XPAND(9.1) XPAND(9.1)
NAME
xpand, picnegate - adjust dynamic range
SYNOPSIS
fb/xpand [ -s ] [ input ] [ lo hi [ inlo inhi ] ]
fb/picnegate [ input ]
DESCRIPTION
Xpand linearly adjusts the dynamic range of the input pic-
ture (default standard input) mapping value inlo to lo, and
inhi to hi. Lo and hi default to 0 and 255. If inlo and
inhi are not specified, the lowest and highest pixel values
in the input image are used. By default, then, xpand
expands the image's dynamic range by mapping its smallest
pixel value to zero and its largest value to 255. Option -s
causes all channels of the input image to be considered
together when computing default values for inlo and inhi,
thus preserving the hue of rgb pictures. Otherwise, each
channel is treated separately. Option -s has no effect if
inlo and inhi are specified on the command line.
There is no requirement that lo be smaller than hi, or that
inlo be smaller than 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,
xpand 0 255 255 0
inverts the pixel values of its input. For convenience,
picnegate is a script that executes this command.
SOURCE
/sys/src/fb/xpand.c
SEE ALSO
picfile(9.6)
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