pnmtopng - convert a portable anymap into a Portable Network
Graphics file
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]
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.
- -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.
Instead of 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.
The program could be much faster, with a bit of code
optimizing.
Copyright (C) 1995-1997 by Alexander Lehmann
and Willem van Schaik.