There's a lot of discussion on the web about the difference between 'Real' HDR and something called 'Pseudo' HDR. You know how it goes; 'Real' HDR is made with more than one image and 'Pseudo' HDR is made with only one image. To all of which I say 'Balls!' If you use HDR tone-mapping algorithms to get everything you can out of a single image then it's as real as HDR can be. In fact, not a lot rides on the outcome of this discussion (it's a variation of the Essentialist fallacy) but I had an experience recently that made me think again about what 'pseudo' HDR might really mean.
I was on Crete last year and, at the palace of Knossos, I took about 600 shots and all of them were more or less defective. It is the Mediterranean after all and so all the shots were either over-exposed or under-exposed but usually both. And yet, while looking at them, I felt that all the detail was really there although pushed to the edges. If only I could find a way to retrieve the detail on both ends of the brightness range. I process my pictures in stages; the first stage employs Lightroom 2.6. So the problem was to find a method of working in Lightroom that would take the rough edges off. Here, for example, is a shot of a wall and a buttress in Knossos that will illustrate a typical starting point.
In this shot the darks are not too bad but what to do about the highlights?
The first thing I did was set the 'Recover' slider to 100. Here's the result:
'Recover' moves brightnesses on the extreme bright end back towards the middle. In other words the effect is to manipulate one end of the histogram without modifying the other .. or at least not very much. By doing this we can see that there is some detail in the brightest stones on the right. They're not completely burnt out. The next step is to turn the brightnesses all the way to the bottom. Here we go:
By doing this we've regained all the detail in the highlights that we're likely to get. In the next step we turn up the fill slider as much as possible consistent with the current state of the brights. Here it is:
Now we have a pretty dim image but all the brightnesses are in agreement with each other. The shadows are suitably dark with respect to the brights. There's full detail in the darks AND full detail in the lights. We're light-years away from where we started. Now we're going to turn up the brightness gradually until the brightest areas of the photo are just under where they should be. Here we go:
Now the steps that I've outlined typically degrade the contrast. The fill slider and the contrast slider are really opposites. The contrast has to be fixed particularly in the lights. I do that in parts. I begin by moving the 'Black' slider up to about 15 (way too high for an ordinary photo). Here's the result:
Before we fix the rest of the Contrast problem I'm going to correct the color cast. If I don't fix the blue cast in the shadows now then changing the contrast will only worsen it. In Lightroom I just decided to use the 'Saturation' slider and I pulled the cursor downward in the shadows on the tops of the rocks on the left. Here's the result:
I present the whole Lightroom screen so you can see what the effect was of the Saturation change. The shadows are now monochromatic (pretty much) and upping the Contrast in the next step shouldn't worsen that. Now it's time to fix the contrast. By moving the Contrast or the Clarity sliders (or both) to the right we push the brights up and the shadows down so the trick in doing this is to increase the contrast without finally burning out the lights and pushing the shadows down so that you're back where you started from.
Here's my final version.
Now this photograph will clearly never interest very many people. Even now it's not really successful but it could be of some small interest to an archaeologist whose specialty happens to be this particular wall. It could use a lot more work. The local operator brush could probably be employed to good effect in the highlights. But what really interested me after doing this more than 550 times was how much like HDR the results of this kind of processing actually look. The final example looks like HDR (at least the shadowed areas do) and next I present another example of before and after shots in which the kind of processing outlined above gave the result an 'HDR' look.
Here's a 'before' shot of Knossos' famous colonnade as it came from the camera (complete with sensor dirt).
Here's the 'after' shot in which I used an aggressive 'fill' as described above.
And also this example. Here's the before picture.
The same picture after processing as I described. If I told you that this 'after' picture was HDR you'd probably have believed me. It just looks like HDR.
The following photo actually was processed with HDR software (FDRTools). The non-HDR version actually looks more like HDR (or our common expectation of it) than the one that actually is HDR.
HDR is always described as having a 'unique look'. But what is that look? Lots of people suppose that it has something to do with aggressive saturation of the image. Sometimes we're told that it makes photos look like paintings although the people saying this have no idea what makes a painting look like a painting. So let's answer that question first. What does make a painting look like a painting? Simple. A reduced tonal range. For technical reasons most painters never, and have never, employed pure blacks or whites. So that giving up those extreme tones right away reduces the tonal range. Also painters do not paint to obscure. They will never (or rarely) paint shadows as dark as they are in real life. In fact one of the chief goals of the painter is not only to paint clearly in the shadows but to paint full color in the shadows. Therefore any picture that appears to have a reduced tonal range will look painterly. (As in everything there are many exceptions. There are certain chiaroscuro painters who DO employ pure blacks and whites and virtually nothing in between. Such paintings gain in drama but relatively few painters actually paint this way.)
In photography HDR algorithms produce a reduced tonal range; in many cases a shorter range than can actually be handled by the output media. The resulting images feature weakened shadows; shadows no darker than if one had simply poured water on the ground. Doing this darkens the ground but does not obscure it and many shadows in HDR look this way. Also many HDR shots seem to show us a perpetual dawn.
So the moral of the story is that if you want 'pseudo' HDR pump up the fill slider.
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