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Thread started 19 Sep 2011 (Monday) 13:17
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Why is it claimed that more megapixels equals less image quality?

 
Fahad79
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Sep 19, 2011 13:17 |  #1

A lot of people online (here and elsewhere) claim that more megapixels is inherently bad for image quality.

I do remember the rather anecdotal evidence put forward by some that more megapixels equals more noise-but never saw anyone post up examples. The use of words like 'cramming' to describe more megapixels on a sensor doesn't give the claims more credibility either.

However, from what images I have generally seen online between the current generation cameras and previous generation cameras, I don't see the claim holding any water. This is not a fact, just my general observations--I'm not a 'pixel-peeper.'

So my question is:

Was this in fact an issue a few generations ago or is it still an issue?

I'm starting to wonder that the claim is nothing more than an urban legend or was just a problem a few generations ago.

Is the claim even testable? Current generation cameras have more megapixels than previous ones, but also have better processors and more technologically-advanced sensors

Would it be fair to compare for example the 5D and the Mark II? Wouldn't most agree that the Mark II produced 'better' images? How about the T2i and the XTi?

How do people KNOW that fewer MP = better IQ?

I am just curious.

cheers : )




  
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HughR
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Sep 19, 2011 14:43 |  #2

The fact of physics is that smaller diameter pixels mean greater photon noise (due to the Poisson statistics of photon emission), which is especially evident at high ISOs like 6400 and 12800. However, image sensors have gotten better, and my 60D 18Mpixel sensor has significantly lower noise than the 6Mpixel sensor in my original Digital Rebel. So my 60D gives me greater detail and resolution with lower noise. However, if Canon were to make the pixels half the diameter so that the same size sensor could contain 72Mpixels, the noise would be extreme. Also, most lenses would not have the resolution to make use of such very small pixels. So the answer to your question is roughly half way between the extremes. More megapixels on the same size sensor will lead to somewhat increased noise but also to increased resolution. Too few pixels results in poorer resolution, but way too many will result in greatly increased noise. Canon & Nikon both work to achieve a balance between these. Hope this helps.


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Sep 19, 2011 14:47 |  #3

Here's a good thread on the subject:
https://photography-on-the.net/forum/showthre​ad.php?t=706255


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Sep 19, 2011 15:34 |  #4

HughR wrote in post #13128498 (external link)
... The fact of physics is that smaller diameter pixels mean greater photon noise...

...my 60D 18Mpixel sensor has significantly lower noise than the 6Mpixel sensor in my original Digital Rebel. ...

No offense intended, just trying to figure out your two seemingly contradictory statements. It sounds like the rule isn't necessarily that smaller diameter pixels create more noise but that inferior sensors produce more noise (which is really just a tautology). Or is it the case that there is some inherent "noise" in light that makes an ultra-sensitive sensor undesirable? If so, wouldn't filter technology possibly come to the rescue?


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Daniel ­ Browning
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Sep 19, 2011 16:42 |  #5

Fahad79 wrote in post #13128022 (external link)
Why is it claimed that more megapixels equals less image quality?

There are three main causes:

1. Mistaken authorities
2. Mistaken reasoning
3. Mistaken analysis

The most common reason is mistaken authorities: that is, beleiving that smaller pixels reduce image quality because a perceived authority on the matter (such as a camera reviewer) said so.

But why does an authority believe it? Because they have made mistakes in reasoning or analysis.

Why do so many photographers make such fundamental errors in reasoning/analysis? And what is the reason for the prevalence of so many myths and urban legends among photographers? I don't know the answer to that. I do not find the same rate of error among other endeavors that I am involved in (software engineering, astronomy).

So you're probably wondering about the reasoning/analysis errors that I referred to. Here is the short version:

Mistaken reasoning is relying on logical fallacies, poor models, and bad analogies of image sensors. For example, one line of reasoning is that a single pixel, in isolation, when reduced in size, has lower performance; therefore, a sensor full of small pixels creates images that have worse performance than the same sensor full of large pixels. But that's not seeing the forest for the trees: it fails to account for the effect of a far greater number of pixels. There are many more.

Mistaken analysis can be broken up into the five most common types:

  • Unequal spatial frequencies.
  • Unequal sensor sizes.
  • Unequal processing.
  • Unequal standards.
  • Unequal technology.


When image analysis is performed correctly, it becomes very clear to the viewer of an image that it is possible for small pixel sensors to have worse performance per pixel, but the same performance when actually displayed or used for the same purpose as a large pixel sensor. Furthermore, that such a condition exists and is common in real world image sensors.

I went into it in a lot more detail in this thread:

Small pixel sensors do not have worse performance

I made some mistakes in that thread, and if I were to rewrite that post now I would emphasize things differently, but overall I still think it's generally correct.

Fahad79 wrote in post #13128022 (external link)
I'm starting to wonder that the claim is nothing more than an urban legend or was just a problem a few generations ago.

It has always been urban legend, it was never true.

Fahad79 wrote in post #13128022 (external link)
Is the claim even testable? Current generation cameras have more megapixels than previous ones, but also have better processors and more technologically-advanced sensors

One method is to compare cameras that have similar pixel counts and technology, but different format sizes. E.g. 7D vs 5D2 (4.3 vs 6.4 micron pixels). Then you can extrapolate what a 5D2 would have been like with 7D-sized pixels, or vice-versa.

Fahad79 wrote in post #13128022 (external link)
How do people KNOW that fewer MP = better IQ?

Same way that they "know" all the other common myths, urban legends, and miscomprehensions (and there are a ton of them). A small sampling of these myths (that are all false):

  • More than 8 MP will not make a difference unless you print larger than 8x10.
  • ISO is an element of exposure.
  • When you hit the difraction-limited f-number, there is no benefit in increased pixel counts.
  • High ISO causes noise, not reduced exposure.
  • Bokeh is just a fancy word for background blur.
  • Smaller pixels are worse for diffraction.
  • Lossy compression is bad.
  • Crop factor applies to focal length, but not f-number.
  • A 2X TC with ISO 1600 has more noise than ISO 400 and cropping.
  • Aperture and f-number are synonyms.
  • Even good lenses have flaws so there is no benefit from increased pixel counts.
  • Removing feature XYZ would make the camera cheaper.
  • Diffraction is light bending around the edge of the lens.
  • Back up and zoom in to get thinner DOF.
  • Zooming with your feet is the same as zooming with focal length
  • f/2 on four thirds gives you more total light than f/2.8 on FF.


Since I don't know *why* these and other myths are so prevalent among photographers, I can't really answer your question.

Hope that helps, anyway.

Daniel

  
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uOpt
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Sep 19, 2011 19:54 |  #6

Why is it claimed that more megapixels equals less image quality?

Noise.

The only progress is better noise reduction software in the camera.


My imagine composition sucks. I need a heavier lens.

  
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Daniel ­ Browning
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Sep 19, 2011 20:00 |  #7

uOpt wrote in post #13129977 (external link)
The only progress is better noise reduction software in the camera.

I don't think I've ever encountered that position before. What leads you to think that the only reason why modern DSLRs have less noise than their predecessors is because of software in the camera?


Daniel

  
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Swins
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Sep 19, 2011 20:22 |  #8

Something about photosites and all kinds of junk crammed into little packages who knows...I worry less about that stuff and more about shooting.

More Megapixels don't actually mean a worse image...only more megapixels on the same size sensor MIGHT mean a "worse picture" if you buy the marketing peoples slant on it.

I have a Hasselblad H3D MK II and an H4D-50 The 50 is base 50.1MP ....and routinely shoot the H4D-60 and now 200MS...all have huge RAW output files and don't even get me started on the TIFF files....BUT they have huge sensors....well compared to a FF camera.




  
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bohdank
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Sep 19, 2011 20:29 |  #9

Although I cannot quantify it, yes, 8 mpixels is all you need if you are printing 8 x 10's but, that is not the same as saying, resampling down, let's say 16 mpixels will not show better detail. There will be things in the 16 mpixel original that the 8 may not have been able to resolve. Let's say, an eyebrow on a full body portrait. The resampling may retain that detail where it would not even exist on the 8 mpixel original image.

Would I be wrong ?


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Sep 19, 2011 20:57 as a reply to  @ Swins's post |  #10

That is not entirely correct statement.

Digital camera megapixel war seem to be over in P&S sector, as Panasonic started to put less megapixel, but better IQ into their P&S camera few years back. And Canon follow with their PowerShop G11 (10MP Vs G10's 14.7MP).

So, in P&S, fewer MP, maybe = better IQ.

In DSLR sector, megapixel war is still hot. And No sign of ending yet. More MP = Better IQ in DSLR :)


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Sep 19, 2011 21:35 |  #11

What I don't get, the better computer monitors and TV's have more pixels is that different than camera sensors? Also didn't Sigma come out with a $6,000 46 megapixel DSLR? I have an older Panasonic TZ3 that takes incredible photos for a 7 mp camera, but if you start cropping and enlarging parts of the shot it's gets very grainy. This does not happen with my T2i though. So what is the point of diminishing return on pixels?


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Sep 19, 2011 21:41 |  #12

Daniel Browning wrote in post #13130000 (external link)
I don't think I've ever encountered that position before. What leads you to think that the only reason why modern DSLRs have less noise than their predecessors is because of software in the camera?

Basically.


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Sep 19, 2011 21:56 |  #13

T2i4me wrote in post #13130526 (external link)
What I don't get, the better computer monitors and TV's have more pixels is that different than camera sensors? Also didn't Sigma come out with a $6,000 46 megapixel DSLR? I have an older Panasonic TZ3 that takes incredible photos for a 7 mp camera, but if you start cropping and enlarging parts of the shot it's gets very grainy. This does not happen with my T2i though. So what is the point of diminishing return on pixels?

The devices you mention emit photons, they don't detect photons in small quantities, barely above the noise floor of the associated amplifiers for each photo-site. A "photosite is a paired photon detector, amplifer, and read gate and makes up a pixel on the sensor. Phase, sampling, and electronic noise is a function of the current level of technology available at any point in time. It is a relative constant for a photosite (Pixel) regardless of how big the photosite. On a given sensor size, more megapixels is a densor sensor with smaller photosites. Smaller photosites hold less pixels, so the ratio of signal (photons detected) to the noise level is low. On a less dense sensor with bigger photosites, you can collect more pixels for a given exposure, and the ratio of signal to noise is much higher. More signal to work with, and you have more data to work with in terms of image optimization, sharpening, and noise reduction.


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Sep 19, 2011 22:02 |  #14

T2i4me wrote in post #13130526 (external link)
Also didn't Sigma come out with a $6,000 46 megapixel DSLR?

Not really. The camera has a 46MP sensor but it creates images that are something like 15MP because it is averaging the values in order to reduce noise and increase dynamic range.


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Sep 19, 2011 22:21 |  #15

bsmotril wrote in post #13130645 (external link)
The devices you mention emit photons, they don't detect photons in small quantities, barely above the noise floor of the associated amplifiers for each photo-site. A "photosite is a paired photon detector, amplifer, and read gate and makes up a pixel on the sensor. Phase, sampling, and electronic noise is a function of the current level of technology available at any point in time. It is a relative constant for a photosite (Pixel) regardless of how big the photosite. On a given sensor size, more megapixels is a densor sensor with smaller photosites. Smaller photosites hold less pixels, so the ratio of signal (photons detected) to the noise level is low. On a less dense sensor with bigger photosites, you can collect more pixels for a given exposure, and the ratio of signal to noise is much higher. More signal to work with, and you have more data to work with in terms of image optimization, sharpening, and noise reduction.

Ummmmmm, ok. I'll just stick to composition and having some artistic fun more technical than I want to be but the answer is very much appreciated as I did not know there were different types of pixels.


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