Re: [Lcms-user] Negative channel values are clipped upon floating point conversions to profiles with true gamma TRCs

[Graeme G. <gr...@ar...>]

Noel Carboni wrote:

> To us negative values can't possibly make sense.

Note that in some contexts they do. Viewed as a 3D space,
there are an infinite range of possible coordinates.

When transforming through different appearance spaces,
you can end up with intermediate values that are valid
(in the sense that they mean something) but that are
imaginary (they correspond to no realizable color).

If you are gamut mapping, then you would like even imaginary
values to be mapped in a way that preserves their fundamental
characteristics (hue, lightness, saturation) as much as
possible, as well as their relationships between each other.

Clipping -ve per component values is easy to implement, but
just like the whiter than the white point case, you can
end up with hue shifts and other undesirable changes to
the intended color.

Graeme Gill.