Manual: pamdepth

Pamdepth User Manual(1)				   General Commands Manual			     Pamdepth User Manual(1)

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 im‐
       age.  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 pro‐
       grams 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 com‐
       patible with pnmdepth and adds the ability to process arbitrary PAM images and the ability to process multi-image in‐
       put 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)