pngtopnm [-verbose] [-alpha | -mix] [-background color]
[-gamma value] [-text file] [-time] [pngfile]
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.
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, trans-
parency 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.
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 for-
mat, 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.
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 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 man-page. These chunks contain text
comments or annotations.
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.
Copyright (C) 1995-1997 by Alexander Lehmann
and Willem van Schaik.
6 January 1997 pngtopnm(1)
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