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

6       g.pnmcomp  - Overlays multiple PPM image files
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KEYWORDS

9       general
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SYNOPSIS

12       g.pnmcomp
13       g.pnmcomp help
14       g.pnmcomp     input=string[,string,...]      [mask=string[,string,...]]
15       [opacity=float[,float,...]]       output=string        [outmask=string]
16       width=integer    height=integer     [background=string]     [--verbose]
17       [--quiet]
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19   Parameters:
20       input=string[,string,...]
21           Names of input files
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23       mask=string[,string,...]
24           Names of mask files
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26       opacity=float[,float,...]
27           Layer opacities
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29       output=string
30           Name of output file
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32       outmask=string
33           Name of output mask file
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35       width=integer
36           Image width
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38       height=integer
39           Image height
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41       background=string
42           Background color
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DESCRIPTION

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

75       Glynn Clements
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77       Last changed: $Date: 2006-03-01 11:02:32 +0100 (Wed, 01 Mar 2006) $
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79       Full index
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81       © 2003-2008 GRASS Development Team
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85GRASS 6.3.0                                                       g.pnmcomp(1)
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