The Objective of HDR
Reflecting on my last article that dealt with the topic of high dynamic range, I cannot help but feel that I glossed over one fundamental concept – the objective. Why would anybody in anyway want to use the techniques if the possible product of the manipulation is a throwback to VW Beatles and tie-dyed t-shirts? Well, in the style of George Lucas, this is the second instalment in a series of articles dealing with the matter of HDR, but it is probably better thought of as Episode 1. In this post, I will try to unpack the question of ‘the objective’. May the force be with you!
To begin understanding the objective of high dynamic range techniques, it is worth looking at one fundamental truth of photography. No matter which era we speak of, the photographic process has never been able to entirely reproduce what the eye sees.
We live on a planet where 14 billion unique versions of the human eye interpret the world for 7 billion equally unique brains. The number of eyes alone, with all their natural variation, means that no mass-produced item or highly repeatable process will ever give rise to the number of possible interpretations of the world that exist, and this is to say nothing of perception. After all, the brain takes the raw data pushed through the optic nerve and paints on top of that its distinct set of prejudices and particularities. These traits have their origins deeply intertwined with the hugely complex worlds of neurology and psychology.
Even if we could create a process that catered for all the variants of the optic organ, as it were, it would be impossible to recreate the lifetime of learning and experience that translates the visual information into exactly what our minds perceive. For example, have you ever considered why your favourite colour is your favourite – yellow in my case – or, more deeply, why you have a favourite at all?
For me, appreciating that photography is intrinsically limited is at the core of the art, as it is in trying to cope with the boundaries that artistic freedom is born. HDR, for example, is simply the name given to various techniques that attempt to overcome the limits of a chosen photographic medium. No light-sensitive material – film, electronic sensor or bitumen on pewter, as it was originally – can simultaneously capture the brightest highlights and darkest shadows visible to the human eye. Indeed, there are only two options available for those who wish to photograph the world using natural light. Either work within the characteristics of your chosen medium and use any process limitations for artistic benefit – an entirely valid approach – or, as with HDR, use techniques that improve upon the intrinsic capabilities of the technology.
The difficulty with the latter option is that in using high dynamic range methods, photographers are not only freed from the shackles of the technology but are, in fact, also unbound from the confines of reality too. It is possible, especially with modern photography, to create images that represent more than what was initially visible.
A simple example of this trickery might be the horizon, with a bright sky and a dimly lit foreground. A photographer may be able to discern all the tones in the scene but given a large enough difference in the relative brightness of the sky and foreground, there will come a point at which a camera will not be able to do the same. The dynamic range of the scene will have exceeded that of the camera.
The HDR solution to this problem would be to take an exposure that perfectly reproduces the brightest parts of the scene and to combine it with another exposure that perfectly reflects the shadows. The final blended image will display details in the highlights and shadows that were originally outside the inherent capability of the camera.
Taking the example a step further: if there were perhaps clouds in the sky that reflected the sunlight and, in doing so, were too bright for even the photographer to look at, the scene would then be said to possess a dynamic range beyond that of human capacity. If an exposure could be taken that managed to accommodate those very bright tones, and this was then blended into the final photograph, the resulting image would represent a range of tones that is greater than those ordinarily visible.
The act of taking a broad gamut of tones and squashing them down so that they fit within the latitude of human optics is referred to as tonal compression. The degree to which compression is applied determines how realistic a photo seems. It was the overuse of compression that brought about the ‘fake look’ that left HDR with a rather poor reputation. On the flip side, the absence of compression altogether is also less than desirable. Without it, photographs can look flat and uninteresting, a detail that brings me back to the central point of this piece – the objective of HDR.
At its most elementary level, HDR techniques exist solely as a mechanism for ensuring that a photograph is a better approximation of reality. It is a way of recovering detail in high dynamic range situations that would otherwise be lost due to the restrictions of the chosen photographic method. At the same time, the ability of HDR to increase the level of compression beyond the bounds of reality has some attractive benefits too. There are less tangible aspects of an image that are often not well reproduced by photographs straight out of the camera, abstract elements such as atmosphere and mood.
Unlocking these complex dynamics depends upon more than simply a beautiful picture. It demands a connection with the emotional side of the human visual system. There are many ways to forge an emotional connection with an audience, and the judicious use of HDR is just one such method. The technique can give an artist the ability to exaggerate detail in parts of a photo that serve to reinforce the underlying feeling, a feat that is sometimes not possible without compression.
Ultimately, photographers are in the business of capturing small fragments of reality, pieces of the world that fit into the viewfinder. The art of the discipline is rooted in the skill to take those small pieces and to reproduce both the visual and atmospheric elements of the original scene. Sometimes, reproducing 'atmosphere' requires more than simply a facsimile and it is here that HDR can help. The techniques exist to provide photographers with the ability to augment reality in the pursuit of an emotional connection – but be warned, straying too far from the truth will likely land you the title of amateur!