GMCPhotographics said:
Sporgon said:
Its interesting how the ability to recover highlights, or at least the useable highlight headroom is never tested or discussed.
Yes...that's because most discussions about DR are really about shadow pull using iso invariance. True high DR would allow us to recover highlights and shadows with the same levels of iso noise as the image was shot with and have a contrast scale beyond the legacy CCD capability of 8.4 stops. It's similar to slide film in it's DR, but way below the capabilities of negative print film's 14 stops of DR. The current fad with shadow recovery has little to do with DR. In the current Nikon and Sony sensors, yes you can pull shadows on a 100 iso image from apparent blackness to 5 stops of mid tones. But the equivalent iso noise is still 5 stops over the base iso 100. That's going to be iso 3200 noise in the shadows > new mid tones. That's really too high and it's not true HDR, it's just pulling noisy shadows using an iso trick.
"True high DR would allow us to recover highlights and shadows with the same levels of iso noise as the image was shot with" --> Same levels of ISO noise as
what tone? Even for a camera with zero read noise, darker tones will have lower SNR, because of simple physics (shot noise, which you can read more about in our article here: http://bit.ly/shotnoise).
And remember: darker tones on a linear capture format (Raw) are only dark because your monitors are extremely dim. Take that same linear Raw file and display it on a bright HDR monitor, and you won't have to push
any shadows to see them.
Does that mean those shadows on that HDR monitor will be clean, even if shot at ISO 100? If they're from the lower end of the Raw file, no, because those tones
inherently have less SNR because of shot noise.
The only way you can make them cleaner is by capturing more total light, which means either (1) a larger sensor, or (2) higher full-well capacity. Medium format or larger might address 1, whereas technologies like ISO 64 on the Nikon D810, which extends full-well capacity, is another way to make those 'shadows' look cleaner.
Both approaches do so by raising SNR of
all tones, but the dark tones will still have lower SNR than the brighter tones. But after a certain SNR threshold, you won't care.
Does that make sense? It's a bit of a complex topic so apologies if I haven't done a good job explaining here.
Rishi