Unbiased noise test.

Started Feb 28, 2009 | Discussions thread
(unknown member) Contributing Member • Posts: 873
DXO

Sorry but I don't believe in DXO. you tell me, how can S/N ratio in 0.1% gray be 7dB lower for 5DII vs D3X. come on 7dB!!!! this means that the mean signal power is 10^7 times higher in D3X that is 10,000,000 times this is total BS.

What this means that Nikon performs some on chip read noise subtraction for which they measure almost no noise for low signal levels. FYI, this is why Nikons are not suitable for astrophotography.

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> http://astrosurf.com/buil/nikon_test/test.htm

BTW, the reference text you cited "The essential physics of medical imaging" is a very bad reference for this issue because it mainly talks about MRI and xray scanning which have different issues, not refractive optics and CMOS imaging sensors. A much better text is Nakamura's sensor design book and lecture notes.

A much better article can be found here http://www.clarkvision.com/imagedetail/digital.sensor.performance.summary/index.html with all the references cited at the end.

sidelight wrote:

Rcihardc wrote:

Even in your crops 5DII has the lowest noise compared to D3X, 1DSIII
and a900. at the same print size, 5DII has the lowest noise of any
DSLR available today. There has been at 10 different posts that have
confirmed this and yours is the last one. Nikon D3X is close to older
Canon 1DSIII with Sony being far behind from either one.

I posted this in an earlier thread about the D3X and the 5DII sensor.
If you can accept DxO's testing, then their results show the 5DII to
have similar noise performance at base ISO to the D3X but not in the
deepest shadows. Their test protocols are described on their site.
I think Iliah has said color temp influences noise as well and this
is not varied. The data below is just one aspect of performance of
course.

"I pulled this sensor data from DxOMark using the Full SNR tabs and
the log plots. The table below compares the signal to noise vs very
low gray levels at base ISO. Essentially it shows that the D3X has
about half the noise as the 5DII and A900 at 0.1% gray. At 1% and 10%
gray, the D3X and 5DII are equal, but about one stop better (3dB)
than the A900. The improvement of the D3X over the similar Sony
sensor at base ISO indicates significant, if small, design
differences.

The second table shows the lowest gray level for each camera at a
signal to noise of 5dB (Rose's criterion - defined below). The D3X is
able to show recognizable detail (distinguishable from noise) at a
deeper black level. Given that this performance also beats the medium
format backs recently tested, I think it shows the D3X meets it's
design goals of best in class low ISO performance for 35mm format.
Differences are obviously getting pretty small now when looking at
overall performance.

Signal to Noise (dB) vs Gray Level

0.1% 1% 10% Gray

D3X_ 14_ 26 37

5DII_ 7 25 37

A900_ 7_ 22 33

Leaf75S_ 8_ 25 37 (ISO50)

3dB = 1 stop and +6dB is equivalent to doubling the noise.

Lowest Gray Level Above Rose Criterion *

@S/N=5dB

D3X_ 0.027%

5DII_ 0.078%

A900_ 0.078%

Leaf75S_0.08% (ISO50)

The Rose criterion (named after Albert Rose) states that an SNR of
at least 5 is needed to be able to distinguish image features at 100%
certainty. An SNR less than 5 means less than 100% certainty in
identifying image details.[2]

[2]^ Bushberg, J. T., et al., The Essential Physics of Medical
Imaging, (2e). Philadelphia: Lippincott Williams & Wilkins, 2006,
p.280"
--
David

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Richard, NC
Never comment on something you don't know about

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