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pngtopnm - convert a Portable Network Graphics file into a portable
anymap
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.
- -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 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.
- -text file
- Writes the tEXt and zTXt chunks to a
file, in a format as described in the pnmtopng man-page.
- -time
- Prints the
tIME chunk to stderr.
All flags can be abbreviated to their shortest unique
prefix.
pnmtopng(1)
, ptot(1)
, pnmgamma(1)
, pnm(5)
Instead of
pngtopnm|pnmtoxxx, a specific converter should be used, if available. E.g.
ptot (PNG to TIFF conversion), etc.
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.
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