pnmtopng(1) pnmtopng(1)
6 January 1997
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
Allows to make one particular color fully transparent. 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
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pnmtopng(1) pnmtopng(1)
6 January 1997
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,
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.
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pnmtopng(1) pnmtopng(1)
6 January 1997
-time yy-mm-dd hh:mm:ss or -time yyyy-mm-dd
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.
- 3 - Formatted: April 18, 2024
