Pngtopnm User Manual(0) Pngtopnm User Manual(0)
pngtopnm - convert a PNG image into a PNM image
pngtopnm [-verbose] [-alpha | -mix] [-background=color] [-gamma=value]
[-text=filename] [-time] [pngfile]
Minimum unique abbreviation of option is acceptable. You may use dou-
ble 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
This program is part of Netpbm(1).
pngtopnm reads a PNG image (Portable Network Graphics) as input and
produces a PPM image as output. The type of the output file depends on
the input file - if it’s black & white, pngtopnm creates a PBM file.
If it’s grayscale, pngtopnm creates a PGM file. Otherwise, it creates
a PPM file.
Display various information about the input PNG image and the
If you want even more information about the PNG image, use
pngcheck (not part of Netpbm).
-alpha Output the alpha channel or transparency mask of the image. The
result is either a PBM file or a PGM file, depending on whether
different levels of transparency appear.
-mix Compose the image with the transparency or alpha mask against a
background. The background color is determined by the bKGD
chunk in the PNG, except that you can override it with -back-
ground. If the PNG has no bKGD chunk and you don’t specify
-background, the background color is white.
This option specifies the background color with which to mix the
image when you specify -mix.
color is as described for the argument of the ppm_parsecolor()
library routine .
If you don’t specify -background, the background color is what
is specified in the PNG image, and if the PNG doesn’t specify
You cannot specify -background unless you also specify -mix.
Before Netpbm 10.27 (March 2005), you could specify -background
with -mix and it was just ignored. (This caused a usability
Converts the image to a new display-gamma value. If a gAMA
chunk is present in the png-file, pngtopnm uses the specified
image-gamma value. If not, pngtopnm considers the image-gamma
to be 1.0. Based on the image-gamma and the display-gamma given
with this option, pngtopnm adjusts the colors written to the
Because the gammas of uncompensated monitors are around 2.6,
which results in an image-gamma of 0.45, some typical situations
are: when the image-gamma is 0.45 (use -verbose to check) and
the picture is too light, your system is gamma-corrected, so
convert with ’-gamma 1.0’. When no gAMA chunk is present or the
image-gamma is 1.0, use 2.2 to make the picture lighter and 0.45
to make the picture darker.
Writes the tEXt and zTXt chunks to a file, in a format as
described in the pnmtopng user manual. These chunks contain
text comments or annotations.
-time Prints the tIME chunk to stderr.
pnmtopng(1), ptot, pnmgamma(1), pnm(1)
For information on the PNG format, see http://schaik.com/png .
A PNG image contains a lot of information that can’t be represented in
Netpbm formats. Therefore, you lose information when you convert to
another format with "pngtopnm | pnmtoxxx". If there is a specialized
converter that converts directly to the other format, e.g. ptot to con-
vert from PNG to TIFF, you’ll get better results using that.
There could be an option to read the comment text from pnm comments
instead of a separate file.
The program could be much faster, with a bit of code optimizing. As
with any Netpbm program, speed always takes a back seat to quick
present and future development.
Copyright (C) 1995-1997 by Alexander Lehmann and Willem van Schaik.
netpbm documentation 24 March 2005 Pngtopnm User Manual(0)
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