Dynamic range and RAW file "bit depth"

Started Jan 25, 2014 | Questions thread
Iliah Borg Forum Pro • Posts: 22,202
Re: Dynamic range and RAW file "bit depth"

GordonBGood wrote:

Iliah Borg wrote:

GordonBGood wrote:

szhorvat wrote:

I found this about linearity. The plots show what you said: it's linear in the shadows and the highlights are compressed. I wonder if this compression is engineered in some way (it would make sense to do it).

The data from your link is does indeed show that the output of sensors is non-linear as it approaches saturation electron density of the sensor substrate, but that is a region that is normally never used in most current digital cameras, which only generally use the sensors in there generally linear range. A very fiew cameras (such as the Pentax K-5 series) do push the sensor up into this non-linear range for their extended "lower than base ISO sensitivity" range, which works fine especially if raw development then compensates for the non-linear response.

From my attempts to systemize it, typical histogram for a camera where the full well is used shows a hump in the blown-out area, like this:

I do not see this type of highlights level distribution on Pentax 5-series at ISO 80 setting. Was it some PTC study you did on "5" that shows the full well is used at ISO 80?

Iliah, the Pentax K-5 series don't push exposure into the non-linear range as far as the camera for which you have shown the raw histogram above with its distinct code density increase toward the brighter end; I estimate that it only pushes about 10% beyond the "normally used" more linear range.

DxOMark full SNR curves for the three Pentax K-5 series cameras (k-5, K-5 II and K-5 IIs) show the effect both numerically and graphically, with the top ISO 80 curve approaching the next ISO 100 curve as the brightness increase toward maximum clipping level, also shown numerically when one curve fits the readings one can obtain by hovering over the graphs as presumably DxOMark have done in order to produce the graphed curves.

If shown in raw histograms, the effect is no where near as strong as you show above with only a slight bump in the curve at the high end.

So it may be that K5 series go into non-linear portion; but even for ISO 80 it does not look that it is more than usual, not full well. If you have it, can you take the data for PTC curve?

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