im_lab_morph - calculate colour differences
int im_lab_morph( IMAGE *in, IMAGE *out,
double L_offset, double L_scale,
double a_scale, double b_scale )
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:
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.
All functions return 0 on success and -1 on error.
National Gallery, 2001
8 March 2001