Too many megapixels? Six is enough for an 8x10.

Started Apr 26, 2009 | Discussions thread
Ergo607
Ergo607 Senior Member • Posts: 1,354
Re: Same goes for dynamic range and several other things

I don't think I completely follow you (must have missed a turn or two... )

All I can say is that I already have problems with the assessment of the LX3 having 10.7 stops DR (it's much lower in my experience), let alone having it some theoretical 12.3 stops...

You're theory may be right or wrong (I am hardly in any position to discuss that since I don't understand it the way you are explaning it), but the practice surely doesn't follow...

Daniel Browning wrote:

Ergo607 wrote:

You're just talking noise in all this. As if that was the most
important factor. I couldn't care less... Talk about DR and come back
then...

Everything said applies to dynamic range as well.

In linear image sensors, dynamic range is simply a function of noise
and light. Noise is determined by quantum efficiency (QE, for the
photon shot noise) and electronics (for the read noise). Light is
determined by the full well capacity and QE.

Full well capacity and QE scales with pixel size, so the only other
factor for dynamic range is read noise. Most discussions of dynamic
range are with regards to ample-light scenes such as outdoors,
studio, etc., so we'll assume ample light and base amplification.
We'll use 1:1 S/N as the lower end of the dynamic range.

Compare the 2-micron pixels of the LX3 (10.7 stops DR) with the
immensely larger 6.4 micron pixels of the 5D2 (11.1 stops DR). Going
by the per-pixel numbers, it seems that the smaller LX3 pixels have
less dynamic range. But remember that the LX3-sized pixel samples a
much, much higher spatial frequency. [See math below if you want the
numbers.]

At the same spatial frequency, the scaled LX3 pixels have 12.3 stops
of dynamic range, 1.2 stops greater.
--
Daniel

5D2 maximum signal: 52,300 e-
LX3 maximum signal: 9,000 e-

5D2 read noise at base ISO: 23.5 e-
LX3 read noise at base ISO: 5.6 e-

5D2 per-pixel DR at base ISO: 11.1 stops (log_2(52300/23.5))
LX3 per-pixel DR at base ISO: 10.7 stops (log_2(9000/5.6))

LX3 scaled maximum signal: 92200 (9000 e- * (6.4µm/2.0µm)^2)
LX3 scaled read noise at base ISO: 17.92 (sqrt(5.6 e-^2 *
((6.4µm/2.0µm)^2)))
LX3 scaled DR at base ISO: 12.3 stops (log_2(92200/17.92))

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