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NAME

       g.pnmcomp  - Overlays multiple PPM image files

KEYWORDS

       general

SYNOPSIS

       g.pnmcomp
       g.pnmcomp help
       g.pnmcomp               input=string[,string,...]               [mask=string[,string,...]]
       [opacity=float[,float,...]]  output=string  [outmask=string]  width=integer height=integer
       [background=string]   [--verbose]  [--quiet]

   Parameters:
       input=string[,string,...]
           Names of input files

       mask=string[,string,...]
           Names of mask files

       opacity=float[,float,...]
           Layer opacities

       output=string
           Name of output file

       outmask=string
           Name of output mask file

       width=integer
           Image width

       height=integer
           Image height

       background=string
           Background color

DESCRIPTION

       (culled from the mailing list)

       From: Glynn Clements
       Subject: Re: [GRASS5] Re: [GRASSLIST:10403] Transparency added
       Date: Sun, 19 Feb 2006 20:17:59 +0000
       g.pnmcomp isn't meant for end users. It's an internal tool for use by
       a Tcl/Tk GUI.
       In essence, g.pnmcomp generates a PPM image by overlaying a series of
       PPM/PGM pairs (PPM = RGB image, PGM = alpha channel).
       The intention is that d.* programs will emit PPM/PGM pairs (by way of
       the PNG-driver code being integrated into libraster). The GUI will
       manage a set of layers; each layer consists of the data necessary to
       generate a PPM/PGM pair.
       Whenever the layer "stack" changes (by adding, removing, hiding,
       showing or re-ordering layers), the GUI will render any layers for
       which it doesn't already have the PPM/PGM pair, then re-run g.pnmcomp
       to generate the final image (just redoing the composition is a lot
       faster than redrawing everything).
       A C/C++ GUI would either have g.pnmcomp's functionality (image
       composition) built-in, or would use the system's graphics API to
       perform composition (for translucent layers, you would need OpenGL or
       the Render extension, or something else which supports translucent
       rendering).
       Tk doesn't support transparent (masked) true-colour images (it does
       support transparent GIFs, but that's limited to 256 colours), and an
       image composition routine in Tcl would be unacceptably slow, hence
       the existence of g.pnmcomp.

AUTHOR

       Glynn Clements

       Last changed: $Date: 2006-03-01 11:02:32 +0100 (Wed, 01 Mar 2006) $

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