Raw Saturation Level

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bclaff
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Raw Saturation Level
5 months ago

Knowing the saturation point of a sensor is necessary in order to compute Dynamic Range (DR).
Most sensors use a 12-bit or 14-bit Analog to Digital Converter (ADC) with values that range from 0 to 4095 or 16383 respectively.
For these sensors the saturation point is invariably where the ADC clips.
(Aside: Saturation is not the same as White Level but they are usually so close together that it makes little computational difference.)

However the F7 and F13 used prior to the F20 have an open ended scale. They don't saturate at some convenient power of 2.

The good news would appear to be that Sigma stores RawSaturationLevel for each plane in the X3F file.

The bad news is that in practice these values cannot be achieved.

Take for example the DP1 that I'm currently torturing.

The RawSaturationLevel values for this camera are 2986, 3084, and 3079.
But the highest values I have observed in grossly overexposed iamges are 2029, 2159, and 2140.
These are each about 70% of the corresponding RawSaturationLevel value.
(It's hard for me not to observe this is 1/sqrt(2) and maybe something Root Mean Squared (RMS) is going on.)

In any case, for now, it complicates computing DR because RawSaturationLevel cannot be used and saturation must be determined by testing.

Any thoughts?

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