Published July 2006
The base image actually looks decent, and with finishing work normally I might be happy to stop there. But this is an article on HDR, so the next step is to combine the three exposures.
Combine the Stitched Images into a Single HDR Image
I will use Photomatix Pro for the HDR work in this example. The process
is identical to the one described for working with a single frame image;
at this point Photomatix does not know or care that the three exposures
being given to it are the result of a stitching exercise. Of course, the
image size being much larger, everything will take longer to run. I would
recommend not working with this size of image unless you have at least
2GB of RAM in your workstation; more would be better.
I combine the three images into an HDR file, and save it. (Trivia point: the 16-bit TIFF images are each 171MB in size, while the HDR image – saved in Open-EXR format with ZIP compression – is only 65MB.) I then bring up the Photomatix tone mapper and adjust the settings:
When I have something that looks good, I hit OK and generate the tone-mapped image. Unfortunately my initial intent to use Smoothing of “High” does not work on this image because of the previously described issues, so I regenerate with “Medium” instead. (This still has some tonal artifacts, for example along the lower left of the image.) Here is the result, which takes about a minute and a half to generate:
I already like it better than the base exposure image, and the finishing work has not yet been done. That comes next.
Do the Finishing Work
I saved the tone-mapped image from Photomatix as a 16-bit TIFF, and I
now load that into CS2 to apply the finishing touches.
Working with this image in CS2 takes a bit of time even on my fairly powerful workstation, with the final file including layers reaching about 970MB in size. However, this highlights a side benefit of doing the majority of the contrast enhancement work in HDR (whether in CS2 or Photomatix) – working with numerous layers using an exposure blending technique would be fairly painful, given an image of this size.
For the sake of illustration, I make only a few adjustments:
- curves and levels layers to create a little more “pop”
- slight noise reduction to compensate for the ISO 400 source images (although the noise level from the 5D truly was not bad even after tone mapping)
- a combination of edge unsharp mask filter and a high pass sharpening layer
After these adjustments are done, the final image looks like this:
It took about four hours to reach this point from the start of the workflow. The single most time consuming stage was the fine tuning work in the stitcher, which took at least three hours – and would take as much again to complete.
Integrating HDR into the process added very little extra time, but produced a pleasing final image superior to anything I could produce with much more effort using blended layer techniques in CS2. The color and tonal transitions are “natural” looking to my eye, the drama in the clouds is clearly evident, and the detail is rich through-out the scene. All of this merely from the extra shooting step of auto-bracketing three exposures at +/- 2 EV, and introducing one extra workflow step of about half an hour!
If you work with stitched panoramic images covering a broad field of view, no doubt you routinely encounter much higher DR than single exposures can accommodate. While many excellent images can be created with single exposure stitches, hopefully this quick overview will encourage you to see what you can produce by adding HDR to your panorama workflow. I for one would be eager to see your results!
Here are a few other HDR images I have created. Some of these have appeared previously in NatureScapes.Net forums while others are new for this article. Hopefully these images and the other examples in this article give you a taste of what HDR can do.
Previous Naturescapes.Net Posts
The available tools as well as my technique in applying them have both improved, but I have not reworked these images since they were originally posted to NatureScapes.Net forums.
Single-frame image and stitched panorama of a sunset over the grasslands at Beaverhill Lake, Alberta:
Single frame image and stitched panorama of a sunrise view of Mt. Rundle at Vermillion Lakes, near Banff, Alberta:
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