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11-12-2017, 04:20 AM   #16
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QuoteOriginally posted by TonyW Quote
If only that was true. Unfortunately I believe the testing and final evaluation flawed. It is not possible to get more DR than the bit depth capture most systems capture 12 or 14 bit, most modern cameras the latter.
It is true, and it all depends on how you define noise.

Two related facts:
- Some sensors have more megapixels then other sensors of the same size
- Averaging several pixels reduces the noise floor

So what is the right ammount of megapixels to compare noise? Is it better to upscale or to downscale images to make them comparable? Do we compare noise at a per pixel scale or at a per image scale? In my opinion the only good way of comparing is to downscale the image with the most megapixels to match the one with fewer megapixels, and then compare at a per image scale. DxOmark uses this method for a number of well thought out reasons. They downscale to 8 Mp of historic reasons, and comparability with cameras as old as 8 Mp cameras are. I wish for one compatibility scale (8 Mp) and one scale for newer cameras (20+ Mp), but I understand it would complicate measurements and be more time consuming. The point here being that averaging/downscaling should be a part of the method to do good scientific comparisons.

11-12-2017, 12:48 PM   #17
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QuoteOriginally posted by Simen1 Quote
- Averaging several pixels reduces the noise floor
If that was true, it would suffice to increase resolution to get lower overall noise floor. Why Canon 5DSr has less dynamic range than Pentax K1 then?
11-13-2017, 03:44 PM   #18
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QuoteOriginally posted by biz-engineer Quote
If that was true, it would suffice to increase resolution to get lower overall noise floor. Why Canon 5DSr has less dynamic range than Pentax K1 then?
It is still true. However you dont take into account that reducing pixel size also increases _per pixel_ noise. Note that we are talking about DR here. Smaller pixels also have 14 bits readout. The bit depth are not reduced accordingly to the pixel size. 14 bit readout on smaller pixels year by year results in the same DR _per pixel_ but higher DR when the image is normalized to lets say 8 Mp.

For a more physical description: When pixel size are reduced the noise gets more fine grained and more white noise-like. A theoretical sensor with nanometer small pixels, if possible, would probably only measure 1 photon or none. Still, when this is averaged over millions of those ultra small pixels to create a micrometer size pixel, you would get back the whole DR range.

Canon 5DSr have low DR because Canon suck at DR. (high amplification or read noise at low ISOs overwhelm the much lower shot noise.)
11-13-2017, 10:45 PM   #19
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QuoteOriginally posted by Simen1 Quote
Canon 5DSr have low DR because Canon suck at DR. (high amplification or read noise at low ISOs overwhelm the much lower shot noise.)
ah ok that's why it shows as DR is clamped to 11bits or so at low ISO, Canon must be having crappy A/D conversion then.

11-14-2017, 05:11 AM   #20
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QuoteOriginally posted by biz-engineer Quote
ah ok that's why it shows as DR is clamped to 11bits or so at low ISO, Canon must be having crappy A/D conversion then.
You may find that this site will offer some insight into Photographic dynamic range pretty much what you can expect in real terms from your camera e.g. Pentax K1 DR =11.4 Canon EOS 5D S R = 9.8
Photographic Dynamic Range versus ISO Setting

Shadow improvement vs ISO
Shadow Improvement of Photographic Dynamic Range versus ISO Setting

If I need to compare I prefer to see Bill Claffs assesments using Photographic DR, but I guess as long as the testing remains constant comparisons under those fixed conditions should reveal the differences between cameras adequately. Still if you are heavily invested in one marque it is unlikely that a +2EV is likely to make you want to jump ship?
As to noise, I strongly suspect this is pretty subjective in as much as I may tolerate more noise in one image than you would or vice versa and also suspect that this may vary dependent on image content and final output.

Simen1 raises another interesting point how do we measure noise when there is a difference in MP count. Upsample or downsample?

Well downsampling is going to improve the appearance of noise in the image whereas upsampling is going to emphasise. I like to try both if I am comparing one camera vs another and can get hold of the raw files from the likes of DPReview etc.
11-14-2017, 06:54 AM   #21
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QuoteOriginally posted by TonyW Quote
Well downsampling is going to improve the appearance of noise in the image whereas upsampling is going to emphasise. I like to try both if I am comparing one camera vs another and can get hold of the raw files from the likes of DPReview etc.
In principle it shouldn’t matter if you up size or down size (or which size you aim for) since the comparison is relative. If it matters then there is something wrong with whole idea.
11-14-2017, 08:45 AM   #22
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QuoteOriginally posted by Gimbal Quote
In principle it shouldn’t matter if you up size or down size (or which size you aim for) since the comparison is relative. If it matters then there is something wrong with whole idea.
The original statement:
"Some sensors have more megapixels then other sensors of the same size"
"So what is the right ammount of megapixels to compare noise? Is it better to upscale or to downscale images to make them comparable?"

I believe it matters or it can in as much as apparent IQ changes due to what happens on several levels including the up/down sampling algorithms and what happens between cameras in the A/DC.

As an example 2 newish FF cameras compared @ ISO 3200 (same lens s/s and f/stop). One a 21 MP camera the other 47 MP camera:

First the 21 MP upsampled to the same size as the 47 MP. Noise is mushy as is apparent loss of resolution. Sharpening needed to bring closer and that sharpening will accentuate the noise

Second the 47 MP downsampled to match the 21 MP. Closer this time but still more resolution before added sharpening.

Bear in mind what you are looking at here is pixel peeping at 100% and the acid test would be to produce prints at the printers native resolution and judge from whatever viewing distance you imagine a print of yours would be seen at - it may or may not be noticeable and if it is then it may or may not be important to you

Last edited by TonyW; 01-16-2018 at 07:21 AM.
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