Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

Started Jun 16, 2014 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: Reply to Just another Canon shooter

Just another Canon shooter wrote:

Anders W wrote:

The old thread expired a second time (after being pruned) so I answer here instead:

Just another Canon shooter wrote:

Anders W wrote:

Noise can't be "blurred". It's not affected by the optical resolution. The E-M1 shows less noise.

Of course it can, it is called NR,

NR blurs the detail. It reduces the noise.

It reduces the noise by blurring it.

A matter of semantics. My assumption was that no NR is applied in any of these cases.

I explained this already, twice. A less aggressive demosaicing can be thought of as NR, if you wish.

Sure. I also simply explained what I had in mind and not. My assumption was that the images are processed in effectively the same way as far as NR is concerned.

The noise in the deep blue has very non-Poisson structure, as simple as that.

Can you please specify mathematically what you mean by a non-Poisson structure and how you can see or measure the deviation from Poisson in this case?

Since images are taken for us to view them, I mostly trust my eyes - it looks like a NR reduced image. Non Poisson is just that - non Poisson. How to test for it - there many tests. The simplest one would be to frop a few squares and use ImageJ to compute the power spectrum - uniformity means Poisson, more or less; lower high frequencies means NR.

And did you perform any such analysis, for example for that dark blue square we are talking about, with the E-M1 at ISO 1600 and the 6D at ISO 6400, as exemplified by you here (with the link borrowed from your post here)?

which can be done after the demosaicing, or incorporated in the demoasicing algorithm. Shot noise is of Poisson type, even on a Bayer sensor. If we make it B&W for simplicity, it has a well defined structure and spectrum. Missing high frequencies with the low frequencies present is an evidence of blurring, or NR, or call it whatever you want.

So are you saying that ACR secretly applies more NR to the E-M1 than to the other cameras although the NR sliders are set 0 in all cases?

You cannot separate demosaicing from NR. The old ACR process, for example, has "hidden NR" in it, by your logic.

So are you saying that ACR uses a different demosaicing algorithm for the E-M1 than for the other cameras?

Of course. With different parameters, at least, and giving different results for different colors.

Specifically in a manner that affects the amount of NR effectively applied? Of course the color profiles used are not the same.

Go to ISO 100. The deep blue square has more blurred borders compared to the others. Look at the 6D crop - no such thing.

The borders are a matter of resolution. Note what I already said about the E-M1 shot not being appropriate for judging resolution.

Resolution magically changes from one color to another?

It does not need to do that in order to blur the border.

It blurs one border but not another, while the camera next to it does not do that.

I have seen plenty of examples where different colors are differently blurred (especially when the border is black) due to properties of the lens rather than the sensor or the processing of the RAW file.

Combine that with the weird low frequency noise inside the blue square, and the lens gets eliminated as a factor.

I wouldn't jump to such conclusions.

But processing can.

Sure. I was just explaining what I had in mind when I said noise can't be blurred.

I'd additionally appreciate a response to the following question included in my previous reply:

We had a poll here recently where two anonymous images were pitted against each other. One had a one stop advantage for SNR at 18 percent and the other had a one stop advantage for DR, but the poll participants didn't know anything about that in advance. The question asked was:

Which picture has higher image quality as far as noise is concerned?

What do you think the verdict of the poll participants was?

Without seeing the experiment, I cannot answer. Was it a bright, a dark image, how processed, etc.

It was the old DPR studio scene and the images were processed identically by means of DCRAW with everything at default.

And I do not really want to get in another long exchange.

The question is obviously relevant to the exchange we are already having.

 Anders W's gear list:Anders W's gear list
Panasonic Lumix DMC-G1 Olympus OM-D E-M5 Olympus E-M1 Panasonic Lumix G Vario 14-45mm F3.5-5.6 ASPH OIS Panasonic Lumix G Vario 7-14mm F4 ASPH +28 more
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