.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
.I lo,
and
.I inhi
to
.I 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
.I 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
.I hi,
or that
.I inlo
be smaller than
.I 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 "SEE ALSO
.IR picfile (9.6)