HDRI under the hood
January 9, 2009
True 32-bit High Dynamic Range Images have too much information to be accurately displayed on traditional computer monitors, so it is necessary to downsample or "develop" the 32-bit information into 8- or 16-bit space—just like a traditional digital photo.
This process is called "Tone Mapping." Tone mappers are powerful conversion engines and you can tailor the results to range from photorealistic to surreal.
In Adobe Photoshop CS4, there’s no obvious button called "Tone Mapping." The Tone map dialog box only appears when you convert bit depth from 32 bits to 8 or 16 bits/per channel. Select Local Adaptation from the dropdown menu and click on the arrow to reveal the curves controller. Then add control points to the curve to adjust the image. Many users find the Photoshop workflow to be challenging, which is why the user-friendly, independent small-shop programs are very popular for HDR enthusiasts.
Photoshop Tone mapping interface:
Photomatix Pro is a wildly popular HDR-specific program with two Tone mappers. Details Enhancer, the local operator, is the more powerful of the two. The slider and button-based interface is a lot less intimidating and a lot more intuitive than the Photoshop interface.
FDRTools Advanced is a cool program with a lot of powerful HDR features, but it can be a bit scary for the beginner. Once you get a feel for the program and its unique workflow, many photographers are hooked.
Dynamic Photo HDR has recently added a MacIntosh version packaged inside a portable Windows emulator. This economical program packs six Tone-mappers and a ton of additional image-tweaking options for the HDR enthusiast.
Dynamic Photo HDR:
*Practical HDRI includes screenshots and tutorials for Adobe Photoshop CS3, but there is almost no change in functions or operations between versions CS3 and CS4.
Jack Howard recently published the book Practical HDRI: High Dynamic Range Imaging for Photographers, available at many bookstores including Amazon.