Pamfix User Manual(1) General Commands Manual Pamfix User Manual(1)
NAME
pamfix - repair a Netpbm image with various corruptions
SYNOPSIS
pamfix
[-truncate] [-changemaxval] [-clip] [-verbose]
[netpbmfile]
Minimum unique abbreviation of option is acceptable. You may use double
hyphens instead of single hyphen to denote options. You may use white
space in place of the equals sign to separate an option name from its
value.
DESCRIPTION
This program is part of Netpbm(1).
pamfix reads a stream that is mostly a Netpbm image but may have certain
types of corruptions and produces a valid Netpbm image that preserves
much of the information in the original.
In particular, Netpbm salvages streams that are truncated and that con-
tain illegally large sample values.
pamfix looks at only on the first image in a multi-image stream.
Truncated Stream
This is a stream that is missing the last part. Netpbm corrects this by
creating an output image that simply has fewer rows.
You select this kind of repair with a -truncate option.
The header of a Netpbm image implies how large the image must be (how
many bytes the file must contain). If the file is actually smaller than
that, a Netpbm program that tries to read the image fails, with an error
message telling you that it couldn't read the whole file. The data in
the file is arranged in row order, from top to bottom, and the most com-
mon reason for the file being smaller than its header says it should be
is because the bottommost rows are simply missing. So pamfix assumes
that is the case and generates a new image with just the rows that are
readable. (technically, that means the output's header indicates a
smaller number of rows and omits any partial last row).
The most common way for a Netpbm file to be small is that something in-
terrupted the program that generated it before it was finished writing
the file. For example, the program ran out of its own input or encoun-
tered a bug or ran out of space in which to write the output.
Another problem pamfix deals with is where the file isn't actually too
small, but because of a system error, a byte in the middle of it cannot
be read (think of a disk storage failure). pamfix reads the input se-
quentially until it can't read any further, for any reason. So it
treats such an image as a truncated one, ignoring all data after the un-
readable byte.
But be aware that an image file is sometimes too small because of a bug
in the program that generated it, and in that case it is not simply a
matter of the bottom of the image missing, so pamfix simply creates a
valid Netpbm image containing a garbage picture.
If you want to test an image file to see if it is corrupted by being too
small, use pamfile --allimages . It fails with an error message if the
file is too small.
If you want to cut the bottom off a valid Netpbm image, use pamcut.
Excessive Sample Value
This is a stream that contains a purported sample value that is higher
than the maxval of the image.
The header of a Netpbm image tells the maxval of the image, which is a
value that gives meaning to all the sample values in the raster. The
sample values represent a fraction of the maxval, so a sample value that
is greater than the maxval makes no sense.
A regular Netpbm program fails if you give it input that contains a
value larger than the maxval where a sample value belongs.
pamfix has three ways of salvaging such a stream:
• Clip to the maxval. Request this with -clip.
• Raise the maxval, thus lowering the fraction represented by every
sample in the image. Request this with -changemaxval.
• Truncate the image at the first invalid sample value. Request
this with -truncate and neither -clip nor -changemaxval.
You cannot specify both -clip and -changemaxval.
OPTIONS
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see ]8;;index.html#commonoptions\ Common Options]8;;\ ), pamfix recognizes the fol-
lowing command line options:
-truncate
Create a truncated output image from all the valid input rows
that could be read.
-changemaxval
Raise the maxval to cope with pixel values that exceed the maxval
stated in the header of the input file.
-clip Change all pixel values that exceed the maxval stated in the
header of the input file.
-verbose
Report details of the transportation to standard error.
SEE ALSO
pnm(1), pam(1), pamcut(1), pamfile(1), pamvalidate(1)
HISTORY
pamfix was new in Netpbm 10.66 (March 2014). But it grew out of pamfix-
trunc, which was new in Netpbm 10.38 (March 2007) and did only the trun-
cated image repair (and for invalid sample values would simply pass them
through to its output, generating an invalid Netpbm image).
DOCUMENT SOURCE
This manual page was generated by the Netpbm tool 'makeman' from HTML
source. The master documentation is at
http://netpbm.sourceforge.net/doc/pamfix.html
netpbm documentation 06 March 2014 Pamfix User Manual(1)
Generated by dwww version 1.16 on Tue Dec 16 06:17:54 CET 2025.