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[filmscanners] Re: opinions? Reviews? of Primefilm 1800 ?




----- Original Message -----
From: "Laurie Solomon" <laurie@advancenet.net>
To: <dickbo@btopenworld.com>
Sent: Saturday, June 08, 2002 6:44 PM
Subject: [filmscanners] RE: opinions? Reviews? of Primefilm 1800 ?


>Bits equals available grey levels per pixel

"That is nice; is this also true when one works in color as opposed to
grayscale or black and white?  Would I be wrong to generalize this and say
"bits equal potentially available tonal levels per pixel" in which the tone
can be any hue or color?"

That is corect except hue and colour mean the same thing

>However, the question in issue, I believe, was not the meaning of "bits"
but
if "bit depth" was intended to be a measure of "dynamic range" or of
"density range, of the "contrast range" from white point limit to black
point limit or of the ability to discriminate between shades or tones within
that contrast range, or more generally between the quantity of informational
data regarding highlights and shadows and the quality of that information in
terms of determining details precisely within that contrast range<.

That is a function of the imaging devices ability to "see" illumination
levels of differing intensity. That is the original analogue signal. The
bits come later.

What you are really talking about is the electrical current being generated
"after" the CCD has "seen" the illuminant.

Once you have a current flowing somewhere you have something from which you
can create "bits" or if you like post analogue is digital, by which I mean
another device converts the analogue signal to a digital one.

Depending on the current levels, so you have the devices original density
range which, I would suggest is non linear in that for equal variations in
illuminamnt you will not get a simlar variation in current except probably
somewhere in the "middle" of the devices sensitivity range.
At the highlight and shadow light levels the CCD will most likely be non
linear, rather like film and paper emulsions. Photographic emulsions all
have their linear response regions beyond which a non linear situation
exists. In film the shadow areas are considered to be limited at that point
where film base+fog density is equal to image density minus fog+base
density.

At the highlight end it is normally considered that where exposure increases
offer no further increase in film density,  then you have reached the limit
of highlight detail.

It is considered normal in electrical photo sensitive imaging devices, to
assume that where random electrical noise equals image electrical output you
will have reached the limits of image shadow response for any given imaging
device.
At the other highlight end where no further increase in current is
generated. you have reached the upper limits of highlight reproduction.
Please note we are talking negatives here baby doll.

Bit depth therefore is the same for any particular original intensity level
except that where device response limits are reached at both ends of the
illumination intensity scale, having say 12 bits or 48 bits per colour
channel will not enable you to "see" any more visual information because
there is non to see, at least not once the illuminant has been digitised.

Look at it this way:
Suppose you have an original colour negative with a density range from
0.35-1.35. Let us say that there is a mid tone area around 0.9-1.0 density.
For each colour you have 8 bits per tone level, that is each pixel can have
any level between 0 up to 256  i.e.let us assume 256=white and 0=black.
It is quite possible for any given area from either CYM image data to have
it's pixel level edited to a number simlar to any other area of CYM level,
and you will observe some tonal difference - or if you will, image making
information - because the information is within the original devices
electrical output range.

At the two extreme ends however things are different because for example in
the case of the shadow end there will be no further detail beyond 0 while at
the highlight end nothing beyond 256.

And that, as they say, is broadly how things work in digital imaging
scanners.

>From the foregoing it would be reasonable to assume that in order to check
any particular manufacturers clims regarding original density response
range, it would be necessary to stick the kit under assesment into a
properly equipmented lab employing properly qualified technicians.

What you would probably find is that just as some lenses of the same mark
and cars of the same model do not perform in exactly the same way, some
scanners in a particular model range will out spec others in the same range
which is why, when you read comments from respondents on this news group,
you should be very careful not to assume a level of know-how that will never
exceed their understanding and subjective opinions regarding their own
particular item of equipment.

As a final comment I would suggest that 16 years as a technical salesman for
Crosfield Electronics taught me one certainty and that is that you will
hardly ever find someone who has a particular item of equipment admit that
they made a mistake when originally evaluating product.

TTFN as they say in the trade.


-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of dickbo
Sent: Saturday, June 08, 2002 3:43 AM
To: laurie@advancenet.net
Subject: [filmscanners] Re: opinions? Reviews? of Primefilm 1800 ?


Bits equals available grey levels per pixel

----- Original Message -----
From: "Laurie Solomon" <laurie@advancenet.net>
To: <dickbo@btopenworld.com>
Sent: Friday, June 07, 2002 4:22 PM
Subject: [filmscanners] RE: opinions? Reviews? of Primefilm 1800 ?


>Another misconception...though equally as common...the number of bits the
converter
>has, have nothing to do with the scanners ability to capture any particular
>density range.

Just out of curiousity and in simple layman's terms, what do the number of
bits that the converter has  have to do with if not the density range? How
does it impact on what is captured?

Austin, I am asking a serious question here out of my lack of knowledge and
sure would appreciate a good discussion in layman's terms so that I can
understand what is being said without having to hire an engineer to
interpret. It has always been my understanding, rightly or wrongly, that the
higher the number of bits the more detailed or refined the informational
date captured from the original that is transmitted as data in the digital
file with respect to highlight and/or shadow detail with the density range
figure represetning the range of contrast that can be captured.  In other
words, "dynamic range" representing the contrast range of the capture's
capabilities, while the bit depth represented the quality of the data
captured within that range particularly the extremes.  If this is wrong,
please explain where and how it is and provide me with a more accurrate
description (but once again, I urge you to try and do it in non-engineering
terms if possible).


-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Austin Franklin
Sent: Friday, June 07, 2002 7:13 AM
To: laurie@advancenet.net
Subject: [filmscanners] RE: opinions? Reviews? of Primefilm 1800 ?



> However, it is rated with 3.2 dynamic range, which is a bit low for a 14
> bit/channel.

Even though they may call it "dynamic range", it is DENSITY range.  Another
misconception...though equally as common...the number of bits the converter
has, have nothing to do with the scanners ability to capture any particular
density range.

Austin

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