Plan 9 - man page for xpand (plan9 section 9)
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xpand, picnegate - adjust dynamic range
fb/xpand [ -s ] [ input ] [ lo hi [ inlo inhi ] ]
fb/picnegate [ input ]
Xpand linearly adjusts the dynamic range of the input picture (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 pre-
serving 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 exe-
cutes this command.
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