Beginner mistakes in HDR
Article by Darin Rogers
Five Mistakes I’ve Made
When Jimmy asked if I would be willing to write a monthly tutorial for this site, I was initially a bit intimidated. I’ve been dabbling in HDR off and on for a couple years now, and putting a lot more energy into it recently, but I certainly do not feel I’m an expert. Of course having been at it for a while now I have learned a few things. And I’ve made quite a few mistakes also, some of which I unfortunately still make from time to time.
Some of these mistakes are what I’m going to cover today. I won’t go into a lot of detail about proper technique or how to correct certain problems related to these mistakes. Most of them have probably been covered here in other articles and in greater detail. My hope, however, is that this helps you avoid some of them yourself.
Not capturing enough exposure range
Three bracketed exposures +/- two stops are typically enough to cover the dynamic range for most situations we encounter. Except when it’s not. There are times when you might need five, seven, maybe even more, exposures to cover the entire dynamic range, and there have been a few times when I haven’t got as many as I needed. Unfortunately my camera will only do a 3-exposure auto bracket so in a sense this has happened due to laziness or simply not paying attention.
A good example of when you might need more than three shots to cover the entire dynamic range is when you are shooting directly into the sun. There will be plenty of highlights in the sky but also potentially a lot of deep shadows that may require more than three shots to pull out all the details.
I’m usually more concerned about getting all the data in the highlights and a little less fussy about not capturing all the shadows. I don’t mind having areas of shadows in an image. I find that removing all shadows tends to reduce some of the realism. This is, of course, a personal aesthetic but the point is that ultimately it’s best to collect as many exposures as needed so that we have that creative option.
Capturing the wrong exposure range
Camera meters are not perfect and can easily be fooled by a number of lighting situations. Rely too much on the camera meter to get that middle exposure and you may find you still haven’t captured enough data. Of course it’s best not to rely on the meter too much in general. I now have a more intuitive feel for situations where this might be a problem, but I am also more conscientious about regularly checking the histogram. Below is a histogram, from a few years back, of a middle exposure of a 3-shot bracket where the camera meter mis-read the lighting and the exposure is weighted too far to the left. Because I wasn’t paying attention, even with three bracketed exposures, I didn’t get the highlights information I needed.
The picture below, while not a particularly exciting image, illustrates a situation where your meter, and you, could be fooled. The camera meter will expose for the dark side of the building and grassy area tending to over-expose the overall image and your three exposure bracket as well. However, in this case I metered off the sky which gave me a properly balanced set of exposures.
A perfect situation to fools your camera’s light meter.
There are of course ways of correcting this in post-processing but it’s always best to get what you need in the camera.
Not understanding the functions in Photomatix
I wonder what this slider does? I’ll just move it way over here and see what happens. Argh! That doesn’t look very good.
To a certain extent, we all probably do that. How else are you going to see what effect it has on your image unless you experiment? While it can be an effective learning method, just guessing what’s going to happen by randomly twisting knobs and turning gears is a haphazard way of going about post-processing.
Although I now have a much better understanding of the sliders and functions in Photomatix, to be honest I still don’t fully understand many of them as well as I should. However, having taken the time to learn some of the functions of the software, and having some idea of how a particular slider is manipulating the pixels and its intended effect on the image, has given me greater confidence and control in achieving my vision.
Not recognizing chromatic aberration
Hmm, why are the edges of that building glowing?
Chromatic aberration typically manifests itself as colored fringing along edges of high contrast. The effect is, in part at least, an optical one caused by your lens. Aside from optics there are a number of other potential contributing factors and as such it is not specifically an HDR issue. However, HDR processing can significantly magnify the problem and seems to introduce some fringing anomalies of its own. This wasn’t a problem I initially noticed or understood but since I’ve recognized it, it’s been a learning process in how to deal with it.
Some images can be a real pain to try and clean up, the image below being a good example. Photomatix has a tick box for reducing chromatic aberrations. I haven’t noticed that it helps all that much, although maybe it helps more than I realize it does. I do most correction in Lightroom – both before and after converting the image to HDR – which with version 4 now has some really useful tools for correcting chromatic aberration and fringing.
Lots of ugly purple fringing
Still not completely perfect, this image took a lot of work cleaning up chromatic aberration and fringing.
When referring to over-processing, I’m not referring to those over-baked HDR images that look like the glowing aftermath of a nuclear accident. Although it may have some artistic merit, it’s never been a look I’ve been particularly interested in. When I refer to over-processing in this case, I’m referring to things like saturation, converting to black and white, and a few other effects that are essentially replicating those available in Lightroom or Photoshop. Making these adjustments in Photomatix will bake those changes into the image, leaving you with a lot less flexibility if you decide later you want to make changes. I only use Photomatix to the extent necessary and do the rest of my processing elsewhere.
Avoid doing black and white conversion in Photomatix.
Darin Rogers is a freelance photographer, writer, and part-time engineer. He is currently based in Darwin, Australia. You can see more of his work at www.darinrogers.net.