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From: macphed@herald.usask.ca (Ian MacPhedran)
Newsgroups: comp.graphics
Subject: Re: Brighten
Message-ID: <1990Jul31.233156.11888@herald.usask.ca>
Date: 31 Jul 90 23:31:56 GMT
References: <1990Jul25.110057.1259@uoft02.utoledo.edu>
Organization: University of Saskatchewan
Lines: 30

From article <1990Jul25.110057.1259@uoft02.utoledo.edu>, by cscon113@uoft02.utoledo.edu:
> 
> I am looking for a package to brighten an image.  I have pbmplus, FBM
> and several conversion routines.  I can't seem to find anything to
> use to brighten an image that won't leaveblack spots where the darkest
> parts of the image were.
> 
> 					Any help appreciated,
> 					James H. Lewallen
James;

Why not use ppmarith to add a constant value image to your image? This
avoids the problem of having zero-value pixels. As well, you could add
a low value (say 2 with a maxval of 255), and then multiply the image
by a constant value. This would give a better spread to the colour map,
yet still have no black spots in the final image.

(Note - I haven't tried this. I prefer to stretch the colourmap, as
pgmnorm does, so that the darker pixels are still dark to give better
contrast.)

Ian.

Ian MacPhedran, Engineering Computer Centre, University of Saskatchewan.
2B13 Engineering Building, U. of S. Campus, Saskatoon, Sask., CANADA S7N 0W0
macphed@dvinci.USask.CA  macphedran@sask.USask.CA  macphedran@sask.BITNET
-- 
Ian MacPhedran, Engineering Computer Centre, University of Saskatchewan.
2B13 Engineering Building, U. of S. Campus, Saskatoon, Sask., CANADA S7N 0W0
macphed@dvinci.USask.CA  macphedran@sask.USask.CA  macphedran@sask.BITNET