Austin wrote:
Typically, the image data only falls in part of the range of the CCD,
and should be more in the middle, not the ends.
Well, that's part of my point.
You're suggesting treating the CCD non-linearly it appears.
No. I'm saying that the signal to noise ratio changes depending on
Typically, the image data only falls in part of the range of the CCD,
and should be more in the middle, not the ends.
Well, that's part of my point.
You're suggesting treating the CCD non-linearly it appears.
No. I'm saying that the signal to noise ratio changes depending on the
input
On Sat, 13 Jan 2001 13:18:46 +1100 Julian Robinson ([EMAIL PROTECTED]) wrote:
http://www.klt.co.jp/Nikon/Press_Release/ls-4000.html
...
Density range 4.2
Hmmm. Except the omission of the word 'optical' is slippery, wibbly-wobbly and
misleading - and doubtless deliberate.
On Fri, 12 Jan 2001 18:21:18 -0500 Austin Franklin ([EMAIL PROTECTED]) wrote:
The scanner manufacturers use Dmax as a specification item
Used by itself like this, it would be a statment of noise level - ie any higher DMax
will be lost in noise, it being below the scanners ability to
On Sat, 13 Jan 2001 13:19:01 +1100 Julian Robinson ([EMAIL PROTECTED]) wrote:
Nikon may argue that their Dmin is measured with the exposure set low, and
Dmax with the exposure set as high as possible. This means that they can
get up to another 2 to 4 stops(!!!) into their claimed DENSITY
Nikon may argue that their Dmin is measured with the exposure set low, and
Dmax with the exposure set as high as possible. This means that they can
get up to another 2 to 4 stops(!!!) into their claimed DENSITY
RANGE. Which might explain why they use the term Density Range and not
Dynamic
Dynamic Range certainly means the range that can be covered
without changing the setup i.e. the range available at one instant.
It depends on what you mean by 'changing the setup'. Dynamic range is a
system measurement. If the system can provide a particular 'dynamic range'
by doing, say,
Hi Austin.
Austin Franklin wrote:
If you do the math, you'll find that using a 14-bit
A/D on most CCD scanners is kind of silly; in such
cases, one LSB generally equates to about 10-50
microvolts of signal.
How do you work out this figure?
I make it more like 170 microvolts,
Of course it does, but the voltage to toggle the LSB of the A/D, *relative
to
the maximum voltage from the CCD*
When talking about number of volts/bit (technically, volts/code) the
measurement is *USUALLY* done relative to the A/D input voltage range...but
if you want to reference to the CCD
I don't think anyone commented on my suggestion that a 14 bit A/D still
gives more detail in the middle part of the range of values (where colour
neg film generally is) precisely because the noise is lowest there?
I understand what you are saying, but I don't believe that's what is done,
or
At 04:44 15/01/01, : [EMAIL PROTECTED] wrote:
.Which might explain why they use the term Density Range and not
Dynamic Range - Dynamic Range certainly means the range that can be
covered
without changing the setup i.e. the range available at one instant.
Hm. Well spotted!
Tony Sleep
Austin wrote:
I don't think anyone commented on my suggestion that a 14 bit A/D still
gives more detail in the middle part of the range of values (where colour
neg film generally is) precisely because the noise is lowest there?
I understand what you are saying, but I don't believe that's what
Typically, the image data only falls in part of the range of the CCD,
and should be more in the middle, not the ends.
Well, that's part of my point.
You're suggesting treating the CCD non-linearly it appears. There is a
thought to that, but I will say, that you're probably not going to get
No, they are claiming even more specifically ... and I quote from
http://www.klt.co.jp/Nikon/Press_Release/ls-4000.html
...
Density range 4.2
Interesting. A Nikon product data sheet for the 4000 ED and model comparison sheet,
provided by Nikon at this past week's Mac World, both use the
Rafe wrote:
Not quite. There's no point going for extra bits,
without a corresponding decrease in overall system
noise. If the noise is equal to one LSB at 8 bits,
then it's 2 LSBs at 9 bits, 4 LSBs at 10 bits, etc.
I take your point Rafe, *but* most of the noise in the CCD is when the
Ray wrote:
Is there anyone out there other than the participants who has any idea
what they are saying?
Sorry if the techno-speak is losing people, Ray.
If you want a short summary of the most important
point it's "Optical Density as quoted by the manufacturer
is probably meaningless as a way of
I'm not sure which thread or topic this really is, but since I really need help, I'll
ask from my confused heart:
Julian wrote:
Now, let's unplug the 8 bit D/A, and plug in a 12 bit D/A instead, to the
same circuit. My point is - NOTHING CHANGES.
Then Ray Amos wrote:
Is there anyone out
Julian wrote:
there is a definite limit to dynamic range prescribed
by the number of bits. An 8 bit scanner can never do
better than a "Dmax" or ~dynamic range of
log10 2^8 = 2.4. This is because the lowest usable
level "step" has to be around one LSB to be meaningful.
OK, I understand
There is a legal term for lies in advertising: It's called 'puffery'. In
principle, I believe it means that if a claim is one that most people would
recognize as nonsense, then it is not a 'crime' or 'tort', for which
redress could be obtained in court. If it is a lie (or omission) that most
On Thu, 11 Jan 2001 23:27:33 -0500 Ray Amos ([EMAIL PROTECTED]) wrote:
Is there anyone out there other than the participants who has any idea
what they are saying?
:-))
Regards
Tony Sleep
http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info
comparisons
On Fri, 12 Jan 2001 12:52:47 +1100 Julian Robinson ([EMAIL PROTECTED])
wrote:
If they state an unqualified figure for Dmax,
then when measured by some "reasonable" process it should meet that
figure. With the likelihood that it will not, this would mean that they
are just plain lying,
Colour could be relevent if the sensor has poor sensitivity
to a particular frequency range, or produces more noise in
that range (eg. blue, which I often hear contains more noise
than other channels :).
Very true, but you have to believe the manufacturer is going to use CCDs
that don't have
- Original Message -
From: "Austin Franklin" [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Friday, January 12, 2001 8:10 AM
Subject: RE: filmscanners: Re: So it's the bits?
Austin:
I Have been following this thread with some intrest and your example below
ties the
Austin writes ...
Yes, it appears you are confused about what DMax is. ...
Second is the ability to discriminate within that voltage
range, which is 'resolution'and that is what DMax is.
DMax is relative in and of itself. ...
And you have always been such a stickler for
On Fri, 12 Jan 2001 12:52:47 +1100 Julian Robinson ([EMAIL PROTECTED])
wrote:
If they state an unqualified figure for Dmax,
then when measured by some "reasonable" process it should meet that
figure. With the likelihood that it will not, this would mean that they
are just plain
Austin writes ...
Yes, it appears you are confused about what DMax is. ...
Second is the ability to discriminate within that voltage
range, which is 'resolution'and that is what DMax is.
DMax is relative in and of itself. ...
And you have always been such a stickler for
Austin writes ...
Scanners use DMax as part of their specs, which is what this whole
discussion has been about. What's your point?
I've never seen any scanner use Dmax as a spec ... they often quote
"dynamic range" or "optical density" but Dmax and Dmin are absolute
terms for the
I've never seen any scanner use Dmax as a spec ...
The Leafscan 45 has listed right in their brochure, and I quote:
"Dynamic range: 5000:1 or 3.7 Dmax"
So, obviously at least one manufacturer does use Dmax as a spec, and I am
sure others do also.
the
ability of measuring Dmax - Dmin, are
Austin writes ...
The pixel values (for which the range of is the
theoretically highest Dmax for the scanner)
are relative to each other, not absolute, ...
Correct ... the "pixel values" associated with measuring Dmax may be
relative ... but "Dmax" is a measured value, is absolute,
Hi Rafe.
rafeb wrote:
The only reason I can see that a greater number of bits would help is that
when you are at the extremities of the CCD's range, more bits should help
resolve meaningful data from noise, or by reducing the size of the steps,
reduce the loss of image information which
The pixel values (for which the range of is the
theoretically highest Dmax for the scanner)
are relative to each other, not absolute, ...
Correct ... the "pixel values" associated with measuring Dmax may be
relative ... but "Dmax" is a measured value, is absolute, and belongs
to film.
At 11:19 PM 1/12/01 +, Pete wrote:
I'm not saying that 14 bit A/Ds can be used to their full advantage by any
means,
but their use isn't entirely wasted. The range of the signal from a CCD
amounts
to about 12 bits, so the last useable 12 dB (0.6D) causes a change of 16
levels,
not just 4, as
At 10:21 13/01/01, Austin wrote:
The pixel values (for which the range of is the
theoretically highest Dmax for the scanner)
are relative to each other, not absolute, ...
Correct ... the "pixel values" associated with measuring Dmax may be
relative ... but "Dmax" is a measured
At 01:09 13/01/01, Tony wrote:
But they aren't AFAIK claiming a DMax figure, nor even an OD range
(DMax-DMin),
but a wibbly-wobbly bit of slipperiness called 'dynamic range'. Really
this is
all horribly reminiscent of output power specs for HiFi amps - 'RMS', 'Music
Power', 'Peak' and so on,
snip
PS There is another issue that comes up here - I have assumed that
Dynamic
range (which until now I would say is the same thing as density range) is
Dmax - Dmin where you measure Dmax and Dmin _with_the_same_setup_ - that
is, during the one scan.
I brought up this point a while ago, I
Julian wrote:
Because it is an 8-bit D/A, the lowest level we can read is 2^8 lower than
1024 = 1024/256 = 4mV. This is the value of one least significant bit
(LSB). Also, let's assume that this is an optimally engineered 8-bit
system. Because it is optimally engineered, let's say that the
"Colin Maddock" [EMAIL PROTECTED] wrote:
Won't the 12bit a/d converter allow the information
between 4mv and the 1mv noise level to be resolved?
It may, but I think Julian's point is valid which is that for
a given sensitivity from the analog circuitry, changing the
A/D won't make any
Because it is an 8-bit D/A, the lowest level we can read is 2^8 lower than
1024 = 1024/256 = 4mV.
The number of bits has NOTHING to do with what voltage it can read.
Different converters have different voltage ranges, AND the input voltage
range can be changed via an analog front end to the
for
a given sensitivity from the analog circuitry, changing the
A/D won't make any difference to the density ranges
that the analog circuitry resolves. It only increases the
accuracy with which we read the range of analog values
that the CCD *does* resolve.
May be I'm slow today...but
On Thu, 11 Jan 2001 13:06:00 +1100 Julian Robinson ([EMAIL PROTECTED])
wrote:
My conclusion from all this is that the manufacturers cheat by saying that
the Dmax is defined by the D/A resolution as a shorthand, which is true if
the IMPLICATION which follows is that the rest of the system
Paragraph is clear enough for me to understand. And is perfectly
correct to my judgement.
Slava
--- Austin Franklin [EMAIL PROTECTED] wrote:
for
a given sensitivity from the analog circuitry, changing the
A/D won't make any difference to the density ranges
that the analog circuitry
It appears to me the word 'sensitivity' was meant as 'range'. Sensitivity
of an analog system is the rate of change. A higher bit A/D could give
higher sensitivity, but would not give a better range (which I believe is
what the paragraph was trying to say), since the range is fixed for a given
Austin wrote:
May be I'm slow today...but that paragraph is really unclear
to me, and I know this stuff quite well. What exactly do
you mean by 'for a given sensitivity from the analog circuitry'?
OK, let me put it another way and try to avoid some of the ambiguous terms.
You have an
Rob,
I agree with what you wrote, except that having read some of Tony's old
posts I think this last point quoted below is not true - rather, there is a
definite limit to dynamic range prescribed by the number of bits. An 8 bit
scanner can never do better than a "Dmax" or ~dynamic range of
Austin this was an ILLUSTRATION, not based on an actual D/A - I was using
an illustrative range of 0 -1024mV just to make a point which is valid
whatever range you choose. I could have talked about -3 to +3 V but the
point would have been even more obscure than it already is.
As you point
: Re: So it's the bits?
Paragraph is clear enough for me to understand. And is perfectly
correct to my judgement.
Slava
--- Austin Franklin [EMAIL PROTECTED] wrote:
for
a given sensitivity from the analog circuitry, changing the
A/D won't make any difference to the density
(I'm ignoring colour for simplicity's sake).
Color isn't relevant. The sensor doesn't have any color information, only
intensity information. The color is deterministic...ie, a particular sensor
has a particular color filter over it.
The real minimum and maximum
light intensities which the
At 05:58 12/01/01, Tony wrote:
. But Nikon's figures, unqualified as they are, tell us
absolutely nothing useful at all, except that someone in marketing thinks
we're a
bit gullible. Of course if they read lists like this, they'd know better :)
Actually in thinking about it, it is worse than
At 09:53 AM 1/12/01 +1000, Rob wrote:
The only reason I can see that a greater number of bits would help is that
when you are at the extremities of the CCD's range, more bits should help
resolve meaningful data from noise, or by reducing the size of the steps,
reduce the loss of image
Colin Maddock wrote:
Julian wrote:
Because it is an 8-bit D/A, the lowest level we can read is 2^8 lower than
1024 = 1024/256 = 4mV. This is the value of one least significant bit
(LSB). Also, let's assume that this is an optimally engineered 8-bit
system. Because it is optimally
Frank Paris asks:
Where along the path from sensor to
scanned image is the mapping performed that actually corresponds to the
psychological way we perceive brightness levels?
When the gamma correction is applied, I think.
Colin Maddock
Tony thanks for pointing me to the archives, which I have now read. (If
anyone is interested, the topic was Bit Depth OD, in late March, early
April 2000).
I think as usual I did not express myself clearly in my last post, judging
by responses, but I take the point that it has been
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