The conversation began when I shared a series of HDR images on my Facebook account. I'll use this one as the example for explaining the process-
The above picture is a combination of 3 exposures:
Standard or "normal" exposure-
(note- the camera seems to have been making it's decision mostly on the clouds and light horizon in this case. It depends on where the photographer is pointing and other internal settings for DSLR's)
Then a shot taken 2 stops lighter-
And a shot taken 2 stops darker-
To show what I think represents the light better that day I took the first shot, normal exposure, and pushed it lighter in Photoshop. It turns out to be 1.25 stops higher than the first shot.
This is more what I think the day looked like-
Notice that we lost some of the cloud detail in the brightest area of the horizon. This is where photography and the human eye diverge. If we stare at the horizon, and it's not too bright, then our eyes will adjust and we'll see nice detail in the clouds. Then if we look down at the grass our eyes will adjust and the scene will appear brighter than what you see in the above picture. Brighter and more colorful.
Now to really stretch our perception of the scene, here is the brightest shot pushed 2 stops brighter in Photoshop-
Look at the green of the tree, the light green at the edge of the path and the light gold of the grass. You can't see the clouds anymore, but the additional details/potential in the foreground are brought to light.
The real world in front of the camera has a wider range of light intensity than a single exposure can capture. Overexposure and underexposure both obliterate detail and color.
I don't know the history of HDR (High Dynamic Range) software so I won't even begin to explain it or research it right now. The purpose of the software, though, is to merge information from what would normally be shadows, bright spots and everything in the middle into one exposure.
First I'll use the above scene to show how it might be done manually, but only in brief.
