two images are then be blended into one using Luminosity Masking techniques. When done well, this achieves a natural looking image, displaying a greater dynamic range as in this example.
HDR and Tone Mapping
An alternative to exposure blending that also involves shooting multiple images is HDR or High Dynamic Range photography. This time rather than the photographer selecting the areas from each image to blend, the computer takes charge. Typically, this type of blending uses a software algorithm to select which pixels to keep. The result is a high dynamic range image recorded in a special 32-bit file.
The problem with 32-bit files is that they are beyond the display capability of most monitors. You need to reply on your software to render something that can be displayed on screen. Then if you want to share the finished image more widely, you need to reduce the image to a 16-bit or 8-bit image. This process is called Tone Mapping.
This problem with Tone Mapping is that it would often produce images which look false. Trying to create a realistic tone mapped image like the one above is quite difficult.
Increasing Camera Dynamic Range
The problem with each of these solutions is that they are all a compromise, requiring additional effort of some type. Even using filters comes with the expense of purchasing them and the effort of carrying and using them.
So why don’t we increase the dynamic range of cameras?
Well, for a while this happened, but then the camera manufacturers began bumping into the laws of Physics. Despite this, the current crop of cameras can already capture a surprising level of dynamic range. The problem is, how can we extract it. The problems areas often become compressed into a very small tonal range, usually the highlights. It’s then extremely difficult to expand that range to help make the details visible.
Some RAW converters do try to address this problem, although the results are limited and not always successful.
Now Adobe seems to have a new solution in development.
The New High Dynamic Range Solution in ACR 15?
When Adobe recently released ACR 15, they included a new technology which may unlock additional dynamic range in existing RAW files. This is what has me excited. Could our RAW files shot over many years have more dynamic range than we assumed. Accessing this may now be within reach using ACR 15.
How to Turn On the New HDR Feature
To use the new HDR feature you first need to change some preferences in Photoshop 23.
You can find the Preferences under the Photoshop menu on a Mac. Currently, I believe this technology is only available to Mac users and also requires a monitor with HDR capability. My main Mac computer is from 2016 but the technology still seems to work.
Select the “File Handling” Preferences in the Photoshop menu to open the Preferences dialog.
You should then see an option for “Camera RAW Preferences”. Click this to open the ACR Preferences.
In the Camera RAW Preferences, click the “Technology Previews” category on the left. This displays a new HDR Output option. Click the option to turn it on and then click the OK button. This will take you back to the Camera RAW Preferences dialog.
Back in the Preferences dialog, select the Technology Preview category and then enable the “Precise color management for HDR display” option. After that click OK to close the dialog and then restart Photoshop.
At this point, I want to say thank you to Greg Benz who did a great video on this, which you will find on his website https://gregbenzphotography.com/photography-tips/acr-15-adds-high-dynamic-range-output/.
Turning On the HDR Option in ACR15
Having configured the Photoshop Preferences as described, you will be able to access the new feature when you open a RAW file. As you probably know, opening a RAW file in Photoshop causes Adobe Camera RAW (ACR) to launch. This is what handles the conversion of the RAW file so that Photoshop can then edit it.
When the RAW file loads in ACR, look below the Histogram and you will see the new HDR option.
Click this and the brightest areas of the image expand.
I would love to be able to show you this in a screenshot, but I can’t. Trying to capture the screen causes it to revert to standard dynamic range. Fortunately, what I can share is how the histogram changes.
Notice that it’s now in two sections. There is the SDR (standard dynamic range) on the left and HDR on the right. The HDR section includes data that previously was outside the SDR range and appeared to be clipping.
Can You Share the Results?
This is where the new technology begins to break down (in my opinion).
The result of processing a RAW file using the HDR technology is a 32-bit image with a Linear P3 profile. What this means is the image needs to be tone mapped before it will display with a regular monitor. This is just like any other 32-bit image created using HDR software. You can view a rendering of it using the software otherwise it needs tone mapping to convert it to an 8- or 16-bit image.
This is at the end of the day a Technology Preview. How Adobe decides to implement it is a complete guess. What is exciting is that there is more data locked up in the RAW file than you might think, which is a good reason to shoot RAW rather than JPEG.
Hopefully we will see further exciting developments in the near future.
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