Compare Tone Mapping of HDR Photographs
Individual high dynamic range images often look great. It’s when you compare two differently tone mapped versions of the same HDR image, however, that you see flaws you missed or something you like better in one but not the other.
Always save the original HDR image. This way, you can load it into your HDR application each time you want to tone map it. This saves you from having to generate it each time.
To compare different approaches to tone mapping an image, follow this general process:
1When you reach a point in tone mapping where you like the result, process the image and save the result.
Make sure to save the settings as well so you have a record of it.
2Save the image as a JPEG.
No need to get fancy here. You want something that loads quickly in a preview program, which improves your ability to discern nuanced differences as you flip back and forth.
3Open the original HDR image and make a change to one setting — something you want to see if you can make better.
Make single changes at a time. Try changing just the Strength, Color Saturation, Smoothing, Luminosity, or Microcontrast setting. It’s harder to gauge the effects of changing multiple settings at once because you don’t know which one might have helped and which one didn’t.
4Save the second image.
You can work up a third image with still another change to the same setting and have three options to choose from.
5Open the images in your editor/organizer (Microsoft Picture and Fax Viewer in Windows/Preview on Mac work best because you can scroll through the images one after another) and look at your versions several times.
The figure illustrates three versions of an image tone mapped with different Strength settings. One is at 50, another at 75, and the last is at 100.
What you’re looking for are subtle (and not so subtle) differences in how you react to each image. All three in this case look good. That isn’t the issue. You’re after which one you like best.
Pay special attention to how the tone migrates from the outside toward the center of the photo as the Strength increases. With a setting of 50, the basketball court is fairly light, and the bleachers are dark. At a Strength of 100, the court has darkened and the seats have lightened.
6Decide on the best one and use that as the basis to move forward. Open the HDR image in Photomatix Pro, load the settings you just approved, and then make another change.
Continue until you’re satisfied. When the process is over, you’ll know for certain which settings you like best.
7Save the final version as a 16-bit TIFF for the best quality and continue editing.
You’re done comparing images.