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g.pnmcomp(1grass) Grass User's Manual g.pnmcomp(1grass)

NAME

g.pnmcomp - Overlays multiple PPM image files

KEYWORDS

general, gui

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: 2011-11-08 12:29:50 +0100 (Tue, 08 Nov 2011) $
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