pnmtopng(1) - phpMan

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 automat-
ically 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
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 im-
age 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 ap-
pear 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 subse-
quent 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-cor-
rections. A good rule-of-thumb is that when the file is created by a software pro-
gram (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 transpar-
ency 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)

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