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Author Topic: 26.4mp 5D Mark III Mid-year? [CR1]  (Read 47953 times)

epsiloneri

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Re: 26.4mp 5D Mark III Mid-year? [CR1]
« Reply #75 on: April 26, 2011, 05:35:58 AM »
Ahhhh...well, then...I hope you don't use a dSLR when you need reach, because it sounds like the Canon PowerShot SX30 IS is the perfect camera for that.
Why are you talking about PS when I'm talking about DSLR?

Perhaps I should let neuroanatomist reply that one to you, but since you don't seem to appreciates each others argument, maybe I can help:

1) You said there are only advantages to having higher pixel densities. That is obviously an exaggeration that you probably did not mean literally.

2) neuroanatomist gave the example of SX30 to show that a higher pixel density is not sufficient. He probably gave the example to make you think and realise why you are wrong in the "high pixel densities always rule" assumption. However, I don't think his example was very successful for that purpose because a) There are many other variables in addition to pixel density that are not kept constant (like sensor size, optics), so it's hard to from this one example to disentangle what the significance of the higher pixel density is. I tried to resolve it in a post above, but perhaps it was too technical to read well. b) He was not very clear with what the example was supposed to demonstrate. c) The tone in his reply was unnecessarily deprecatory, bound to fail an explanatory purpose and trigger the reaction you gave.

To be clear, here is an explicit list of some disadvantages with higher pixel densities (in approximate order of significance):

a) Readout noise increases with number of pixels
b) Slower readout time (limits your images per second rate)
c) More quickly gets limited by diffraction, so needs faster optics to be useful
d) Requires proportionally smaller tolerances for the camera house / optics to make use of the pixels
e) More sensitive to illumination direction (limb darkening)
f) Space/processing requirements increase
g) More expensive to manufacture

Note that I don't list noise as a disadvantage, since the quantum efficiency and collecting area does not change much with pixel density (only in the case where you are read-out noise limited will higher pixel densities produce a noisier image). Also, the dynamic range will not change significantly either, because the storage capacity of pixels is usually determined by their areas, so even if pixels are smaller and have smaller capacities, the number of photons they have to take care of is proportionally smaller.

The list of advantages with higher pixel density I can think of is much shorter, but very significant:

a) Potentially resolves finer detail in an image

I say potentially, because this statement is only true within certain limits. E.g., there is a limit how fine detail the optics will resolve. For small apertures, this limit may well be the diffraction limit (this is a physical limit); in general it is probably more common with imperfect optics. It also assumes that you have sufficient light and short enough exposure time for the pixels to be well exposed without introducing motion blur at the pixel scale.

There is always a balance between the advantages and disadvantages that sets the optimum pixel density. Depending on how much weight you give the different properties, this optimum balance will shift. For FF cameras with current optics, I think a practical upper limit on the number of pixels is around 50 Mpix, approximately the pixel density of 7D. Going beyond that does not make much sense to me, unless there is a revolution in lens manufacturing. I expect higher resolution images will be the domain of larger size sensors, medium or large format, as it is much easier to produce appropriate optics for them. I believe this will be even more true in the future, as sensors will be increasingly better and less expensive, while I don't expect manufacturing of optics to improve at the same pace.

I'll be happy to discuss any items above you may disagree with.

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Re: 26.4mp 5D Mark III Mid-year? [CR1]
« Reply #75 on: April 26, 2011, 05:35:58 AM »

neuroanatomist

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Re: 26.4mp 5D Mark III Mid-year? [CR1]
« Reply #76 on: April 26, 2011, 02:00:49 PM »
However if they could make a FF with a, high quality, PS sensor density and image quality per area unit I would buy it since it would easily outperform 5Dmk2 , as I use now, at low ISO and have equal or better nosie and sharpness at high ISO.

Sorry, but I just don't buy that statement.  For a given sensor size, smaller pixels will resolve more (potentially, provided they aren't limited by some other part of the system, e.g. lens resolution or diffraction), but will also be noisier.

Here's an example with both quantitative and qualitative information: Super Small, Sub 2μm Pixels for Novel CMOS Image Sensors, G.Agranov, R.Mauritzson; S.Barna, J.Jiang, A.Dokoutchaev, X.Fan; X.Li, in Proc, 2007 International Image Sensor Workshop, Ogunquit, Maine, USA  June 7-10, 2007.

In the paper, they describe and test three sensors of the same size (1/4") but with different pixel densities and thus different sizes (from 5.6 μm, which is about the same as the 1DIV, down to 1.75 µm, which is a bit smaller than the S95/G12).  They make the point that with the smaller pixels, they achieve increased resolution while maintaining similar sensitivity.  If you look at Figure 7, the smaller pixels clearly offer a resolution advantage - no argument there.  If you look at the lower panels (low light), it's also clear that with the same size sensor, as the pixels get smaller the image noise increases in light-limiting conditions.
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epsiloneri

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Re: 26.4mp 5D Mark III Mid-year? [CR1]
« Reply #77 on: April 26, 2011, 03:50:48 PM »
They make the point that with the smaller pixels, they achieve increased resolution while maintaining similar sensitivity.  [...]  If you look at the lower panels (low light), it's also clear that with the same size sensor, as the pixels get smaller the image noise increases in light-limiting conditions.

Thanks for the link to the paper. I glanced through it quickly. I find it interesting, though, that according to the authors, the image noise does not change with pixel scale. That seems to be their major conclusion, and is linked to maintaining sensitivity when shrinking pixel size. That seems at odds with what you say about the small-pixel pitch low-light sub-image in Fig 7 being noisier. I have two possible explanations:

1) I agree that the small pixel pitch image looks noisier, but it's hard to be quantitative "by eye" looking at what are probably strongly under-sampled images in print (with an unknown sub-sampling algorithm). It could be, that if you measure the noise at the same spatial scale, then all three examples would be equally noisy, i.e. show the same S/N (this is in fact what the authors claim). It would have helped if they provided a sub-image enlargement as they did for the 1000 lux case.

2) The authors focus on the sensitivity, or quantum efficiency (QE), and they show that the QE can be kept more or less constant with pixel scale (with their particular technology), at least down to 1.75 μm. They don't pay too much attention to read-out noise, however. For bright conditions, photon-shot noise and thus QE will dominate the S/N, while in faint conditions, the read-out noise will become important. It could very well be that the authors ignored that aspect, or deemed it insignificant, thus overstating their conclusion that "IQ and low light sensitivity of the sensors with these smaller pixels is comparable with a 5.6 μm pixel-based imager".

BTW, interesting that cross-talk seems to be such a big issue in CMOS sensors, I had no idea.

neuroanatomist

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Re: 26.4mp 5D Mark III Mid-year? [CR1]
« Reply #78 on: April 26, 2011, 04:04:24 PM »
They make the point that with the smaller pixels, they achieve increased resolution while maintaining similar sensitivity.  [...]  If you look at the lower panels (low light), it's also clear that with the same size sensor, as the pixels get smaller the image noise increases in light-limiting conditions.

For bright conditions, photon-shot noise and thus QE will dominate the S/N, while in faint conditions, the read-out noise will become important. It could very well be that the authors ignored that aspect, or deemed it insignificant, thus overstating their conclusion that "IQ and low light sensitivity of the sensors with these smaller pixels is comparable with a 5.6 μm pixel-based imager".

That was my interpretation. 
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hallwal

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Re: 26.4mp 5D Mark III Mid-year? [CR1]
« Reply #79 on: April 26, 2011, 09:32:25 PM »
If you look at Figure 7, the smaller pixels clearly offer a resolution advantage - no argument there.  If you look at the lower panels (low light), it's also clear that with the same size sensor, as the pixels get smaller the image noise increases in light-limiting conditions.
True, but towards the bottom of those low light images, the text on the large-pixel image is indistinguishable, but the text on the small-pixel image is quite readable.  It seems that it would be fairly easy (noise reduction or some other filter) to make the bottom-right image look just like the bottom left image;  it would be impossible, however, to do the other way around.  In other words, I'd rather have the rightmost image (small pixel) in every example, including the low-light one.

NotABunny

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Re: 26.4mp 5D Mark III Mid-year? [CR1]
« Reply #80 on: April 27, 2011, 04:32:09 AM »
Here's an example with both quantitative and qualitative information: Super Small, Sub 2μm Pixels for Novel CMOS Image Sensors, G.Agranov, R.Mauritzson; S.Barna, J.Jiang, A.Dokoutchaev, X.Fan; X.Li, in Proc, 2007 International Image Sensor Workshop, Ogunquit, Maine, USA  June 7-10, 2007.

Great find.

Personally, I like best the image with 2.2 um pixels. To me it looks like their technology scales best around that size. The image with the 1.75 um pixels has too much noise and too much edge bleeding.

It's odd that although all the sensors are theirs, the colors are so different.

Also, in spite of their comment that "in spite of a large difference in the pixel area, image quality and low light sensitivity of the sensors with these smaller pixels is comparable with a 5.6μm pixel-based imager." I find that the low-light image with the 5.6 um pixels looks much worse than the one with 2.2 um pixels.
« Last Edit: April 27, 2011, 04:38:35 AM by NotABunny »

kirillica

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Re: 26.4mp 5D Mark III Mid-year? [CR1]
« Reply #81 on: April 27, 2011, 04:59:12 AM »
Well 5Dm2 pixel size is 6.4µm, 7D - 4.3µm.
Question: What this paper means to us?

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Re: 26.4mp 5D Mark III Mid-year? [CR1]
« Reply #81 on: April 27, 2011, 04:59:12 AM »

Lawliet

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Re: 26.4mp 5D Mark III Mid-year? [CR1]
« Reply #82 on: April 29, 2011, 01:08:38 AM »
I mostly use just the central focus point... all the other are just used to confirm focus on ladnscapes.

But don't complain about dodgy metering. With advice like that its no surprise people think of ETTL as a game of chances...

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Re: 26.4mp 5D Mark III Mid-year? [CR1]
« Reply #82 on: April 29, 2011, 01:08:38 AM »