I understand what the origin of HDR is/was. But this is a photography forum. The vast majority of the people here are photographers. The vast majority using HDR will be doing so for photography related reasons, not CG. I'd venture that very few are doing 3D CG rendering. So in that context, I think my comments are valid.
As others pointed, we can talk about HDR imaging
in digital photography without the need for bracketing (a sensor with enough DR to capture the entire scene in a single shot, use of ND filters to reduce the effective DR hitting the sensor,...), so it's nonsense to say bracketing is a part of the definition of HDR. Anyway I think this is a rather semantic discusion since we all know what we mean.
However I would like to make a consideration that is seldom made: since capturing DR in a sensor is all about noise in the shadows, and visible noise in the shadows is reduced (because SNR increases statistically) when an image is downsized, the ability to capture a given DR by a camera strongly depends on the ouput size of our application.
Quick numbers example: Canon 5D2, let's assume it has an effective DR of
9 stops at full resolution (21Mpx). If in our application we just want to upload a 800x533 image to our website, the effective DR the camera is capable of capturing for that size is larger:
- Original resolution: 5616 x 3744 = 21Mpx
- SNR slope in the shadows for 5D2 (SNR curves): 6dB/EV (typical in read noise limited cameras), this means DR will increase by 1 stop for each 6dB in SNR improvement
- SNR improvement for rescaling 5616 x 3744 (21Mpx) to 800 x 533 (0,43Mpx): 20*log10[(21/0,43)^0,5] = 16,9 dB = 16,9/6 stops = 2,8 stops
- Effective DR of 5D2 at web sized images: 9 + 2,8 = 11,8 stops
If our real world scene has 11 stops of DR, the 5D2 will need bracketing to produce a sufficiently clean of noise image for a large print at full res. But if we just plan to upload the resulting HDR image to a website, one shot will be enough. Both images are HDR, they simply have different requirements.
The formula to calculate SNR improvement when downsizing is simple statistics. See Emil's article about noise to know more.