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 dou-
ble 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 cer-
tain types of corruptions and produces a valid Netpbm image that pre-
serves 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 common 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 indi-
cates 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
unreadable 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 ev-
ery 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
Common Options ⟨index.html#commonoptions⟩ ), pamfix recognizes the
following 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 max-
val 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 pam-
fixtrunc, which was new in Netpbm 10.38 (March 2007) and did only the
truncated 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)
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