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 width=integer height=integer
16       [background=string]
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18   Parameters:
19       input=string[,string,...]
20           Names of input files.
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22       mask=string[,string,...]
23           Names of mask files.
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25       opacity=float[,float,...]
26           Layer opacities.
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28       output=string
29           Name of output file.
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31       width=integer
32           Image width.
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34       height=integer
35           Image height.
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37       background=string
38           Background color.
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DESCRIPTION

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

71       Glynn Clements
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73       Last changed: $Date: 2006/03/01 10:02:32 $
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75       Full index
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79GRASS 6.2.2                                                       g.pnmcomp(1)