Black Body Callibration

[davidvj (David Vincent-Jones)]

I notice that when color calibrating many of my daylight images (CAT-16) the result is shown as ‘black-body’. If I use a custom setting of ‘daylight’ on the image the resulting color temperature remains the same.

[Newerth (Jan Šmucr)]

Yes but at least in my experience, the tint of the black body calibration is a bit on the green side while daylight goes a bit more purple. There’s definitely a difference.

[davidvj (David Vincent-Jones)]

I guess my question really is … what is it in the processing prior to that point that swings the calibration to black-point rather than daylight?

[priort (Todd Prior)]

This in not black point… explained here…

Check the curve…

Introducing color calibration module (formerly known as channel mixer rgb)

[Screenshot_20201109_024706] TL; DR : this is a full rewrite in clean unbounded RGB of the channel mixer in darktable. The old one had some computational mistakes in it, plus clipped RGB at 100%. This also introduces much requested normalization options, that will keep the sum of parameters to 1, trying to preserve – rougly – luminance (actually, perceptual luminance is much more than a simple sum of R + G + B, since it depends on hue, but… TL; DR). Ok. But it’s named color calibration becaus…

Edit : Explained in and around here how CC behaves… “But… the temperature, which is actually called correlated color temperature (CCT), can be used to refer to an idealized light spectrum : the black body radiator heated at the CCT. That is, only illuminant which color is close enough to the parabola below, can be described by their CCT because the models linking spectrum to CCT hold:”