TH XPAND 9.1
SH NAME
xpand, picnegate \- adjust dynamic range
SH SYNOPSIS
B fb/xpand
[
B -s
] [
I input
] [
I lo hi
[
I inlo inhi
] ]
PP
B fb/picnegate
[
I input
]
SH DESCRIPTION
I Xpand
linearly adjusts the dynamic range of the
I input
picture (default standard input)
mapping value
I inlo
to
IR lo ,
and
I inhi
to
IR hi .
I Lo
and
I hi
default to 0 and 255.
If
I inlo
and
I inhi
are not specified, the lowest and highest pixel values in the input image are
used.
By default, then,
I xpand
expands the image's dynamic range by mapping its smallest pixel value to zero
and its largest value to 255.
Option
B -s
causes all channels of the input image to be considered together when computing
default values for
I inlo
and
IR inhi ,
thus preserving the hue of
B rgb
pictures.
Otherwise, each channel is treated separately.
Option
B -s
has no effect if
I inlo
and
I inhi
are specified on the command line.
PP
There is no requirement that
I lo
be smaller than
IR hi ,
or that
I inlo
be smaller than
IR inhi ,
nor that any of those values be in the range 0 to 255.
Output values not in the range 0 to 255 are clamped.
For example,
EX
       xpand 0 255 255 0
EE
inverts the pixel values of its input.
For convenience,
I picnegate
is a script that executes this command.
SH SOURCE
B /sys/src/fb/xpand.c
SH "SEE ALSO
IR picfile (9.6)

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