pngtopnm(1)pngtopnm(1)NAMEpngtopnm - convert a Portable Network Graphics file into a
portable anymap
SYNOPSISpngtopnm [-verbose] [-alpha | -mix] [-background color]
[-gamma value] [-text file] [-time] [pngfile]
DESCRIPTION
Reads a Portable Network Graphics as input. Produces a
portable anymap as output. The type of the output file
depends on the input file - if it's black & white, a pbm
file is written, else if it's grayscale a pgm file, else a
ppm file.
OPTIONS-verbose
Display the format of the input file and the type
of the output file. If the chunks are part of the
png-file, the alpha, transparency and gamma-values
will be indicated.
-alpha Output the alpha channel or transparency mask of
the image. The result is either a pbm file or pgm
file, depending on whether different levels of
transparency appear.
-mix Compose the image with the transparency or alpha
mask against a the background. When a background
chunk is available that color is taken, else black
will do.
-background color
If no background color chunck is present in the
png-file, or when another color is required this
parameter can be used to set the background color
of images. This is especially useful for alpha-
channel images or those with transparency chunks.
The format, to specify the color in, is either (in
the case of orange) "1.0,0.5,0.0", where the values
are floats between zero and one, or with the syntax
"#RGB", "#RRGGBB" or "#RRRRGGGGBBBB" where R, G and
B are hexa-decimal numbers.
-gamma value
Converts the image to a new display-gamma value.
When a gAMA chunk is present in the png-file, the
image-gamma value will be used. When not, the
image-gamma is considered to be 1.0. Based on the
image-gamma and the display-gamma given with this
option the colors written to the pnm-file will be
adjusted.
Because the gamma's 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 pic
ture 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 pic
ture darker.
-text file
Writes the tEXt and zTXt chunks to a file, in a
format as described in the pnmtopng man-page.
These chunks contain text comments or annotations.
-time Prints the tIME chunk to stderr.
All flags can be abbreviated to their shortest unique pre
fix.
SEE ALSOpnmtopng(1), ptot(1), pnmgamma(1), pnm(5)NOTE
Instead of pngtopnm|pnmtoxxx, a specific converter should
be used, if available. E.g. ptot (PNG to TIFF conver
sion), etc.
BUGS
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 opti
mizing.
AUTHORS
Copyright (C) 1995-1997 by Alexander Lehmann
and Willem van Schaik.
6 January 1997 pngtopnm(1)
