Ciderhouse is going to southern France.

Ciderhouse is unavailable for a month since S and I are going to Barcelona and then into southern France (Arles, Nimes, Nice, Aix de Provence, etc.).  We leave tomorrow and will be back on April 19.  I'd love to see fans of Squinchpix or Ciderhouse on the way and we'll be twittering in the hope of making contact.  Best to all of you until we come back and, in the meantime, you might like to look at some blog entries that I think might be helpful to you.
 Real HDR vs. Pseudo HDR
 FDRTools and the Compressor Algorithm
Dynamic Photo HDR and Photomatix: Color Compare
Why Photomatix is a poor choice
Dynamic Photo HDR and the Halo-Matix Algorithm
Doing HDR in pieces
A Simple HDR Workshop
Single Pixel shift in HDR alignment. What does it mean?
Noise in Single Image HDR. A Workshop.
Manipulating L-channel in Lab with HDR

Until we get back ...

Lars Roglin writes

One of my readers, Mr. Lars Roglin, of (I think) the Netherlands (see his gallery here) writes the following in response to one of my old posts:


Hi Bob,

interesting calculations, but I think you have one major flaw in your assumptions. You state: "Let’s say that the time to make all these exposures is 10 seconds."

With modern DSLRs this might be the case for long exposures and night shots but e.g. my EOS 40D is able to shoot at ~6 fps (the EOS 1D Mark IV even at ~12 fps) at full speed. So your 10 seconds change to .5 seconds for a series of -2EV,0EV,+2EV (0.25 or 1/4s respectively)!

In addition, I would assume that for most typical landscape shots clouds might be further away than a mile, so proper alignment should avoid stuttering.

If you want to push it to the limit, you could perhaps limit yourself to 2 exposures, which would push it to 1/8s which should even allow portrait shots (although perhaps with a higher reject rate - but shutter speeds of 1/8s and even 1/4s is not unusual in available light photography!)

Curious what you think about that.

Cheers,
Lars






My answer is as follows:

Hi Lars,

   Whatever you're doing your gallery shows that it's successful.   I did use a large number for the time it would take to make multiple exposures.  Great cameras like yours allow for much less time to accomplish the same number of exposures so the problems I outlined would be minimized for you.

  

   Two points:

  

   1. I shouldn't allow myself to be drawn into the 'average cloud thing'  but I can't resist.  So, in the spirit of fun, let's say that the average cloud height is about 2000 feet.  And let's say that the angle to the nearest cloud in the landscape photo that you're taking is 45 degrees.  Simple trig tells us that the hypotenuse of the resulting triangle (the hypotenuse is the direct distance from the camera to the nearest cloud as defined above) is 2828.4 feet.  If that cloud is moving faster than about 1.92 miles per hour (in parallel with the sensor plane) then that's a displacement of 1 pixel in half a second. (I'll leave the math to you, Lars).  It's not unusual for a cloud to travel about 20 mph and those conditions would translate into a 10 pixel offset even in half a second.  These numbers are full of assumptions and I'm not trying to prove that you will necessarily have a problem with your equipment.  But the fact is that we see a lot of cloud displacement (and foliage displacement) in multiple image HDR.  It must be caused by something (perhaps it's not coming from Canons?) and the math (even highly speculative math like this)  suggests what it is.  I'm just not personally optimistic about such a technique but that means nothing if you can make it work.

  

   2. I want to approach this from a different angle.  Let's say that you wrote me a letter and said "Bob, I invented this great new way to shoot photographs!  Instead of using f8 at 250th of a second for normal lighting, I've pioneered what I call the 'slow shutter'(tm) technique.  The benefits of a small f-stop are so obvious to me that I always shoot at f78 at one/half second even, I repeat, in normal lighting conditions."  And then you would carry on, perhaps, about the incredible depth-of-field and that everyone should always shoot at speeds  of 0.5 seconds or even longer.   Well, if I received (or if you received) such a letter we would suspect that our correspondent was cracked.  But that's what you seem to actually be advocating.

      However, I know that the f64 school of American photographers (Weston and Adams and the like) actually did shoot this way so maybe I need to go back and review what they actually did and what problems they encountered.  Perhaps you would be interested enough to look into it and write back about what you find?  Thanks for your letter.

  

   Best,

Bob

Real HDR vs. Pseudo HDR

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.