libvips/man/im_invertlut.3

42 lines
1.1 KiB
Groff

.TH IM_INVERTLUT 3 "June 2001"
.SH NAME
im_invertlut \- turn a set of greyscale measurements into a gamma-correcting
LUT
.SH SYNOPSIS
#include <vips/vips.h>
int
.br
im_invertlut( DOUBLEMASK *input, IMAGE *output, int lut_size )
.SH DESCRIPTION
Given a mask of target values and real values, generate a LUT which
will map reals to targets. Handy for linearising images from
measurements of a colour chart. All values in [0,1].
Extrapolate head and tail to 0 and 1.
Eg. input like:
4 3
0.1 0.2 0.3 0.1
0.2 0.4 0.4 0.2
0.7 0.5 0.6 0.3
means a patch with 10% reflectance produces an image with 20% in
channel 1, 30% in channel 2, and 10% in channel 3. A patch with 20%
reflectance makes an image with 40% red, 40% green and 20% blue, and so on.
Inputs don't need to be sorted (we do that). Generate any precision
LUT ... typically ask for 256 elements.
It won't work too well for non-monotonic camera responses (should fix this).
Interpolation is simple piecewise linear; ought to do something better really.
.SH RETURN VALUE
-1 on error, otherwise 0
.SH SEE ALSO
im_histgr(3), im_hsp(3), im_heq(3), im_identity(3).
.SH COPYRIGHT
2001, National Gallery