HDR is the most important development in photography since the discipline was invented.
That’s because photography and photographers have always lived with a dirty little secret; the brightness range reproducible by straight photographic techniques is laughably small. HDR has now expanded that by, let’s say, doubling the capturable brightness range.
HDR is an idea about brightness.
It is not an idea about color. Color is lovely and because of that people always assume that color is more important in image-making (painting or photography) than it really is. But, compared to the importance of brightness in these disciplines, color is nothing. All painting and photography is a meditation about brightness. Nearly all changes in these disciplines involve a new way of thinking about how to render shadows.
HDR processing consists of two phases. In the first phase multiple pictures are mapped from a 12- or 14-bit capture space onto a 32-bit picture space. In the second phase the entire brightness range actually used in the 32-bit space is tone-mapped back onto a smaller space; one which is, perhaps, as wide as nine bits. This is done because no viewable medium can display more than nine bits of information (most display less). This is starting to change with certain (scarce) wide-range display devices but it doesn’t affect us yet. For us nine bits is still a hard parameter. If you want to see it then it has to fit into about nine bits of displayable space.
As I mentioned above people currently are mapping multiple images into 32-bit space in order to extend the brightness range. This is a time-honored technique and it is as old as photography itself. I honor those who are working in this area; they are getting amazing results and teaching us a great deal.
A case can also be made for single-image HDR. Multiple-image HDR is difficult to do right. It's almost impossible to align multiple digital exposures correctly as a look at most multiple-image HDR photos will clearly show. Even one pixel off will degrade the picture. The insistence on multiple-image HDR must exclude certain important types of photography (sports, racing, nature photography, children, candids: anything with rapidly moving objects). More affirmatively I think that tone-mapping techniques have revealed to us just exactly what we’ve missed in our single images. Tone-mapping techniques have led to the potential rejuvenation of every photograph ever taken as long as we have it in its original form (RAW file, TIF file, photo negative, etc). Personally I was astounded to discover the actual brightness limitations I’d been living with over the years. Single-image HDR does have its challenges and I think there’s a lot of work to carefully define those challenges and how to overcome them. That is the purpose of this blog. None of this is intended to denigrate people working in multiple-image HDR. I recognize both the hard work and the astounding results. There’s room for everyone. People often use the term ‘pseudo-HDR’ when referring to single-image HDR. I, for one, think that we should eschew the use of this term. Why? Because it doesn’t aid the thinking process. There’s nothing phony or false about single-image HDR. It’s simply an HDR that skips the 32-bit space mapping function. Or if it is done then it is idempotent. With single-image HDR, in effect, we go straight to the tone-mapping phase. It’s just my personal hobby-horse but I know that the single-image HDR workers also have something to tell us.
Remember, though, that multiple-image HDR and single-image HDR are simply rapidly passing technological phases. But multiple-image HDR will pass first for the simple reason that there are billions more single images out there that would benefit from HDR processing (a business opportunity for someone). It’s inevitable that the camera manufacturers will support an HDR mode directly and they’re going to do it sooner rather than later. The ideal solution would be a sensor that captures, say, 16 brightness zones and a camera that incorporates it and which makes the number of desired capture zones user-selectable. Does anyone doubt that the next three years will produce such a camera? I don’t.
Extended brightness range is not the answer to every pictorial problem. Many photographs are taken expressly because much of the picture space is effectively blank through over-exposure or under-exposure. This is the modern photographic aesthetic and we should remember that HDR flies directly in its teeth.
HDR practitioners sometimes suppose that extended range is always desirable.
It isn’t.
To support the continuously articulated picture surface that HDR promises will require a new aesthetic. One that’s more characteristic of modern art (or art before the fifteenth century) than ‘photographic realism’. (There are good remarks about all this in Hockney’s Secret Knowledge, 2001). At the very least HDR (in whatever form it comes) will force us to re-learn that every picture is an artifact; a completely artificial creation. For example, there’s a photograph on HDRCreme of the Spanish town Ronda (http://hdrcreme.com/photos/3236-Ronda-Panorama). When confronted with this picture one of the anonymous reviewers said: “I'm not sure it needed the full HDR treatment, which in my mind adds a level of un-reality to what is otherwise a good shot.” Inadvertently Mr. Anonymous uncovered a profound truth in his remark. The only thing is that Mr. Anonymous didn't realize that all pictures are profoundly unreal. There is no purity in art. Every image, no matter how it is made, is completely artificial. There is no ‘realism’ in photography as a good look at that Ronda picture will tell you.
So here is my manifesto:
a. Every picture is an artifact pure and simple.
b. Multiple-image and single-image HDR are just passing phases and they will be replaced with a camera that supports extended brightness ranges.
c. We should investigate the older decorative aesthetics in order to find guidance to this new world of the continuously articulated picture space.
d. Stop the flames. Flames will not help us. There is nothing sillier than grown men (and we are mostly men) arguing about the appearance of a picture. We can learn from everyone.
e. Let’s stop beating up on the extreme-color people. This nearly out-of-gamut color is a mark of the earliest phases of HDR. No one, even the designers, really knows how to use these sliders for optimal results. Most books on HDR recommend that you move the sliders around and ‘play with them’ in order to learn how it’s done. There’s a place for expressionist color in photography as much as there is a place for it in painting.
f. We have much to learn from our painter cousins. They have been practicing local brightness optimization for centuries before Chevreul pronounced the Law of Simultaneous Contrast of Tones. They could instruct us if we had the humility to listen.
g. We have an important task in hand and that is: How is HDR to be controlled? How, for example, do we modify brightnesses without modifying colors? What shall we do about the noise in single-image HDR? What shall we do about the lack of contrast inherent in all HDR? What does it mean (if it means anything) to tone-map color? How many images is optimal in multiple-image HDR before the lowered contrast degrades tones in the brightness ranges of interest? We need to know the answers to these and a myriad of other basic problems before we can convince others that HDR is the advance which it really is.
h. I mentioned it above but, above all, humility. Wynton Marsalis says: ‘The humble get better.’
Robert Consoli
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