HDR: It shoots two images with different exposures, and then overlays the bright area of the underexposed image and the dark area of the overexposed image to create an image with rich gradation. The highlight detail in an HDR is better than that of D-Range Optimizer and also reduces the noise.
It is recommended to use this function when the subject is motionless or does not blink. Otherwise, the recorded picture may look like multiple exposures when shooting a moving subject because the shutter is released twice for one shot.
DRO: It analyses the contrast and produces the picture with optimal brightness and gradation.
You can use this function even while the subject is moving or during the continuous shooting. Be aware, however, that the DRO can produce a little bit of noise in a picture.
NOTE: Both functions compensate for the brightness and contrast automatically.