Section: User Commands (1)
Updated: 6 January 1997Index
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pnmtopng - convert a portable anymap into a Portable Network Graphics file
[-chroma wx wy rx ry gx gy bx by]
[-phys x y unit]
[-time [yy]yy-mm-dd hh:mm:ss]
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
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.
step is not necessary.
Display the format of the output file.
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 (Adam7).
- -alpha file
The alpha channel of pixel (or image) specifies the transparency of a pixel.
To create this fourth pixel value a separate
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
- -transparent color
marks the specified color as transparent in the PNG image.
You specify the color as in
If the color you specify is not present in the image,
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,
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.
issues an information message when this is the case.
- -background color
To create a background color chunck in the
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
the software that lateron will display the
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
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.
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
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
Here is an example:
Author your name
Description how to include a text-chunk
into a PNG file
"Creation date" 3-feb-1987
- -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.
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.
Instead of xxxtopnm|pnmtopng, a specific converter should be used, if
(GIF 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.
- SEE ALSO