NAME

       pamdepth - change the depth (color resolution) in a Netpbm image

SYNOPSIS

       pamdepth newmaxval [netpbmfile]

DESCRIPTION

       This program is part of Netpbm(1).

       pamdepth  reads  a  Netpbm  image  as  input,  changes  its  depth (color resolution), and writes out the
       resulting Netpbm image.  I.e. the output has a different maxval from the input, but all the  same  colors
       (apart from rounding error).

       Reducing the depth results in some loss of information.

       Here  is  an  example of the effect at the image format level: Assume you start with an image with maxval
       100 and sample values of 50 and 100.  You tell pamdepth to change it to depth 150.  The output has maxval
       200 and sample values 75 and 150.

       This program works on multi-image streams.

       Be careful of off-by-one errors when choosing the new maxval.  For instance, if you want the color values
       to be five bits wide, use a maxval of 31, not 32.

       One important use of pamdepth is to convert a new format 2-byte-per-sample PNM file to the older  1-byte-
       per-sample  format.   Before  April 2000, essentially all raw (binary) format PNM files had a maxval less
       than 256 and one byte per sample, and many programs may rely on that.  If you specify  a  newmaxval  less
       than  256,  the  resulting file should be readable by any program that worked with PNM files before April
       2000.

   Output Format
       The output format (PBM, etc.) and, in the case of PAM, tuple type, of the output is usually the  same  as
       the input.

       However,  changing  the  depth  of  a black and white image does not make sense, except to turn it into a
       grayscale image, so if the input is a black and white image, pamdepth makes the output grayscale.  To  be
       more  precise,  if the input is a PBM image, the output is PGM, and if the input is a PAM with tuple type
       BLACK_AND_WHITE  or  BLACK_AND_WHITE_ALPHA,  the  output  is  a  PAM  with  tuple   type   GRAYSCALE   or
       GRAYSCALE_ALPHA, respectively.

       This conversion happens even if the new maxval is 1.

       Before  Netpbm  10.92 (September 2020), pamdepth failed if the input was PAM with a black and white tuple
       type and the new maxval was anything but 1.  But it always promoted PBM to PGM.

OPTIONS

       There are no command line options defined specifically for pamdepth, but it recognizes the options common
       to all programs based on libnetpbm (See  Common Options .)

SEE ALSO

       pnm(1), pam(1), pnmquant(1), ppmdither(1) pambrighten(1) pamfunc(1)

HISTORY

       pamdepth was new in Netpbm 10.32 (February 2006).  It replaced pnmdepth, by Jef Poskanzer.   pamdepth  is
       backward compatible with pnmdepth and adds the ability to process arbitrary PAM images and the ability to
       process multi-image input streams.  pnmdepth handled only PNM images and ignored all but the first in any
       stream.

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/pamdepth.html

netpbm documentation                             26 August 2020                          Pamdepth User Manual(1)