this is a unified module to handle important things concerning colour. the input is in camera rgb and the output will be rec2020.
it supports two modes of operation: using 3x3 colour matrices and profiles
created from spectral response curves of the cameras colour filter array (CFA).
to use such a profile, first create one for your camera using the profiling
toolchain. then set the matrix parameter to clut.
to route the profile data to the input here, there is a clut.pst preset.
the second, more simplistic mode of operation applies a 3x3 matrix. this kind of input transform is known to be imprecise especially for saturated colours and produce all kinds of artifacts (say way out of gamut dark blue tones).
to fine tune calibration or for artistic purposes, this module comes with a corrective radial basis function (RBF) applied after white balance and matrix (or clut). it allows to map arbitrary source to target points in 3d rec2020 colour space.
this mechanism be used to calibrate the input colour against a measured test chart (for instance a ColorChecker24), or for artistic colour manipulation.
you can directly change the target values and source values of each data point.
these can also be filled using the colour picker (using the import button) and from a
preset (see the ColorChecker.pst preset for the 24 ColorChecker patches).or, of
course, by editing the .cfg file by hand, the rbmap parameter is a series
of src r:src g:src b:tgt r:tgt g:tgt b elements, the number of source and
target pairs is given by the cnt parameter.
white balancing (using CAT16) will adjust rec2020 D65 white to the colour
represented by the three white sliders. to input alternative source colours
instead of D65, connect the picked input from an instance of a colour picker
module, operating on the input to this colour module. the
picked patch will be used as source colour and white balancing will be adjusted
such that it will match the destination colour defined by the sliders. in
conjunction with skin tone presets (cf. colour-monk-[0-9].pst), this is
useful to match skin rendition precisely in difficult lighting situations.
to pick a neutral spot, you can use the pick-neutral.pst preset.
the gamut parameter employs a few lookup tables to
work. in particular the optional inputs abney and spectra have to be
connected. you can easily do this by applying the gamut.pst
preset (press ctrl-p and start to type gamut.pst until it shows as the
first entry in the list, then press enter).
once this is done, the parameter is closely intertwined with the sat control:
if gamut is set to unlimited, increasing chroma will quickly push colours
outside of the spectral locus, which can be observed by connecting an instance
of a ciediag module between this module and the hist
display for instance. limiting to spectral locus instead will only show an
effect if sat is increased, and never push colours off limits. the two other
options (rec2020 and rec709) first scale down all colours such that the
theoretical maximum (on the spectral locus boundary) will fit into the
respective colour space. sat can then be used to increase saturation again
from there, but will never produce values outside the respective tristimulus
gamut.
exposure linear light exposure correction in ev/stops.sat saturation control using dt UCS or the optional lookup tables if they are connected.mode switch the radial basis function (rbf) mapping on or off.
the rbf mode works on an aribtrary list of source and target points which
can be given in the parameters as source and target list of points.
this parameter runs a ui group, so it will show/hide a few other elements.gamut the gamut can be left untouched, projected to spectral locus, rec2020, or rec709.
works only if the abney and spectra inputs are connected.clip this is a last-resort brute force method to avoid pink highlights in case the highlight reconstruction
module does not produce satisfactory results. this can be the case if chromatic aberration or noise is
interpolated into the clipped region. clipping highlights here will simply set all channels to the minimum
clipping threshold, producing a neutral colour.clipmax 1.0 would be the ideal clipping thresholdpicked what to do with the picked input colour, if it is connected to the picked connector.
it can be used as source for white balancing and/or deflickering.matrix input device transform mode: use the image matrix or a selection of presets, or the colour lut.temp if a clut is used, this allows to blend between the two illuminants. usually this
is illuminant A and D65 and reflected in the values of the temperature here.white the white balance destination colour. 1 1 1 is D65. setting this to 0 0 0 (doubleclick to default) will try to load the camera white balance.mat a hidden parameter containing the coefficients of the image matrix.cnt the number of patches to use in the rbf mappingrbmap the patch source and destination coloursimport press this button to import source and destination colours from a
colour picker by the instance name as entered to the right. the picker should
be attached to the output of this module and you have to keep the saturation
slider at 1.0 when doing this. also set the number of patches in the rbf to zero.
reference numbers for the picker can be obtained by presets for your target (such as ColorChecker.pst).input the input colour buffer in camera rgboutput the output in rec2020 rgbclut (optional) the color lookup table generated by the mkclut utilitypicked (optional) route picked colour for white balancing source in hereabney (optional) point to data/abney.lut for hue constant saturation and gamut compression, see the gamut.pst presetspectra (optional) point to data/spectra.lut for hue constant saturation and gamut compression, see the gamut.pst preset