Manual: pamfix

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 contain 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 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 interrupted the program that generated it before
       it was finished writing the file.  For example, the program ran out of its own input or encountered 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 sequentially  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 con‐
       taining 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  Common Options ),
       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 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 pamfixtrunc, 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)