The objective of High Dynamic Range (HDR) photography is to capture the full range of tones within a scene, including those that are beyond the dynamic (brightness) range of the image sensor. Even the best sensors have cut-off points where highlights are recorded with the maximum raw value (i.e. pure white) and shadows are ‘blocked up’ to black.
You can’t get any more image data out of the top end, while details in the shadows are obscured by increased noise. Because the shadows threshold depends on noise, it’s influenced by noise reduction processing and how much the image is enlarged or downscaled due to cropping and/or viewing parameters.
When we last looked at it in May 2012, HDR was a mostly manual technique that required the photographer to shoot a series of frames of the subject, varying the exposure frame-by-frame to take in
