Auto High Dynamic Range (HDR):
The Auto HDR function shoots three images with different exposures and then overlays the bright areas of the under exposed image and the dark areas of the over exposed image to create an image with an extended range from highlight to shadow (aka gradation). The highlight detail in auto HDR is better than that in DRO, and with reduced noise. However, using this function is not recommended for moving subjects. The recorded image may look hazy if the subject is moving and in an environment where there is a large difference in brightness.
Dynamic Range Optimizer/D-Range Optimizer (DRO):
The DRO function analyzes the contrast and produces an image with optimal brightness and recovered shadow detail. You can use this function while the subject is moving or during continuous shooting. The image may appear noisy because the image is corrected with image processing.
NOTE: Both of these functions automatically compensate for the brightness and contrast for still images.