.TH NPNG 1
.SH NAME
npng \- view PNG pictures
.SH SYNOPSIS
.B npng
[
.B -39cdknvt [-a α-val]
] [
.I PNG-file ...
]
.br
.SH DESCRIPTION
This program reads and displays image files in PNG format.
.IR Npng
reads files and, by default, displays
them in the current window; options cause it instead to convert the images
to Plan 9 image format and write them to standard output.
.PP
The default behavior of
.IR npng
is to display the
.IR file ,
or standard input if no file is named.
Once a file is displayed, typing a character causes the program to display the next image.
Typing a
.BR q ,
DEL, or control-D exits the program.
For a more user-friendly interface, pipe the output of the
.IR -9
option to
.IR page (1),
which will display it and will offer scrolling, panning, and other useful image manipulation
operations.
.PP
These are the options:
.TP
.B -a α-val
Force the alpha (transparency) channel to the given value.  If no alpha channel is present, it is added.
.TP
.B -n
This is mutually exclusive with option
.BR -a
above and causes an existing alpha channel to be completely removed from the image.
.TP
.B -k
Convert and display the image as a black and white (really grey-scale) image.
.TP
.B -t
Convert the image, if it is in color, to a true color RGB image.
.TP
.B -3
Like
.BR -t ,
but force the image to RGB even if it is originally grey-scale.
.TP
.B -v
Convert an image to RGBV based on the Plan 9 system palette.
.TP
.B -d
Suppress display of the image; this is set automatically by
any of the following options:
.TP
.B -c
Convert the image to a Plan 9 representation, as defined by
.IR image (6),
and write it to standard output.
.TP
.B -9
Like
.BR -c ,
but produce an uncompressed image.
This saves processing time, particularly when the output is
being piped to another program such as
.IR page (1),
since it avoids compression and decompression.
.PD
.PP
.SH SOURCE
.B /sys/src/pub/npng.c
.SH "SEE ALSO"
.IR jpg (1),
.IR page (1),
.IR image (6).
.SH BUGS
The
.BR -D
option can be used to obtain debugging information as processing takes place.
.PP
The
.BR -t
option is the default.
.PP
.IR Npng
is a rehash of
.IR png(1)
as distributed with the Plan 9 release.  It has been modified to
operate with the Open Source
.IR libpng
and
.IR zlib
libraries and may be subject to various licence restrictions.  Any
errors in the implementation are the responsibility of the author:
<lucio@proxima.alt.za>.