Daaaaaaaamn! Check out the D5200 sensor!

Started Jan 24, 2013 | Discussions thread
Jack Hogan
Veteran MemberPosts: 4,023
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Re: Aptina?
In reply to bobn2, Jan 28, 2013

bobn2 wrote:

Well, the curve fit extracts the well behavedness of that curve, and gets the anomalous results.

Hm, I see what you mean. This shouldn't matter if the underlying data is fitted with a reasonable r^2 in the zone of interest (for my measurements at around 2% of full scale at ISO100). But I guess without the original data we'll never know.

I believe the answer lies in a different unity gain being applied at ISO100 vs the rest , resulting in a different G in Bob's formula: take a look at the 'relative gain' in my table to see what I mean. Viewed from the point of view of the raw data, the sensitivity of the sensor has changed differently than expected at ISO100.

I'm not sure what you mean by 'unity gain' - the gain is the gain.

From Emil's page (I changed the symbols to reflect those in the formula you showed above)

"G = U/Iso where Iso is the ISO setting, and U is a constant (which differs for different camera models) known as the unity gain."

Remember that the non-linearity I am talking about would only manifest itself at the top end of the scale, near to saturation level, you wouldn't see it anywhere else. Remember also that DxOmark's curves are themselves fitted to their measured data, so if the 100% saturation was off it might be flattened.

Yes to both comments, but if I understand correctly DxO says that they actually accurately measure the Exposure at which the sensor - the Raw data really - saturates (i.e. at the top end of the scale) for the various in-camera ISO settings. It'd be dumb to change the most accurate data points you have, no?

One way I can imagine they could obtain this result would be to have a different U for the ISO 100 setting than for the others (i.e. 1.45 vs 2), but the output of the ADC is scaled digitally 2/1.45 before writing it to the Raw file. This way they would fool DxO but not curve peekers

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