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FORUMS Photography Talk by Genre General Photography Talk 
Thread started 07 Jun 2009 (Sunday) 22:20
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Small pixel sensors do not have worse performance

 
Rudeofus
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Jun 08, 2009 16:38 as a reply to  @ post 8071896 |  #16

CDS,

there is a flurry of similarly sounding threads (I counted 3), but if you look carefully they cover very different aspects so it's hard to imagine that they are just spill over from some other forum. Sensor size has other impact on IQ than individual pixel size so I'm glad they're discussed separately. The third and imho most expendable thread was closed by you anyway. While this particular thread starts with many references to dpreview forum, the cited posts are months old and not from one thread (which contradicts your accusation of spill over) - Daniel appears to have done some research on this topic, something I consider a good thing.

And to be honest: I AM VERY HAPPY this forum finally gets some deep technical discussions. These two threads actually made me enjoy the forum a lot more and if you read joe mamas, Daniels, Bobs and Richards contributions you learn more about the underlying technology of digital photography than from all the "which lens is sharper" and "please help me with my homework" - threads combined.


Discovery is not accidental. We discover only when we make ourselves ready to receive and photographers seek discovery by mastering their craft. But it begins somewhere else. It begins with daisies, kids, awful scenes, falling in love, or growing old. It begins with that which matters to you. And it ends with visual statements that express what matters to you about these things. It is not sight the camera satisfies so thoroughly, but the mind. - Christian Molidor

  
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chauncey
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Jun 08, 2009 17:09 as a reply to  @ Rudeofus's post |  #17

I apologize to being the dimmest bulb in the closet but, is the OP trying to claim that a smaller sensor, with the same number of "pixels" as a larger sensor,
in all circumstances, will have equal IQ in the print, regardless of print size, assuming equal electronics and such?


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Daniel ­ Browning
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Jun 08, 2009 23:23 |  #18

E-K wrote in post #8070407 (external link)
Be careful what you are comparing though--a 10MP full frame compared to a 10MP APS-C will have the full frame winning out SNR-wise, assuming similar technologies, because the pixels/sensels/photosi​tes are bigger when comparing like resolutions.

I would state that a little differently. Even if the full frame sensor had smaller pixels than the APS-C sensor, it would still be superior thanks to the greater sensor size. Therefore, the superiority could not be due to pixel size. The 10 MP full frame is superior because of it's larger sensor.

Rudeofus wrote in post #8071023 (external link)
This is certainly an interesting article with the aim to debunk all these folks who scream for fewer and larger pixels (cf. the D700 vs. 5DII debate).

Thanks for the response, Redeofus.

Rudeofus wrote in post #8071023 (external link)
You claim that the Micron paper postulates better results with smaller sensor cells, which is not the case.

Do you think their data contradicts their own conclusion? ("In summary, Micron sensors have achieved "scaled" performance, preserving sensitivity and SNR performance when compared to similar optical format sensors, but with the added benefit of higher spatial resolution as the pixels shrink.")

Rudeofus wrote in post #8071023 (external link)
Their 2.2µ 2. gen cell smokes their 1.75µ 2. gen cell. If you look at the 1. gen cells posted in the same plot: 5.6µ is better than 3.6µ is better than 2.8 µ is a lot better than 2.2µ.

Are you referring to the per-pixel numbers? If so, how do you think the performance compares after scaling for the difference in spatial frequency (i.e. similar real life uses)?

Rudeofus wrote in post #8071023 (external link)
* Eric Fossum writes in the dpreview forum that "Fill factor pretty much has scaled with technology". I'd interpret this as: once chip technology improved and finer structures could be built (ADC, interconnects), chip makers used the improvements to bump up pixel density.

That sounds right to me; I don't see the contradiction with what I wrote. If you are saying that semiconductor process shrink and the ingenuity of sensor designers are the reason why performance has scaled with pixel size, then I would agree.

Rudeofus wrote in post #8071023 (external link)
If, with the current technology you'd implement the 5DII sensor with gazillions of 1µ pixels, you'd get terrible fill factors.

Are you saying that you think that 1µm pixels have worse fill factor than large (6µm+) pixels? Or all small pixels (1.4µm - 4µm)? If so, what experimental results or references would you give to support that position?

Rudeofus wrote in post #8071023 (external link)
* The article posted by E-K spends half a page explaining why small sensor sizes have no detrimental effect on noise performance. They should spend at least as much explaining why their theory doesn't hold at high ISO settings, where the 1D3 clearly outguns anything else in the comparison.

Emil spent sufficient time explaining both, IMHO.

Rudeofus wrote in post #8071023 (external link)
The practical results posted by [EMil] clearly support that large pixels perform better than small pixels at high ISOs, which is exactly the regime where sensor performance becomes relevant. If ISO 100 is all we ever needed, nobody would even talk about pixel area.

I kindly disagree. There are many photographers that care greatly about dynamic range at base amplification (low ISO). I would even argue that it is more important, more often, to more photographers than low light performance (high ISO). For me, personally, the latter is more important, but I think I'm in the minority.

My thoughts about low light performance (high ISO) are in the section on "Read Noise" in the OP.

CyberDyneSystems wrote in post #8071896 (external link)
I have to ask, is this recent activity on this subject matter over spill from another forum?

I've been working on a draft of this post for over a year now. I've posted earlier, junky versions on other forums, most recently DPR, each time getting good feedback and making major edits. This is the first version I felt was good enough to post here.

CyberDyneSystems wrote in post #8071896 (external link)
If so, to the POTN members, please do not bring arguments from other forums to our humble abode. No reason to play out the same war on two battlefields.

Agreed.

chauncey wrote in post #8073266 (external link)
is the OP trying to claim that a smaller sensor, with the same number of "pixels" as a larger sensor...

No. The "Unequal sensor sizes" section is attempt to make that clear.


Daniel

  
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CAL ­ Imagery
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Jun 09, 2009 00:04 |  #19

CyberDyneSystems wrote in post #8071822 (external link)
Great post Daniel!


writ small;

The comparison can only be made when "all else is equal"
Technology shifts and evolves, and in every new generation "all else is never equal"

Our 10,001 threads on the subject have been saying this since the 10D and 1Ds were on the shelves.

I believe in the history of Canon sensors there was only one time that there were two CMOS sensors of absolute equal design and density but differing formats (size) being sold at one time in DSLRs.. ( 1D MkII and 5D )

However even then the two bodies had differing electronics.. so "all else" was still NOT equal.
Their noise handling performance is however virtually identical.

Thanks for the clip notes...


Christian

  
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tkbslc
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Jun 09, 2009 00:30 |  #20

All I know is that smaller sensor = worse image quality at any output size above a postage stamp. Argue the rest however you want.


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Rudeofus
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Jun 09, 2009 03:34 |  #21

Daniel Browning wrote in post #8075240 (external link)
Do you think their data contradicts their own conclusion? ("In summary, Micron sensors have achieved "scaled" performance, preserving sensitivity and SNR performance when compared to similar optical format sensors, but with the added benefit of higher spatial resolution as the pixels shrink.")

Micron concluded that thanks to process improvements they could downscale the sensor without running into performance problems. This is, however, not, what your thread starting post claims. The sentiment of this thread is that given same technology there are advantages to using more but smaller pixels (so sensor size stays the same). This is not confirmed by the micron paper imho.

Daniel Browning wrote in post #8075240 (external link)
Are you referring to the per-pixel numbers? If so, how do you think the performance compares after scaling for the difference in spatial frequency (i.e. similar real life uses)?

I refer to the following quote:

Figure 6 presents the normalized per-pixel area scene light intensity, providing luminance SNR equal to 10 for Micron’s pixels with different sizes. (Conditions correspond to those used earlier for Figure 4.) As can be seen from the plot, the 1.75µm pixel has a normalized SNR equal to or very close to those pixels larger in size, and respectively will provide similar sensitivity as those larger pixels in the same optical format.

If Figure 6 showed single pixel performance, the conclusion would be dramatically improved image SNR (as joe mama coined the term when he compared sensor sizes), something the paper doesn't claim at all. What the paper claims is that thanks to technological improvements they could keep the SNR at acceptable levels while boosting spatial resolution. That's precisely what P&S, 5DII and mobile phone camera sensors have done: maintain acceptable performance @ISO100 and crank up pixel count.

Daniel Browning wrote in post #8075240 (external link)
Are you saying that you think that 1µm pixels have worse fill factor than large (6µm+) pixels? Or all small pixels (1.4µm - 4µm)? If so, what experimental results or references would you give to support that position?

People often neglect that a sensor does not only consist of the photo sensitive cells. A CMOS sensel consists of photo sensitive cell, variable gain amplifier and an ADC. The only way around is to shrink the silicon process, which is exactly what micron did:

however, keeping the same level of pixel performance in regards to fill factor and pixel capacity becomes a significant challenge. This is partially resolved by using an advanced 95nm manufacturing processes for the pixel array.

Daniel Browning wrote in post #8075240 (external link)
I kindly disagree. There are many photographers that care greatly about dynamic range at base amplification (low ISO). I would even argue that it is more important, more often, to more photographers than low light performance (high ISO). For me, personally, the latter is more important, but I think I'm in the minority.

I guess that explains our different approach. Interesting enough I saw an article comparing a medium format digital back to a full frame DSLR and the DSLR smoked the digital back at high ISO. Obviously people still find the digital back worth the money, so you seem to have a valid point here.


Discovery is not accidental. We discover only when we make ourselves ready to receive and photographers seek discovery by mastering their craft. But it begins somewhere else. It begins with daisies, kids, awful scenes, falling in love, or growing old. It begins with that which matters to you. And it ends with visual statements that express what matters to you about these things. It is not sight the camera satisfies so thoroughly, but the mind. - Christian Molidor

  
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E-K
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Jun 09, 2009 08:30 |  #22

Daniel Browning wrote in post #8075240 (external link)
I would state that a little differently. Even if the full frame sensor had smaller pixels than the APS-C sensor, it would still be superior thanks to the greater sensor size. Therefore, the superiority could not be due to pixel size. The 10 MP full frame is superior because of it's larger sensor.

Yup you're right; that's worded rather horribly :) I'll take it out to avoid confusion. I was trying to get across something about native resolving power but ultimately more photons hit a larger sensor than a smaller one so the number of pixels is generally irrelevant.

e-k




  
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joe ­ mama
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Jun 09, 2009 12:35 |  #23
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E-K wrote in post #8076661 (external link)
Yup you're right; that's worded rather horribly :) I'll take it out to avoid confusion. I was trying to get across something about native resolving power but ultimately more photons hit a larger sensor than a smaller one so the number of pixels is generally irrelevant.

e-k

The only ways a larger sensor system can get more light than a smaller sensor system is by using a larger aperture (which will result in a more shallow DOF, softer corners, and more vignetting, in case these things matter to the photographer for the image in question) or by using a longer shutter speed.


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E-K
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Jun 09, 2009 13:21 |  #24

joe mama wrote in post #8078108 (external link)
The only ways a larger sensor system can get more light than a smaller sensor system is by using a larger aperture (which will result in a more shallow DOF, softer corners, and more vignetting, in case these things matter to the photographer for the image in question) or by using a longer shutter speed.

I don't agree. Say I want to take a picture of a uniformly white wall. I meter it such that the proper exposure is ISO100, f/8, 1/200. No matter what lens I use that would be the exposure setting.

The number of photons per unit area is necessarily the same between say a full frame and APS-C sensor in those circumstances. Since the larger sensor has a greater area it by definition collects more light.

e-k




  
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joe ­ mama
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Jun 09, 2009 13:43 |  #25
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E-K wrote in post #8078402 (external link)
I don't agree. Say I want to take a picture of a uniformly white wall. I meter it such that the proper exposure is ISO100, f/8, 1/200. No matter what lens I use that would be the exposure setting.

The number of photons per unit area is necessarily the same between say a full frame and APS-C sensor in those circumstances. Since the larger sensor has a greater area it by definition collects more light.

e-k

Please read this thread(at least my posts) all the way through, since I don't want to repeat all the arguments I did in it. In particular, you need to distinguish between exposure (photons per area) and total amount of light (total number of photons that fall on the sensor) -- they are not the same. The reason that the distinction is important is because it is the total amount of light, not the exposure, that is the primary element in total image noise.

Again, read the threadfirst, and then, if you have any questions or disagreements, please cite the post from that thread that you disagree with, since I'm pretty sure that no one, least of all me, wants to rehash all that again so soon.


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E-K
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Jun 09, 2009 14:10 |  #26

joe mama wrote in post #8078533 (external link)
Please read this thread(at least my posts) all the way through, since I don't want to repeat all the arguments I did in it. In particular, you need to distinguish between exposure (photons per area) and total amount of light (total number of photons that fall on the sensor) -- they are not the same. The reason that the distinction is important is because it is the total amount of light, not the exposure, that is the primary element in total image noise.

Again, read the threadfirst, and then, if you have any questions or disagreements, please cite the post from that thread that you disagree with, since I'm pretty sure that no one, least of all me, wants to rehash all that again so soon.

If all you are talking about is the physical aperture being larger, then fine I don't disagree -- that's a given assuming you want the same framing and perspective.

Now if you want to keep the same DoF and shutter speed your only option is to bump the ISO which bumps the noise. However, you are also enlarging the smaller sensor size image more so noise is more noticeable.

That being said, there are a number of circumstances were the above pre-conditions do not need to be adhered to in which case one can accept a shallower depth of field and keep the ISO the same.

e-k




  
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Jun 09, 2009 14:29 |  #27

tkbslc wrote in post #8075507 (external link)
All I know is that smaller sensor = worse image quality at any output size above a postage stamp. Argue the rest however you want.

That appears to be one of those old rules that is still true after two centuries of photography, definitely true if everything else is equal, and even true most of the time if darned near everything else favors the smaller format.

With regard to more and smaller sensels in the same format, what we've seen so far is that technology has not yet hit a wall in delivering more pixels with even higher overall image quality. I don't give a rodent's bootay about "per pixel" image quality any more than I cared about "grain-edge acutance" thirty years ago.


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Jun 09, 2009 21:07 as a reply to  @ RDKirk's post |  #28

If what you're saying is true, ( and I'm not knowledgeable enough to argue either way) why aren't we seeing dslr sensors with the pixel (sensel?) density of point and shoots?


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chauncey
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Jun 09, 2009 21:14 as a reply to  @ Bodog's post |  #29

How dare you....to interject common sense into this debate.


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Daniel ­ Browning
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Jun 09, 2009 23:08 |  #30

Rudeofus wrote in post #8076155 (external link)
Micron concluded that thanks to process improvements they could downscale the sensor without running into performance problems. This is, however, not, what your thread starting post claims. The sentiment of this thread is that given same technology there are advantages to using more but smaller pixels (so sensor size stays the same). This is not confirmed by the micron paper imho.

You're right. Thank you for the correction.

Bodog wrote in post #8080992 (external link)
If what you're saying is true, ( and I'm not knowledgeable enough to argue either way) why aren't we seeing dslr sensors with the pixel (sensel?) density of point and shoots?

For the reasons I outlined in my post under "other considerations". For a given amount of heat and cost in the camera, there is a limited amount of processing power. With current technology and software, a 200 MP DSLR would be too slow. The cameras would be rated in "seconds per frame" instead of "frames per second". Not to mention the file size and post-processing speed.


Daniel

  
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Small pixel sensors do not have worse performance
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