Ugly Hedgehog - Photography Forum
Home Active Topics Newest Pictures Search Login Register
Main Photography Discussion
Why does cropping reduce dynamic range?
Page <prev 2 of 10 next> last>>
Feb 25, 2021 13:52:30   #
bleirer
 
Ysarex wrote:
Noise increases because of the different total areas of the sensor used. Use the whole sensor and you record more total light than if you use the smaller cropped area. Noise will increase/decrease with the total amount of light recorded. SNR is a ratio and goes up or down with the total amount of light recorded.

Try this analogy: You have two cookie pans -- one is 11 x 15 inches and the other is 9 x 12 inches. You put them both out in the rain together and allow them to collect water for 1 minute. That 1 minute is exposure time. After a minute it stops raining and you measure the depth of water in each pan -- it's the same. That's exposure. But now pour the water from both pans into two separate bowls. Do both bowls have the same amount of water? The larger pan collected more water. In the same way a larger sensor will collect more light. Noise (shot noise which is the noise we're concerned with) as a ratio to the signal will decrease with more light collected -- stronger signal.

All else the same, bigger sensors are less noisy than smaller sensors. Noise limits DR.
Noise increases because of the different total are... (show quote)


I'm not saying I understand at this point. So a full frame image cropped in post but not resized in any way would have more noise in the cropped portion even though those pixels are identical to the original? Or would the cropped portion have to be resized to equal the original dimensions before the relative noise increased?

Reply
Feb 25, 2021 14:04:23   #
lamiaceae Loc: San Luis Obispo County, CA
 
Ysarex wrote:
Noise increases because of the different total areas of the sensor used. Use the whole sensor and you record more total light than if you use the smaller cropped area. Noise will increase/decrease with the total amount of light recorded. SNR is a ratio and goes up or down with the total amount of light recorded.

Try this analogy: You have two cookie pans -- one is 11 x 15 inches and the other is 9 x 12 inches. You put them both out in the rain together and allow them to collect water for 1 minute. That 1 minute is exposure time. After a minute it stops raining and you measure the depth of water in each pan -- it's the same. That's exposure. But now pour the water from both pans into two separate bowls. Do both bowls have the same amount of water? The larger pan collected more water. In the same way a larger sensor will collect more light. Noise (shot noise which is the noise we're concerned with) as a ratio to the signal will decrease with more light collected -- stronger signal.

All else the same, bigger sensors are less noisy than smaller sensors. Noise limits DR.
Noise increases because of the different total are... (show quote)


That is probably a good explanation though I more or less think of sensor characteristics per pixel or photo site. So a function of pitch as well. But as I have heard before, much of the science of digital photography is related to audio engineering, signal and noise, and less to traditional film based photography. But your explanation seems to cover it.

Reply
Feb 25, 2021 14:07:01   #
larryepage Loc: North Texas area
 
bleirer wrote:
When I go to the dynamic range section of the photonstophotos website and plot any full frame camera in full frame mode next to the same camera in crop mode, the dynamic range of the crop mode is always less by the same amount at every point.

So the same camera, the same sensor, the same test conditions, the only difference is that one is measuring the cropped area of the same sensor while the other measures the full frame portion of the same sensor.

So why does cropping alone reduce dynamic range?
When I go to the dynamic range section of the phot... (show quote)


So just for fun, I went back to the P to P site and plugged in the D500 against the D850 and the D850 DX. That produced even more interesting results (at least to me). Specifically, despite having slightly smaller sensor elements and a little bit older sensor technology (and no BSI design), the D500 shows as being better than the D850 in DX mode by about 0.3 stop, all the way down the line. I am personally convinced that the D500 is quite a bit better than most on this forum give it credit for being, but still believe that this is also a surprising result...perhaps even more surprising to me than your initial discovery.

I'm not too disturbed by any of this, because I firmly believe that actual performance and experience trumps any test results claimed by any single source. But I do think that an inquiry to Photons to Photos asking why they are displaying these at least apparently inconsistent results is not out of order.

Reply
 
 
Feb 25, 2021 14:07:37   #
Rongnongno Loc: FL
 
A crop does not reduce the Dynamic Range. A crop limits the size of a capture in pixels as well as the number of possible colors but does not change the DR capabilities of a sensor.

Reply
Feb 25, 2021 14:09:42   #
Rongnongno Loc: FL
 
rmalarz wrote:
https://www.dpreview.com/forums/thread/4248398
--Bob

err... DR vs ISO, not VS cropped... See my answer above.

Reply
Feb 25, 2021 14:12:08   #
larryepage Loc: North Texas area
 
Rongnongno wrote:
A crop does not reduce the Dynamic Range. A crop limits the size of a capture in pixels as well as the number of possible colors but does not change the DR capabilities of a sensor.


I agree with you. But that is not what the P to P chart seems to show.

Reply
Feb 25, 2021 14:16:18   #
PHRubin Loc: Nashville TN USA
 
Ysarex wrote:
In a word: noise.

The smaller sensor area is noisier (because it's smaller) and so the data is noise swamped sooner.



That makes no sense to me. You crop noise energy and signal energy by the same amount. DR is related to signal to noise ration (SNR).

Reply
 
 
Feb 25, 2021 14:33:38   #
TriX Loc: Raleigh, NC
 
The author of most of the papers on the Photons to Photos site and the main contact there is Bill Claff (bclaff) who is a member of this forum. I’ll shoot Bill a PM and ask him to comment.

Reply
Feb 25, 2021 14:41:15   #
bleirer
 
Rongnongno wrote:
A crop does not reduce the Dynamic Range. A crop limits the size of a capture in pixels as well as the number of possible colors but does not change the DR capabilities of a sensor.


The same relationship seems to hold for every full frame vs. Crop sensor, though. My thought was it was related to magnifying noise if you resized so the two images were equal.


(Download)

Reply
Feb 25, 2021 14:53:30   #
bleirer
 
larryepage wrote:
So just for fun, I went back to the P to P site and plugged in the D500 against the D850 and the D850 DX. That produced even more interesting results (at least to me). Specifically, despite having slightly smaller sensor elements and a little bit older sensor technology (and no BSI design), the D500 shows as being better than the D850 in DX mode by about 0.3 stop, all the way down the line. I am personally convinced that the D500 is quite a bit better than most on this forum give it credit for being, but still believe that this is also a surprising result...perhaps even more surprising to me than your initial discovery.

I'm not too disturbed by any of this, because I firmly believe that actual performance and experience trumps any test results claimed by any single source. But I do think that an inquiry to Photons to Photos asking why they are displaying these at least apparently inconsistent results is not out of order.
So just for fun, I went back to the P to P site an... (show quote)


That's a common theme in the 'crop your full frame camera vs. buy a crop sensor camera' debate. At some point in cropping the crop sensor camera wins.

Reply
Feb 25, 2021 15:04:32   #
larryepage Loc: North Texas area
 
bleirer wrote:
That's a common theme in the 'crop your full frame camera vs. buy a crop sensor camera' debate. At some point in cropping the crop sensor camera wins.


Understood. But I don't accept that it is necessarily true. And if it is, I don't understand the mechanism that would make it the case.

Reply
 
 
Feb 25, 2021 15:09:51   #
Ysarex Loc: St. Louis
 
bleirer wrote:
I'm not saying I understand at this point. So a full frame image cropped in post but not resized in any way would have more noise in the cropped portion even though those pixels are identical to the original?

No.
bleirer wrote:
Or would the cropped portion have to be resized to equal the original dimensions before the relative noise increased?

Yes.

The noise is always there. The noise that we're concerned about in this case and that limits DR is shot noise. It's in the signal and it's always in the signal. For us to see it we have to enlarge the image.

Reply
Feb 25, 2021 15:14:42   #
Ysarex Loc: St. Louis
 
PHRubin wrote:
That makes no sense to me. You crop noise energy and signal energy by the same amount. DR is related to signal to noise ration (SNR).


In the illustration below the red box and the blue box are not the same amount. The blue one is bigger. The same amount of noise is more apparent from the red box crop in images of equal size.


(Download)

Reply
Feb 25, 2021 15:17:36   #
Ysarex Loc: St. Louis
 
Rongnongno wrote:
A crop does not reduce the Dynamic Range. A crop limits the size of a capture in pixels as well as the number of possible colors but does not change the DR capabilities of a sensor.


The data is clear and the data says you're wrong:

https://www.photonstophotos.net/Charts/PDR.htm#Nikon%20Z%207,Nikon%20Z%207(DX)
https://www.photonstophotos.net/Charts/PDR.htm#Sony%20ILCE-9,Sony%20ILCE-9(APS-C)

Reply
Feb 25, 2021 15:19:49   #
Ysarex Loc: St. Louis
 
bleirer wrote:
The same relationship seems to hold for every full frame vs. Crop sensor, though. My thought was it was related to magnifying noise if you resized so the two images were equal.


Exactly correct.

Reply
Page <prev 2 of 10 next> last>>
If you want to reply, then register here. Registration is free and your account is created instantly, so you can post right away.
Main Photography Discussion
UglyHedgehog.com - Forum
Copyright 2011-2024 Ugly Hedgehog, Inc.