A close look at High Dynamic Range (HDR) imaging vs. using Graduated ND Filters

Professional outdoor photographer and author Darwin Wiggett provided us with his personal comparison of two popular ways to capture a wider range of brightness levels when photographing high-contrast outdoor scenes with a digital camera. To better compare the images, be sure to click on them for a larger view.

One of the latest techniques arising from the digital era is something called high dynamic range (HDR) imaging. Mostly this is a technique that tries to overcome the biggest shortcoming of digital sensors -- their narrow latitude in capturing different levels of brightness across a scene. Black-and-white and color print film capture a much wider range of tonal values than any digital sensor, and contrast and tonal control is done mostly during printing in the darkroom. Slide film has a tonal range similar to that of digital sensors, and taming contrast is something that is done in-camera using either supplemental light to fill in shadow detail (e.g. fill flash) or filters such as graduated neutral density filters to reduce the brightness of the highlights.

Many digital photographers are intrigued by the idea of HDR capture as a technique that produces images that more closely approximate the way the human eye sees. The most popular HDR software used is Photomatix (www.hdrsoft.com) which is easy to use and generally produces excellent results. To create an HDR image the photographer usually makes three exposures of the same scene, one to capture the mid-tones, one for the highlights, and one for the shadows. Then Photomatix software is used to blend the three exposures into one complete image with a wider tonal range (see Photo 1 above). As you can see, the Photomatix blended photo is colorful, has detail in both the highlights and shadows, and produces an image that most photographers would be happy with.

Of course similar results can be obtained in-camera using graduated neutral density filters (see photo 2 above). To tame the high contrast in this same scene, I simply used a 3-stop soft-edge ND grad that I pulled down over the sky, the mountain and the reflection with the bottom edge of the gradient area positioned just above the foreground rocks. I found the ND grad also does an excellent job of taming the contrast in the scene.

Comparing the two results (Photomatix HDR vs. the ND grad filter) side-by-side, you can see subtle but distinct differences. The Photomatix image has a distinct “HDR look” that is characterized by cartoonish colours and flatter contrast making the image look less dimensional than the grad filter shot. The ND grad filter shot has truer colours, snappy three-dimensional contrast and a ‘feel’ that seems truer to the eye (Photo 2 above).

On closer examination, there are also other important differences between the two techniques. Because Photomatix calls for three or more bracketed exposures, anything that moves in the scene (wind-blown grass, flowing water, floating clouds) will often have ghosting artifacts that simply don’t occur in the single frame grad filter capture (these can be seen by clicking on photo 3 above).

Also the highlights in the Photomatix version are not as crisp and distinct, giving the image a ‘muddier’ look. Photomatix gets the nod, however, for better shadow detail but only in areas where the grad filter darkened the existing shadows (photo 4 above).

In recent months, I have done tests of various scenes using grad filters and the HDR technique. In almost every case, I feel the quality and realism of the images is better with grad filters. There are some scenes where grads can not be used because the grad pattern would be obvious in important parts of the scene (such as this shot), but for 80-90% of my work, ND grads successfully solve my high-contrast imaging issues faster and better than HDR techniques.

The other great benefit of using ND grads is the time saved in post-production. I can process a grad-filtered RAW exposure in about 5 minutes. To do the same shot in Photomatix takes about 20 minutes from start to finish. So ND grads reduce my post-processing time by 75%. That's a huge consideration when I have hundreds of photos to process from a photo trip.

Do I use HDR software? You bet! But I only use HDR when it's absolutely necessary. I will always carry and reach for my grads first. I simply get better pictures, faster, and with less fuss with filters, which in the end means I can spend more time in the field. And that, for me, is the bottom line.

--Darwin Wiggett, DarwinWiggett.com