In order to show a HDR photo, you’ll need to map its tones. This is largely due to the fact that you are converting from an image with 32 bits per channel to one that is 16 or even 8 bits per channel. Think of it this way, you’re going from an image with a dynamic range of 100,000:1 down to as low as 255 to 1 per channel.
Why get rid of this valuable information? Well it’s a technical necessity as most displays and printing devices just can’t show that range. The goal with tone mapping is to give the image an appearance of having a higher dynamic range while still making an image that can be printed or shown on standard displays.
This is an excerpt from my new lynda.com class on HDR images and Photomatix Pro.