From: Ken Watson (watsok@frii.com)
Date: 12/02/02-02:47:24 PM Z
While I agree where there is noise it will happen at random locations, how
do you determine which are noise caused artifacts from a few scans?
In astronomy you are looking at a constant image doing many scans or samples
of the same image. As I understand things they are constantly integrating
the photons they get so a million samples is a trivial issue. IF you did 16,
or the more the better scan's of the same image and had the software to
utilize these scans it might help.
The other place where this is completely different with astronomy, and would
confuse a program ,is that with each scan the bulbs heat up, and the sensor
along with it's electronics heat up. There is a shift in color of the bulbs
and they add more infra red into the mix. In addition, as they are warm up,
their intensity is increased as I remember. The sensor is extremely
sensitive to IR. The rest of the electronics response will also shift as
they are used / with heat. With the sky, the color temp remains about the
same over long periods of time and astronomers tend to pay more than a few
hundred dollars for their equipment to avoid a lot problems suggested.
If you had control over the exposure time you could first expose for the
darkest areas and let the lightest areas bloom and reject them. Then another
exposure for the thinnest areas with the shadows becoming completely black
and they could be rejected. By combining these scans it would give much
better results. This would be effectively increasing the number of bits of
resolution you would have. Then the issue is determining where the two
scans meet in density.
Noise in scanning can be seen as speckles in the black area's ( minimum
number of electrons ) if anyone wants to check. There are also non
linearity's that multiple scans will not correct for. Also has anyone
noticed it is impossible to get fluorescent colors correct? There is an
issue using only three colors to try and get a good color map off a scan.
The peak sensitivity of the sensor and the peak emission of the lamps do not
correlate. Also some of the blue light leaks into the green channel and the
green channel is sensitive to a lot of the "red" spectrum. Engineering
compromises. It has been explained to me that to get real accurate color
reproduction it will take 4 to 6 different color strips in the sensors.
Given what we have things look mostly pretty good.
----- Original Message -----
From: "nze christian" <christian_nze@hotmail.com>
To: <alt-photo-process-l@skyway.usask.ca>
Sent: Monday, December 02, 2002 12:20 PM
Subject: Re: Scanning for greater dynamic range
> Hi,
>
> The double scan result in a better , because the 2 scans will be
different;
> the noise will not happen on the same point. The sofware will do an
average
> which mean that when the scan give the same result for a point, the
software
> let them like they are but when it give different result it will make the
> average of the to point. this method is used in microscopy ofr astronomy
> where single pmt are used. They often average to 8 or 16 which mean that
> they scan 8 16 to avoid noise. a point should always give the same result
> on the 8 scan, if not it apply a function or delete the point considered
as
> pure noise.
>
> In our case the noise just come from the receptor, as there is no change
in
> the light and in the photo. so this way to work avoid to many machine
noise.
>
>
> <If you double scan you still have the same signal to noise ratio,
> <therefore
> <no increase in dynamic range because you are just summing together to
> <scans
> <with the same signal to noise ratio. Unless you have software that can
> <detect noise and remove it one is just fooling self. As far as I know
> <this does not exist.
>
> Amicalement
>
> Nzé Christian
> mailto:christian_nze@hotmail.com
> http://www.c-nze.com
>
>
> > >
>
>
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