HDR Timelapse – Tutorial

This is a follow up to the previous intro to timelapse photography and will discuss using HDR images as the input. I started a group on Vimeo for HDR timelapse and there’s some absolutely stunning work in the collection from some truly talented artists. I’d suggest checking out if you’re looking for some creative inspiration.  HDR timelapse is a very cool sub-genre of timelapse that I was first introduced to a little over a year ago by Walter Arnold of The Digital Mirage.  I haven’t decided yet whether to thank him or curse him for it.  😉  I would really like to see him do some more of this kind of thing though because the clips I saw that got me interested in the technique were very good.

HDR timelapse isn’t any different from regular timelapse once the shooting and HDR merging/tonemapping is done. Where it ups the complexity level is in the shooting. In addition the regular intervalometer, you need an interval timer that will combine with bracketing to get your input images for HDR merging. Shooting Nikon, I’m fortunate that some Nikons have that functionality built in. Other camera makers don’t and getting it can be a bit tricky. The Promote Control mentioned in the previous tutorial will allow you to combine the two. If you’re a Nikon or Canon shooter, Chris Breeze of Breezebrowser fame has developed some software for shooting tethered to a laptop that allows you to combine interval timing and bracketing. The downside is, of course, that you have to be tethered which limits the usefulness of the application in some situations. Canon’s EOS Utility doesn’t offer the combined functionality, nor does shooting tethered via Lightroom v3.x. It’d be very cool if a smartphone app could be developed that would allow you to control the camera via an iPhone or Blackberry (or other smartphone) but still capture to the onboard memory card (sometimes I really do wish I could do programming…… well, no, not really).  When I used to shoot Canon I tried a couple third party intervalometers and while I could get them to combine with in camera AEB, it was kludgy at best.  Some of them top out at 99 shots before having to be reset so if you’re doing a 3 shot bracket, you only get 33 brackets before having to stop to reset the intervalometer.  I don’t believe something like the Canon TC 80N3 can be used to combined interval timing and AEB.

What mode do I shoot in? This is a matter of a fair bit of debate in timelapse circles.  It’s also a bone of contention in non-HDR timelapse but seems to come more into play when HDR is added to the mix.  There are those who believe full manual is the only way to shoot timelapse and particular HDR timelapse.  Their reasoning is that they don’t trust the ‘automatic’ part of modes like Av and feel there’s too much inconsistency in shutter speeds to be reliable.  Personally, I don’t put a lot of stock in that.  I recognise there can be variations but don’t feel they’re significant enough to cause problems.  In addition, I want the shutter speed to be variable to account for changing light conditions.  If I start shooting in cloudy conditions and over time the sun comes out, if I’m shooting in manual I’m going to be overexposing in the brighter conditions.  Shooting in Av, the shutter speed will adjust automatically and help keep my exposures consistent.  The unwanted side effect of shooting in anything but manual, according to some is a thing called ‘flicker’.  Flicker is a visible variation in light levels in the video clip that, in extreme cases can have an almost stroboscopic effect.  While I recognise flicker can and does happen, I’m not convinced the major cause is shooting in a programmed mode like Av.  Light levels change naturally over time.  In timelapse those changes in light level are sped up and can appear as flicker.  In addition, I think the added post-capture processing of merging and tonemapping HDR sequences can have an impact on flicker.  Tonemapping algorithms, even if the settings are the same from set to set, are going to process each set differently.  There are reasons for this.  Again, changing light levels from set to set will cause the tonemapping operators to be applied differently.  In addition, HDR is still a relatively new technology in photography and tonemapping operators are still being improved and refined.  The newness of the technology I think helps contribute to some of the inconsistencies in tonemapping from set to set.  So while I don’t completely dismiss the concept that shooting in manual will help minimise flicker, I’m not convinced that it’s the major contributor some feel it is.  Bottom line, shoot manual or Av, whichever you’re comfortable with.  In addition, if you want to try to capture what the hardcore timelapsers call the ‘Holy Grail’ – the transition from sunrise to daytime or daytime to sunset – you really have to shoot Av because the light levels are changing so much and so quickly.

What format do I shoot in? The same concepts apply here as with regular timelapse.  RAW gives you more flexibilty but takes up more card space.  JPEG takes up less card space but gives you less flexibility in editing so you need to be more careful in setting up the shoot to be sure you’re not cooking in something like a wonky white balance that will affect the rest of the processing later on.  Keep in mind that HDR merging will exaggerate colours and colour casts in source images so if you’re going to shoot JPEG you want to take extra care in setting WB and in setting up the camera processing settings to give you JPEGs that are tamer in terms of saturation and contrast than if you were doing single shots.

What should the spacing between shots be? This can get a little tricky with HDR timelapse.  Because you’re capturing a bracketed set, you need to make sure that the time between sequences is long enough that you can capture the full bracketed sequence before the counter gets to zero for beginning the next sequence.  The reason for this is that most interval timers start counting down automatically when the shutter is opened the first time; not when the shutter closes the last time.  There are some that don’t start counting till the single shot is done or the seqence of shots is done but most don’t.  You need to build your total shutter speed for the sequence into your spacing between sequences as a result.  So, if the total shutter speed for a 5 shot sequence is 8 seconds, you can’t have the interval timer set for 6 seconds.  It needs to be 9 or longer.  The other thing to consider is if you are going for the Holy Grail and going from light to dark (daylight to sunset) your shutter speeds are going to get longer over time.  You want to build some slack into your timing so that you’re not having to reset the timer all the time.  Use an aperture that’s a stop or two wider than you might normally or an ISO setting that’s higher than you normally would to give you that working time.  Depending on how dark you’re going to go, you may need to stop the camera and reset the sequence but you just don’t want to be doing it all the time.  When you touch the camera to reset the sequence (not a problem if you’re using a remote), there will be some jostling and pronounced shake.  You can use this to your advantage.  You can use it to adjust the focal length or camera position include a transition or two in the sequence which can add visual interest.  That’s what I did in this particular sunset clip.

How long to I need to shoot for? Same methodology applies as in regular timelapse.

How many shots do I need to take? The same math applies as in regular timelapse with one exception.  You need to multiply the number of shots by the number you’re capturing in your bracket.  So if I need 240 shots for a 10 second clip and I’m taking a 5 shot bracket, I need to actually shoot 1200 images.  Card space becomes vital when doing HDR timelapse because of the huge numbers of shots being captured.

OK, I’ve got my shots, now what do I do? The first step, obviously, is to process and tonemap your HDR images.  Ideally you’ll want to use an HDR software application with batching capability.  Also ideally you want to use an application that will allow you to save a preset and apply that preset to tonemap the images in batch mode.  Take one sequence, merge and tonemap it manually.  When you’ve got the settings where you want them for the look you want in the resulting video clip, save those settings as a preset.  In batch mode, have the software save the intermediate 32 bit images – this way if you don’t like the tonemapping results you can come back and reprocess them with different settings – and have it apply your tonemapping preset and save the tonemapped images.  Some HDR apps will let you choose a custom name followed by a numerical suffix.  This will let you get your sequencing done at the same time as you process your HDR images.

From there, the steps are the same as with regular timelapse.  Import the sequence into your software of choice and export the video clip.

In the next instalment, I’ll work through a sequence from start to finish in a free piece of software called Virtualdub (Windows only).  Vdub has some nice plugins that can help you deal with flicker as well as camera movement such as wind buffeting.

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