5400 II multiscan feature

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fiatuni

Good evening,

What is the main purpose of the multiscan feature . I'm not sure to see
a great difference with or without it.

Regards

Fia
 
fiatuni <[email protected]> said:
Good evening,

What is the main purpose of the multiscan feature . I'm not sure to see
a great difference with or without it.
Click to expand...
Multiscan improves the signal to noise of the scanner - whether you see
it as significant depends on the source material. Basically, the signal
to noise of a CCD is limited by two things, a fixed noise at the readout
stage and a statistical noise based on the amount of signal available.
Both of these could be improved if the CCD could store more signal, but
the available space per pixel is limited. Multiscanning simulates a
larger signal storage space by giving the CCD several "looks" at each
image point and accumulating the signal in the computer instead of on
the chip. In theory, the signal to noise ratio should improve by the
square root of the number of multiscan operations - in practice it is
very slightly less than this. You will see more benefit from multiscan
with low contrast negatives than you will with a high contrast slide
scan.
 
fiatuni said:
Good evening,

What is the main purpose of the multiscan feature . I'm not sure to see
a great difference with or without it.
Click to expand...

Multi-scanning is taking more than one readout of the same scan line,
and then averaging these together.

It is intented to reduce noise in the final image, since noise is random
and as such will tend to cancel out when averaging multiple scans.

If you can't see the effect, try this: scan the same target twice --
once normally and once with 2x multi-sampling.

Then open both images in Photoshop, or the GIMP, or whatever, open
Levels, and bring the whitepoint down to the same value (make it 50,
dunno, depends on the picture) in both images.

You should now see that there is less noise in the multi-sampled scan.

Whether this improvement is useful versus the increased time needed for
scanning is obviously your decision.

by LjL
(e-mail address removed)
 
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