Sunday, March 29, 2009

HDR - a leap in the evolution of tools for high contrast scenes

The problem of dealing with high-contrast situations has been with photographers for ages.  The human eye can see a much wider range of light than can be recorded by film or digital cameras, or that can be displayed on prints.  In many lighting situations, this leads to photographs that are missing much of the shadow or highlight detail that you see out in the field, and disappointing results when you process the image.

Over the years, the solutions for this problem have evolved.  Ansel Adams was a master at recording as much dynamic range as possible with his Zone system and knowledge of processing chemistry, and printing techniques.  The earliest technique that I learned about was dodging and burning an image in the darkroom to get more detail on the print -- more texture in the clouds or in the shadows.

Later when I was using colour slide film, the technique changed to using split-density filters.  These filters would typically lower the amount of light from the sky, and allow the film to capture more detail and colour in both the sky and foreground.  I also used (and still use) a polaroid filter to tone down the highlights and darken the sky.

 Mill of Kintail, March 2009.  
Simple Raw processing only.

Now with digital photography, I have often used the same technique as split-density filters, but now I make more than one exposure of an image -- one to capture the highlights, and one to capture the shadows. I combine them, often with considerable amount of time and effort, to produce an image that comes close to what I saw while taking the photograph.

I have also used a tool from Kodak, called Digital SHO Professional, a plugin for Photoshop that also works nicely with Corel Paint Shop Pro.  This plugin expands the detail in shadows and highlights of an image, and can significantly improve many high contrast images.  This tool was a big improvement over other manual methods, but it sometimes gives quite unrealistic images, especially with the the amount it boosts saturation.  I often have to reduce the saturation considerable over the default values in the tool, and sometimes I blend the resulting image with the original to mute the effects, and make the final image look more authentic.

Mill of Kintail, March 2009.  
Processed with Kodak Digital SHO Professional plugin.

Also available in the recent releases of Raw image processing software such as Capture One, there are tools that can expand the detail in highlights and shadows.  I have also been using these tools increasingly often to deal with high contrast scenes.  With tools that operate on a single image, it helps to photograph using the lowest ISO possible, to avoid noise in the shadows that these tools make much more apparent.

Over the last year or two, HDR (High Dynamic Range) software has been developed that makes a huge leap in the tools available for managing high contrast scenes.  The big difference is that these tools take a series of images that represent the range of tones in the scene, and combine them to produce an image that represents the whole range of tones.  Typically, you would use three or more images ranging from +2 or +3EV to -2 or -3EV, giving you a wide range of tones to work with.  Then, the HDR tool essentially compresses the wide range of tones in the scene into a representative range in the image file.  It automates the technique that had been done earlier by hand, but does so with a much higher level of precision than could be achieved before.  The results can be spectacular.

Mill of Kintail, March 2009.  
Four images (+2, 0, -2 and -4EV), processed with Photomatix Pro.

Last week I tested out a couple of different tools, but by far the best was Photomatix from HDRSoft.  Photomatix is a bit on the expensive side ($99 US for the standalone program), but it produced the best results of the programs I tried, and gives you lots of control over the look of the final image.  There are two steps to the process: first, you read in all of the images and align them into a single "HDR" image, and second, you map the tones in the image into a final image.  The tone mapping stage allows you to control the intensity of the HDR process, saturation, luminosity, colour temperature, and other options to let you get the effect that you want.

After processing the final image, Photomatix allows you to save the image as a 8-bit or 16-bit tiff file, or as a jpeg.  I have found that I still want to process the image afterwards, to fine tune the brightness and contrast. Even with the various controls available, I haven't found the right combination to produce the final image (although I haven't spent enough time yet to try out all the options).

One caution:  in browsing the HDR images on the web, there are lots of spectacular examples of HDR images.  However, there are also examples where the HDR effect is overdone to the extent that it dominates the photograph, and produces a highly unrealistic result.  This may have been the intention of the photographer, and that's okay.  This technique can produce some fascinating results, but not necessarily good photographs.

Personally, I prefer more subtle results that look good, but where the technique does not overpower the subject matter of the photograph.  As with any tool, you have to understand it's strengths, and know when and how to use it to benefit the image.  HDR tools are a valuable step in the evolution of techniques to manage high contrast scenes.  Although Photomatix is expensive for a stand-alone tool, in reality, it only costs a third of the cost of a single split ND filter that I used to use for film (and I needed several with different grades).  I look forward to taking advantage of it in the future.

. . . Rob Williams