When you create a high dynamic range image, you’ll often be given the chance to save it as an HDR file for later use. Whether you save it as an HDR file depends partly on preference and partly on what you plan on doing.
Normally, you’ll jump right into tone mapping, save the final low dynamic range result, and never miss not having an HDR file stored on your hard drive.
In cases where you might be testing a number of different settings on a single HDR image, however, saving an HDR file the first time through will save you time in the long run because you won’t have to continually re-create it. You can load the HDR file and work with new settings in a snap.
Another scenario where using an HDR file saves you time and trouble is if you want to share it with someone and don’t want the hassle of tracking multiple photo files. Generate the HDR, and then make that available for others to tone map.
If you decide to save an HDR file, you must choose a format from several competing HDR file formats. Three, however, are very widespread and deserve special attention — these are summarized in the table.
| Format | Extension | Bits per Pixel | Why to Use |
|---|---|---|---|
| Radiance RGBE | .hdr | 32 | Superlative dynamic range; sacrifices some color precision but results in smaller file size |
| OpenEXR | .exr | 48 | High color precision at the expense of some dynamic range; can be compressed |
| Floating point TIFF/PSD | .tiff .psd |
96 | Very accurate with large dynamic range but results in huge file sizes and wasted internal data space |
Generally the Radiance format is recommended when you need to save an HDR file because it preserves the greatest dynamic range without excessive file bloating — and it’s the first file type in the Save as Type drop-down list in Photmatix Pro. (Find more information about Radiance RGBE and OpenEXR formats.)
Thankfully, HDR photography comes down to the photos. This isn’t a contest to see who can create the HDR file with the greatest dynamic range or a strict comparison of bits and precision. It’s about taking and presenting beautiful pictures.