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 resolu-
tion), 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 in-
stance, 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-sam-
ple 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 in-
put 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, re-
spectively.
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
]8;;index.html#commonoptions\ Common Options]8;;\ .)
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)
Generated by dwww version 1.16 on Sun Dec 7 17:07:44 CET 2025.