Effective Pixels in Digital Cameras

clay@claysturner.com wrote:
> On Tuesday, December 3, 2013 10:50:17 AM UTC-5, Greg Berchin wrote:

(snip)
>> >> This seems to indicate that typical digital camera image sensors are still
>> >> nowhere near the resolution limits of film or lenses.

(snip)
>> >  http://kbesios.com/blog/2012/07/06/nikon-d800e-vs-6x9-medium-format-film

(snip)

> One thing to remember about grains is they are either on or off. 
> It is the statistical combination of "ons" and "offs" that create an 
> effective midlevel. So don't let the scanner resolution needed for 
> resolving grains indicate a picture's resolution.

This is true, but grains have different sizes. For analog audio, the
magnetic crystals are all about the same size, with more or less
magnetices in each direction. A normal contrast film has grains ranging
from small, low sensititivity to large, high sensitivity. At lower
exposures in the shadows, it is the larger grains that make up the
actual image. (For negative film.)

For reversal (slide) film it is the grains that were not exposed in the
camera that make up the image. That usually means not the largest ones, 
and so the grain (or dye cloud for color) is smaller.

> A real hint to the effective resolution limit comes from the 
> maximum F number you can use before diffraction starts to 
> harm the resolution.

Compared to digital, though, film has a fairly smooth transition
at the ends of the dynamic range, at "toe" and "shoulder" ends of
the BH curve. Also, with the variable grain size, the resolution
doesn't have the sharp cutoff of digital, but more gradual.

-- glen
 

On Tuesday, December 3, 2013 3:47:35 PM UTC-5, glen herrmannsfeldt wrote:
> clay@claysturner.com wrote:
> 
> > On Tuesday, December 3, 2013 10:50:17 AM UTC-5, Greg Berchin wrote:
> 
> 
> 
> (snip)
> 
> >> >> This seems to indicate that typical digital camera image sensors are still
> 
> >> >> nowhere near the resolution limits of film or lenses.
> 
> 
> 
> (snip)
> 
> >> >  http://kbesios.com/blog/2012/07/06/nikon-d800e-vs-6x9-medium-format-film
> 
> 
> 
> (snip)
> 
> 
> 
> > One thing to remember about grains is they are either on or off. 
> 
> > It is the statistical combination of "ons" and "offs" that create an 
> 
> > effective midlevel. So don't let the scanner resolution needed for 
> 
> > resolving grains indicate a picture's resolution.
> 
> 
> 
> This is true, but grains have different sizes. For analog audio, the
> 
> magnetic crystals are all about the same size, with more or less
> 
> magnetices in each direction. A normal contrast film has grains ranging
> 
> from small, low sensititivity to large, high sensitivity. At lower
> 
> exposures in the shadows, it is the larger grains that make up the
> 
> actual image. (For negative film.)
> 
> 
> 
> For reversal (slide) film it is the grains that were not exposed in the
> 
> camera that make up the image. That usually means not the largest ones, 
> 
> and so the grain (or dye cloud for color) is smaller.
> 
> 
> 
> > A real hint to the effective resolution limit comes from the 
> 
> > maximum F number you can use before diffraction starts to 
> 
> > harm the resolution.
> 
> 
> 
> Compared to digital, though, film has a fairly smooth transition
> 
> at the ends of the dynamic range, at "toe" and "shoulder" ends of
> 
> the BH curve. Also, with the variable grain size, the resolution
> 
> doesn't have the sharp cutoff of digital, but more gradual.
> 
> 
> 
> -- glen

True, plue lenses themselves have long spatial frequency roll offs as well. It is interesting to see the comparisons between using a high density sensor on a lens and using a medium density sensor on the same lens that is using a teleconvertor. The high density sampling is often advantagous to using a teleconvertor - not to mention not having to take a hit on the light loss.

The slow roll off of the lens response allows for using a nominally medium resolving lens with a high density sensor and getting a lot more detail from the lens. Several have reported this effect with a 28-300mm zoom on a D800E.  Still this is not as good as using a high resolving lens in the 1st place, but it is pretty amazing.


The hard limits of the dynamic range issue are easily mitigated digitally via HDR (High Dynamic Range) imaging where multiple shots are taken with different exposures.

Clay

clay@claysturner.com wrote:

(snip, I wrote)

>> Compared to digital, though, film has a fairly smooth transition
>> at the ends of the dynamic range, at "toe" and "shoulder" ends of
>> the BH curve. Also, with the variable grain size, the resolution
>> doesn't have the sharp cutoff of digital, but more gradual.

(snip)

> True, plue lenses themselves have long spatial frequency roll offs 
> as well. It is interesting to see the comparisons between using a 
> high density sensor on a lens and using a medium density sensor 
> on the same lens that is using a teleconvertor. The high density 
> sampling is often advantagous to using a teleconvertor - not to 
> mention not having to take a hit on the light loss.

I hadn't thought about that one. In optics class, the usual description
is of a perfect lens with a finite size, which has a pretty sharp 
spatial frequency limit, at least on axis. But for real lenses,
especially the not top quality ones, there are plenty of other
ways to reduce resolution with longer tails.
 
> The slow roll off of the lens response allows for using a nominally 
> medium resolving lens with a high density sensor and getting a lot 
> more detail from the lens. Several have reported this effect with 
> a 28-300mm zoom on a D800E.  Still this is not as good as using a 
> high resolving lens in the 1st place, but it is pretty amazing.

Remember the pictures from the original Hubble telescope, after
deconvolution? With enough S/N you can do pretty well. 
 
> The hard limits of the dynamic range issue are easily mitigated 
> digitally via HDR (High Dynamic Range) imaging where multiple 
> shots are taken with different exposures.

I am not sure how much is lost in the JPEG conversion compared to
raw, but yes. Seems to me that one could even process the image
to generate something like the film response with smooth tails.

-- glen