Can we have too much Dynamic Range?

Started 7 months ago | Discussions thread
alanr0
Senior MemberPosts: 1,261
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More than 8 bits DR from JPG
In reply to Gerry Winterbourne, 7 months ago

Gerry Winterbourne wrote:

Fogel70 wrote:

meland wrote:

Fogel70 wrote:

A default jpg image from a camera with 15 stops of DR does not have to look any different from a camera with 10 stops of DR. The camera with higher DR just throw away more image data when producing jpg images.

OK, what does it throw it? What are the parameters for making those decisions of what to throw away?

To simplify, the camera throws away the brightest and darkest parts away. Lets say a jpg image contains 8 stops of DR. On a camera with 10 stops of DR the brightest and darkest stop of information is thrown away. On 15 stop DR camera it's the brightest and darkest 3.5 stops of information that is thrown away.

I think your numbers are wrong. I'm sure that what happens is that it's always about 1/2 to 1 stop of highlight DR that's discarded. with the rest going from the shadows. DPR used to talk of "raw headroom" when measuring DR: that's the amount that can be recovered from a raw file but is clipped in the corresponding OOC JPG.

So on both cameras it's the same 8 stops of information left in the image.

As Gerry points out, it is usually only 1/2 to 1 stop of highlight DR that is lost.

The idea that a JPG image only encodes 8 bits of DR is also wrong.  sRGB encoding is non-linear, with the smallest step corresponding to 1/3295 of the maximum signal.  There is potential for 11.7 bits of dynamic range, depending how much noise and posterisation you can tolerate in the shadows.  In addition, most cameras do not follow the sRGB curve exactly, with some softening the highlight clipping, or offering an increase in highlight dynamic range with options such as highlight correction or Nikon's active D-lighting enabled.

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Alan Robinson

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