Part 14 - Yes You Can

In my last post, I mentioned that a picture I judged in a recent local photo competition was the trigger for writing Parts 13 and Part 14 of this blog. Shown below is my version of the image as it was presented as a print in the contest:

South Falls in Silver Falls State Park, Oregon

By the way, when you inevitably pass through your "waterfall picture-taking" period, you have to go to Oregon -- the waterfall capital of the world.

Although this waterfall picture is dramatic, to me the dark areas of the image are too dark and lacking in detail. The ledge from which the falls begin is totally black and difficult to recognize. The lush greenery below the falls is nearly lost.

At the same time, the sky and trees in the background are striking and well exposed. Was this a photographic exposure error? Since I went to the same location to recreate this photograph, I can say that the problem was created by the high dynamic range of the original scene. This is the correct exposure for the sky and background trees. But it's underexposed for the cliff and greenery. Looking at my camera's histogram, it becomes apparent that I've walked myself into a high dynamic range situation:

Camera's histogram for waterfall picture above.

The lightest part of this image is represented on the right side of the histogram, and those densities are all within the borders of the graph. The camera is saying, "No problem with the light areas of this picture (the sky and farthest background trees). They will reproduce just fine."

The histogram goes on to say, "However, forget about the darker areas of the picture (left side of graph). Those densities -- like the cliff and dark foliage under the falls -- are dead zones. They will reproduce as dark with minimal detail or totally black."

I know I can use the camera's exposure compensation controls to move the densities within the histogram. I can also do the same thing by switching to manual mode and selecting a larger aperture opening (smaller f/stop number). Making these adjustments will allow me to move the entire density distribution toward the right (in effect lightening the whole picture).

For the sake of demonstration, I did just that. I shot another picture at 1.5 f/stops lighter using my exposure compensation control (opened the aperture 1.5 stops):

Here's the resulting image and histogram at 1.5 f/stops increase in exposure. It's better, and it's worse. As the histogram indicates, the entire graph moved to the right and detail is now visible in the shadow areas. The bad news is the increased exposure has moved my highlights beyond the far right hand border of the graph. Now I've lost the sky and background tree detail. I've "blown out" the highlights.

This seems like a "no win" situation. I can't make an adjustment that will bring both the highlights and shadow areas of the picture within the borders of the histogram at the same time. The dynamic range of this scene is beyond the capability of my camera's sensor to record.

Ideally, the solution would be a combination of these two images that captures the highlight and shadow detail important to this picture.

Enter digital imaging technology. You can do just that using your camera, tripod and any imaging software that accommodates High Dynamic Range processing. Here's how I married these two pictures:

Camera mounted on tripod to create multiple exposures for HDR processing.
Notice the histogram display.

• Mount camera on tripod and compose the picture in viewfinder (make certain the camera is rigid and will not move throughout this process)
• Paying close attention to the camera's histogram shoot an exposure that captures the shadow densities (shadow portion of the graph is within the left hand borders of the graph)
• Now take a second picture that captures all the highlight detail within the right hand side of the histogram plot.

This example uses only two pictures to create the final HDR image. To be safe, I recommend you take three pictures (one over, one under and one at the suggested exposure) in most situations to ensure you capture all the entire range of densities your picture requires. In some extreme high dynamic range instances, I have seen some photographers take as many as 5 separate images at different exposure settings.

The separate image files are now downloaded to your computer. In programs like Photoshop, you next identify the individual image files that you want to combine. The program will automatically do the work for you, or allow you to "tweak" the image as it is being processed.

Below is the image that resulted from combining my two exposures:

Final combined HDR image

Final HDR histogram with highlights and shadows within reproducible limits

When compared to the original photograph and histogram, this image has good detail and color in both the shadows and highlights. In essence, this digital manipulation has allowed me to photograph a scene that is beyond the dynamic range capability of my camera's sensor to capture in a single exposure.

Some notes:

• a tripod must be used to ensure that each image aligns in every detail (otherwise the image will appear "soft" or out of focus)
  
• objects within the picture area should be stationary. (It appears I violated this rule in the waterfall picture. But, in this case, the motion of the water didn't affect the image's visual impact. Just be careful.)

Your autumn landscape pictures will generally fall within these parameters. The possible exception will be leaves moving in the breeze. But light motion in distant leaves will usually not be noticeable. Avoid hurricanes and tornadoes.

A future post in my digital darkroom blog, Hub's iDarkroom, will cover the details of using the HDR feature within Photoshop.

How will you know when HDR should be considered as an option? Keep your eye on the camera's histogram EACH time you take a picture. It will graphically tell you.

Hope this helps during your fall shooting excursions. If you have any questions or comments, please let me know.