Finally, a D300 Near UniWB JPEG

Started Apr 3, 2008 | Discussions thread
GaborSch Veteran Member • Posts: 7,203
Real sensor histogram

antimonite wrote:

I don’t think that it would be possible to get the real sensor
histogram due, as you say, to the jpeg processing (Tone, saturation,
sharpening…)

Tone, saturation, sharpening, etc. can be "disabled" (neutralized) in the camera, that's not the problem.

There are two additional issues:

1. the mapping of the originally linear values on a nonlinear fashion, like sRGB is doing (often called "applying gamma").

2. the transformation from the camera's color space to sRGB or aRGB. Make a shot of a red sheet with a tiny white card to pick WB on and take a look at the raw and RGB histograms. I created a demo:

1. the raw histogram,

2. the histogram shown by ACR after WB on the white letters,

3. the histogram shown by Rawnalyze after WB and sRGB mapping,

4. selection stats on a red area.

Note, that the green channel is much higher (one and a third stops) than the red, but that is due to the white letters on the box; the red is dominant on the red areas, see the fourth screen capture. However, even on that red-dominant area, the average of reds is 901, the greens average at 417 and the blues at 221, while the ACR stats on a selection is RGB=(200, 47, 36) (averages).

However, all the above is irrelevant from the point of judging the exposure: these facts do not affect the right end, i.e. how close the exposure is to clipping or if it has clipped already.

(Btw, the WBd histogram of Rawnalyze shows, that the reds, greens and blues end at the same level; that is due to the white letters. The histogram is logarythmic, therefor the white appears to be quite much).

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