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1 perry 1 pgmtopbm
2 !!!pgmtopbm
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 OPTIONS
7 REFERENCES
8 SEE ALSO
9 AUTHOR
10 ----
11 !!NAME
12
13
14 pgmtopbm - convert a portable graymap into a portable bitmap
15 !!SYNOPSIS
16
17
18 __pgmtopbm__ [[__-floyd__|__-fs__|__-threshold__
19 |__-hilbert__
20 |__-dither8__|__-d8__|__-cluster3__
21 |__-c3__|__-cluster4__|__-c4__
22 |__-cluster8__|__-c8__] [[__-value__ ''val'']
23 [[__-clump__ ''size''] [[''pgmfile'']
24 !!DESCRIPTION
25
26
27 Reads a portable graymap as input. Produces a portable
28 bitmap as output.
29
30
31 Note that there is no pbmtopgm converter. Any program that
32 uses the Netpbm libraries to read PGM files, including
33 virtually all programs in the Netpbm package, will read a
34 PBM file automatically as if it were a PGM
35 file.
36
37
38 If you are using a less intelligent program that expects PGM
39 input, use __pnmdepth__ to convert the PBM file to PGM.
40 As long as the depth is greater than 1, __pnmdepth__ will
41 generate PGM. This less intelligent program quite probably
42 is also not intelligent enough to deal with general maxvals,
43 so you should specify a depth of 255.
44 !!OPTIONS
45
46
47 The default quantization method is boustrophedonic
48 Floyd-Steinberg error diffusion (__-floyd__ or
49 __-fs__). Also available are simple thresholding
50 (__-threshold__); Bayer's ordered dither
51 (__-dither8__) with a 16x16 matrix; and three different
52 sizes of 45-degree clustered-dot dither (__-cluster3__,
53 __-cluster4__, __-cluster8__). A space filling curve
54 halftoning method using the Hilbert curve is also available.
55 (__-hilbert__);
56
57
58 Floyd-Steinberg will almost always give the best looking
59 results; however, looking good is not always what you want.
60 For instance, thresholding can be used in a pipeline with
61 the ''pnmconvol'' tool, for tasks like edge and peak
62 detection. And clustered-dot dithering gives a newspaper-ish
63 look, a useful special effect.
64
65
66 The __-value__ flag alters the thresholding value for
67 Floyd-Steinberg and simple thresholding. It should be a real
68 number between 0 and 1. Above 0.5 means darker images; below
69 0.5 means lighter.
70
71
72 The Hilbert curve method is useful for processing images
73 before display on devices that do not render individual
74 pixels distinctly (like laser printers). This dithering
75 method can give better results than the dithering usually
76 done by the laser printers themselves. The __-clump__
77 flag alters the number of pixels in a clump. This is usually
78 an integer between 2 and 100 (default 5). Smaller clump
79 sizes smear the image less and are less grainy, but seem to
80 loose some grey scale linearity. Typically a PGM image will
81 have to be scaled to fit on a laser printer page (2400 x
82 3000 pixels for an A4 300 dpi page), and then dithered to a
83 PBM image before being converted to a postscript file. A
84 printing pipeline might look something like: pnmscale
85 -xysize 2400 3000 image.pgm | pgmtopbm -hil | pnmtops -scale
86 0.25 __
87
88
89 All flags can be abbreviated to their shortest unique
90 prefix.
91 !!REFERENCES
92
93
94 The only reference you need for this stuff is
95
96
97 The Hilbert curve space filling method is taken from
98 !!SEE ALSO
99
100
101 pbmreduce(1), pgm(5), pbm(5), pnmconvol(1), pnmscale(1),
102 pnmtops(1)
103 !!AUTHOR
104
105
106 Copyright (C) 1989 by Jef Poskanzer.
107 ----
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