Message “…not enough dynamic range…” occurs when you use Merge To HDR (Photoshop CS2)
Source: Photoshop Support Knowledgebase
Issue: When you use the Merge To HDR command, Adobe Photoshop returns the message, “There is not enough dynamic range in these photos to construct a useful HDR image.”
Detail
The images were created by saving a single camera raw file multiple times with different exposure settings.
Solution: Apply Merge To HDR to multiple images taken at different exposures.
For more information about the Merge To HDR command, see The Merge To HDR Command in the Photoshop Help.
Background information
A single camera raw file does not contain enough dynamic range to generate a High Dynamic Range (HDR) image. Changing the exposure setting changes the relative brightness of the pixels, not the exposure value of the entire image.
Photoshop uses the exposure values in the EXIF data in image files, if available, to determine if there is enough dynamic range to generate an HDR image.