| .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 |
| |
