1Pamdepth User Manual(0)                                Pamdepth User Manual(0)
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NAME

6       pamdepth - change the depth (color resolution) in a Netpbm image
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SYNOPSIS

10       pamdepth newmaxval [netpbmfile]
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DESCRIPTION

14       This program is part of Netpbm(1).
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16       pamdepth  reads a Netpbm image as input, changes its depth (color reso‐
17       lution), and writes out the resulting Netpbm image.   I.e.  the  output
18       has  a  different maxval from the input, but all the same colors (apart
19       from rounding error).
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21       Reducing the depth results in some loss of information.
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23       Here is an example of the effect at the image format level: Assume  you
24       start  with  an  image with maxval 100 and sample values of 50 and 100.
25       You tell pamdepth to change it to depth 150.  The output has maxval 200
26       and sample values 75 and 150.
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28       This program works on multi-image streams.
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30       Be  careful  of  off-by-one  errors  when choosing the new maxval.  For
31       instance, if you want the color values to be five bits wide, use a max‐
32       val of 31, not 32.
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34       One  important  use  of pamdepth is to convert a new format 2-byte-per-
35       sample PNM file to the older 1-byte-per-sample  format.   Before  April
36       2000,  essentially  all raw (binary) format PNM files had a maxval less
37       than 256 and one byte per sample, and many programs may rely  on  that.
38       If  you specify a newmaxval less than 256, the resulting file should be
39       readable by any program that worked with PNM files before April 2000.
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42   Output Format
43       The output format (PBM, etc.) and, in the case of PAM, tuple  type,  of
44       the output is usually the same as the input.
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46       However,  changing  the  depth of a black and white image does not make
47       sense, except to turn it into a grayscale image, so if the input  is  a
48       black and white image, pamdepth makes the output grayscale.  To be more
49       precise, if the input is a PBM image, the output is  PGM,  and  if  the
50       input    is    a    PAM    with    tuple    type   BLACK_AND_WHITE   or
51       BLACK_AND_WHITE_ALPHA, the output is a PAM with tuple type GRAYSCALE or
52       GRAYSCALE_ALPHA, respectively.
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54       This conversion happens even if the new maxval is 1.
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56       Before  Netpbm 10.92 (September 2020), pamdepth failed if the input was
57       PAM with a black and white tuple type and the new maxval  was  anything
58       but 1.  But it always promoted PBM to PGM.
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OPTIONS

63       There  are  no  command line options defined specifically for pamdepth,
64       but it recognizes the options common to all programs based on libnetpbm
65       (See
66        Common Options ⟨index.html#commonoptions⟩ .)
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SEE ALSO

70       pnm(1), pam(1), pnmquant(1), ppmdither(1) pambrighten(1) pamfunc(1)
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HISTORY

74       pamdepth  was  new  in  Netpbm  10.32  (February  2006).   It  replaced
75       pnmdepth, by Jef  Poskanzer.   pamdepth  is  backward  compatible  with
76       pnmdepth  and  adds the ability to process arbitrary PAM images and the
77       ability to process multi-image input streams.   pnmdepth  handled  only
78       PNM images and ignored all but the first in any stream.
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DOCUMENT SOURCE

81       This  manual  page was generated by the Netpbm tool 'makeman' from HTML
82       source.  The master documentation is at
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84              http://netpbm.sourceforge.net/doc/pamdepth.html
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86netpbm documentation            26 August 2020         Pamdepth User Manual(0)
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