Moon Maid's sensor comparison (PART 2)

Started Mar 1, 2012 | Discussions thread
Luke Kaven Veteran Member • Posts: 5,705
Re: A pleasant surprise

Marianne Oelund wrote:

Marius D wrote:

There is another possible explanation: 3) reducing ADC reference voltage (V.ref) to match the input analog domain as ISO raises. . . . Reset voltage and optical-black are both very low, reducing ADC's V.ref make sense for a precise digital conversion of these values.

I've completed the missing-code analysis for ISO 800, 1600, 3200 and 6400, so I now have the digital scaling values for those settings.

The surprise is that digital scaling at ISO 1600 is only 5.0%, which is much less than expected. Above 1600, the numerical scaling is precisely in proportion to the ISO value.

This clears up most of the mystery, leaving only a relatively small factor to explain at the highest ISO settings (6400+). I'm happy to leave that until later.

All of this implies that the D800 is truly exhibiting lower read noise than expected at ISO 1600 and up, and there is no indication of filtering, up to at least ISO 3200.

The closer we look at this camera, the more impressive it becomes - just as with its images.

I woke up today wondering if you'd gotten to the bottom of this. Definitely a very pleasant surprise.

So if I understand correctly, locating the missing codes gave you the signature of the digital scaling function. The missing codes helped to confirm that there is no additional filtering (e.g., soft NR) occurring thereafter. If there had been soft NR or other filtering, then the missing codes would almost certainly have been smoothed out, is that it?

So does the hypothesis narrow down to gain-sharing? I wonder what advances would have favored that strategy. Can't wait to see the revised plots.

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