Not the HDR you love to hate

You probably already have some understanding of what HDR images are, and equally probably, a moderate-to-strong opinion about their artistic merit. But you’re likely to hear a lot about HDR in the coming years that has nothing to do with the eye-popping candy-colored processing you’re thinking of.

A standard DR impression of the HDR difference

This is a necessarily limited representation of the difference between SDR and HDR images, constrained by your SDR display.

On an HDR monitor, capable of brighter whites and darker blacks, the shadow region would be brighter and able to express more contrast, while the sky would be brighter still and more distinct from the foreground, just as it would be in the real world. However, it’s impossible to convey the capabilities in a JPEG image, viewed on an SDR display, so all we can do is try to maintain the distinction between the sky and foreground.

The technologies that make this possible are displays that can achieve a wider color gamut, a greater maximum and minimum brightness than conventional displays, and that can show more subtle gradations of tones from this brightest point down to black. This means they can show a more convincing representation of the real world, but requires content that makes use of this possibility.

What we currently think of as HDR images are usually high dynamic range scenes tone-mapped to fit into the constraints of standard dynamic range (SDR) displays and print. But a new generation of displays: OLED and other high-end TVs and many mobile devices, are able to display a wider range of tones than before. And, crucially, this isn’t about eye-catching effects, it’s about representing the world more realistically.

HDR in video

This capability has already been exploited in cinema. Directors and DoPs are increasingly shooting and grading their movies to utilize the wider dynamic range offered by modern cameras and displays. The latest HDR TVs allow us to gain this same experience in the home.

The push toward HDR TV has spawned a series of standards, from the sophisticated Dolby Vision to the less ambitious HDR10, via HDR10+, which sits somewhere in between. There’s also the more simplistic Hybrid Log Gamma, which is the one you’re most likely to have already heard of.

HLG was developed by broadcasters to look good on an SDR display, but better on HDR screens

Dolby Vision, HDR10 and HDR10+ are being used to various degrees by content streaming services, where it’s possible to deliver different streams to users whose systems can report that they’re HDR compatible and those that aren’t. This means they don’t have to be cross-compatible with older, SDR screens. Hybrid Log Gamma was developed by broadcasters and is designed so that it looks good on an SDR display, but looks better on HDR screens. This was necessary since broadcasters have to deliver the same signal to everyone.

Ultra HD Blu Ray discs get round the problem of how to accommodate SDR viewers by providing a standard Blu Ray disc alongside the HDR 4K version (HDR 10 in this instance)

There’s scope for cynicism here: we’ve just watched a wave of enthusiasm for 3D movies and TVs surge and ebb, so it’s no surprise that there’s another technology rushing towards us, in the hope it drives us to all upgrade our TVs to the latest spec. But this one has a more direct benefit for photographers.

HDR in stills

At present, the JPEGs produced by cameras are designed with the expectation they’ll be viewed on standard definition displays. This limits how much of the dynamic range of the real world can be shown before everything begins to looking flat and washed-out, or tips over into the hyper-real look of aggressively tone-mapped HDR images.

So far we’ve seen two camera manufacturers go further and try to take any advantage of the arrival of more capable displays. Panasonic’s S-series cameras have a mode that can output images based around the HLG standard. These files can be viewed on the majority of HDR TVs if you connect the camera using HDMI. Images shot using HLG Photo mode are output as .hsp files (defined in the HLG standard), whose wider user and acceptance is currently unclear. The cameras can also output .hsp files using in-camera Raw conversion.

Not all the elements necessary for exploiting HDR’s photographic potential are in place yet

The first sign of Canon exploiting HDRTVs’ capabilities is that you get a higher DR preview of Raw files from its recent cameras, if you connect them to a 10-bit display over HDMI.

But the big news being that the EOS-1D X Mark III will output 10-bit files designed for HDR displays in the HEIF image format.

HEIF is already in use for HDR imagery on Apple’s phones (though not, yet, its Mac computers, which can open HEIF files but don’t display the HDR version of the image). HEIF/HEIC is a broad standard, and the files from Canon and Apple are not cross-compatible with one another, but its use by two such large players in the imaging industry significantly increases the likelihood of third-party software offering support.

We may start to see HDR displays become a leading way to exhibit photography

Canon’s HEIF files use the response curve used in both the Dolby Vision and HDR10 standard. This should aid compatibility across HDR systems, but it is not backwards compatible with SDR systems.

It’s worth noting that the HEIF standard includes the option to include multiple image files: so it could potentially offer a way of delivering both an HDR and SDR version of an image, without any compromises to maintain cross-compatibility.

So what does this mean?

For now, there’s no standard workflow for producing HDR images, so it’s not something you can easily start doing today. But it’s worth being aware that the possibility is coming and it could change what you can do with your photos.

For instance, since the latest HDR screens can show a much more convincing version of the world than bright lights reflected off good quality prints, we may start to see HDR displays become a leading way to exhibit photography. If that’s your target, you wouldn’t need to worry about also producing a more restrictive version for SDR display, so you could process your images on an HDR display with HDR output in mind.

Apple’s Photos software, running on latest Mac Pro and combined with the rather pricey Apple XDR display, is one of the few combinations to currently let you edit photos for HDR displays.

Alternatively, embracing a Hybrid Log Gamma workflow would mean that nearly everybody could view your photos but that those with SDR monitors wouldn’t miss out on the subtlety in the brighter parts of the image. Or perhaps there’ll be a need to prepare two versions of your best images: one optimized for HDR and a second that still looks good to everyone else.

If you haven’t already drawn this conclusion: it’s early days for HDR photography and not all the elements necessary for exploiting its photographic potential are in place, yet. But it is coming. And your next TV could be a chance to expand your photography beyond a set of limitations you might not even have realized were confining you.


SDR/HDR demonstration by Rishi Sanyal with help from Dan Bracaglia

Author: Go to Source