Re: streaks in scan

I've read the other replies but I didn't see anyone ask you about or mention
the light source in the scanner. While I can't speak for your scanner, my
scanner uses a compact fluroescent lamp as its light source. Just like the
fluorescent bulbs in the kitchen, they have to warm up for a bit (20-30m or
so) before they acheive their rated level of performance.

One of the things that I was experiencing with scans off of a 'cold' lamp
(IE: I just turned the unit on and started scanning) were exactly the kinds
of artifacts that you described. The scanner driver contains code that
reads the output level of the bulb across the whole width of the CCD. In
places where it sees dips or bumps in the curve (IE: the gasses inside are
still charging up and are visibly swirling around), it applies a digital
correction. If then the bulb is allowed to warm up and the scanner is not
recalibrated, the digital correction that was applied is then not required
(or it needs to be applied elsewhere).

Try warming up your scanner for 20 minutes before you scan something for
real. If you just set it to scan a full-page, full color 16-bit pass or so
for 20 minutes, that should do it. Once 20 minutes has elapsed, turn the
scanner off and then quickly back on again. The bulb will still be warmed
up but you'll trick the scanner into recalibrating itself.

I have to do this with my $2500 quirky-as-hell Minolta SMP or the results
are guaranteed to be ass-tastic.

-Jon

----- Original Message -----
From: "Jon Lybrook" <jon@terabear.com>
To: <epson4870@yahoogroups.com>; <alt-photo-process-l@skyway.usask.ca>
Sent: Monday, April 26, 2004 10:46 AM
Subject: streaks in scan

> Hi All,
>
> I'm scanning a 4x5 transparency at 48bit on the Epson 4870 Pro using
SilverFast,
> converting it to greyscale and am getting vertical streaks in the file.
The
> streaks aren't noticeable until I apply an adjustment curve or otherwise
> brighten the image. I've managed to minimize them by doing a multipass
scan,
> but they still exist. They are apparent in the file and on whatever
output
> device I send them to, so I know it's not a printer problem.
>
> Is this ugly artifact in the subtle black areas simply to be expected from
the
> flatbed scanners or is there something I'm doing wrong?
>
> Thanks,
> Jon
>
Received on Tue Apr 27 17:19:06 2004