Originally posted by kh1234567890 Oh no, not the myth that downsampling reduces noise. It will do, but only on a linear encoded image - not on a gamma encoded JPEG.
Pages and pages of debate on this issue, on
how it reduces 'noise', if it even really
does, and if it does
how much, and how inneficient it is as a
method vs. as simply a by-product compared to actual noise reduction algorithms.
Based on my experience with my D800 and lesser-MP cameras, and what I see at different display sizes when using no NR, and what I see in the measured results form the 24mp vs. the 36mp sensors.... I'm coming down on the side of DXOmark and the others who say it's not a myth
You are free to disagree of course.
---------- Post added 10-11-14 at 11:35 AM ----------
Originally posted by wombat2go JSH, Yes I follow most of your post #204 .
But the "Total light" has nothing to do with a bigger sensor frame being a better performer in terms of signal to noise ratio and resultant dymamic range and hence that concept can't support the title of this thread.
For example if Total Light is a figure of merit, we could take an imaginary 4 sensors from an ist d glue them together, put on a lens with same FOV and then see less noise at iso 1600 from the 4 glued sensors compared a normal ist d. Of course we know by intuition that can't be true.
Actually unless I misunderstand what you're saying it
would be true if you maintained the FOV while using all four of those glued-together sensors to make the image. In other words, if you a big enough lens + used a different FL, which would need to result in a greater physical aperture used for the same exposure. It's not going to be a linear increase because I don't think the underlying *istD tech would support it, but your frankenstein sensor there would conceivably perform somewhere between the original *stD and... something bigger - given a matching lens.
The main reason it's not just 'make it so then' is because of yields and wafer cost such a sensor would be enormously expensive, not to mention that it would need a whole new mount and line of lenses. I don't think we're going bigger than cropped medium format anytime soon because of those economics and what the market can support.
Quote: If that were true there would be an enormous difference in signal to noise ratio between a Pentax camera and a pro-grade digital back, and (I haven't checked lately) they are not so different are they?.
The main limitation there is the lenses' physical apertures, and the sensor tech itself. I think most 'fast' MF lenses are around f/2.8. Add to that the sensor efficiency typically is lower as you move up - 645D case in point, a fairly low-efficiency MF CCD sensor.
Also, the difference in sensor area between say the 645D/Z and FF is smaller than the delta between aps-c and FF, so we probably wouldn't expect to see the same jump in performance anyway, even with equally efficient sensors. We'll see more when we see the 645Z numbers.
Quote:
And the signal to noise ratio of each well varies across the image, being high on bright and low on dark.
Each well has a particular signal to noise ratio unless the image is a uniform flat plane and Cosfourth of the lens is ignored.
That very point was actually brought up in response to The_Suede's post in that thread, I think you should really read through the thread as it's addressed. Basically what you say is true, but is true for any sensor size and isn't fully pertinent to the discussion of total light for the image. (please read the thread carefully, I don't think we should be translating and pasting here, especially when the original contributors are living/breathing people who can be queried directly with a PM.)
Quote: The luminous flux level we set for the sensor is based on setting the f/- and shutter to the ISO rating of the sensor and is unrelated to the sensor size.
Yes, we've gone over this
That's the exposure. Not the radiant flux, not the total light. We have no disagreement re exposure.
.
Quote: Again we know that by common sense, I have 5 format sizes here from m4/3 to 4x5, and the same light meter can set tham all.
Light meter judges exposure values.
Quote: The reason bigger sensors can be better is to do with their more modern technology,.
No - really not the Case. The ancient Canon 5D sensor performs slightly better than the more modern K-5/Sony (in resulting image noise,) and the almost equally ancient D700 still performs about a stop better. In those cases the more modern technology of the aps-c sensor is mitigating the effects of total light - in the case of the
much less efficient Canon, the mitigation is much more successful because the sensor is that much worse.
Last edited by jsherman999; 10-12-2014 at 10:45 AM.