pnmtopng(1) - man - phpMan

Che Dong

pnmtopng(1) General Commands Manual pnmtopng(1)

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 automati‐
cally 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 cre‐
ate 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 be‐
tween 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.

6 January 1997 pnmtopng(1)