NAME

       pbm - Netpbm bi-level image format

DESCRIPTION

       This program is part of Netpbm(1).

       The  PBM  format is a lowest common denominator monochrome file format.  It serves as the common language
       of a large family of bitmap image conversion filters.  Because the format pays no heed to efficiency,  it
       is  simple  and general enough that one can easily develop programs to convert to and from just about any
       other graphics format, or to manipulate the image.

       The name "PBM" is an acronym derived from "Portable Bit Map."

       This is not a format that one would normally use to store a file or to transmit it to someone -- it's too
       expensive and not expressive enough for that.  It's just an intermediary format.  In it's purest use,  it
       lives only in a pipe between two other programs.

THE LAYOUT

       The format definition is as follows.

       A  PBM  file  consists of a sequence of one or more PBM images. There are no data, delimiters, or padding
       before, after, or between images.

       Each PBM image consists of the following:

       •      A "magic number" for identifying the file type.  A pbm image's magic number is the two  characters
              "P4".

       •      Whitespace (blanks, TABs, CRs, LFs).

       •      The width in pixels of the image, formatted as ASCII characters in decimal.

       •      Whitespace.

       •      The height in pixels of the image, again in ASCII decimal.

       •      A single whitespace character (usually a newline).

       •      A raster of Height rows, in order from top to bottom.  Each row is Width bits, packed 8 to a byte,
              with  don't  care  bits  to  fill out the last byte in the row.  Each bit represents a pixel: 1 is
              black, 0 is white.  The order of the pixels is left to right.  The order of their  storage  within
              each  file  byte is most significant bit to least significant bit.  The order of the file bytes is
              from the beginning of the file toward the end of the file.

              A row of an image is horizontal.  A column is vertical.  The pixels in the image  are  square  and
              contiguous.

       •      Before  the  whitespace  character  that delimits the raster, any characters from a "#" to but not
              including the next carriage return or newline character, or end of  file,  is  a  comment  and  is
              ignored.

              (Before June 2024, the carriage return or line feed was specified to be
                part of the comment and ignored, but in the 22 years that comments had
                existed in the specification, Netpbm never implemented that).

       All characters referred to herein are encoded in ASCII.  "newline" refers to the character known in ASCII
       as  Line  Feed  or  LF.   A  "white space" character is space, CR, LF, TAB, VT, or FF (I.e. what the ANSI
       standard C isspace() function calls white space).

   Plain PBM
       There is actually another version of the PBM format, even more  simplistic,  more  lavishly  wasteful  of
       space  than  PBM,  called Plain PBM.  Plain PBM actually came first, but even its inventor couldn't stand
       its recklessly squanderous use of resources after a while and switched to what we now know as the regular
       PBM format.  But Plain PBM is so redundant -- so overstated -- that it's virtually impossible  to  break.
       You  can  send it through the most liberal mail system (which was the original purpose of the PBM format)
       and it will arrive still readable.  You can flip a dozen random bits and easily piece back  together  the
       original image.  And we hardly need to define the format here, because you can decode it by inspection.

       Netpbm  programs  generate  Raw PBM format instead of Plain PBM by default, but the common option  -plain
       chooses Plain PBM.

       The difference is:

       •      There is exactly one image in a file.

       •      The "magic number" is "P1" instead of "P4".

       •      Each pixel in the raster is represented by a byte containing ASCII '1' or '0', representing  black
              and white respectively.  There are no fill bits at the end of a row.

       •      White space in the raster section is ignored.

       •      You can put any junk you want after the raster, if it starts with a white space character.

       •      No line should be longer than 70 characters.

              Here is an example of a small image in the plain PBM format.
              P1
              # feep.pbm
              24 7
              0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
              0 1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 1 0
              0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 1 0
              0 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 1 0
              0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0
              0 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 1 0 0 1 0 0 0 0
              0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

       There is a newline character at the end of each of these lines.

       You can generate the Plain PBM format from the regular PBM format (first image in the file only) with the
       pnmtoplainpnm program.

       Programs  that  read this format should be as lenient as possible, accepting anything that looks remotely
       like a bitmap.

INTERNET MEDIA TYPE

       No Internet Media Type (aka MIME type, content type) for PBM has been registered with IANA, but the value
       image/x-portable-bitmap is conventional.

       Note that the PNM Internet Media Type image/x-portable-anymap also applies.

FILE NAME

       There are no requirements on the name of a PBM file, but the convention is  to  use  the  suffix  ".pbm".
       "pnm"  is  also  conventional, for cases where distinguishing between the particular subformats of PNM is
       not convenient.

COMPATIBILITY

       Before July 2000, there could be at most one image in a PBM file.  As a result, most tools to process PBM
       files ignore (and don't read) any data after the first image.

SEE ALSO

       libnetpbm(1), pnm(1), pgm(1), ppm(1), pam(1), programs that process PBM(1)

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/pbm.html

netpbm documentation                              27 June 2024                                 The PBM Format(5)