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Robert brings up an important issue here:
There are different bit depth values! Whatever you do, you eventually have
to digitize an analog camera into a digital one. In most cases 8 or 16-bit
digitizers are used. But even if you use a 16-bit digitizer does not mean
that your image has 16 bit resolution, as Robert explained in his email. In
fact, a 30,000 electron well width chip will normally have much less, taking
into account the noise. It is therefore important to find out if the
"16-bit" specification relates to the S/N ratio, or to the digitizer.
To my knowledge there are no 12-bit digitizers, so any camera that claims 10
or 12 bit resolution most likely refers to the S/N ratio, but the situation
is not clear with 16-bit (for that reason we refer to our Cantega2k as a
"true 16-bit" camera).
mike
Michael Bode, Ph.D.
Soft Imaging System Corp.
12596 West Bayaud Avenue
Suite 300
Lakewood, CO 80228
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-----Original Message-----
From: Robert Atkinson [mailto:[log in to unmask]]
Sent: Thursday, March 04, 2004 09:42
To: [log in to unmask]
Subject: Re: 8 bit or 12 bit?
Hi Daniel,
The choice of intensity resolution depends on a number of factors. These
include the dynamic range of the object (or source) being imaged, the
dynamic range of the sensor, the system signal to noise ratio and the
intended use of the image.
If you are just viewing the raw image on a computer screen then 8 bits
are adequate. Likewise there is no point in attaching a high resolution
analogue to digital converter to a limited dynamic range sensor. There
are a number of cooled CCD cameras on the market that claim 16 bit
resolution when the well depth of the CCD is less than 30,000 electrons.
How do you measure 1/2 an electron? Alternatively if you have a high
quality PMT and amplifiers, 16 bit resolution IS appropriate for a
fluorescent microarray scanner were samples with a large range of
expression are being analysed by software.
In short it depends what you are doing. Look at the whole system from
sample to finished output and ensure that all the elements are
appropriate to the task. Look at the detailed specifications not just
the advertising headlines. There is no point in a digital display that
reads to 10.000 if it only has 0.01 accuracy.
-----Original Message-----
From: Daniel Mackay [mailto:[log in to unmask]]
Sent: 04 March 2004 14:48
To: [log in to unmask]
Subject: 8 bit or 12 bit?
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Hi,
Some advice please.
As a relative "newbie" to this game, I'm curious as to why one would
want
to use 12 bit pixel depth when capturing images at 1024X1024 images.
This
would give over 4000 grey scales as opposed to 255 (8 bit). Isn't 255
enough?
Here are some comments I received wrt some images I recently produced.
These were made for metamorph quantification, not necessarily for high
resolution.
Only 8 bit pixel depth (256 gray scales) imaging used, not
appropriate with 1024X1024 image sizes, which defeats the purpose
acquiring high of resolution images from these large scans.
Should use 12 bit imaging as minimum with frame scan (can use 12
bit 1024x1024 for images to be printed.
??????
Danny.
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