libvips/man/im_lab_morph.3

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2007-08-29 18:23:50 +02:00
.TH IM_LAB_MORPH 3 "8 March 2001"
.SH NAME
im_lab_morph \- calculate colour differences
.SH SYNOPSIS
#include <vips/vips.h>
int im_lab_morph( IMAGE *in, IMAGE *out,
.br
DOUBLEMASK *mask,
.br
double L_offset, double L_scale,
.br
double a_scale, double b_scale )
.SH DESCRIPTION
This function tweaks the colour in an LAB image. It's useful for
making a 'tweaked' image for sending to a colour printer.
It performs three corrections: first, it straightens the neutral axis (this is
useful if your printer tends to tint shadows slightly red, for example); it
moves L* by adding an offset and then multiplying by a scale (useful if your
printer thinks in relative colorimetry, for example), and finally scales a*
and b* by a factor (useful if your printer desaturates to avoid gamut
clipping).
The neutral axis straightening is specified as a DOUBLEMASK containing L*, a*
and b* readings taken from a print of a neutral greyscale (one with a* and b*
zero). For example:
3 4
14.23 4.8 -3.95
18.74 2.76 -2.62
23.46 1.4 -1.95
27.53 1.76 -2.01
This is interpolated to make an a/b offset for each input value of L*. The top
and tail are interpolated towards [100,0,0] and [0,0,0]. Entries in the mask
can be in any order.
.SH RETURN VALUE
All functions return 0 on success and -1 on error.
.SH COPYRIGHT
National Gallery, 2001