Why does cropping reduce dynamic range? (Page 7): So agreeing that cropping reduces dynamic range if the image is resized, by magnifying noise, is it possible to make a rule of thumb...

bleirer

So agreeing that cropping reduces dynamic range if the image is resized, by magnifying noise, is it possible to make a rule of thumb, even an approximate; for example for every x amount of area cropped you lose y stops of dynamic range?

selmslie Loc: Fernandina Beach, FL, USA

Canisdirus wrote:

... The dynamic range doe not change if the same sensor is cropped. ...

Dynamic range is measured based on standard sized print at a standard viewing distance. For example, an 8x10 image to be viewed from 10 inches. That's like the basis for DOF calculations.

The visibility of the noise is also judged at a standard gray value. For example, DxOMark uses 18% gray. That's how they can see the DR go down as the ISO increases. They have to reduce the exposure to stay at 18% gray. Lowering the exposure increases the visibility of the noise.

The DR doesn't change due to the crop until you enlarge the result to make a standard size print/display. Then it magnifies the noise in proportion to the crop factor.

The same thing happens if you crop the full frame image in the computer to make a standard size print or image.

It also becomes more visible when you pixel-peep since you are no longer viewing a standard sized image from a normal viewing distance.

As noise becomes more visible the DR goes down.

selmslie Loc: Fernandina Beach, FL, USA

bleirer wrote:

So agreeing that cropping reduces dynamic range if the image is resized, by magnifying noise, is it possible to make a rule of thumb, even an approximate; for example for every x amount of area cropped you lose y stops of dynamic range?

That's a simple way to look at it.

For the D850 you lose about a full stop of DR going from FX to DX, 1.5 crop factor. You lose a little more with Canon because the crop factor is 1.6.

The more rigorous method that Photons to Pixels uses gives us a more precise number but it's not much different.

Canisdirus

Ysarex wrote:

I acknowledged that pixel size plays a role. You mentioned only pixel size. Pixel size is the lesser factor. So much so that it borders on insignificance. The difference in sensor area is the dominant factor and should be noted as such. Here's a reference: https://www.dpreview.com/articles/8189925268/what-s-that-noise-shedding-some-light-on-the-sources-of-noise

Not sure why you keep concentrating on noise when the subject is dynamic range.
They are not in parallel.
The Sony A7RIV has some noise issues...but also has a high dynamic range.

Ysarex Loc: St. Louis

Canisdirus wrote:

Not sure why you keep concentrating on noise when the subject is dynamic range.

Dynamic range is noise limited. Less noise = more DR and more noise = less DR.

Canisdirus wrote:

They are not in parallel.
The Sony A7RIV has some noise issues...but also has a high dynamic range.

selmslie Loc: Fernandina Beach, FL, USA

Canisdirus wrote:

Not sure why you keep concentrating on noise when the subject is dynamic range.
They are not in parallel.
The Sony A7RIV has some noise issues...but also has a high dynamic range.

If it weren’t for noise all full frame cameras would have the same DR.

bleirer

selmslie wrote:

That's a simple way to look at it.

For the D850 you lose about a full stop of DR going from FX to DX, 1.5 crop factor. You lose a little more with Canon because the crop factor is 1.6.

The more rigorous method that Photons to Pixels uses gives us a more precise number but it's not much different.

So, roughly, I crop by 1/3 to lose one stop DR. I crop by 1/2 to lose _____? Would it be a simple ratio?

Canisdirus

selmslie wrote:

If it weren’t for noise all full frame cameras would have the same DR.

No, because not all FF have the same pixel density and size.

Since larger photosites can contain a greater range of photons, dynamic range is generally higher for digital SLR cameras compared to compact cameras (due to larger pixel sizes).

selmslie Loc: Fernandina Beach, FL, USA

bleirer wrote:

So, roughly, I crop by 1/3 to lose one stop. I crop by 1/2 to lose _____? Would it be a simple ratio?

The loss of DR can be reduced to a simple ratio but, as with DOF or pornography, you only need to recognize it when you see it.

bleirer

Canisdirus wrote:

No, because not all FF have the same pixel density and size.

Since larger photosites can contain a greater range of photons, dynamic range is generally higher for digital SLR cameras compared to compact cameras (due to larger pixel sizes).

We are talking about the impact of cropping on dynamic range for an image from the exact same sensor on the same camera.

selmslie Loc: Fernandina Beach, FL, USA

Canisdirus wrote:

No, because not all FF have the same pixel density and size.

Since larger photosites can contain a greater range of photons, dynamic range is generally higher for digital SLR cameras compared to compact cameras (due to larger pixel sizes).

But DR is still measured from the noise up, regardless of the pixel size.

bclaff Loc: Sherborn, MA (18mi SW of Boston)

bleirer wrote:

So agreeing that cropping reduces dynamic range if the image is resized, by magnifying noise, is it possible to make a rule of thumb, even an approximate; for example for every x amount of area cropped you lose y stops of dynamic range?

That is only a rough approximation. The details as to why not are in the article I cited earlier:
DX Crop Mode Photographic Dynamic Range
For example, for the Nikon D850 the drop in Photographic Dynamic Range (PDR) from FX to DX is about 3/4 stops while your reasoning would imply something closer to 7/6 stops.

bclaff Loc: Sherborn, MA (18mi SW of Boston)

selmslie wrote:

Dynamic range is measured based on standard sized print at a standard viewing distance. For example, an 8x10 image to be viewed from 10 inches. That's like the basis for DOF calculations.

At PhotonsToPhotos but not at DxOMark.

selmslie wrote:

The visibility of the noise is also judged at a standard gray value. For example, DxOMark uses 18% gray.

Not true. At DxOMark their dynamic range is based entirely on something called (pixel) read noise and "normalized" for pixel size (resolution).
The SNR 18% charts have nothing to do with their dynamic range.

selmslie wrote:

...
The DR doesn't change due to the crop until you enlarge the result to make a standard size print/display. Then it magnifies the noise in proportion to the crop factor.

The same thing happens if you crop the full frame image in the computer to make a standard size print or image.

It also becomes more visible when you pixel-peep since you are no longer viewing a standard sized image from a normal viewing distance.

As noise becomes more visible the DR goes down.

Except that it's not in proportion to the crop factor.

bclaff Loc: Sherborn, MA (18mi SW of Boston)

Canisdirus wrote:

...
Since larger photosites can contain a greater range of photons, dynamic range is generally higher for digital SLR cameras compared to compact cameras (due to larger pixel sizes).

For a measure like PhotonsToPhotos Photographic Dynamic Range (PDR) (and even DxOMark Landscape Score) pixel size is largely irrelevant; what matters is pixel performance per unit area.
The differences between sensors come down to differences in how cleanly the pixel data is read out (read noise) as well as differences in something called Full Well Capacity (FWC).

bclaff Loc: Sherborn, MA (18mi SW of Boston)

The original post:

bleirer wrote:

When I go to the dynamic range section of the phot... (show quote)

The quick answer:
Since you mention PhotonsToPhotos to are talking about Photographic Dynamic Range (PDR).
PDR is measured using a standard final image size and viewing distance (not unlike Depth of Field (DOF))
PDR also uses a Signal to Noise Ratio (SNR) criteria (unlike DxOMark which uses only read noise).
Since the DX image has to be enlarged more than the FX image the SNR is lower resulting in a lower PDR.
Pixel size does not matter.
Also, remember, we're talking about the capability of the sensor and not some specific image of a scene with a particular dynamic range (the horsepower of your car is the same travelling at 10 mph than it is at 55 mph you're just using less of it).