Some CCDs feature anti-blooming so that this does not happen.
I think all current generation CCD's try to do this, but there's still a
point at
which charge leaks between pixels.
This may be true for linear CCDs, but it is definitely not standard for
scientific CCDs. When I last
Rafe thanks - I do this sort of thing regularly (shows I am not good at
taking flat, well-lit shots!). The problem I was discussing arises when
you get blooming from one scanner exposure to another - then it becomes
difficult if not impossible to combine them satisfactorily using these
On Tue, 16 Jan 2001, Shough, Dean wrote:
more specific method? I have the same problem when trying to extract the
most from some high contrast slides, and have not been really happy with
some of my multiple exposure scans for this reason.
Regards,
Julian
It's not too difficult
On Mon, 15 Jan 2001 10:28:56 -0800 Shough, Dean ([EMAIL PROTECTED]) wrote:
Some CCDs feature anti-blooming so that this does not happen.
I think all current generation CCD's try to do this, but there's still a point at
which charge leaks between pixels.
Regards
Tony Sleep
At 10:17 AM 1/17/01 +1100, Julian wrote:
At 04:42 17/01/01, Rafe wrote:
It's not too difficult to make intelligent
"composites" from multiple passes of a slide
or negative -- provided the scanner and driver
have good registration from pass to pass.
Rafe thanks - I do this sort of thing
Not really following this thread so I may be missing your intent...but
whenever I've tried increasing exposure beyond "proper exposure", the CCD
saturates (ie blooms) on those pixels that were already bright. This
spills
over into the neighbouring dark pixels and ruins them.
Some CCDs
At 07:45 15/01/01, Pete wrote:
All the available CCDs on the market today are limited to a dynamic range of
5000:1 (~12 bits) at normal temperatures.
Aha! That is the figure I was wondering about. Thanks so much for this
useful and factual piece of info. Given the physics I would guess that
On Fri, 12 Jan 2001 12:22:47 +1100 Julian Robinson ([EMAIL PROTECTED])
wrote:
In other words number of
bits does NOT define Dmax, it only defines what the best possible might
be.
Odd, 'cos that was the point of the whole original argument :) IE that bit
depth constrains maximum OD range
Hi Pete,
At 10:11 13/01/01, [EMAIL PROTECTED] wrote:
And nobody, as far as I've read, is arguing that bit depth DOES define Dmax..
What I understood from Ed's and others' original point was that
manufacturers were stating their Dmax (or dynamic range or density range)
based only on their D/A
On 10 Jan 2001 09:04:51 -0800 Frank Paris ([EMAIL PROTECTED]) wrote:
I'm still not convinced that there's a
necessary mapping between actual density and ADC resolution.
It's not 'necessary' inasmuch as it /could/ be done differently, but AFAIK the
only CCD prosumer unit to do non-linear
On Wed, 10 Jan 2001 23:16:57 + photoscientia
([EMAIL PROTECTED]) wrote:
Oh no!
Not this again.
The answer is one word - linearity.
My reaction entirely :-)
Regards
Tony Sleep
http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info
comparisons
On Wed, 10 Jan 2001 12:54:31 -0500 Austin Franklin ([EMAIL PROTECTED]) wrote:
Devices are not really linear. There are a number of 'distortions'. One is
offset, the second is linearity, and the third is gain.
CCD's are AIUI inherently very linear. 'Offset' = CCD noise in this context, gain
Oh no!
Not this again.
The answer is one word - linearity.
My reaction entirely :-)
But linearity explains only one half of the issue - that is, that you can't
do BETTER for dynamic range than what is implied by the number of
bits. Linearity doesn't make the most useful point that
Devices are not really linear. There are a number of 'distortions'.
One is
offset, the second is linearity, and the third is gain.
I think Austin was refering to the analogue pre-amplifiers built into a
lot of A/D
converters.
You are correct, but I was not limiting the source of the
Finally!?
- Original Message -
From: Austin Franklin [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Thursday, January 11, 2001 5:59 PM
Subject: RE: So it's the bits? (Was: filmscanners: Sprintscan 120 nowon B+H
web
In other words number of
bits does NOT define Dmax, it only defines
Hi!
A 14 bit number means a range 2 raised to the power of fourteen, that is
16384.
Density units are log 10 so we get log (16384) - 4.21
A simpler way:
1 bit means essentially one one aperture stop which is 0.3 Density units (log
2).
14 * 0.3 - 4.2
Or you could also say that the range is
Can someone help me here with some basic facts regarding this
dynamic/density range business?
I am having a fundamental problem comprehending why the number of bits is
even vaguely related to any supposed density range. I understand the maths
quoted here and in many other posts, but fail to
: "Julian Robinson" [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Wednesday, January 10, 2001 8:41 AM
Subject: Re: So it's the bits? (Was: filmscanners: Sprintscan 120 now
on B+H web site ...)
Can someone help me here with some basic facts regarding this
dynamic/density range busine
No I did mean 10^12 being the approximate result of my postulated 40 bits
i.e. 2^40 = 1.0995x10^12 ~= 10^12
I should have said...
The difference of course is the resolution...
In the former case, there are only 2^4 = 16 levels between darkest and
lightest density.
In the latter case, there
Julian writes ...
Can someone help me here with some basic facts regarding this
dynamic/density range business?
I am having a fundamental problem comprehending why the
number of bits is even vaguely related to any
supposed density range. ...
For example, I could have a density range of
]
[mailto:[EMAIL PROTECTED]]On Behalf Of Tony Sleep
Sent: Wednesday, January 10, 2001 5:36 AM
To: [EMAIL PROTECTED]
Subject: Re: So it's the bits? (Was: filmscanners: Sprintscan 120 now
On Wed, 10 Jan 2001 19:41:35 +1100 Julian Robinson
([EMAIL PROTECTED])
wrote:
I am having a fundamental
On Wed, 10 Jan 2001 19:41:35 +1100 Julian Robinson ([EMAIL PROTECTED])
wrote:
I am having a fundamental problem comprehending why the number of bits is
even vaguely related to any supposed density range. I understand the maths
quoted here and in many other posts, but fail to understand
/AlbumList?u=62684
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of Tony Sleep
Sent: Wednesday, January 10, 2001 5:36 AM
To: [EMAIL PROTECTED]
Subject: Re: So it's the bits? (Was: filmscanners: Sprintscan 120 now
On Wed, 10 Jan 2001 19:41:35
In summary, dynamic range is just another way of saying how
many bits the A/D converter uses:
10 bits = 3.0
12 bits = 3.6
14 bits = 4.2
Would you please explain this more? What is the source of the information,
or the algorithm, you used to come up with these numbers?
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