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Digital P&S and color bit depth

 
 
Roger N. Clark (change username to rnclark)
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      10-28-2006
http://www.velocityreviews.com/forums/(E-Mail Removed) wrote:

> David J Taylor wrote:
>
>>(E-Mail Removed) wrote:
>>
>>
>>>The Lecia DMR produces 16 bit/channel RAW files. How much of those 16
>>>bits is usable, I don't know.

>>
>>Thanks for that. I couldn't find that camera listed at D P Review. Do
>>you happen to know how many bits the camera's ADC uses?
>>
>>David

>
>
> You can read about the DMR here:
> http://www.leica-camera.us/photograp...gital-modul-r/
>
> The DMR uses a Kodak KAF-10010 CCD image sensor. From the data sheet,
> the sensor has a dynamic range of 67 dB. If I remember my signal
> processing facts, that corresponds to a hair over 11 bits. The data
> sheet is here:
> http://www.kodak.com/ezpres/business...10LongSpec.pdf
>
> BTW, the Lecia M8 uses a newer KAF-10050 sensor. It has a dynamic
> range of 76 dB, almost 13 bits. The M8 is on dpreview:
> http://www.dpreview.com/reviews/spec...a/leica_m8.asp
>

Interesting.

With 6.8 micron pixels, and 40,000 electron full well, and assuming
ISO 100 is set to maximize the full well capacity, that sets the
12-bit unity gain at just under ISO 1,000. That would plot
just to the lower right of the Canon 350D on Figure 6 at:
http://www.clarkvision.com/imagedeta...el.size.matter

I searched for a data sheet on the KAF-10050 sensor, but could
not find one. The data sheet for the KAF-10010 is great and more
complete than older Kodak data sheets. The off-axis response
could have helped in a long thread on purple fringing in the NG
a few months ago.

6.8 microns and 40,000 electron full well is about average for chips
that size, but the 17 electron read noise of the KAF-10010 is high,
especially compared to Canon's CMOS chips which run under 4 electrons.
Presumably the KAF-10050 has improved the read noise, but the full well
is probably about the same as the KAF-10010 at about 40,000.

Roger
 
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AAvK
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      10-28-2006

> I though thats what you were getting at. I agree, more bit depth is
> needed, but it's more complicated than that.
>
> For one thing, about 1/3 of the bit depth is useless, on the dark end
> of the color. More bits help with that, giving you more upper end bits
> to work with.
>
> But the big sticking point is color interpolation, a "feature" of bayer
> sensors. You do not get real-world, true pixel per pixel color from a
> bayer sensor. Instead, you get an estimate, based on whatever
> algorythm the camera maker uses, of the real color. The computer in
> the camera fills in the blank spots with it's guess of what color was
> really in that pixel. Unlike, say, slide film. Bayer sensors do not
> have true color, the dif. color pixels are dispersed in a pattern.
>
> Which is why I now shoot slide film now, and scan it in with a Nikon
> Coolscan 5000. True color, because the scanner scans every color for
> every pixel by stepping across the film. I can't stand digital color,
> it's so blah. Nothing beats the black you get from slide film, either!
> The trade off is a lack of sharpness, cause digital is sharp, got to
> give it that. But I find a few sharpenings with a photo editor gets
> pretty close. A full scan, from the Nikon scanner, yields a 131mb
> file, from a 35mm slide. I find 5mb is ok for 4x6's. And you get real
> bokeh back, too! So that's how I solved my artistic problem, I was not
> happy with digital at all. In five years or so, that might change, new
> sensors coming online.


You know, I fully agree with you from an artistic standpoint.
That other tech_maniac_guy, good grief.

I accept the idea of scanning positive and negative (and I do it)
more than a dij-cam because these colors are pure by develop-
ement in a natural, flowing chemical processes and can be
scanned in 48 bit color.

But you've got to realize, I have a Umax powerlook III and
I didn't know but I suspected it had a "bar of CCD sensors"
going across the 8-1/2" width to scan... I took it apart to clean
it internally - nope, it's got a small square CCD behind a round
1 inch O.D. lens, the lamp reflects light off the subject - the
image is concentrated through a complex of bowed silver
surfaced mirrors and into that lens to the CCD.

But it is a "CCD" which means Bayer, just like in your Nikon
5000, though yours doesn't have the mirrors. Why it is better
than a dij-cam, you can get your image as a more pure form of
color, and 48 bit color depth. If I had $1900.00 I would buy
that big current one (9000?) no sweat, I'd like to get the V ED
just for my current collection of 35 negs and poz's, and keep
on shooting 35!

So, I'm not going to defend dij-cams compared to fine scanning,
no way. But that $550 - $1900 Nikon scanner is too expensive
and a dij-cam with 12 bits per RG and B is cheaper and far more
convenient to simply get the image onto my HD, you know. My
point is, as_good _a_quality_as_possible, economically.

--
}<)))*> Giant_Alex
cravdraa_at-yahoo_dot-com
not my site: http://www.e-sword.net/

 
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Dave Martindale
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      10-29-2006
"AAvK" <(E-Mail Removed)> writes:

>I accept the idea of scanning positive and negative (and I do it)
>more than a dij-cam because these colors are pure by develop-
>ement in a natural, flowing chemical processes and can be
>scanned in 48 bit color.


So chemical processes are more "natural" than electronic ones? The way
that CCDs convert photons into electrons is just as natural as the way
that photons chemically change silver bromide crystals so they can be
developed.

>But you've got to realize, I have a Umax powerlook III and
>I didn't know but I suspected it had a "bar of CCD sensors"
>going across the 8-1/2" width to scan...


There *are* scanners like that, e.g. the Canon LiDE scanners.
But that has its own advantages and disadvantages.

>I took it apart to clean
>it internally - nope, it's got a small square CCD behind a round
>1 inch O.D. lens, the lamp reflects light off the subject - the
>image is concentrated through a complex of bowed silver
>surfaced mirrors and into that lens to the CCD.


If you look carefully, you'll almost certainly find that all the mirrors
are flat front-surface ones. They only act to fold the light path into
a small space. All the focusing is done by the lens.

>But it is a "CCD" which means Bayer, just like in your Nikon
>5000, though yours doesn't have the mirrors.


Here you're dead wrong. CCD just refers to the light-measuring
technology, and there are CCDs with and without Bayer filters.
In particular, the CCDs used in flatbed and film scanners are
"trilinear" arrays, which have 3 rows of sensing locations. Colour
comes from a red filter in front of one row, green in front of another,
and blue in front of the third row. (There's sometimes a 4th row I
won't get into here). So every time the scanner head moves, it captures
three different lines on the page in three different colours. After
some processing to line up the three images, you end up measuring all 3
colours at every pixel.

>Why it is better
>than a dij-cam, you can get your image as a more pure form of
>color, and 48 bit color depth.


48 bit is just the output bit depth. Plenty of digital cameras can
output 48-bit image files when shooting in RAW mode. But the A/D
converter resolution is less, probably about 12 bits in both cases.

Dave
 
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Raphael Bustin
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      10-29-2006
On Sun, 29 Oct 2006 21:43:42 +0000 (UTC), (E-Mail Removed) (Dave
Martindale) wrote:

>"AAvK" <(E-Mail Removed)> writes:


>>But it is a "CCD" which means Bayer, just like in your Nikon
>>5000, though yours doesn't have the mirrors.

>
>Here you're dead wrong. CCD just refers to the light-measuring
>technology, and there are CCDs with and without Bayer filters.
>In particular, the CCDs used in flatbed and film scanners are
>"trilinear" arrays, which have 3 rows of sensing locations. Colour
>comes from a red filter in front of one row, green in front of another,
>and blue in front of the third row. (There's sometimes a 4th row I
>won't get into here). So every time the scanner head moves, it captures
>three different lines on the page in three different colours. After
>some processing to line up the three images, you end up measuring all 3
>colours at every pixel.



And just to be clear, if it's a Nikon film scanner like
the LS-8000/9000, it's a *monochrome* CCD with
no filters at all over it. Instead, the Nikons use three
sets of LEDs -- red, green and blue, and alternate
these rapidly -- just as in a Canon LIDE flatbed scanner,
though the Canon uses a CIS sensor, rather than CCD.

In the LS8000/9000 there is exacly one mirror and
it is a small perfectly flat front-surface mirror.

The lens in the LS8000/9000 is quite a beauty.
Probably a lot more sophisticated than even my
favorite Canon L zoom lens.

Film scanners *do NOT* use Bayer sensors.


rafe b
www.terrapinphoto.com
 
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Xiaoding
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      10-30-2006

ASAAR wrote:
> On 27 Oct 2006 09:57:08 -0700, Xiaoding wrote:
>
> > Which is why I now shoot slide film now, and scan it in with a Nikon
> > Coolscan 5000. True color, because the scanner scans every color for
> > every pixel by stepping across the film. I can't stand digital color,
> > it's so blah. Nothing beats the black you get from slide film, either!
> > The trade off is a lack of sharpness, cause digital is sharp, got to
> > give it that. But I find a few sharpenings with a photo editor gets
> > pretty close. A full scan, from the Nikon scanner, yields a 131mb
> > file, from a 35mm slide. I find 5mb is ok for 4x6's. And you get real
> > bokeh back, too! So that's how I solved my artistic problem, I was not
> > happy with digital at all. In five years or so, that might change, new
> > sensors coming online.

>
> Just a question about your mention of bokeh. Isn't that a
> function of the lens? Meaning, whether used on a digital or film
> camera, wouldn't the bokeh be the same?


Well, yes, in theory. But your average P&S has a small sensor, which
means less bokeh. Full size sensors would have the same, but then you
got to spend a lot more money, and you still got the color problems.
So I went for the scanner, since I already had film gear.

 
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slin100@yahoo.com
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      10-30-2006

Roger N. Clark (change username to rnclark) wrote:
> I searched for a data sheet on the KAF-10050 sensor, but could
> not find one.


It's here.
http://www.kodak.com/ezpres/business...00LongSpec.pdf

 
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Dave Martindale
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      10-30-2006
Raphael Bustin <(E-Mail Removed)> writes:

>And just to be clear, if it's a Nikon film scanner like
>the LS-8000/9000, it's a *monochrome* CCD with
>no filters at all over it. Instead, the Nikons use three
>sets of LEDs -- red, green and blue, and alternate
>these rapidly -- just as in a Canon LIDE flatbed scanner,
>though the Canon uses a CIS sensor, rather than CCD.


Good point; I neglected to mention this way of handling the colour.

It can work really well when scanning film, because you know that the
film image is really made up of three dyes, so the ideal light source
for digitizing it is three pretty narrow-band (pure colour) sources.
The manufacturer would choose the wavelength of the red light source so
it is strongly absorbed by the cyan dye, but almost unaffected by the
yellow and magenta dye, and so on for the other two colours. This
minimizes crosstalk between colours. (It also makes it easy to add a
4th measurement channel using IR light for "ICE" processing).

On the other hand, it's not so good for a flatbed scanner, which is
supposed to reproduce colour accurately for anything you put in it.
There, you really want the light source and sensor filters, taken
together, to have a response more like the human eye colour-matching
functions, and that eliminates single-frequency light sources. (The
difference is that with a film scanner, there *are* only 3 colours in
the film that you care about, while with real-world objects you have the
whole visible spectrum to consider).

(Despite that, the LiDE scanners use a monochrome sensor and RGB LEDs.)

>Film scanners *do NOT* use Bayer sensors.


Nope, there's no need to. Bayer sensors show up only where you *have*
to capture the whole image at the same time. A slide scanner can take
its time building up the image one line at a time. (This also has
advantages in reducing lens flare, since the light source can be a line
instead of the full frame area).

Dave
 
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Raphael Bustin
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      10-31-2006
On Mon, 30 Oct 2006 18:17:05 +0000 (UTC), (E-Mail Removed) (Dave
Martindale) wrote:


>It can work really well when scanning film, because you know that the
>film image is really made up of three dyes, so the ideal light source
>for digitizing it is three pretty narrow-band (pure colour) sources.
>The manufacturer would choose the wavelength of the red light source so
>it is strongly absorbed by the cyan dye, but almost unaffected by the
>yellow and magenta dye, and so on for the other two colours. This
>minimizes crosstalk between colours. (It also makes it easy to add a
>4th measurement channel using IR light for "ICE" processing).
>
>On the other hand, it's not so good for a flatbed scanner, which is
>supposed to reproduce colour accurately for anything you put in it.
>There, you really want the light source and sensor filters, taken
>together, to have a response more like the human eye colour-matching
>functions, and that eliminates single-frequency light sources. (The
>difference is that with a film scanner, there *are* only 3 colours in
>the film that you care about, while with real-world objects you have the
>whole visible spectrum to consider).



FWIW, according to Mike Chaney (the designer of Profile
Prism, a print-profiling package) the Canon LIDE scanners
are work well with his scanner-based profiling package.

Presumably this would be another benefit of the narrow-
band illumination? And now that I think of it, does that not
(in general) contradict your claim? After all, most prints are
also made with CMYK dyes or pigments (though these
may not be as narrow-band as the dye layers in film)


rafe b
www.terrapinphoto.com

 
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Dave Martindale
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      10-31-2006
>On Mon, 30 Oct 2006 18:17:05 +0000 (UTC), (E-Mail Removed) (Dave
>Martindale) wrote:


>>It can work really well when scanning film, because you know that the
>>film image is really made up of three dyes, so the ideal light source
>>for digitizing it is three pretty narrow-band (pure colour) sources.
>>The manufacturer would choose the wavelength of the red light source so
>>it is strongly absorbed by the cyan dye, but almost unaffected by the
>>yellow and magenta dye, and so on for the other two colours. This
>>minimizes crosstalk between colours. (It also makes it easy to add a
>>4th measurement channel using IR light for "ICE" processing).


>>On the other hand, it's not so good for a flatbed scanner, which is
>>supposed to reproduce colour accurately for anything you put in it.
>>There, you really want the light source and sensor filters, taken
>>together, to have a response more like the human eye colour-matching
>>functions, and that eliminates single-frequency light sources. (The
>>difference is that with a film scanner, there *are* only 3 colours in
>>the film that you care about, while with real-world objects you have the
>>whole visible spectrum to consider).


Raphael Bustin <(E-Mail Removed)> writes:
>FWIW, according to Mike Chaney (the designer of Profile
>Prism, a print-profiling package) the Canon LIDE scanners
>are work well with his scanner-based profiling package.


>Presumably this would be another benefit of the narrow-
>band illumination? And now that I think of it, does that not
>(in general) contradict your claim? After all, most prints are
>also made with CMYK dyes or pigments (though these
>may not be as narrow-band as the dye layers in film)


Photographic prints have just 3 channels of information, represented by
3 dyes. 4-colour ink printing also has just 3 channels, really - the
black ink makes up for limitations in the 3 colour inks. So 3
narrowband sources might well give good results scanning these subjects,
particularly if you can profile the scanner.

On the other hand, suppose you place a tree leaf showing its fall
colours into your flatbed. I think that will have a wider range of
colours present, and there you're likely to see more colour errors if
narrowband light is used.

Dave
 
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