From: Bob Newman on
On 21 Jul, 18:00, ejmartin <ejm_60...(a)yahoo.com> wrote:

> Also, a followup point to the comment about capacitance dropping out
> of pixel DR in your model; it means the DR is independent of fill
> factor (only affecting QE I suppose), which also doesn't sound right
> to me.

Why should DR have anything to do with fill factor?
From: John Sheehy on
Steve <steve(a)example.com> wrote in
news:3k09849l6caa4uafvlmqttb8as8pfhlhi9(a)4ax.com:

> On Mon, 21 Jul 2008 06:30:04 GMT, "David J Taylor"
> <david-taylor(a)blueyonder.neither-this-bit.nor-this-bit.co.uk> wrote:

>>Although some would choose 6MP, I bet a majority would choose 12MP,
>>which suggests to me that either marketing has succeeded, or that they
>>really do prefer resolution over noise.

> Or, that for an APS-C sensor size, you're in the area of the S/N vs.
> Pixel Density curve where it's still relatively flat. So you don't
> give up all that much S/N when moving from 6 to 12MP for an APS-C DSLR
> like you would for a 1/1.8 pocket camera, which has about 10 times
> less sensor area.

It doesn't really seem to be a problem there, either. P&S cameras that
do RAW (you can't tell a thing about sensors from cameras that do JPEG
only) suggest that QE is not taking a toll from high pixel count, and
pixel-level read noise doesn't seem to be on much of a rise, if any, so
image-leve read noise is maintaining or improving.

All the anecdotes about more noise from higher pixel density in P&S
cameras come from viewing at 100%, or impressions made from NR designed
for 100% pixel views.


--

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John P Sheehy <JPS(a)no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
From: ejmartin on
On Jul 21, 2:24 pm, Bob Newman <bob.csx...(a)gmail.com> wrote:
> On 21 Jul, 16:39, ejmartin <ejm_60...(a)yahoo.com> wrote:
>
> > On Jul 21, 8:04 am, Bob Newman <bob.csx...(a)gmail.com> wrote:
>
> > > On 20 Jul, 23:45, ejmartin <ejm_60...(a)yahoo.com> wrote:

>
> > What puzzles me about your analysis is that you get the input-referred
> > read noise proportional to the sensel capacitance, with no appreciable
> > dependence of the front end noise Nf on sensel size;
> Yes
> > I would think
> > also that the FWC is also proportional to the sensel capacitance.
> > Then the DR per pixel is totally independent of the capacitance of the
> > sensel, which doesn't seem right to me.
>
> Why should it not be? What we have done is a simple scale, and none of
> the noise sources (or significant ones) appears to be dimension
> related.> Moreover, it predicts DR/area
> > actually goes up in inverse proportion to the pixel spacing, which
> > also seems a bit goofy.
>
> Whether it's goofy or not just depends on your preconceptions. If you
> look at it another way, we're reading through a greater number of
> 'channels', why should that not cause less noise? Also, it also seems
> to work in the limit, the one electron pixel, which requires little
> pixel DR (note to self: have a look at the DR in a dynamic RAM cell)
> to produce an image with zero read noise. Remember also that we're
> talking here only about the read noise, shot noise controlled DR is of
> course smaller per pixel and the same per area.
> Still, if you don't believe it, find the hole in the reasoning.

OK, I found an interesting recent article by James Janesick etal

http://www.laserfocusworld.com/display_article/332970/12/none/none/Feat/CMOS-Detectors:-Scientific-monolithic-CMOS-imagers-come-of-ag

where they say that

"Fundamentally, CMOS read noise is limited by random telegraph signal
(RTS) noise and background flicker noise associated with surface
states in output metal-oxide-semiconductor field-effect-transistor
(MOSFET) pixel amplifiers. These noise sources can be reduced
considerably with the old CCD invention of using buried channel
MOSFETs to curtail bias-current surface interaction. This technology
will undoubtedly produce a subelectron noise floor in the very near
future, thus surpassing CCD read noise."

Is RTS the same as 1/f noise? If so, then the little summary sheet
you linked to says that the 1/f noise power spectrum goes like 1/area,
so RMS voltage fluctuations scale linearly with pixel spacing and DR
per pixel does go down with pixel size.

It's not clear when they talk about subelectron read noise what size
pixels they have in mind; they say that 2 electrons is the state of
the art.
From: ejmartin on
On Jul 21, 6:52 pm, ejmartin <ejm_60...(a)yahoo.com> wrote:

>
> Is RTS the same as 1/f noise?  If so, then the little summary sheet
> you linked to says that the 1/f noise power spectrum goes like 1/area,
> so RMS voltage fluctuations scale linearly with pixel spacing and DR
> per pixel does go down with pixel size.
>
> It's not clear when they talk about subelectron read noise what size
> pixels they have in mind; they say that 2 electrons is the state of
> the art.

Though perhaps what you'll tell me is that the readout frequency goes
up in inverse proportion to the pixel area if we want to keep the
frame rate constant.
From: Steve on

On Mon, 21 Jul 2008 22:08:01 GMT, John Sheehy <JPS(a)no.komm> wrote:

>Steve <steve(a)example.com> wrote in
>news:3k09849l6caa4uafvlmqttb8as8pfhlhi9(a)4ax.com:
>
>> On Mon, 21 Jul 2008 06:30:04 GMT, "David J Taylor"
>> <david-taylor(a)blueyonder.neither-this-bit.nor-this-bit.co.uk> wrote:
>
>>>Although some would choose 6MP, I bet a majority would choose 12MP,
>>>which suggests to me that either marketing has succeeded, or that they
>>>really do prefer resolution over noise.
>
>> Or, that for an APS-C sensor size, you're in the area of the S/N vs.
>> Pixel Density curve where it's still relatively flat. So you don't
>> give up all that much S/N when moving from 6 to 12MP for an APS-C DSLR
>> like you would for a 1/1.8 pocket camera, which has about 10 times
>> less sensor area.
>
>It doesn't really seem to be a problem there, either. P&S cameras that
>do RAW (you can't tell a thing about sensors from cameras that do JPEG
>only) suggest that QE is not taking a toll from high pixel count, and
>pixel-level read noise doesn't seem to be on much of a rise, if any, so
>image-leve read noise is maintaining or improving.

Personally, I don't care much about just the sensor. I care about the
entire image. So I can tell something from cameras that just do JPEG.
If the camera trades off image softness for NR, resolution for S/N,
etc., that will be obvious in the JPEGs also.

>All the anecdotes about more noise from higher pixel density in P&S
>cameras come from viewing at 100%, or impressions made from NR designed
>for 100% pixel views.

I agree that a fairer comparison is to take a particular picture size,
say 8"x10", and compare the 6MP P&S to the 12MP P&S at that size. That
lets the higher MP camera take advantage of those pixels in the NR
algorithms. I'm still not sure that a small sensor at 12MP can
compete when you start pushing the ISO up to, say 400 or 800, with a
6MP P&S in terms of image noise though, even if you do have those
extra pixels.

Steve