*HDR 101, Part 1 – Capturing Dynamic Range

the scale of luminance values as far as the eye can see…

Politics, Religion, Economics, HDR.  There seems to be little in the photographic world that starts such heated discussions as the concept of HDR photography and processing.  Truth of the matter is, it is a very popular technique and can be done with a multitude of results, some more visually shocking than others, but I believe HDR gets a bad rap too often.  Let me start off by saying, I am not an HDR expert.  I do not feel that my techniques are an end all by any means, but I have figured out some very helpful techniques that I feel can benefit those looking to get into, or better understand capturing and processing HDR imagery.  For me, capturing the dynamic range of a scene is the primary concern while the way these bracketed images are processed is an entirely personal decision.  Too often, I see people tonemapping single images, or running them through an HDR-like software to give it that grungy, gritty look and calling it “HDR.”  While many of those images have a very cool look to them in their own right, it still doesn’t quite qualify as a high dynamic range photo by definition in many cases.  C’mon in and we can discuss ways to capture the whole dynamic range of any particular scene along with some tips and tricks.

Dynamic range in an image or scene, is the measurement between the brightest bright and darkest dark in regards to luminance translated into photographic stops.  The dynamic range that humans are capable of viewing is many times greater than what current film and digital sensors are capable of reproducing in a single image file.  Herein lies the idea behind capturing and processing a greater dynamic range into a single image to produce a wider range of luminance value closer to what we are capable of seeing.  HDR (High Dynamic Range) imagery is the capture and processing of multiple exposures made at differing exposure values to attempt to blend properly exposed highlights, shadows and everything in between.  Many software programs have been developed recently that combine these bracketed exposures by way of local tone mapping, which is a method of blending the range of tonality and luminance from multiple exposures into a singular file.  This can produce a vast spectrum of results based on which software you use, or how you adjust the image within the software.

I have been intending to write a short series on HDR having spent the last year trying to fine tune my technique in both capture and processing, so this will be part 1.  I’m sure there are many other photographers out there with differing techniques, but these two have worked for me and are good starting points from which to gather the info to process into an HDR image.

Let’s make a quick note about the actual dynamic range capable of being reproduced on a computer screen and in print.  Most all computer screens, printers and photographic papers are incapable of displaying or reproducing the dynamic range and digital bit depth that any high contrast scene may actually present in true/real world luminance as the eye sees it.  That said, it shouldn’t stop us from using more info in an image file, so let’s get to it.

I’ve used two separate capture techniques at different times as well as a variety of different processing techniques when wanting to extend the dynamic range of any given image or scene.  We’ll start with capturing a wide dynamic range and move into processing in the next post.

For this technique, it will be handy to know how to shoot in Manual (for an article on how to shoot in Manual, click HERE), as well as being able to switch, and understand your metering mode (for an article on Metering, click HERE).

Capturing Dynamic Range.

There are two basic ways to capture bracketed exposures, AEB (auto exposure bracketing) and Manually, but to truly determine the dynamic range of a scene, I feel it beneficial to put the work in as depending on the actual dynamic range, there may only be one way to truly capture all the necessary values, but on the other side of the coin, conditions may limit the capture techniqe.

Establishing and Capturing Dynamic Range Manually:

        First, establishing the dynamic range of a given scene;

  • Set your camera up to Aperture Priority (A, Ap, Av, etc) and set your working aperture.  It entirely depends on what you’re shooting, and how you want to work with your depth of field in the scene, but for the sake of our exercise, let’s set our aperture to f/8.  The reason we use Aperture Priority is because when we are bracketing our exposures, we want to make sure our DOF and point of focus stays consistent.
  • To determine the Dynamic Range, I find the best way to do so is to set my camera up to SPOT METER.  If you’re unaware of how to do this, read the metering link above, do a quick google search on your camera, or pull out the manual and look for the “Metering” section.  Spot metering is essentially recording proper exposure (unadjusted at “midtone” by default) for whatever light is falling on/reflecting off of whatever you are metering in a very small point on the sensor which enables you to pinpoint exposure values in the scene.  What we are wanting to do here is use our spot meter on the brightest and darkest part of the scene which we are wanting to capture detail in.

The highlight “bookend” exposure

    • Find the brightest area in the scene, spot meter so that your light meter reads the highlighted area as the midtone (right in the middle of the light meter) and write down/remember the shutter speed that it lists to achieve that exposure.  (if your shutter speed cannot get fast enough, adjust your aperture to a smaller setting/higher f number).  Don’t take a picture yet…

The shadow “bookend” exposure

    • After recording the shutter speed for the brightest bright, do the same for the darkest area in the scene sticking with whichever aperture setting you used to record the highlight exposure value.  We will call these our “bookend” exposures, so remember the two shutter speed settings from these two steps.
(*If you are looking to more “naturally” represent your scene, and have a decent understanding on metering, if by your eye you notice that the shadow areas are lacking detail and you want to replicate that, you can under expose those by eliminating the slower of the bookended exposures which will keep those shadow areas at a stop below 18% gray (zone V) when capturing.  Alternatively you can do the same for highlights if you feel it would benefit the final scene.  For myself, I choose to capture the entire range and can always re-introduce muddled shadow detail or blown highlights later in post production.)
        Secondly, capturing the dynamic range manually;
By establishing the shutter speeds needed to record both the brightest highlights and darkest shadows in a given scene, we have basically determined the dynamic range necessary to capture all of the information we need to process the entire range.  My example was a 7 stop swing between my highlight and shadow bookend shots (where I took 7 shots in 1 stop increments).  Now that we have our beginning and ending shutter speeds (our bookend exposures), we can get to the actual capturing of the scene.
  • Firstly, for the best results, use a tripod.  I’d also suggest to employ your camera’s mirror lockup feature as well as switching the drive mode to self timer so that you minimize any camera shake.
  • Establish your focus and make sure to turn off Auto Focusing.
  • On the tripod, frame your scene and switch to “M” (manual) mode on your camera’s mode dial.  Set it to the aperture you used to determine the highlight and shadow exposures in the steps above.  Now, set to one of your “bookend” exposure shutter speeds.
  • We will adjust our shutter speed by one full stop with each shot until we reach our other “bookend” exposure, so after the first shot, adjust your shutter speed by one stop in the direction (either slower or faster depending on which bookend you started with) toward your second “bookend” exposure ending at that second bookend exposure.
That’s about it for Manually establishing and capturing the dynamic range.  Easy enough right?  Well, this technique works well unless you have a lot of moving elements due to wind, etc.  Once you get the basics down, you can capture six or seven shots in about 10-20 seconds (largely depending on self timer, etc) which is fine for static subjects.  You can cut that down to about 4 seconds or so by not using a self timer, but if the conditions allow for it, I’d suggest using the timer to eliminate as much camera shake/vibration as possible.  What if you’re trying to shoot on a nice clouded day where the clouds are moving (even slowly) or a light breeze may be moving trees, grass, etc?  Well…
Capturing Dynamic Range using Auto Exposure Bracketing:
At the potential sacrifice of the total dynamic range, you can employ your camera’s Auto Exposure Bracketing function when you need to fire off the frames more quickly.
Every camera is a little different and may offer a different range within it’s AEB function (search your camera manual for AEB if you’re not familiar).  Mine allows for me to shoot 3 shots, and normally I will space those out as far as possible, which for me is -2 stops, 0 and +2 stops.  Some cameras allow for 5 shots, some 7 with ranges as far as -3/+3 stops in 1 stop, 1/2 stop or even 1/3 stop increments.  To me, single full stops work well for most all scenes, or in a pinch I’ll use 2 stop brackets for scenes with high contrast.  The big trick with AEB is to determine what “O” is which is the scene’s midtone.  “O” on your light meter is midtone (zone V for those familiar with the zone system) or 18% gray.  Go into your custom functions menu and find bracketing sequence.  I choose to shoot at “0, -, +” meaning my first exposure in my sequence is my “0” or middle/midtone exposure which allows me to spot meter for the midtone, and use my Exposure Lock to set my midtone exposure before I recompose my scene.  Alternatively, if you choose not to spot meter when using AEB, I’d suggest to use your Evaluative/Matrix/Scene Average  meter setting which should do a decent job at establishing settings for a multi shot bracket.
  • Make sure you’re set to Aperture priority (or Manual) and have your drive mode set to continuous.
  • Establish your focus and make sure to turn off Auto Focusing.
  • If using the spot metering method, find something in your scene that you want to establish as your midtone.  On Aperture priority (or Manual), set your spot meter on that midtone, and use your Exposure Lock to set that to your “O” exposure.
  • With your midtone determined, frame your scene and set the camera up on your tripod.
  • With our AEB set and our exposure locked, fire away.  On continuous drive mode, you should be able to capture at least 3 frames per second or so which will minimize any movement in a scene.
These are two different ways to capture bracketed shots which we will open up in an HDR software for tonemapping and processing next here: HDR 101 part 2, processing Dynamic Range.  And here is a more in depth post processing HDR imagery using Photomatix  HERE.
Feel free to subscribe via the email link at the top of the page to receive email notifications when new articles are released.
Happy shooting, and we’d love to see any results in our Flickr Group here!
Tyson
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12 thoughts on “*HDR 101, Part 1 – Capturing Dynamic Range

  1. Good points! I couldn’t possibly care less about HDR and what it is or isn’t but bracketing shots is something I definitely ought to do more of (of which I ought to do more?) …sometimes English fails me.

    We just went on a 4 day trip to Malheur for birds (116 species!) and the changes in light that the eye forgets about makes a huge difference when you get back and see things under (usually) or over-exposed. Too late, Malheur’s nearly 400 miles away by the time the pics hit Photoshop.

    Sadder but wiser.
    -Terry

    The Flickr collection is at: http://www.flickr.com/photos/35742767@N04/collections/72157626694048239/

    The Malheur scenery set is decent.

    • Yeah, there usually isn’t much of a middle ground when it comes to HDR. Believe it or not, I think the processing of HDR as we do it now, will become less and less mainstream in the coming years. I think we’re close to seeing the HDR “Craze” peak. With each new iteration, digital sensors are becoming more and more capable of capturing a much wider range of exposure in a single file. I think this next round (largely driven by Canon, Sony and Nikon’s next offerings) are going to up the game with a larger jump than we’ve seen in the last couple releases. So many compacts (as well as the NEX cams, etc) are already providing an in camera multiple exposure processing to gain more shadow and highlight info and I don’t see that going away. In a few years, we’re going to have to underexpose our shadows and intentionally blow our highlights to get our images to “look like film” or at least replicate the exposure range that we’re capable of now. I guess, I’m a fan of having the info there in the first place and using it to further visualize your scene after the fact. I can always throw pixel info away, but trying to get it where it didn’t exist in the first place is much harder, hence these types of HDR software programs.

      I’ve been reading Ansel Adams book series and cant help but pull some similarities to the exposure and zone system printing techniques from modern dynamic range stretching techniques. Software will never be the same as darkroom development and enlarging, but I can’t help but wonder what AA or other prominent photographers of yesteryear would be doing with the tools available to us today. Is it something entirely different, or just a progression?

      I dunno, and honestly a couple years ago my opinion on certain techniques were very different than they are now after I’ve tried to understand them and implement them into my own workflow. And that has opened me up to many things I doubt I would have even tried lately. That photography keeps evolving for me, and my interest is continually fueled is a boon I guess.

      Thanks as always for the read Terry. Looking through your Malheur sets, I realize that I need to do some traveling! Great shots, it looked like a beautiful trip.

      All the best,

      Tyson

    • I think you might like it Inna. I’ve played around with a shallow dof and a multi shot HDR processing effect to play around with bokeh, but I certainly have to practice more… :) I am working on another post where I’m actually gonna walk through the processing side of it using a couple different methods, so, stay posted!
      ;) – t

  2. i will stay tuned :)
    i like it, T…. your HDR not overdone! and has glooming effect too…
    you are neat! neat one…
    hey, after practice your bleach bypass…
    right now i cant live without it… :D
    thanks T…

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