Leandro Ribeiro authored Mar 18, 2024 and Pekka Paalanen committed Mar 26, 2024

Until now, all the curves would be represented with 3x1D LUT's. Now we
support LINPOW and POWLIN curves (arbitrary names that we've picked).
We can use these curves to represent LittleCMS curves type 1, 4 and
their inverses -1, -4. The reason why we want that is because we gain
precision using the parametric curves (compared to the LUT's);

Surprisingly we had to increase the tolerance of the sRGB->adobeRGB MAT
test. Our analysis is that the inverse EOTF power-law curve with
exponent 1.0 / 2.2 amplifies errors more than the LUT, specially for
input (optical) values closer to zero.

That makes sense, because this curve is more sensible to input values
closer to zero (i.e. little input variation results in lots of output
variation). And this model makes sense, as humans are more capable of
perceiving changes of light intensity in the dark.

But the downside of all that is that for input values closer to zero, a
little bit of noise increases significantly the error.

Signed-off-by: Leandro Ribeiro <leandro.ribeiro@collabora.com>