Too many megapixels? Six is enough for an 8x10.

Started Apr 26, 2009 | Discussions thread
S p i t z e r Forum Member • Posts: 92
Re: Bad example

strawman_John wrote:

The example linked to is more about ADC system noise than sensor
noise. you see there is so little signal what you are seeing is noise
in the ADC system and electronics, no surprise a similar result
because that test by John takes out the sensor as a significant input.

Shot noise is a function of the total light, and both images received the same amount of total light as they were the same exposure, so the shot noise was the same for each.

I can and have done a simple test. Here is examples of why you need
no more than 6mp for a 10x8 print. I took the same view with the same
lens at the same ISO (ISO 100) on a 300D and a 40D. Printed at 10x8 I
could not see any difference in resolvable noise and detail in the

This is not the issue at hand. An 8x10 print will render 325 PPI on a 40D and 250 PPI from a 300D -- I doubt you can tell the difference. The issue is that more pixels do not result in more noise at the same level of detail.

So to take your arguments apart, I can see the logic of for 10x8
prints about 6mp marks the point of no more benefit for more pixels.
In fact as you make the pixels smaller the dynamic range falls off.
The noise you can combat, to an extent by applying more filtration,
swapping resolution for lower noise.

The DR for the entire image is not adversely affected by more pixels, either.

And if it helps, I do have an electronics degree, a couple of
patents and have even designed imaging equipment, so I get the maths
behind all this also.


So if you want to convince me that for a given sensor technology step
smaller pixels do not mean more noise and lower dynamic range, and
that for a given print size more pixels always make for a better
picture (once you have factored in lens limitations also) please send
me the maths.

The maths have already been provided in this thread (in more than one place, as I recall) by Bob. In addition, tests and charts have been provided as well. What I have not seen is an image made with fewer pixels having "higher IQ" than an image made with more pixels, which is what Bob has been arguing, but examples to the contrary have been presented.

Whether or not one "needs" more than 6 MP for an 8x10 print is an entirely different matter. For the record, in my opinion, I don't think it makes any discernable difference unless heavy cropping is taking place. But more pixels most certainly do not hurt, and that was the argument being put forth.

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