1IM_LAB_MORPH(3)            Library Functions Manual            IM_LAB_MORPH(3)
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NAME

6       im_lab_morph - calculate colour differences
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SYNOPSIS

9       #include <vips/vips.h>
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11       int im_lab_morph( IMAGE *in, IMAGE *out,
12         DOUBLEMASK *mask,
13         double L_offset, double L_scale,
14         double a_scale, double b_scale )
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DESCRIPTION

18       This function tweaks the colour in an LAB image. It's useful for making
19       a 'tweaked' image for sending to a colour printer.
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21       It performs three corrections: first, it straightens the  neutral  axis
22       (this is useful if your printer tends to tint shadows slightly red, for
23       example); it moves L* by adding an offset and  then  multiplying  by  a
24       scale (useful if your printer thinks in relative colorimetry, for exam‐
25       ple), and finally scales a* and b* by a factor (useful if your  printer
26       desaturates to avoid gamut clipping).
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28       The  neutral axis straightening is specified as a DOUBLEMASK containing
29       L*, a* and b* readings taken from a print of a neutral  greyscale  (one
30       with a* and b* zero). For example:
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32                 3 4
33                 14.23   4.8     -3.95
34                 18.74   2.76    -2.62
35                 23.46   1.4     -1.95
36                 27.53   1.76    -2.01
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38       This  is interpolated to make an a/b offset for each input value of L*.
39       The top and  tail  are  interpolated  towards  [100,0,0]  and  [0,0,0].
40       Entries in the mask can be in any order.
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RETURN VALUE

44       All functions return 0 on success and -1 on error.
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47       National Gallery, 2001
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52                                 8 March 2001                  IM_LAB_MORPH(3)
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