D600 High ISO in DX

Started Nov 23, 2012 | Questions
JimPearce
JimPearce Veteran Member • Posts: 9,201
We won't know until the D5200 is tested...

So far, the D800 and D600 in DX mode both slightly outperform the D7000, D3200. This does not seem to correlated with pixel size as the D800 and D600 perform about the same, as do the D7000 and D3200.

-- hide signature --

Jim

 JimPearce's gear list:JimPearce's gear list
Nikon D7100 Nikon D500
Leo360 Senior Member • Posts: 1,141
Clarkvision.com analysis

Leo360 wrote:

So far from what I saw on Bill Claff's charts is that D600(DX mode) dynamic range outperforms D7000 at all ISOs. I have no reason to think that with D5200 it will be any different.

Leo

For those interested in the subject of sensor performance with all the gory details, please, read the sensor section at the clarkvision.com. Highly recommended read!

Leo

 Leo360's gear list:Leo360's gear list
Nikon D5100 Nikon D750 Nikon AF-S DX Nikkor 18-200mm f/3.5-5.6G ED VR II Nikon AF-S Nikkor 24-120mm F4G ED VR Nikon AF-S Nikkor 50mm f/1.8G
bobn2
bobn2 Forum Pro • Posts: 62,177
Re: pixel pitch and SNR
1

Leo360 wrote:

bobn2 wrote:

Photosite (or even pixel) size has very little connection to sensor efficiency and therefore low light performance. The pixels might be bigger, but you have fewer of them, so in the end the same amount of light gets collected.

There are two different things here. There is photon count per pixel and number of photons collected per unit area.

Those are indeed two different things.

The latter does not depend on the pixel pitch but the former does. And SNR per pixel gets larger with more photons collected by that pixel (photon shot-noise per photon gets weaker). For the same exposure larger pixels capture more photos and, thus, have higher SNR. This is why pixel peeping reveals more noise-per-pixel for smaller photosites.

Indeed, bt that is of little relevance to what we are actually trying to do in photography, which is make a picture that we can look at.

The price to pay is reduced resolution.

The resolution is identical, if you look at individual pixels, because a pixel just describes the value of light where it is. There is only 'resolution' when you look at an area, and if you want to compare 'resolution' it makes sense to compare the same area (or equivalent areas when magniified to the size of the final image). So, the bottom line is that 'resolution' makes no sense at the pixel level, and nor, in terms of image quality, does the SNR.

With proper down-sampling (bicubic, etc) to the same level of detail one can hope to recover the SNR back by effectively combining outputs of multiple smaller pixels into an aggregate one but doing so does not entirely compensate for read-noise increase.

The 'downsampling' argument is a red herring. All that is required is to look at the images produced the same size.

Correct me if I am wrong, but I think that you will have to jump through several hoops to match 4x4 um pixel SNR to 6x6 um one.

You cannot measure SNR in a single pixel in a single photograph. Now think on the implications of that.

-- hide signature --

Bob

bobn2
bobn2 Forum Pro • Posts: 62,177
Re: Clarkvision.com analysis
1

Leo360 wrote:

Leo360 wrote:

So far from what I saw on Bill Claff's charts is that D600(DX mode) dynamic range outperforms D7000 at all ISOs. I have no reason to think that with D5200 it will be any different.

Leo

For those interested in the subject of sensor performance with all the gory details, please, read the sensor section at the clarkvision.com. Highly recommended read!

Only highly recommended if you want to end up getting all kinds of stuff wrong. Which seems to be what you have done. Particularly, the section on the effects pixel size is extremely confused.

-- hide signature --

Bob

noirdesir Forum Pro • Posts: 13,632
Re: pixel pitch and SNR
1

John Motts wrote:

noirdesir wrote:

John Motts wrote:

Leo360 wrote:

bobn2 wrote:

Photosite (or even pixel) size has very little connection to sensor efficiency and therefore low light performance. The pixels might be bigger, but you have fewer of them, so in the end the same amount of light gets collected.

There are two different things here. There is photon count per pixel and number of photons collected per unit area. The latter does not depend on the pixel pitch but the former does. And SNR per pixel gets larger with more photons collected by that pixel (photon shot-noise per photon gets weaker). For the same exposure larger pixels capture more photos and, thus, have higher SNR. This is why pixel peeping reveals more noise-per-pixel for smaller photosites. The price to pay is reduced resolution. With proper down-sampling (bicubic, etc) to the same level of detail one can hope to recover the SNR back by effectively combining outputs of multiple smaller pixels into an aggregate one but doing so does not entirely compensate for read-noise increase.

Correct me if I am wrong, but I think that you will have to jump through several hoops to match 4x4 um pixel SNR to 6x6 um one.

Leo

Doesn't anyone use their eyes anymore?

When you buy tomatoes, to 'weigh' them with your hands to figure out which box contains more or do you put them on a balance? If something can be done faster and more accurately with the help of technology, it is usually more sensible to use the technology.

Simple statistics tell us that the read noise component for a combination of these four smaller pixels is: rn(com) = square root of (1.5^2 + 1.5^2 + 1.5^2 + 1.5^2) = 3 e-

Fair comment, but everyone knows how to use scales.

However it's a good deal more straightforward to just compare images with your eyes than to go into this technical depth that leaves most people in the dark. Your "simple" statistics quoted above for example.

There are people coming in to photography who read all the techno stuff but still haven't got a clue about the most basic concepts.

Photography is getting unnecessarily complex and it is this that leads to the most unbelievable misunderstandings of quite basic photographic concepts that we so often see on these forums.

Very little of this techno stuff is essential to produce good photography and is more relevant to camera design rather than camera use.

I don't wish to take anything away from your technical knowledge and it's great if you're interested in that area, but it's specialist stuff and it's a shame if we lose sight of photography itself.

But if somebody has a question that is easily answered with simple statistics, why not give him him or her the answer if you know it?

bobn2
bobn2 Forum Pro • Posts: 62,177
Re: We won't know until the D5200 is tested...
1

JimPearce wrote:

So far, the D800 and D600 in DX mode both slightly outperform the D7000, D3200. This does not seem to correlated with pixel size as the D800 and D600 perform about the same, as do the D7000 and D3200.

The D800 and D600 have a higher quantum efficiency than the D7000, which in turn has a higher QE than the D3200.

-- hide signature --

Bob

noirdesir Forum Pro • Posts: 13,632
Re: pixel pitch and SNR
2
Leo360 wrote:

noirdesir wrote:

In an ideal world, read noise is proportional to pixel size.

Why is that? I think that in ideal world read-noise should be independent of pixel size and should only depend on the temperature (even ideal world has thermal noise).

So, let's take a 2x2 μm pixel with a read noise of 6 e- (ie, a standard deviation of 6 e-). Now compare that to a 2x2 pixel array of 1x1 μm pixels, where each pixel has a read noise of 1.5 e-.

I don't think so. What makes you think that read-noise std.dev. scales quadratic with pixel pitch. Please, provide some rational for this behavior.

This is based on explanations by bobn, you'll have to ask him for details. But I have seen anybody showing that this premise as first order assumption was incorrect. And it does not sound unreasonable to me that read noise could be partly based on a phenomena that is proportional to the size of the pixel.

Simple statistics tell us that the read noise component for a combination of these four smaller pixels is:

rn(com) = square root of (1.5^2 + 1.5^2 + 1.5^2 + 1.5^2) = 3 e-

The formula above is based on a questionable assumption.

Following your line of thoughts I will consider 2x2 um pixel against a group of 100 of 0.2x0.2 um pixels with the read-noise sigma= 0.06. This follows from your own read-noise scaling rule! Now based on your summation formula I will conclude that

rn = 10x0.06 = 0.6 which is 10 times smaller that original 2x2 pixel.

After signal aggregation from all 100 micro-pixels the 2x2 pixel SNR increased 10 times. Seems too good to be true or is it?

Nope, only the noise contribution from read noise decreases that much, there is also photon shot noise which for most situations will swamp the read noise, thus SNR will not increase nearly as much as only looking at the read noise component will tell you.

And I said that this is an idealised assumption that only gives a general idea of one of the phenomena involved.

Bottom line, sensor noise performance is messy and contains lots of proprietary stuff in processing chain that we are not privy to.

That is why I added several real world examples where smaller pixels result in either equal or lower read noise contribution to total noise. My aim was not to postulate that read noise only depends on pixel area size but to refute those who claim that smaller pixels will result in more read noise in the final image.

So far from what I saw on Bill Claff's charts is that D600(DX mode) dynamic range outperforms D7000 at all ISOs. I have no reason to think that with D5200 it will be any different.

Bill Claff's dynamic range definition (PDR) is based on a noticeably higher minimum SNR than the engineering definition of DR. As a result, photon shot noise (and thus QE) have much higher influence than read noise for his results. And the D600 has a higher QE than the D7000. Moreover, Bill's PDR chart is also plotted over manufacturer ISO not an ISO normalised to saturation which adds another usually small source of bias for some cameras.

JimPearce
JimPearce Veteran Member • Posts: 9,201
Yes, I see that Bob...

Actually, I find Bill's results for the D3200 somewhat suspect given the dramatically lower QE and the fact that the D7000 is clearly a little better in dxomarks testing. I'm certainly hoping that the "new" sensor is an improvement.

-- hide signature --

Jim

 JimPearce's gear list:JimPearce's gear list
Nikon D7100 Nikon D500
Leo360 Senior Member • Posts: 1,141
Re: Clarkvision.com analysis

bobn2 wrote:

Leo360 wrote:

Leo360 wrote:

So far from what I saw on Bill Claff's charts is that D600(DX mode) dynamic range outperforms D7000 at all ISOs. I have no reason to think that with D5200 it will be any different.

Leo

For those interested in the subject of sensor performance with all the gory details, please, read the sensor section at the clarkvision.com. Highly recommended read!

Only highly recommended if you want to end up getting all kinds of stuff wrong. Which seems to be what you have done. Particularly, the section on the effects pixel size is extremely confused.

And how exactly it is confused?

Roger has a more accessible essay "Does Pixel Size matter?" which is also a recommended reading for those who believe (not you) that read noise scales up linearly with pixel area.

Leo

 Leo360's gear list:Leo360's gear list
Nikon D5100 Nikon D750 Nikon AF-S DX Nikkor 18-200mm f/3.5-5.6G ED VR II Nikon AF-S Nikkor 24-120mm F4G ED VR Nikon AF-S Nikkor 50mm f/1.8G
Leo360 Senior Member • Posts: 1,141
Re: pixel pitch and SNR

bobn2 wrote:

Leo360 wrote:

There are two different things here. There is photon count per pixel and number of photons collected per unit area.

Those are indeed two different things.

The latter does not depend on the pixel pitch but the former does. And SNR per pixel gets larger with more photons collected by that pixel (photon shot-noise per photon gets weaker). For the same exposure larger pixels capture more photos and, thus, have higher SNR. This is why pixel peeping reveals more noise-per-pixel for smaller photosites.

Indeed, bt that is of little relevance to what we are actually trying to do in photography, which is make a picture that we can look at.

The price to pay is reduced resolution.

The resolution is identical, if you look at individual pixels, because a pixel just describes the value of light where it is. There is only 'resolution' when you look at an area, and if you want to compare 'resolution' it makes sense to compare the same area (or equivalent areas when magniified to the size of the final image). So, the bottom line is that 'resolution' makes no sense at the pixel level, and nor, in terms of image quality, does the SNR.

The resolution of a digital image depends (among other things) on your sampling rate (Nyquist theorem) and pixel size has A LOT to do with it.

With proper down-sampling (bicubic, etc) to the same level of detail one can hope to recover the SNR back by effectively combining outputs of multiple smaller pixels into an aggregate one but doing so does not entirely compensate for read-noise increase.

The 'downsampling' argument is a red herring. All that is required is to look at the images produced the same size.

It is not a red herring. Producing images at the same size with the same dpi  means that we have to resample an output of hi-res camera to match the sampling rate of a low-res camera. Otherwise your prints will be of different size (dpi is the same, right?)

Correct me if I am wrong, but I think that you will have to jump through several hoops to match 4x4 um pixel SNR to 6x6 um one.

You cannot measure SNR in a single pixel in a single photograph. Now think on the implications of that.

-- hide signature --

Bob

Did I say anything about a single photograph? To measure pixel readings statistics one shoots repeatedly in controlled environments with constant light, exposure, etc. You get mean, variance, probability distribution etc in due course of statistical analysis.

Leo

 Leo360's gear list:Leo360's gear list
Nikon D5100 Nikon D750 Nikon AF-S DX Nikkor 18-200mm f/3.5-5.6G ED VR II Nikon AF-S Nikkor 24-120mm F4G ED VR Nikon AF-S Nikkor 50mm f/1.8G
Leo360 Senior Member • Posts: 1,141
Re: We won't know until the D5200 is tested...

bobn2 wrote:

JimPearce wrote:

So far, the D800 and D600 in DX mode both slightly outperform the D7000, D3200. This does not seem to correlated with pixel size as the D800 and D600 perform about the same, as do the D7000 and D3200.

The D800 and D600 have a higher quantum efficiency than the D7000, which in turn has a higher QE than the D3200.

I guess that D5200 will be using the same sensor and processing chain as D3200. And in Bill Claff's charts D600(DX) still outperforms D3200 by a quarter of a stop.

Leo

 Leo360's gear list:Leo360's gear list
Nikon D5100 Nikon D750 Nikon AF-S DX Nikkor 18-200mm f/3.5-5.6G ED VR II Nikon AF-S Nikkor 24-120mm F4G ED VR Nikon AF-S Nikkor 50mm f/1.8G
bobn2
bobn2 Forum Pro • Posts: 62,177
Re: pixel pitch and SNR
1

noirdesir wrote:

This is based on explanations by bobn, you'll have to ask him for details.

http://en.wikipedia.org/wiki/Image_sensor_format#Read_noise

-- hide signature --

Bob

Leo360 Senior Member • Posts: 1,141
bobn2's explanation of read-noise scaling

noirdesir wrote:

Leo360 wrote:

I don't think so. What makes you think that read-noise std.dev. scales quadratic with pixel pitch. Please, provide some rational for this behavior.

This is based on explanations by bobn, you'll have to ask him for details. But I have seen anybody showing that this premise as first order assumption was incorrect. And it does not sound unreasonable to me that read noise could be partly based on a phenomena that is proportional to the size of the pixel.

It seems that I could not find Bob's explanation anywhere. Could someone point me to it. Or better if bobn2 could weight in himself.

Leo

 Leo360's gear list:Leo360's gear list
Nikon D5100 Nikon D750 Nikon AF-S DX Nikkor 18-200mm f/3.5-5.6G ED VR II Nikon AF-S Nikkor 24-120mm F4G ED VR Nikon AF-S Nikkor 50mm f/1.8G
Leo360 Senior Member • Posts: 1,141
Re: pixel pitch and SNR

bobn2 wrote:

noirdesir wrote:

This is based on explanations by bobn, you'll have to ask him for details.

http://en.wikipedia.org/wiki/Image_sensor_format#Read_noise

Thanks Bob. Reading verbatim from the link you provided:

"In general for a planar structure such as a pixel, capacitance is proportional to area, therefore the read noise scales down with sensor area, as long as pixel area scales with sensor area, and that scaling is performed by uniformly scaling the pixel."

Which is exactly the opposite of what noirdesir stated citing you.

Leo

 Leo360's gear list:Leo360's gear list
Nikon D5100 Nikon D750 Nikon AF-S DX Nikkor 18-200mm f/3.5-5.6G ED VR II Nikon AF-S Nikkor 24-120mm F4G ED VR Nikon AF-S Nikkor 50mm f/1.8G
bobn2
bobn2 Forum Pro • Posts: 62,177
Re: Clarkvision.com analysis
1

Leo360 wrote:

bobn2 wrote:

Leo360 wrote:

Leo360 wrote:

So far from what I saw on Bill Claff's charts is that D600(DX mode) dynamic range outperforms D7000 at all ISOs. I have no reason to think that with D5200 it will be any different.

Leo

For those interested in the subject of sensor performance with all the gory details, please, read the sensor section at the clarkvision.com. Highly recommended read!

Only highly recommended if you want to end up getting all kinds of stuff wrong. Which seems to be what you have done. Particularly, the section on the effects pixel size is extremely confused.

And how exactly it is confused?

Where to start? I've done this so many times. If I was sensible I would just keep a bookmark, but I'm not that organised. OK, going from the top:

Dynamic range is defined in this document and elsewhere on this site as:

  • Dynamic Range = Full Well Capacity (electrons) / Read Noise (electrons)

Roger has a more accessible essay "Does Pixel Size matter?" which is also a recommended reading for those who believe (not you) that read noise scales up linearly with pixel area.

Leo

Just as misleading, I counsel people form drawing any conclusions unless they have the background to see the flaws. Once again the examples compare cameras with radically different sensor sizes then ascribe the observed differences to pixel size.

The overall pint is this,Roger (and you) is obsessed with comparing things at the pixel sampling frequency, which means making comparisons over different bandwidths. That produces nonsense results, particularly nonsense if what you are interested in is, if you take like photos from the two cameras being compared, which looks better.

-- hide signature --

Bob

bobn2
bobn2 Forum Pro • Posts: 62,177
Re: bobn2's explanation of read-noise scaling

Leo360 wrote:

noirdesir wrote:

Leo360 wrote:

I don't think so. What makes you think that read-noise std.dev. scales quadratic with pixel pitch. Please, provide some rational for this behavior.

This is based on explanations by bobn, you'll have to ask him for details. But I have seen anybody showing that this premise as first order assumption was incorrect. And it does not sound unreasonable to me that read noise could be partly based on a phenomena that is proportional to the size of the pixel.

It seems that I could not find Bob's explanation anywhere. Could someone point me to it. Or better if bobn2 could weight in himself.

Leo

I did.

-- hide signature --

Bob

bobn2
bobn2 Forum Pro • Posts: 62,177
Re: pixel pitch and SNR
1

Leo360 wrote:

bobn2 wrote:

noirdesir wrote:

This is based on explanations by bobn, you'll have to ask him for details.

http://en.wikipedia.org/wiki/Image_sensor_format#Read_noise

Thanks Bob. Reading verbatim from the link you provided:

"In general for a planar structure such as a pixel, capacitance is proportional to area, therefore the read noise scales down with sensor area, as long as pixel area scales with sensor area, and that scaling is performed by uniformly scaling the pixel."

Which is exactly the opposite of what noirdesir stated citing you.

Leo

No it isn't. The article there is talking about the effect of different size sensors (I am perplexed why you, Roger and all the others of your persuasion cannot distinguish between the size of a sensor and the size of a pixel, and understand that if you want to observe how things change as a parameter changes, you need to change only that parameter). So the stated assumption for that discussion is that the sensor area falls, but pixel count remains the same, which means pixel size must get smaller ('as long as pixel area scales with sensor area, and that scaling is performed by uniformly scaling the pixel'). So, it discusses the effect of pixel size on read noise. The full quote is this:

The read noise is the total of all the electronic noises in the conversion chain for the pixels in the sensor array. To compare it with photon noise, it must be referred back to its equivalent in photoelectrons, which requires the division of the noise measured in volts by the conversion gain of the pixel. This is given, for an active pixel sensor, by the voltage at the input (gate) of the read transistor divided by the charge which generates that voltage, CG= Vrt/Qrt . This is the inverse of the capacitance of the read transistor gate (and the attached floating diffusion) since capacitance C= Q/V. Thus CG=1/Crt.

In general for a planar structure such as a pixel, capacitance is proportional to area, therefore the read noise scales down with sensor area, as long as pixel area scales with sensor area, and that scaling is performed by uniformly scaling the pixel.

This makes it clear that read noise scales down with pixel size.

-- hide signature --

Bob

bobn2
bobn2 Forum Pro • Posts: 62,177
Re: pixel pitch and SNR
1

Leo360 wrote:

bobn2 wrote:

Leo360 wrote:

There are two different things here. There is photon count per pixel and number of photons collected per unit area.

Those are indeed two different things.

The latter does not depend on the pixel pitch but the former does. And SNR per pixel gets larger with more photons collected by that pixel (photon shot-noise per photon gets weaker). For the same exposure larger pixels capture more photos and, thus, have higher SNR. This is why pixel peeping reveals more noise-per-pixel for smaller photosites.

Indeed, bt that is of little relevance to what we are actually trying to do in photography, which is make a picture that we can look at.

The price to pay is reduced resolution.

The resolution is identical, if you look at individual pixels, because a pixel just describes the value of light where it is. There is only 'resolution' when you look at an area, and if you want to compare 'resolution' it makes sense to compare the same area (or equivalent areas when magniified to the size of the final image). So, the bottom line is that 'resolution' makes no sense at the pixel level, and nor, in terms of image quality, does the SNR.

The resolution of a digital image depends (among other things) on your sampling rate (Nyquist theorem) and pixel size has A LOT to do with it.

Yes, but you were talking of the resolution of a pixel. There is no 'resolution' at a pixel level, only when you look at areas containing many pixels.

With proper down-sampling (bicubic, etc) to the same level of detail one can hope to recover the SNR back by effectively combining outputs of multiple smaller pixels into an aggregate one but doing so does not entirely compensate for read-noise increase.

The 'downsampling' argument is a red herring. All that is required is to look at the images produced the same size.

It is not a red herring. Producing images at the same size with the same dpi means that we have to resample an output of hi-res camera to match the sampling rate of a low-res camera. Otherwise your prints will be of different size (dpi is the same, right?)

That is untrue. You do not resample the output of a high res camera to match the sampling rate of a low res camera. Generally you resample it to match the sampling rate demanded by the output image. You will generally resample all cameras so.

Correct me if I am wrong, but I think that you will have to jump through several hoops to match 4x4 um pixel SNR to 6x6 um one.

You cannot measure SNR in a single pixel in a single photograph. Now think on the implications of that.

-- hide signature --

Bob

Did I say anything about a single photograph? To measure pixel readings statistics one shoots repeatedly in controlled environments with constant light, exposure, etc. You get mean, variance, probability distribution etc in due course of statistical analysis.

This now becomes throughly artificial, that you make the multiple observations of the same pixel over multiple exposures. It is not even guaranteed that the noise so observed would match the noise observed in the spatial domain. A thoroughly artificial result of no interest.

-- hide signature --

Bob

Leo360 Senior Member • Posts: 1,141
Re: Clarkvision.com analysis

bobn2 wrote:

Leo360 wrote:

bobn2 wrote:

Leo360 wrote:

Leo360 wrote:

So far from what I saw on Bill Claff's charts is that D600(DX mode) dynamic range outperforms D7000 at all ISOs. I have no reason to think that with D5200 it will be any different.

Leo

For those interested in the subject of sensor performance with all the gory details, please, read the sensor section at the clarkvision.com. Highly recommended read!

Only highly recommended if you want to end up getting all kinds of stuff wrong. Which seems to be what you have done. Particularly, the section on the effects pixel size is extremely confused.

And how exactly it is confused?

Where to start? I've done this so many times. If I was sensible I would just keep a bookmark, but I'm not that organised. OK, going from the top:

Dynamic range is defined in this document and elsewhere on this site as:

  • Dynamic Range = Full Well Capacity (electrons) / Read Noise (electrons)

Moreover, Roger predicts that 5um is the optimum pixel pitch for any CMOS sensor. Bob, what is your take on it?

The overall pint is this,Roger (and you) is obsessed with comparing things at the pixel sampling frequency, which means making comparisons over different bandwidths. That produces nonsense results, particularly nonsense if what you are interested in is, if you take like photos from the two cameras being compared, which looks better.

I cannot speak for Roger but I am NOT comparing across pixel sampling frequencies. On the contrary, I am re-sampling the higher freq. image (think down-sampling) to a common sampling rate and then comparing at the same reference frequency. And  down-sampling (when performed properly) tends to improve SNR.

Leo

 Leo360's gear list:Leo360's gear list
Nikon D5100 Nikon D750 Nikon AF-S DX Nikkor 18-200mm f/3.5-5.6G ED VR II Nikon AF-S Nikkor 24-120mm F4G ED VR Nikon AF-S Nikkor 50mm f/1.8G
Leo360 Senior Member • Posts: 1,141
Re: pixel pitch and SNR

bobn2 wrote:

Leo360 wrote:

bobn2 wrote:

noirdesir wrote:

This is based on explanations by bobn, you'll have to ask him for details.

http://en.wikipedia.org/wiki/Image_sensor_format#Read_noise

Thanks Bob. Reading verbatim from the link you provided:

"In general for a planar structure such as a pixel, capacitance is proportional to area, therefore the read noise scales down with sensor area, as long as pixel area scales with sensor area, and that scaling is performed by uniformly scaling the pixel."

Which is exactly the opposite of what noirdesir stated citing you.

Leo

No it isn't. The article there is talking about the effect of different size sensors (I am perplexed why you, Roger and all the others of your persuasion cannot distinguish between the size of a sensor and the size of a pixel, and understand that if you want to observe how things change as a parameter changes, you need to change only that parameter). So the stated assumption for that discussion is that the sensor area falls, but pixel count remains the same, which means pixel size must get smaller ('as long as pixel area scales with sensor area, and that scaling is performed by uniformly scaling the pixel'). So, it discusses the effect of pixel size on read noise. The full quote is this:

The read noise is the total of all the electronic noises in the conversion chain for the pixels in the sensor array. To compare it with photon noise, it must be referred back to its equivalent in photoelectrons, which requires the division of the noise measured in volts by the conversion gain of the pixel. This is given, for an active pixel sensor, by the voltage at the input (gate) of the read transistor divided by the charge which generates that voltage, CG= Vrt/Qrt . This is the inverse of the capacitance of the read transistor gate (and the attached floating diffusion) since capacitance C= Q/V. Thus CG=1/Crt.

In general for a planar structure such as a pixel, capacitance is proportional to area, therefore the read noise scales down with sensor area, as long as pixel area scales with sensor area, and that scaling is performed by uniformly scaling the pixel.

This makes it clear that read noise scales down with pixel size.

Now my head is spinning and I feel dizzy. Please, correct me if I wrong. The larger the pixel the larger the read-transistor capacitance and, hence, the smaller the Conversion Gain (CG). And smaller CG means MORE read-noise (the same voltage fluctuations result in more noise electorns). Then, disabuse me from my misunderstanding, why you (and Wikipedia) say "read noise scales down" rather then "scales up" with pixel size??

Leo

 Leo360's gear list:Leo360's gear list
Nikon D5100 Nikon D750 Nikon AF-S DX Nikkor 18-200mm f/3.5-5.6G ED VR II Nikon AF-S Nikkor 24-120mm F4G ED VR Nikon AF-S Nikkor 50mm f/1.8G
Keyboard shortcuts:
FForum MMy threads