Re: Digital Camera Sensor: 14bit sucks?

[A complimentary Cc of this posting was sent to
Roger N. Clark (change username to rnclark)
<username@xxxxxxxxx>], who wrote in article <47B28E69.3080608@xxxxxxxxx>:
There are two (at least) amplification steps to get the signal
off of an electronic sensor. 1) the read (also called sense) amplifier,
which is a fixed gain (does not change with ISO). This is the
source of the sensor read noise. 2) Second amplifier, which
may be integrated with the ADC. The amplifier changes gain
with ISO.

Sensor read noise comes from the first amplification
stage off the pixel/chip. It does not change with ISO.
Ilya says the the lower (read) noise seen in the low ISO 1DIII
is due to the capacitance of the smaller pixel.

What I said was close to this:

a) The area of newer sensel is about 77% of the old one ((7.2/8.2)**2);

b) The low-ISO read noise of the newer sensor+ADC (in electrons) is
about 79% of the old one (24.4/30.6).

Assuming capacitance change proportional to the area change, and
taking into account V = Charge/Capacitance, this means that

*) The low-ISO read noise of the newer amplifiers+ADC (in volts) is
about 103% of the old one.

My statement does not depend on any particular detail of how the
measurement pipeline is designed.

But the noise at low ISO is dominated by the second stage amplifier
(the ADC system) not the read amplifier.

The details of the pipeline are irrelevant to what I wrote. What a
change to 14-bit output could improve was performance at low-ISO (one
does not need more than 9-10bits for high ISO). It did not.

[I had no chance to read the rest, so I comment only on this part of
your post.]

Thanks for your clarifications anyway,
Ilya
.

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