Tutorial: Basic HDR with Photomatix

More than a trend, it can really improve your photos

We often photograph high-contrast scenes in which a camera can’t capture the full dynamic range of the detail our eyes can see in shadows and highlights. But that's changing.

In recent years, software has been developed to combine several digital exposures, some underexposed to capture highlight detail and some overexposed to capture shadow detail, to give one image containing all the detail in the scene. This technique is called high dynamic range imaging, HDR for short, and it is not just the next fad. It is a revolutionary development in photography that is still in its infancy.

HDR imaging consists of two steps: capturing the full dynamic range of a scene and then tone mapping it into the much lower range of a monitor, projector or print. Tone mapping reduces contrast similar to the way soft lighting on a cloudy day would render a scene. This kind of contrast reduction is much more sophisticated than anything we can do with the Brightness and Contrast adjustment or Curves. The final image can be made to look natural or given a very surrealistic appearance.

Here is a typical image where there is bright sun on parts of the scene and deep shadows in other parts.


 

In order to render full detail, a set of exposures must be captured which encompasses the full dynamic range of the scene, and, other than exposure, they must be pin-registered as closely as possible. Here is a checklist to insure the images match:

•    No subject movement.
•    Vary the exposure by shutter speed, not aperture.
•    Camera on a tripod or held very steady.
•    Minimize disturbance of the camera between frames by setting it to burst mode and using a remote shutter release to fire off the shots.
•    Shoot a sufficient exposure range to capture shadow and highlight detail.

You may use exposure auto-bracketing or exposure compensation to vary the exposure. (See your camera manual if you are not familiar with these terms.) You generally want to shoot a normal exposure and then one stop under and one stop over, or else two stops under and two stops over. If you use exposure bracketing, with most cameras you will be limited to a three-exposure set.  That is usually enough. 

If this is not enough range, you can combine auto-bracketing and exposure offset to shoot two sets that encompass a wider range. For instance, you can shoot three bracketed exposures at 1-stop intervals starting at an exposure offset of -1, to get:
-2, -1, 0
and then three more by advancing the offset to +2 to get:
+1, +2, +3.

If you are shooting two sequences with different exposure offset you will have to touch the camera to change the offset. A sturdy tripod, preferably weighted down, and a light touch will minimize any registration shift due to camera movement.

You will want to look at the histograms of your series to see if you have captured all the information; that is, the darkest exposure doesn’t show any highlight blowout and the lightest exposure doesn’t show any blocked-up dark tones. The darkest and lightest histograms should taper to the corners of the box and not be pushed up to the ends, as shown in the figures below. These histograms are shown in Photoshop but the histograms that are shown on the camera’s LCD screen should be accurate enough, although they are from in-camera JPEGs. When in doubt, bracket further. That might not be a bad idea with these images.

 

 

 

 

The harsher the light the more exposure range you will need. The decision whether to shoot exposures separated by one stop or two doesn’t seem to be critical as long as the histograms to have decent overlap. The software will take it from there. In my experience, the software will want the exposure intervals to all be the same.

A popular HDR program is Photomatix, from www.hdrsoft.com. You can download a fully functional trial version that never expires. It will put a watermark on the image and buying the license will remove the watermarking.

There are several versions of the program, which have changed as the product has evolved. Check their web site for the latest information and trail downloads. If you are a Lightroom user you will want Photomatix Pro ($99), as you can select your set of images in Lightroom and go right to Photomatix from File > Plug-in Extras > Export to Photomatix Pro. Or you can select the desired set of exposures in Bridge and go to File > Open With > Photomatix Pro. There is a single-image tone mapping plug-in for Photoshop (included in Photomatix Pro) and a stand-alone Photomatix Light ($39). There is a separate plug-in version for Aperture ($79). Updates have been fairly frequent and are free to registered users. I am using the current version as of this writing, Photomatix Pro 3.2.7, on a Mac platform.

Going for it

Open Photomatix and from the Menu bar choose Process > Generate HDR to get the screen shown below. Accessing the program from Lightroom or Bridge with images already chosen jumps over some steps, but I’ll show the whole workflow here.

 

 
Choose Generate HDR Image and you get a dialog box that lets you browse for or drag and drop the desired files.  For best results they should be raw files so there is no variation in adjustments. You can adjust certain parameters such as color temperature in the raw files, but adjustments affecting exposure and tonalities will be ignored.

 

 
Next you are taken to the Settings screen. The first option, Fuse Exposures, is a simpler setting that gives limited results but may work for a realistic result. For more control choose Generate HDR Image.

 

When you click Export, the program does some heavy lifting and when it is done you will get a preview window:

 

 
At this stage you have an HDR file, which, similar to a raw file, is not yet an image. It is a 32 bit file whose range of tonalities the monitor can’t display. You can mouse over the image and the preview window in the upper left shows how much detail there is in various areas. In the screenshot above, my mouse is in the dark area shown by the red square and the preview window shows the detail there. There are no decisions to be made here, but you do have the opportunity to save the 32 bit file (File > Save HDR as…). This gives you the option to return to it later to try other tone mapping settings without having to rebuild it from the separate exposures. After saving or not, click Tone Mapping, to get to the fun part. This step will reduce the HDR file to a 16 bit image.

 

 
You now have a choice of two tabs: Details Enhancer and Tone Compressor. The latter is a simple option, similar to the Fuse Exposures choice above. The former allows more creative interpretation and is what most people prefer, even for an image you want to look realistic. That is what I’ll use in this tutorial. The adjustments are made in the panel on the left. Your last-used settings will come up, and you can click Default, near the bottom, if you want a generally realistic starting point.

As the sliders are adjusted you can see their effect in the image window and on the histogram. You can also click in the image to bring up a magnified view to see details.

The choices are complex and the sliders are interrelated; moving one may necessitate changing others. But after a little practice you learn to juggle the choices. There is no right or wrong in the slider positions, but here are some guidelines.

•    Move the sliders aggressively to see their effect.
•    Generally work from the top down, but be prepared to go back and tweak things as you move subsequent sliders.
•    Near the bottom of the window there are three sub-sets of sliders: Tone settings, Color settings, and Miscellaneous settings. The Tone and Color settings will be familiar to Photoshop users.
•    The two sliders that most strongly determine the overall look are Strength and Smoothing. A more natural look is generally achieved with a moderate Strength and high Smoothing, and a more surreal look with a high Strength and low Smoothing.
•    There are two different flavors of Smoothing, a slider and boxes. The checkbox labeled Light Mode toggles between them.
•    Luminosity supposedly has more effect in shadows than in midtones and highlights, while Gamma (in the Tone settings section) affects all tonalities, but I’m never sure I can see any difference.
•    In the Miscellaneous settings section, for maximum small-scale contrast (to enhance texture) lower Micro-smoothing and raise Microcontrast. For a more realistic look, do the opposite. As they work in opposite ways, don’t raise or lower both equally.
•    Depending on other settings, some sliders may have no noticeable effect or may have a sharp threshold where they cause changes.

Solving problems

If your image looks flat, try a high Luminosity and a low Gamma.

If there is excessive grain or noise in an area that should have a smooth surface, such as clouds, try lowering Strength and Luminosity, and raising Smoothing, Highlights Smoothness and Micro-smoothing.

If noise appears in dark areas, try lowering the Saturation Shadows slider.

It is easy to get halos in clear areas such as skies. They can be reduced by lowering Strength and increasing Smoothing and Highlights Smoothness. A similar solution works when areas that should be white go gray. 

Posterization may occur in smooth areas with a slight tonal gradient such as a sky. It can be minimized by reducing Color Saturation and Highlights Smoothness, although the latter may only conceal it.

The grunge look

In addition to a realistic look, the adjustments in the Details Enhancer tab can be used to create a surreal effect that is currently popular. This is generally done by maximizing Strength and Microcontrast, minimizing Smoothing and minimizing settings in the Miscellaneous settings section. Although it isn’t very successful on this image, here is an example of some general slider positions for this look.

 

 
When you are satisfied click Process. The image will look more dramatic on the “big screen” than in the preview you have been using. Often images need more work in Photoshop, for global and local contrast and color tweaks. In some cases it may be desirable to composite two images, one adjusted for smoother areas such as skies and one for more detailed areas.

One of the best resources on the topic of HDR comes from Adorama's own Jack Howard, who has written Practical HDR (Rocky Nook). When you're ready to take your HDR from the beginners' real to the next step, get his book or start by reading some of his excerpts, linked to from the right side of this page.

Diane Miller is a widely-exhibited freelance photographer who lives north of San Francisco, in the Wine Country, and specializes in fine-art nature photography. Her work, which can be found on her web site, www.DianeDMiller.com, has been published and exhibited throughout the Pacific Northwest. Many of her images are represented for stock by Monsoon Images and Photolibrary.

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