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What are accepted figures for signal/noise (SNR) and dynamic rangefor CRT? LCD? Film? Human eye?

 
 
jeff miller
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      02-22-2005
I'm converting my old analog scanning electron microscopes to digital/pc
based.

One of the important questions is how many bits of resolution ie: levels
of greyscale are required. I've heard the analog front ends of the
scopes have a maximum SNR of about 72 dB, or 12 effective bits, and to
give me some flexibility for digital image processing that's about what
I'll shoot for: a bit better if I can get it.

But on the other end of the scale, I'm wondering what are accepted
figures for signal to noise or dynamic range of various display
technologies, and of the human eye.

It seems to me the published "contrast" figures for LCD displays of
about 600:1 peg them at about 49dB dynamic range.

What is generally accepted for B&W film? Is it highly dependent on film
type and processing? Anyone know some typical figures for various
processes? Is "silver print," which in my mind is marked by high
contrast, a special technique or just a fancy word for black and white?

How about for CRT's? Deos it depend in part on the design and
construction of the CRT, and do dedicated monochrome CRTs have a greater
dynamic range for greyscale than color CRT's used to display greyscale
images?

And what about the human eye, for that matter? It's been suggested the
human eye has only about 6 bits or 36 dB dynamic range/SNR for greyscale
images. Is that about right? Bonus question: I know the sensitivity of
the human eye varies with color, being most sensitive at about 555 nM
green. How about dynamic range and SNR? Deos it vary with color, too?

Thanks!

-Jeff
 
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Tim Wescott
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      02-22-2005
jeff miller wrote:

> I'm converting my old analog scanning electron microscopes to digital/pc
> based.
>
> One of the important questions is how many bits of resolution ie: levels
> of greyscale are required. I've heard the analog front ends of the
> scopes have a maximum SNR of about 72 dB, or 12 effective bits, and to


--snip--

> images. Is that about right? Bonus question: I know the sensitivity of
> the human eye varies with color, being most sensitive at about 555 nM
> green. How about dynamic range and SNR? Deos it vary with color, too?
>

Most of what you ask I don't know, but what I _do_ know is this:

In infrared imaging (which is what I'm familiar with) you take as many
bits as you can get at the sampling rates you need -- this is currently
14 bit ADC's at 10MHz on high-end systems. Even so you need some
up-front gain selection (in the form of allowing the user to select a
few different integration times) to get the best picture for the
conditions. This data gets processed, gained up linearly or
non-linearly, possibly spatially and/or temporally filtered, then
presented to the user on video with an 8-bit DAC. Needless to say you
throw away a _lot_ of information when you go through the
user-presentation layer.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
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Dimitrios Tzortzakakis
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      02-22-2005
I am not certain about the technical data, you should ask some electronic
engineer, but it's very difficult to construct a lcd or tft scrren that can
compete a good crt, because the picture in the crt is made by tiny bits of
phosphorus struck by the cathod rays, also emitting their own light.Besides
that, crts have a developing history of more than 50 years.

--
Tzortzakakis Dimitri?s
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
? "jeff miller" <(E-Mail Removed)> ?????? ??? ??????
news:GyxSd.9722$(E-Mail Removed) m...
> I'm converting my old analog scanning electron microscopes to digital/pc
> based.
>
> One of the important questions is how many bits of resolution ie: levels
> of greyscale are required. I've heard the analog front ends of the
> scopes have a maximum SNR of about 72 dB, or 12 effective bits, and to
> give me some flexibility for digital image processing that's about what
> I'll shoot for: a bit better if I can get it.
>
> But on the other end of the scale, I'm wondering what are accepted
> figures for signal to noise or dynamic range of various display
> technologies, and of the human eye.
>
> It seems to me the published "contrast" figures for LCD displays of
> about 600:1 peg them at about 49dB dynamic range.
>
> What is generally accepted for B&W film? Is it highly dependent on film
> type and processing? Anyone know some typical figures for various
> processes? Is "silver print," which in my mind is marked by high
> contrast, a special technique or just a fancy word for black and white?
>
> How about for CRT's? Deos it depend in part on the design and
> construction of the CRT, and do dedicated monochrome CRTs have a greater
> dynamic range for greyscale than color CRT's used to display greyscale
> images?
>
> And what about the human eye, for that matter? It's been suggested the
> human eye has only about 6 bits or 36 dB dynamic range/SNR for greyscale
> images. Is that about right? Bonus question: I know the sensitivity of
> the human eye varies with color, being most sensitive at about 555 nM
> green. How about dynamic range and SNR? Deos it vary with color, too?
>
> Thanks!
>
> -Jeff



 
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Jerry Avins
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      02-22-2005
jeff miller wrote:
> I'm converting my old analog scanning electron microscopes to digital/pc
> based.
>
> One of the important questions is how many bits of resolution ie: levels
> of greyscale are required. I've heard the analog front ends of the
> scopes have a maximum SNR of about 72 dB, or 12 effective bits, and to
> give me some flexibility for digital image processing that's about what
> I'll shoot for: a bit better if I can get it.
>
> But on the other end of the scale, I'm wondering what are accepted
> figures for signal to noise or dynamic range of various display
> technologies, and of the human eye.
>
> It seems to me the published "contrast" figures for LCD displays of
> about 600:1 peg them at about 49dB dynamic range.
>
> What is generally accepted for B&W film? Is it highly dependent on film
> type and processing? Anyone know some typical figures for various
> processes? Is "silver print," which in my mind is marked by high
> contrast, a special technique or just a fancy word for black and white?
>
> How about for CRT's? Deos it depend in part on the design and
> construction of the CRT, and do dedicated monochrome CRTs have a greater
> dynamic range for greyscale than color CRT's used to display greyscale
> images?
>
> And what about the human eye, for that matter? It's been suggested the
> human eye has only about 6 bits or 36 dB dynamic range/SNR for greyscale
> images. Is that about right? Bonus question: I know the sensitivity of
> the human eye varies with color, being most sensitive at about 555 nM
> green. How about dynamic range and SNR? Deos it vary with color, too?


Man! you ask a lot of good questions! I suspect that many of the answers
are to be found in papers of the SMPTE.

I recall that the contrast between printer's ink and glossy paper is
about 10:1 and B&W prints on glossy paper are a bit better (but on
matte, a bit worse). The contrast ratio of newsprint can be as low as
3:1 before the ink starts to look gray. Discouraging, no?

Look at your TV screen when the set is off. No part of it gets darker
when the set is on, but it sure looks like it does.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
 
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Jerry Avins
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Posts: n/a
 
      02-22-2005
Jerry Avins wrote:

...

> I recall that the contrast between printer's ink and glossy paper is
> about 10:1 and B&W prints on glossy paper are a bit better (but on


Correction: 30:1.

> matte, a bit worse). The contrast ratio of newsprint can be as low as
> 3:1 before the ink starts to look gray. Discouraging, no?


Typical newsprint before the now-common biodegradable soy ink was 10:1.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
 
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Nicholas O. Lindan
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      02-22-2005
"Jerry Avins" <(E-Mail Removed)> wrote

> > I recall that the contrast between printer's ink and glossy paper is
> > about 10:1 and B&W prints on glossy paper are a bit better (but on

>
> Correction: 30:1.


Photographic paper can get to 2.0 od reflected, a range of 10 ^ 2 = 100:1.

I just took a measurement from a printed page on coated stock, it
yielded 1.27 => 1.3 => 10 ^ 1.3 => 20:1.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
To reply, remove spaces: n o lindan at ix . netcom . com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/
 
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Jerry Avins
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      02-22-2005
Nicholas O. Lindan wrote:
> "Jerry Avins" <(E-Mail Removed)> wrote
>
>
>>>I recall that the contrast between printer's ink and glossy paper is
>>>about 10:1 and B&W prints on glossy paper are a bit better (but on

>>
>>Correction: 30:1.

>
>
> Photographic paper can get to 2.0 od reflected, a range of 10 ^ 2 = 100:1.
>
> I just took a measurement from a printed page on coated stock, it
> yielded 1.27 => 1.3 => 10 ^ 1.3 => 20:1.


Thanks for the reality check. The 30:1 figure was the best available,
typically found in (new) eye charts and photographic resolution targets
when I played with that stuff 40 years ago.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
 
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Nicholas O. Lindan
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      02-22-2005
Jeff miller wrote:
> I'm converting my old analog scanning electron microscopes to digital/PC

based.
>
> One of the important questions is how many bits of resolution i.e.: levels
> of grayscale are required ... the eye ... film ...


The eye is comfortable with a brightness range of ~50-100x in one scene
with no pupilary/retinal adaptation, 1000:1 is viewable without noticing
much adaptation - after images or time for pupil to adjust. The eye can
accommodate a brightness range from reflected starlight on a field
(remember clean air and no streetlights?) to sun on fresh snow (except
in extreme cases, mountains, clean air ...). This about a 25 bit/zone
range or ~32,000,000:1 and has no relevance to viewing a CRT.

Within a 2.0 OD range it can easily discriminate to .005 OD in the middle
of the range. However, OD is logarithmic and photocells and CRTs aren't.
Figure you will need about 12 bits for very good fidelity, but 8 bits
looks just fine on a CRT.

Numbers above are from memory, you should check with a good text on
human visual response if the values are important.

Negatives have close to no relation to photoptic response. Exposure
and development of film are such as to yield the thinnest (least dense)
negative that will yield a good print. This figure depends on scene
contrast, film contrast, paper contrast and the method used to image the
negative on the film.

I have to confess I don't see much relevance in all this to an SEM. All
you want is the range of signal that presently goes to the current
analog display and be able to accommodate that. 8 bits resolution should
be adequate.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
To reply, remove spaces: n o lindan at ix . netcom . com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/
 
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Tim Giles
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      02-22-2005
jeff miller <(E-Mail Removed)> wrote:
[...]
>But on the other end of the scale, I'm wondering what are accepted
>figures for signal to noise or dynamic range of various display
>technologies, and of the human eye.


In normal lighting, the cones on the retina can detect contrasts of aprox.
2% over a range of 2 orders of magnitude. Their dynamic range is closer
to 4 orders of magnitude, but their ability to differentiate shades drops
rapidly at the lower (darker) end of the scale.

A 13 or 14 bit (linear) number would cover the same range, with the same
(or better) ability to separate shades. (Aside: Computer displays manage
with 8 bits, partly because they don't have a contrast ratio of 1:10^4 and
partly because they are not linear.)

There's a lot of good stuff at
http://webvision.med.utah.edu/
and
http://faculty-web.at.northwestern.e...uman%20eye.pdf

>What is generally accepted for B&W film? Is it highly dependent on film
>type and processing? Anyone know some typical figures for various
>processes? Is "silver print," which in my mind is marked by high
>contrast, a special technique or just a fancy word for black and white?


The response of B&W film covers about 3 orders of magnitude. For B&W
paper, the reflectivity ratio between white and the deepest black is about
100:1. Ilford publish a lot of useful data on photographic materials at
www.ilford.com

-Tim
 
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Jerry Avins
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      02-22-2005
Nicholas O. Lindan wrote:

...

> The eye is comfortable with a brightness range of ~50-100x in one scene
> with no pupilary/retinal adaptation, 1000:1 is viewable without noticing
> much adaptation - after images or time for pupil to adjust. The eye can
> accommodate a brightness range from reflected starlight on a field
> (remember clean air and no streetlights?) to sun on fresh snow (except
> in extreme cases, mountains, clean air ...). This about a 25 bit/zone
> range or ~32,000,000:1 and has no relevance to viewing a CRT.


Yes. There's more light reflected from a lump of coal in sunlight than
from a bowl of snow indoors. The eye/brain isn't fooled.

> Within a 2.0 OD range it can easily discriminate to .005 OD in the middle
> of the range. However, OD is logarithmic and photocells and CRTs aren't.
> Figure you will need about 12 bits for very good fidelity, but 8 bits
> looks just fine on a CRT.
>
> Numbers above are from memory, you should check with a good text on
> human visual response if the values are important.
>
> Negatives have close to no relation to photoptic response. Exposure
> and development of film are such as to yield the thinnest (least dense)
> negative that will yield a good print. This figure depends on scene
> contrast, film contrast, paper contrast and the method used to image the
> negative on the film.


For high-resolution work, we used to dye the emulsion black to avoid
exposing interior grains. After all, the image can't be in focus
throughout the emulsion depth. To make the film a little faster, we
would etch away the top few microns of the emulsion, leaving an exposed
layer of grains, like in sandpaper.

> I have to confess I don't see much relevance in all this to an SEM. All
> you want is the range of signal that presently goes to the current
> analog display and be able to accommodate that. 8 bits resolution should
> be adequate.


The question of which 8 bits can be important. I can adjust images from
my 12-bit flat-bed scanner in ways that just don't apply to 8 bits.

Jerry
--
Engineering is the art of making what you want from things you can get.
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