primax: primaxd with gamma problem?
Subject:
Re: primaxd with gamma problem?
From:
####@####.####
Date:
28 Mar 2002 19:34:09 -0000
Message-Id: <Pine.LNX.4.33L2.0203282000210.2005-100000@localhost.localdomain>
On Wed, 27 Mar 2002, Louco.com [iso-8859-1] você na internet. wrote:
> I tried using the gamma correction, color etc, but I couldn't scan this image
> with primad equal to the win-image.
>
> Note1: My scanner is an colorado 300.
> Note2: Its happen with couple of images.
My scanner is also a colorado 300.
Same problem.
I wrote Andre about this a while ago, here is the answer he gave:
--------------------------------------------------------
A better solution is to use xscanimage. It has a difficult to use but
mighty histogramm function. Create a line with a very low gamma value.
This worked for me.
[ note: xscanimage is the interface gimp uses for scanning ]
I send you a snapshot of my setting. The diagram creates a mapping from
the input color values to the output color values. The x axis is the input
color - the more right the more white. The higher the value at a point the
whiter the output color. So a point in the top right corner means: "map a
full white input value to a full white output value". A point in the
bottom left corner says: "Map black input values to black output values".
The points between these are up to you. What you want for your pencil
drawings is: "Map only the really white imput to white output - all others
shall be black". You can get this by selecting a really low gamma value.
This creates a appropriate mapping. The problem: (1) Xsane has a lower
limit - you cannot select really low one. (2) XScanimage has a bug. If you
create the mapping with the gamma button there are negative values in the
mapping. So it inverts the image. I will write a bug report to the
author.
The solution: create the mapping by hand. XScanimage has a cool spline
interpolation function (the topmost button). Create some points and it will
connect them with smooth a line.
-----------------------------------------------------------------
Andre's suggestion works quite well, actually, but when I have to scan
really faded images or really light pencil drawings I still have to switch
over to windows or use the old primax scan program instead of primaxd.
--
Michele Alzetta
