pnmtopng(1)
NAME
pnmtopng - convert a portable anymap into a Portable Net-
work Graphics file
SYNOPSIS
pnmtopng [-verbose] [-downscale] [-interlace] [-alpha
file]
[-transparent color] [-background color] [-gamma value]
[-hist] [-chroma wx wy rx ry gx gy bx by] [-phys x y unit]
[-text file] [-ztxt file] [-time [yy]yy-mm-dd hh:mm:ss]
[-filter type] [-compression level] [-force] [pnmfile]
DESCRIPTION
Reads a portable pixmap as input. Produces a Portable
Network Graphics file as output.
Color values in PNG files are either eight or sixteen bits
wide, so pnmtopng will automatically scale colors to have
a maxval of 255 or 65535. Grayscale files will be pro-
duced with bit depths 1, 2, 4, 8 or 16. An extra pnmdepth
step is not necessary.
OPTIONS
-verbose
Display the format of the output file.
-downscale
Enables scaling of maxvalues of more then 65535 to
16 bit. Since this means loss of image data, the
step is not performed by default.
-interlace
Creates an interlaced PNG file (Adam7).
-alpha file
The alpha channel of pixel (or image) specifies the
transparency of a pixel. To create this fourth
pixel value a separate .pbm- or .pgm-file is
needed. In this file black (0) stands for fully
transparant and white (1) will become opaque. The
sizes of both pbm/pgm/ppm-files must be the same.
If the information contained in the alpha mask can
also be represented as a transparency index, it
will be used, since this should result in a smaller
image file.
-transparent color
Allows to make one particular color fully transpar-
ent. The format to specify the color is either
(when for example 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.
-background color
To create a background color chunck in the png-
file, which can be used for subsequent alpha-chan-
nel or transparent-color conversions. See -trans-
parent for format of color.
-gamma value
Creates an gAMA chunk. By providing the gamma-value
of the pnm-file the software that lateron will dis-
play the png-file will be able to do the necessary
gamma-corrections. A good rule-of-thumb is that
when the file is created by a software program
(like a CAD-program or a ray-tracer) the value is
probably 1.0. When the pnm-file looks good on a
non-gamma corrected PC display (which has itself a
gamma-value of 2.2 - 2.8), a value of 0.45 should
be given.
-hist Use this parameter to create a chunk that specifies
the frequency (or histogram) of the colors in the
image.
-chroma white point X and Y, red X and Y, green X and Y,
and blue X and Y
To specify the white point and rgb values following
the CIE-1931 spec.
-phys x y unit
When your image should not be displayed with square
but with rectangular pixels this option should be
used to create a pHYS chunk. When the unit-value is
0 the x and y only gives the ratio of pixel width
and height. When it is 1 the x and y specify the
number of pixels per meter.
-text file
Allows to include comments in the text-chunk of the
png-file. The format of the text-file is as fol-
lows: when the first column does not contain a
blank or a tab, the first word is considered to be
the keyword. For keywords to contain spaces,
enclose them in double-quotes.
When the first character on a line is a blank or
tab, the rest of the line is a new line of the cur-
rent comment. Note that the initial spaces are not
considered to be part of the comment line.
Here is an example:
-------------------------------------------
Title PNG-file
Author your name
Description how to include a text-chunk
into a PNG file
"Creation date" 3-feb-1987
Software pnmtopng
-------------------------------------------
-ztxt file
The same as -text, but now the text will be com-
pressed.
-time yy-mm-dd hh:mm:ss or -time yyyy-mm-dd hh:mm:ss
This option allows you to specify the (modifica-
tion)time. The year parameter can be given as a
two- or a four-digit value.
-filter type
When the types of filters must be restricted you
can specify here which filter you want to use.
Allowed values are: 0 (none), 1 (sub), 2 (up), 3
(avg) and 4 (paeth).
-compression level
To explicitly set the compression level of zlib use
this parameter. Select a level between 0 for no
compression (max speed) and 9 for maximum compres-
sion.
-force When set, -force limits the optimizations of pnm-
topng. A png-file similar to the pnm-input is as
much as possible enforced. For example no paletted
files will be created and alpha-channel images will
not be converted to images with a transparency
chunck.
All flags can be abbreviated to their shortest unique pre-
fix.
SEE ALSO
pngtopnm(1) gif2png(1) pnmgamma(1) pnm(5)
NOTE
Instead of xxxtopnm|pnmtopng, a specific converter should
be used, if available. E.g. gif2png (GIF conversion),
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.