cineSpace

[Michael Chenery]

Recently I was asked about the slight saturation differences that could be seen when using equalEyes to match different types of devices. For example CRT vs LCD vs Projector vs Wide gamut displays.

The differences that are seen are a result of using a 1D LUT as opposed to
a 3D LUT. The reason for this is that a 1D LUT can only effect the mix of
the red, green and blue primaries of a device but not the actual colour of
the primaries. This means that a 1D LUT is able to give an excellent match
along the grey ramp (a mix of the primaries) but as colours become more
saturated the error between what is displayed and what should be displayed
increases.

For example if we have two monitors A and B.
Monitor A has a wide gamut with the R, G and B primaries being very spread out on a CIE xy chromaticity diagram.
Monitor B has a standard gamut with the R, G and B primaries close to the Rec709 (HD) primaries on a CIE xy chromaticity diagram.

If each device is profiled and equalEyes (or any type of 1D transform) is
used to calibrate the two monitors then both will give a well matched grey
ramp but Monitor A will appear more saturated, this effect will be more
obvious the more saturated the colours are in the image being viewed.

The only way to fix this is to use a 3D transform / LUT. A 3D LUT is able to
specify the colours of the primaries and so gives accurate colours and
saturation (within the limits of the gamut of each device).

Cheers,
Mike