But is it HDR?

I'm going to diverge a little here from the topic of my own photography to talk for a moment about photography in general and HDR and post processing in particular.

I'm sure that many of you are familiar with the work of Trey Ratcliff, the king of HDR on the Internet, reigning from this throne at Stuck in Customs. Trey's images are punchy and evocative with kaleidoscopic colors and silky smooth gradients, and tens (or hundreds?) of thousands of people follow him almost religiously. He is known for his extensive use of HDR and tonemapping as much as for his extensive travels around the globe.

A little digression here to clarify terms. HDR simply means High Dynamic Range (image). The human eye is estimated to perceive a scene with a dynamic range of about 14 EV (much more if you count the time consuming [10-20 minute] adjustments from extreme dark to extreme light conditions), while the typical high-end digital camera sensor can only register 12 EV, and the JPEG file format and most computer displays are capable of representing a mere 9 EV (which on LCDs is very sensitive to viewing angle). Strictly speaking, none of the images you see one the web in JPEG format are HDR images (there are other file formats capable of encoding true HDR images, but JPEG is not). What they are is Low Dynamic Range (LDR) representations of an HDR image--arrived at by the application of some tonal curve or algorithm. A process known as exposure fusion can pick the properly exposed pixels from a set of bracketed exposures and produce a low dynamic range (LDR) composite image which, although it is LDR, contains all of the relevant image detail from the HDR set which would normally be lost in black shadows and blown-out highlights. Such an image would not look very "HDRish", however. What we usually colloquially call HDR is in fact the result of a tonemapping operator. Usually a very specific one (Trey uses a proprietary program called Photomatix, which, of course, doesn't mention which tonemapping operator they use, although there is little doubt that they have appropriated one of the several published operators). Generally, what we call an HDR image on the web is really an LDR rendering of an HDR image after it has been put through the process of exposure fusion and tonemapping, although often (depending on the dynamic range of the scene) the fusion step can be skipped and only tonemapping used to produce the characteristic result. Confused yet? Don't be. The point is that yes, 'HDR' can be a laborious process involving a tripod and 15 bracketed exposures--or it can be as simple as applying a tonemapping 'filter' to a single image.

Lately Trey has been very active on the new Google+ beta system. He has (as expected) a large number of followers and each time he posts an image from his archive, a flurry of comments ensues. I've noticed that a common response to Trey's images (and also, now, any photograph which contains vibrant colors) is "But is it HDR"? People ask this for several reasons, but many of the comments go a little further to indicate their disdain for HDR processing, effectively saying "I think I like this photograph, but only if it is not HDR". "I like some HDR, but only if it is well-executed" (which is apparently never, in their estimation). Firstly, anyone looking at Trey's work should know right off the bat that most of it is tonemapped, even if it's not exposure fused, but most of it is both, and in the rare instance that it's not tonemapped, it's still heavily color-tweaked and smoothed. People follow Trey's work because they like it, but many of them seem conflicted about the issue of post processing--seeming to feel like they are only supposed to like beautiful images if they are 'real' and HDR images can't be 'real'.

Trey himself attempts to address these concerns with various justifications, saying that the HDR process produces images more in keeping with the natural perceptions of human beings than does ordinary photography--or that a certain object was "really that red" or "really that blue" to him when he was physically observing the scene of the photograph. These statements may or may not be true. The question I'm raising is: is it relevant? Does HDR require such justification? Even the people who question Trey's process still seem to enjoy his imagery.

Think about it. When was the scene depicted in a black and white photograph really that black and white? Rarely--never, if you count issues of lighting and color temperature. Did its tonal and spectral range accurately represent reality? Likewise impossible. These are simply the limits of the technology. Which are similar to, but significantly different from, the limits of human perception. Does that make a black and white photograph and less beautiful? I think not. Does it make it any less authentic? Again, I think not--certainly given the limits of the technology in terms of spectral and tonal accuracy.

The only authenticity to be found in a photograph is related to the camera itself. Certainly, a photograph can be authentic to the machine. It can be compared against reference charts photographed through the same apparatus. But take two differently designed cameras and use them to photograph the same subject and you will undeniably get qualitatively and quantitatively different results--none of which will have a whole lot to do with the vast amount of information that was actually there, radiating from the scene (ask Leica M9 owners about this or anyone else with a piece of camera equipment purported to be endowed with so called pixie dust).

Does it really matter to anyone that every one of the awe inspiring galactic images from the Hubble space telescope are in fact false color composites made in Photoshop and that the various nebulae depicted don't 'really' look like that? If not, then why do we care so much whether an image is HDR or not? If you like it, then like it. If you don't, then don't. That's fine. There are plenty of gaudy HDR photographs that everybody hates--including Trey. As with any image manipulation, it is possible to apply it to the point of distraction--and many people do. That's where the artistry comes in--and why are we so keen to insist that artists stop using artistry? After all, it seems obvious that while one man can use a hammer and nails to build a strong and impressive house, another can only use them to make matters worse. The difference is inherent in the wielder and not the tool.



Does the HDR process produce images that more closely represent reality than ordinary photography?

Yes and no. No, because, quite plainly, tonemapping and exposure fusion have nothing to do with the reality of the scene. And yes, because both are psycho-visual tricks which exploit specific aspects of the human visual system to make images seem more 'real' than they otherwise would or even appear surreal. In other words, they function like any optical illusion--not real, but, nonetheless, real to us. MP3 files aren't accurate representations of reality either, but they do offer massive compression of data, and that's very similar to what happens with a 15 exposure HDR set going into an exposure fused and tonemaped JPEG.

Is an HDR photograph any less valid or artistic than a so-called in-camera photograph?

Clearly not. The in-camera photograph is just as 'un-real' as the HDR rendering and in many cases the HDR rendering seems more 'real'. Obviously the impression is subjective. No photograph is accurately representative of reality in scientific terms. At best, it is an extremely limited sample of reality.


In terms of art, it doesn't matter how the image was generated. It could be a spontaneous snapshot or a laborious pure CG endeavor. If it's good, it's good. And if you can't even tell how it was done, then all the better. So why ask?

Personally, I like Trey Ratcliff's work--certainly not all of it, but due to the subject rather than the process (Seth Green is, after all, not a pretty man). I also like the work of the many great landscape photographers who don't (yet) use HDR (often getting by with GND filters, masking [a manual form of exposure fusion] and color-tweaking). Frankly, I don't think it matters in the slightest just how they manage to communicate their vision--what matters is whether or not they succeed.


Wikipedia's HDR article Trey Ratcliff's Google+ Profile Jim Goldstein's article: Why I Hate HDR: Photo Technology Porn