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Geoff Thompson <[log in to unmask]>
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SciArt-L Discussion List-for Natural Science Illustration- <[log in to unmask]>
Mon, 2 Jun 2003 20:00:15 +1000
text/plain (72 lines)
My scanner has software with a threshold built in. At present I scan at high
resolution in black and white (bitmap) and discard scans until I get one I'm
happy with. Sounds like scanning in grey scale and converting would cut down
on discarded scans and therefore save time.
    So thanks for the tips,
----- Original Message -----
From: "Liz Day" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, June 02, 2003 7:16 AM
Subject: Re: a few questions...Grey Scale

> >...scanning in grey scale.  What is the purpose of that and why not just
> in black/white?
> The greyscale gives you more control over how the final product
> looks.   When you scan it as black and white line art, the computer does
> not always reproduce the drawing exactly - you may get lines that are
> thinner or thicker than you want, and the whole effect often will not look
> right.  (Try it).  This happens because the scanner has to look at the
> edge of each line, where there is usually a grey area, and decide exactly
> where it stops being black and starts being white.   (This effect is much
> less noticeable on drawings done in very black ink on very white paper
> on drawings done in those micro pens or with dark pencil, which both
> produce a dark grey that we see as black but the computer sees as 51% grey
> or 67% grey or 94% grey or whatever.)  But when you scan in greyscale, it
> reproduces (depending on the scanner settings) the whole range of these
> greys, and you don't have this edge problem.  Yet.
>  >I have noticed that my ink drawings do not scan well.  The black does
> look as rich and dark as it should.
> That's normal, that's how greyscales look.
>  >Is this solved by the grey scale or the resolution?
> Neither.   It's solved during step 2, when you convert the greyscale into
> "bitmap" file (pure black and pure white).   Try it.  (Image>Mode>Bitmap,
> choose "50% threshold".)  Everything grey will turn either 100% black or
> 100% white.
> Now comes the control part.
> *Before* you convert it to bitmap, adjust the threshold
> (Image>Adjust>Threshold).   Move the triangle back and forth on the
> threshold box;  you can see your black lines get fatter or thinner.   This
> lets you control how they will look on the final result.   This gives you
> the control that scanning in black and white does not give you, because
> when you scan in black and white the *computer* sets the threshold and
> you're stuck with it.  Whereas if you save a copy of the greyscale file,
> then if you don't like how your thresholded, bitmapped version of the
> comes out in print, you can go back to the greyscale  file and try again.
> HTH,
> Liz
> -------------------------------------------------------------
> Liz Day
> Indianapolis, Indiana, central USA.
> (The center of nothing in the middle of nowhere.)
> [log in to unmask]
> -------------------------------------------------------------