NAME¶
pnmtopng - convert a portable anymap into a Portable Network 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 produced 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 present 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 distance 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 transparent. 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-channel or transparent-color
conversions. See -transparent for format of color.
- -gamma value
- Creates an gAMA chunk. By providing the gamma-value of the
pnm-file the software that lateron will display 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 follows: 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 current 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
compressed.
- -time yy-mm-dd hh:mm:ss or -time yyyy-mm-dd
hh:mm:ss
- This option allows you to specify the (modification)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 compression.
- -force
- When set, -force limits the optimizations of pnmtopng. 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 prefix.
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 optimizing.
AUTHORS¶
Copyright (C) 1995-1997 by Alexander Lehmann
and Willem van Schaik.