Natural HDR Processing

November 23, 2012  •  Leave a Comment

 

HDR: The Science, Art and Philosophy of High Dynamic Range Imaging

(Prepared for the December 6, 2012 IEPC meeting in Temecula, CA)

 

There is much already written about High Dynamic Range (HDR) imaging, especially the science of it, so I won’t go into that too much here. Essentially, the purpose of HDR imaging is to expand (or contain if you prefer) the range of light in a scene from the brightest areas to the darkest areas.  That is, to retain the details in both the very bright and very dark areas at the same time in a single image. This will approximate what our eyes are capable of seeing. Generally, if you shoot in full shade or at dawn or dusk, HDR imaging isn’t generally necessary because the camera can usually render the detail in the bright and dark areas--the scene’s range of contrast.  

 

Before HDR software like HDRSoft’s Photomatix or Nik’s HDR Efex Pro, (and now many others) we had to control capture through the use of graduated and split neutral density filters, or bracket our shots and then manually mask multiple layers to show all the detail in a single image.  Today we have the availability of sophisticated software tools that can do much of that for us; including Adobe Photoshop’s ever improving HDR capability.  Even camera manufactures have started implementing HDR functions within the camera and applied at time of capture.

 

In a nutshell, HDR software compiles all the data from bracketed images into a single image. In fact there is so much data that output devices are unable to display it all.  The HDR software then Tone Maps it so output devices like your LCD monitor can display it. In a sense, we are tone mapping when we mask multiple bracketed shots. However, HDR software is essentially capable of mapping at the pixel level.   At this point all of the data is present in memory and is available for selective manipulation through the HDR software interface. Most HDR programs have various pre-set starting points, usually shown as thumbnail images for you to select from.  I find most of these basically unsatisfactory for final use, so just consider them as settings to start from.

 

Unfortunately, but perhaps expectably, HDR imaging has become synonymous with a “look;” the HDR Look.  I say its unfortunate because it is a tool capable of much more than its ubiquitous illustrative look.  A lot of my photography includes some HDR workflow in it, but it’s not often obvious that it does. To be fair, sometimes I do create an image that has the look, and I think there’s a definite place for it.  However, as my skills and tastes have evolved, I’ve been moving back towards a more natural photographic result, but I still utilize bracketing and HDR tone mapping at times to provide the detail I desire in the bright and dark areas.

 

I first started using Photomatix in 2007 and I was enamored with the look. So much so, that I, like many others, was a bit heavy handed.  I could make a photograph stand out (where it wasn’t going to on its own) by giving it the HDR Look.  I found this very satisfying, at least until it was no longer novel since so many others had started doing the same thing.  As I improved as a photographer my tastes changed.  I also became more sensitive to a significant downside of poorly administered HDR imaging.  That is the tendency of HDR applications to create halos around areas of strong contrast, over saturated electric colors, muddy whites, dull blacks, and unacceptable levels of noise.  The good news is, most of these issues can be overcome with knowledgeable and discriminating application of the software’s controls.  This is where the art and philosophy of HDR imaging really comes in.  Before I share my personal preferences, let me reiterate that I think there is a place for the HDR Look, but preferably without the unpleasant aforementioned artifacts. First off, much of photography is art and thus subjective.  As art, there is no real right or wrong.  If you like it, then by all means go for it.  However, I believe that there is a universal aesthetic that governs what we perceive as attractive.  In the same way that music can be either pleasant or just noise. 

 

Fig-1. My early first attempt and example of a bad HDR image

 

For some good examples of images successfully utilizing HDR technique, take a look at www.stuckincustoms.com.  Trey Ratcliff, in my opinion, has mastered HDR imaging.  Some of his images are subtle, while others are much more severe in result.  Who’s to say you can’t do both?  Trey’s blog is a great resource for all kinds of things photography so be sure to visit it when you have the chance.

 

I like to employ the HDR Look in situations where the photo on its own will look rather boring.  I especially like what HDR does to wood like in old barns, or its effect on rusty cars, or where things are overly busy, even ugly, like junk yards or construction sites.

 

Most of the time my preference for HDR is to expand the detail in the contrast range of my photographs.  This is especially true in landscapes and architecture. I’ve tried several HDR applications, but my preference is still for Photomatix. Perhaps because its the one I first used and am most familiar with.  For that reason I’ll use Photomatix in my examples.

 

Before you can load your 3 to 5 or even 9 or more image files into HDR software, you need to properly capture bracketed images with your DSLR camera.  It’s at this point someone wants to know if you can just take one image file and save it back out over and under exposed to put through HDR software.  You can certainly do that to get something similar to the Look, but its not really HDR because dynamic range of data just isn’t there.  You can get similar results with in Photoshop or a plugin from someone like Topaz Labs.

 

 

Although others may have some different advice, I find the suggestions below to work well and not be overly complicated. 

 

  1. Shoot RAW!  There’s no point trying to expand the amount of data with anything less.
  2. Select the minimum acceptable ISO to minimize noise and provide the best quality.
  3. Be sure to set your camera to Aperture Priority.  Its faster and easier than Manual mode.  If you were to choose Program mode, the camera may adjust aperture between shots changing depth of field focus.
  4. Use a tripod.  I know its possible for the software to align the images, but your results will be much better if you’re using a tripod.  Also, a tripod will give you the ability to use a slower shutter speed for situations like smoothing water.
  5. Set the camera to fastest burst mode available.  This will keep trees and other objects influenced by wind relatively unchanged between shots.  Although its now possible to select a single image to minimize the effects of moving object ghosting, small details like moving leaves are often difficult to solve. A fast shutter speed with little lag between shots will help alleviate those situations significantly. 
  6. At a minimum, select a bracketed range of at least 3 frames and 2 f-stops apart. For example, the equivalent of EV-2, EV0, EV+2.  Some cameras can’t spread the values two f-stops apart in one frame.  If your camera can only spread stops by one between frames, then set the bracket to at least five frames: EV-2, EV-1, EV0, EV+1, EV+2.  I find Photomatix works a little better with smaller jumps between frames. Although the software will except an even number of files, I prefer to always provide an odd number as this gives me an equal range of under and over exposed images.
  7. If the contrast range of the scene is really great, increase the frame captures to 7, 9 or even more. If you wish to be precise, you can use the light meter in the camera to determine the distance between the brightest and darkest areas. Don’t forget to take advantage of the histogram as well.  In most cases, 3 frames two f-stops apart will deliver satisfying results.
  8. When your done, don’t forget to reset your bracketing or you may ruin your next non-HDR shooting.

 

Now that you have your 3, 5 or more RAW files, what do you do with them?  If you have the stand alone version of Photomatix (my preference) you can select the group and just drag and drop onto the program’s icon.  Without going through every step, you’ll end up with something like Fig-2.

 

Fig-2. Photomatix Pro Preprocessing Options Screen

 

Once you Preprocess the images, you’ll end up with a screen similar to Fig-3.  You can explore different settings by clicking on the Preset Thumbnails. You can also choose from two different Processes: Tone Mapping or Exposure Fusion, as well as different Methods for each.  I generally stick with the Tone Mapping Process and Details Enhancer Method.  However, different images may work better with one of the other selections.

 

Fig-3. Main Photomatix Processing Screen

 

The biggest problem most beginners have with HDR processing is over doing it and not knowing how to deal with the inherent artifacts like halos and muddy whites.  With regard to the first issue, there is a tendency for new users to want to go stronger.  The idea being if a little looks good than more ought to look even better.  I like to think of it like a lady’s makeup, where as a little can make a women look beautiful, but too much makeup can make her look clownish (or worse).  To moderate my impulse to go too strong, I like to toggle back to a copy of the neutral exposure of the original image.  

 

Fig-4. Original EV-0 Image.

 

It’s surprising to see just how far the HDR version has actually come by comparison and helps keep me from going overboard.

 

How I approach the second issue of tell tale HDR artifacts, I usually start with a preset I saved that often gives me a dynamic yet reasonably realistic look.  From there I make adjustments based on my image desires and on controlling artifacts.  

 

Here is the basic group of settings I generally start with:

 

Process = Tone Mapping, Method = Details Enhancer

Strength = 62

Luminosity = 6

Detail Contrast = 6

Lighting Adjustments = +2

White Point = 300% or greater

Black Point = 10% or greater

Micro Smoothing = As needed; usually 8 to 20

 

Fig-5. Developing the HDR Image

 

All other controls are left at the startup default, and I only change them if it seems really necessary.  An example would be color and temperature.  I find the Photomatix setting of 46 is plenty saturated and is on the cool side temperature wise.  I much prefer to make these adjustments in Photoshop or Lightroom.

 

I make adjustments to my preferred preset as the dictated by the image. There is no one good formula that works for all images despite what some have published.  It’s just a place to start from. Additionally, I don’t begin to try to do it all in Photomatix. Once I think I’ve gotten all I can from Photomatix I save it and then open the file in Adobe Camera Raw, make some adjustments and then complete my work in Photoshop. That part of the workflow is better left for another discussion.

 

Lets get back to dealing with those troubling artifacts I mentioned earlier. Here is where, in my opinion, some of the philosophy of aesthetics comes in.  HDR software does a brilliant job of mapping the wide range of available levels of contrast and tone.  In so doing, it tends to spread or flatten out the tonal detail in all parts of the image, which often leaves it looking rather dull or flat.  We need to restore some of the contrast, especially in the middle tones. That also often means we need to add some brightness to the now muddy whites and add some deeper tone back in the shadows but still keep as much of the detail as possible.  Perhaps you can begin to see how philosophy and artistic choices come into all of this.  

 

When it comes to muddy whites, try increasing White Point and Smooth Highlights values.  For a final touch try increasing Micro-smoothing.  To improve dull shadow tones, increase the Black PointShadow Smoothness can also help.  Luminosity and Detail Contrast settings will help improve middle tone contrast.

 

Halos around areas of strong contrast, like trees and the roof lines of buildings are a dead give away of poor HDR processing.  Often the only way to deal with it, is lowering (moving the slider to the left) the overall Strength setting.  Increasing the Lighting Adjustment slider to the right will help smooth out the transition.  Increasing Micro-smoothing can also be a benefit. These same controls can also help the noisy areas, especially found in the shadows.  

 

Finally, what we can’t do in Photomatix, we will do in Photoshop or Lightroom.  If I can’t quite handle the full range of things like halos, color shift or noise, I’ll make those repairs in ACR, Photoshop or Lightroom, and with applications like Nik Software, Topaz Labs or other 3rd party software.

 

Fig-6. Final Image after ACR and Photoshop CS5 adjustments

 
 

Fig-4. Original EV-0 Image for comparison to Final Image in Fig-6

 

My personal philosophy and goal regarding HDR, is to produce a final result that other photographers familiar with HDR suspect, but aren’t sure if, I’ve used actually used HDR software.  In those instances I’m content that I’ve accomplished what I had intended to.

 

A final word on HDR imaging...

 

If your goal is to produce images that have increased dynamic range but desire to keep the final result quite realistic, there are other methods worth considering.  For example, layer masking bracketed shots or double processing RAW files using Smart Objects with Layer Masking.   These methods, however, are best discussed in another article.

 


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