1Pamfix User Manual(0)                                    Pamfix User Manual(0)
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NAME

6       pamfix - repair a Netpbm image with various corruptions
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SYNOPSIS

10       pamfix
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12       [-truncate] [-changemaxval] [-clip] [-verbose]
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14       [netpbmfile]
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16       Minimum  unique abbreviation of option is acceptable.  You may use dou‐
17       ble hyphens instead of single hyphen to denote options.   You  may  use
18       white space in place of the equals sign to separate an option name from
19       its value.
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DESCRIPTION

24       This program is part of Netpbm(1).
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26       pamfix reads a stream that is mostly a Netpbm image but may  have  cer‐
27       tain  types  of corruptions and produces a valid Netpbm image that pre‐
28       serves much of the information in the original.
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30       In particular, Netpbm salvages streams that are truncated and that con‐
31       tain illegally large sample values.
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33       pamfix looks at only on the first image in a multi-image stream.
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37   Truncated stream
38       This  is  a stream that is missing the last part.  Netpbm corrects this
39       by creating an output image that simply has fewer rows.
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41       You select this kind of repair with a -truncate option.
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43       The header of a Netpbm image implies how large the image must  be  (how
44       many  bytes  the  file  must contain).  If the file is actually smaller
45       than that, a Netpbm program that tries to read the image fails, with an
46       error  message  telling  you that it couldn't read the whole file.  The
47       data in the file is arranged in row order, from top to bottom, and  the
48       most  common  reason for the file being smaller than its header says it
49       should be is because the bottommost rows are simply missing.  So pamfix
50       assumes  that  is the case and generates a new image with just the rows
51       that are readable.  (technically, that means the output's header  indi‐
52       cates a smaller number of rows and omits any partial last row).
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54       The  most  common  way  for a Netpbm file to be small is that something
55       interrupted the program that generated it before it was finished  writ‐
56       ing  the  file.   For  example, the program ran out of its own input or
57       encountered a bug or ran out of space in which to write the output.
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59       Another problem pamfix deals with is where the file isn't actually  too
60       small, but because of a system error, a byte in the middle of it cannot
61       be read (think of a disk storage  failure).   pamfix  reads  the  input
62       sequentially  until  it  can't read any further, for any reason.  So it
63       treats such an image as a truncated one, ignoring all  data  after  the
64       unreadable byte.
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66       But be aware that an image file is sometimes too small because of a bug
67       in the program that generated it, and in that case it is not  simply  a
68       matter  of  the bottom of the image missing, so pamfix simply creates a
69       valid Netpbm image containing a garbage picture.
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71       If you want to test an image file to see if it is  corrupted  by  being
72       too small, use pamfile --allimages .  It fails with an error message if
73       the file is too small.
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75       If you want to cut the bottom off a valid Netpbm image, use pamcut.
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79   Excessive Sample Value
80       This is a stream that contains a purported sample value that is  higher
81       than the maxval of the image.
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83       The  header of a Netpbm image tells the maxval of the image, which is a
84       value that gives meaning to all the sample values in the  raster.   The
85       sample  values  represent  a  fraction of the maxval, so a sample value
86       that is greater than the maxval makes no sense.
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88       A regular Netpbm program fails if you give it  input  that  contains  a
89       value larger than the maxval where a sample value belongs.
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91       pamfix has three ways of salvaging such a stream:
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95       ·      Clip to the maxval.  Request this with -clip.
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97       ·      Raise  the  maxval,  thus  lowering  the fraction represented by
98              every sample in the image.  Request this with -changemaxval.
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100       ·      Truncate the image at the first invalid sample  value.   Request
101              this with -truncate and neither -clip nor -changemaxval.
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104       You cannot specify both -clip and -changemaxval.
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SEE ALSO

109       pnm(1), pam(1), pamcut(1), pamfile(1),
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HISTORY

113       pamfix  was  new in Netpbm 10.66 (March 2014).  But it grew out of pam‐
114       fixtrunc, which was new in Netpbm 10.38 (March 2007) and did  only  the
115       truncated image repair (and for invalid sample values would simply pass
116       them through to its output, generating an invalid Netpbm image).
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DOCUMENT SOURCE

119       This manual page was generated by the Netpbm tool 'makeman'  from  HTML
120       source.  The master documentation is at
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122              http://netpbm.sourceforge.net/doc/pamfix.html
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124netpbm documentation             06 March 2014           Pamfix User Manual(0)