pnmtopng(1)pnmtopng(1)NAMEpnmtopng - convert a portable anymap into a Portable Net
work Graphics file
SYNOPSISpnmtopng [-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
ppmtogif marks the specified color as transparent
in the PNG image.
You specify the color as in ppmmake(1).E.g. red or
rgb:ff/00/0d. If the color you specify is not pre
sent in the image, pnmtopnm selects instead the
color in the image that is closest to the one you
specify. Closeness is measured as a cartesian dis
tance between colors in RGB space. If multiple
colors are equidistant, pnmtopnm chooses one of
them arbitrarily.
However, if you prefix your color specification
with "=", e.g.
-transparent =red
Only the exact color you specify will be transpar
ent. If that color does not appear in the image,
there will be no transparency. pnmtopng issues an
information message when this is the case.
-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 ALSOpngtopnm(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.
6 January 1997 pnmtopng(1)
