[LONG] Theoretical estimates for film-equivalent digital sens

[A complimentary Cc of this posting was sent to
HvdV
], who wrote in article :
In any decent photographic system the most important component
of performance/price ratio is the lenses. Since the price of the
lens scales as 4th or 5th power of its linear size, decreasing
the size of the sensor (while keeping S/N ratio) may lead to
very significant improvements of performance/price.
---
with some examples?
The tradeoff of lens aperture and expense vs sensor size determines
ultimately the size and shape of the digital camera. After the 'fashion
factor' of course.

a) First of all, my assumption on how rescaling the lense affects
image quality was "incomplete" (read: wrong ;-). Part of fuzziness
due to difraction does not change; but part of fuzziness due to
optical imperfection scales up with the lense linear size (since
all the light rays passing through the system scale up, the spot in
the focal plane which is the diffraction-less image of a
point-source will scale up as well).

This has two effects: sweet spot (in F-stops) scales up (i.e., to
the worse) as sqrt(size); and best resolution scales down as
1/sqrt(size). So my estimates for "perfect lense" for an ideal
36x24mm sensor were wrong, since I erroneously assumed that the
sweet spot does not change.

b) One corollary is that when you scale sensor size AND LENSE up n
times, it makes sense to scale up the size of the pixel sqrt(n)
times. In other words, you should increase the sensitivity of the
sensor and number of pixels both the same amount - n times.
Interesting...

c) The estimages on price vs. size: IIRC, this was from a review in a
technical magazine on optical production ("Scientific publications
of LOMO" or some such) in end of 80s. Since technology could have
changed meanwhile (digitally-controlled machinery?), the numbers
could have changed...

Hope this helps,
Ilya

Ilya Zakharevich wrote:
[]
Judge for yourself: visit

http://ilyaz.org/photo/random-noise

Yours,
Ilya

Grey is one colour to test this on - what about a more sensitive colour
like skin-tones?

Cheers,
David

[A complimentary Cc of this posting was sent to
David J Taylor
], who wrote in article :
Judge for yourself: visit

http://ilyaz.org/photo/random-noise

Grey is one colour to test this on - what about a more sensitive colour
like skin-tones?

The script is there. Feel free to edit it to change the base value.
Or just modify the .png by adding a constant bias...

Yours,
Ilya

[A complimentary Cc of this posting was sent to
Scott W
], who wrote in article .com:
A very nice write up, I will admit I have not gone through all of it
yet in detail. One thing to consider is that CCD have a read out noise
of around 10 electrons, whereas this noise level will not greatly
effect the signal to noise when looking at 400 detected photons with an
noise level of 20 electrons it will start to dominate in darker parts
of the scene. For instance by the time you are down 5 stops from full
white the readout noise will be larger then the photon noise, by a
small amount.

On the second thought, maybe this issue is not as crucial as it may
sound. Remember that 12 electrons noise is present on Mark II, and
its 800ISO setting is "considered nice". It has S/N=28 at Zone V; so
the electron noise at Zone III should be about 13 electrons; while 12
electrons readout noise will increase this to total about 17
electrons, we must conclude that such a noise (S/N=9) at Zone III is
not very bad. Likewise for Zones II and I.

So: either Mark II produces noticable noise in zones I--III, or
readout noise 12 electrons is already small enough to be "not
important".

Yours,
Ilya

[A complimentary Cc of this posting was NOT [per weedlist] sent to
Ilya Zakharevich
], who wrote in article :
Judge for yourself: visit

http://ilyaz.org/photo/random-noise

Grey is one colour to test this on - what about a more sensitive colour
like skin-tones?

The script is there. Feel free to edit it to change the base value.
Or just modify the .png by adding a constant bias...

Actually, it may be a little bit more than just changing the base
value. Luminance is calculatable from Luma only very close to neutral
gray; thus having a skin-tone with luma-less noise may have
significant luminance noise.

One needs to experiment with both constant-luma noise and
constant-luminance noise, and see which one is less perceivable by
eye. Summary: one may need also to modify the vector 0.2126 0.7152
0.0722 to take into account gamma (via derivatives of x^2.2 at R'G'B'
values of skin tone).

Yours,
Ilya

Ilya Zakharevich wrote:

Judge for yourself: visit


http://ilyaz.org/photo/random-noise


...Luminance is calculatable from Luma only very close to neutral
gray; thus having a skin-tone with luma-less noise may have
significant luminance noise.

One needs to experiment with both constant-luma noise and
constant-luminance noise, and see which one is less perceivable by
eye. Summary: one may need also to modify the vector 0.2126 0.7152
0.0722 to take into account gamma (via derivatives of x^2.2 at R'G'B'
values of skin tone).



Any chance of an executive summary of this study. I just cannot see what
the exercise is all about.

The photoshop RAW converter has color (chrominance) & regular
(luminance) noise reduction & I noticed the color noise reduction does
almost nothing. It seems you are saying color noise is indeed
insubstantial in comparison but maybe I'm missing the boat on that?

thanks!

Ilya Zakharevich wrote:
[A complimentary Cc of this posting was NOT [per weedlist] sent to
Ilya Zakharevich
], who wrote in article
:
Judge for yourself: visit

http://ilyaz.org/photo/random-noise

Grey is one colour to test this on - what about a more sensitive
colour like skin-tones?

The script is there. Feel free to edit it to change the base value.
Or just modify the .png by adding a constant bias...

Actually, it may be a little bit more than just changing the base
value. Luminance is calculatable from Luma only very close to neutral
gray; thus having a skin-tone with luma-less noise may have
significant luminance noise.

One needs to experiment with both constant-luma noise and
constant-luminance noise, and see which one is less perceivable by
eye. Summary: one may need also to modify the vector 0.2126 0.7152
0.0722 to take into account gamma (via derivatives of x^2.2 at R'G'B'
values of skin tone).

Yours,
Ilya

Thanks, Ilya. I don't have the time to do detailed work on this right
now, but at least I hope it triggers /someone/ to check this out. Your
comments about the gamma remind me of the "constant luminance failure"
errors in colour TV - takes me back a long time.

http://www.poynton.com/notes/video/C...luminance.html

Cheers,
David

[A complimentary Cc of this posting was sent to
paul
], who wrote in article :
Judge for yourself: visit

http://ilyaz.org/photo/random-noise

Any chance of an executive summary of this study. I just cannot see what
the exercise is all about.

Did you see the pictures on the URL above?

The photoshop RAW converter has color (chrominance) & regular
(luminance) noise reduction & I noticed the color noise reduction does
almost nothing. It seems you are saying color noise is indeed
insubstantial in comparison but maybe I'm missing the boat on that?

How I see the pictures, the eye sensitivity for chrominance noise is
not much higher than 10% of sensitivity for luminance one. [But my
eyes are kinda special, so I would appreciate if somebody else - with
normal vision - confirms this.]

Yours,
Ilya

Ilya Zakharevich wrote:
[A complimentary Cc of this posting was sent to
paul
], who wrote in article :

Judge for yourself: visit


http://ilyaz.org/photo/random-noise


Any chance of an executive summary of this study. I just cannot see what
the exercise is all about.


Did you see the pictures on the URL above?


The photoshop RAW converter has color (chrominance) & regular
(luminance) noise reduction & I noticed the color noise reduction does
almost nothing. It seems you are saying color noise is indeed
insubstantial in comparison but maybe I'm missing the boat on that?


How I see the pictures, the eye sensitivity for chrominance noise is
not much higher than 10% of sensitivity for luminance one. [But my
eyes are kinda special, so I would appreciate if somebody else - with
normal vision - confirms this.]


So that's equal noise on left & right? No doubt the left looks 90% more
noisy. I suppose if I zoomed way in, I could see the color noise.

Hi Ilya,
[A complimentary Cc of this posting was sent to
HvdV
], who wrote in article :
Substitute 'hans' for 'nohanz', sorry for the paranoia.

In any decent photographic system the most important component
of performance/price ratio is the lenses. Since the price of the
lens scales as 4th or 5th power of its linear size, decreasing
the size of the sensor (while keeping S/N ratio) may lead to
very significant improvements of performance/price.
---
with some examples?
The tradeoff of lens aperture and expense vs sensor size determines
ultimately the size and shape of the digital camera. After the 'fashion
factor' of course.


a) First of all, my assumption on how rescaling the lense affects
image quality was "incomplete" (read: wrong ;-). Part of fuzziness
due to difraction does not change; but part of fuzziness due to
optical imperfection scales up with the lense linear size (since
all the light rays passing through the system scale up, the spot in
the focal plane which is the diffraction-less image of a
point-source will scale up as well).

This has two effects: sweet spot (in F-stops) scales up (i.e., to
the worse) as sqrt(size); and best resolution scales down as
1/sqrt(size). So my estimates for "perfect lense" for an ideal
36x24mm sensor were wrong, since I erroneously assumed that the
sweet spot does not change.
Hm, not so sure you were very wrong. I don't know much about lens design, but
I do know errors like spherical aberration scale up in a non-linear fashion
if you increase aperture. And that's only one of the many errors.
Then there are amplifying econimical factors like a much smaller lens copy
number.
BTW, if you keep aperture constant the diffraction spot stays the same. It
scales with the wavelength, the sine of the half-aperture angle, and for
completeness, also the refractive index of the medium.

b) One corollary is that when you scale sensor size AND LENSE up n
times, it makes sense to scale up the size of the pixel sqrt(n)
times. In other words, you should increase the sensitivity of the
sensor and number of pixels both the same amount - n times.
Interesting...
Sizing up the lens and sensor gets you more information about the object,
with the square of the scale. You can average that information with bigger
pixels to get a better SNR, but you could do that also in postprocessing.

c) The estimages on price vs. size: IIRC, this was from a review in a
technical magazine on optical production ("Scientific publications
of LOMO" or some such) in end of 80s. Since technology could have
changed meanwhile (digitally-controlled machinery?), the numbers
could have changed...
It's clear that it is cheaper now to make aspherical lenses, and there are
also new glasses available.
I was hoping for a plot with a lenses with similar view angles in it with on
the horizontal axis the formats and vertically the price. I guess it should
be possible to dig this out of ebay..

-- Hans