Both Hikvision & Dahua camera specifications indicate WDR is either 120dB (sometimes 140dB) or DWDR. It appears to me that the higher the WDR, the price of the camera also go higher. When the spec state DWDR, what is the equivalent dB ?
120dB WDR is sensor based WDR. The sensor outputs one set of two or four frames with different exposure times. In this case, the gain can also be set separately for each frame in addition to the exposure time. The set of frames are combinded.
DWDR takes only one frame. The Dark areas in the picture will be made brighter like you could do this in photoshop manually. The qualitiy of DWDR depends on the resolution of the A/D converter. 14 bit is much better than 10 bit.