convert a portable anymap into a Portable Network Graphics
[-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]
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.
Display the format of the
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.
Creates an interlaced PNG 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.
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.
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
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.
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
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
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.
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
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
Here is an
Author your name
Description how to include a text-chunk
into a PNG file
"Creation date" 3-feb-1987
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.
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).
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
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
All flags can
be abbreviated to their shortest unique prefix.
gif2png(1), pnmgamma(1), pnm(5)
xxxtopnm|pnmtopng, a specific converter should be used, if
available. E.g. gif2png (GIF conversion), etc.
There could be
an option to read the comment text from pnm comments instead
of a separate file.
could be much faster, with a bit of code optimizing.
1995-1997 by Alexander Lehmann
and Willem van Schaik.