From: ejmartin on
On Jul 21, 6:52 pm, ejmartin <ejm_60...(a)yahoo.com> wrote:
> 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/Fe...
>
> 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."
>

A couple more references:

www.imagesensors.org/Past%20Workshops/2007%20Workshop/2007%20Papers/056%20Leyris%20et%20al.pdf

www-isl.stanford.edu/~abbas/group/papers_and_pub/1_f_noise.pdf



From: Ray Fischer on
David J Taylor <david-taylor(a)blueyonder.neither-this-bit.nor-this-bit.co.uk> wrote:
>Ray Fischer wrote:
>> David J Taylor
>> <david-taylor(a)blueyonder.neither-this-bit.nor-this-bit.co.uk> wrote:
>>> Ray Fischer wrote:
>>>> David J Taylor
>>>> <david-taylor(a)blueyonder.neither-this-bit.nor-this-bit.co.uk> wrote:
>>>>> Ray Fischer wrote:
>>
>>>>>> Who cares? People don't care about "pixel densities". People
>>>>>> care abut noise per pixel, not noise per sensor area.
>>>>>
>>>>> So why buy a 12MP APS-C DSLR over a 6MP APS-C DSLR if people don't
>>>>> care about pixel densities?
>>>>
>>>> 6MP.
>>>>
>>>> Duh.
>>>
>>> Which suggests that you /do/ care about the pixel density....
>>
>> No, it says that they care about the number of pixels. Notice that
>> you
>> didn't ask about pixel density? You asked about number of pixels?
>>
>> That should have been a clue.
>
>You said: "People care abut noise per pixel, not noise per sensor area".
>Now you say "they care about the number of pixels". Which is it to be?

You are the one who asked about number of pixels. Did you forget?

> I
>was careful to specify the same size sensor.

But you made no mention of noise.

>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.

You really are being an idiot since I never said otherwise. I said
that people don't care about noise PER SENSOR AREA. Of course noise
counts as detailed reviews on DPReview show. People DON'T care about
noise per sensor area.

--
Ray Fischer
rfischer(a)sonic.net

From: David J Taylor on
Ray Fischer wrote:
> David J Taylor
> <david-taylor(a)blueyonder.neither-this-bit.nor-this-bit.co.uk> wrote:
>> Ray Fischer wrote:
>>> David J Taylor
>>> <david-taylor(a)blueyonder.neither-this-bit.nor-this-bit.co.uk> wrote:
>>>> Ray Fischer wrote:
>>>>> David J Taylor
>>>>> <david-taylor(a)blueyonder.neither-this-bit.nor-this-bit.co.uk>
>>>>> wrote:
>>>>>> Ray Fischer wrote:
>>>
>>>>>>> Who cares? People don't care about "pixel densities". People
>>>>>>> care abut noise per pixel, not noise per sensor area.
>>>>>>
>>>>>> So why buy a 12MP APS-C DSLR over a 6MP APS-C DSLR if people
>>>>>> don't care about pixel densities?
>>>>>
>>>>> 6MP.
>>>>>
>>>>> Duh.
>>>>
>>>> Which suggests that you /do/ care about the pixel density....
>>>
>>> No, it says that they care about the number of pixels. Notice that
>>> you
>>> didn't ask about pixel density? You asked about number of pixels?
>>>
>>> That should have been a clue.
>>
>> You said: "People care abut noise per pixel, not noise per sensor
>> area". Now you say "they care about the number of pixels". Which is
>> it to be?
>
> You are the one who asked about number of pixels. Did you forget?
>
>> I
>> was careful to specify the same size sensor.
>
> But you made no mention of noise.
>
>> 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.
>
> You really are being an idiot since I never said otherwise. I said
> that people don't care about noise PER SENSOR AREA. Of course noise
> counts as detailed reviews on DPReview show. People DON'T care about
> noise per sensor area.

Not mentioning noise was intentional. I think that people actually care
most about the final image results, not noise per pixel, or noise per
sensor area. To understand /why/ an image is pleasing or not could
involve either of those parameters, though.

David


From: Bob Newman on
On 22 Jul, 00:52, ejmartin <ejm_60...(a)yahoo.com> wrote:
> 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/Fe...
>
> 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.- Hide quoted text -
>
> - Show quoted text -

Busy day today, won't get much chance to look at this (earning money
gets in the way sometimes) but interesting article. Playing the
'glances though and select quotes supporting my argument' game, we
have:
"In addition, increasing the V/e- conversion gain will further reduce
noise proportionally. For example, the 2 e- noise floor demonstrated
by the 5T CMOS imager described previously is generated by 50 µV/e-
pixels. The conversion gain can be made as high as 200 µV/e- with 0.18
µm CMOS design rules ", which seems to support my argument somewhat.
I think the truth is that so far as read transistor noise is
concerned, I am essentially on the right lines. However, there is a
point at which 1/f noise and other sources which don't scale with V/e-
will become significant and produce the 'noise floor' this article
talks about. At that point, small pixels will cease to be better. What
we don't know, is how far away from that we are. However, none of our
current commercial imagers is close to sub e- read noise, so it looks
like there's a bit to go yet. (Incidentally, JPS suggested he had
picked up somewhere that sub e- read noise is possible, and was
lampooned for it (not by you, I hasten to add) - this article
corroborates that statement).
From: John Sheehy on
rfischer(a)sonic.net (Ray Fischer) wrote in
news:4885745e$0$17151$742ec2ed(a)news.sonic.net:

> You really are being an idiot since I never said otherwise. I said
> that people don't care about noise PER SENSOR AREA. Of course noise
> counts as detailed reviews on DPReview show. People DON'T care about
> noise per sensor area.

Well, they should, if they have in mind a camera with a certain sized
sensor, which people often do. In that context, being concerned with
noise per pixel would be foolish:

"I've decided to buy a FF DSLR."

"Oh; nice. Which one are you going to buy?"

"The one that looks cleanest at 100% pixel view on my 96 PPI monitor, of
course, because I am very slow upstairs."

"Why not get the one that shows the best combination of resolution and
image noise, printed at a standard size?

"No one cares about quality per unit of area."

--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS(a)no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><