No behavior change.
(Well, technically mix() uses the other simple implementation of lerp
and the two have slightly different behavior if the arguments are of
very different magnitude and in various corner cases. But in practice,
for ICC profiles, it shouldn't matter. For a few profiles I tested, it
didn't have a measurable effect.)
The values aren't 100% self-consistent, but it probably doesn't make
a difference for u8 color data. Good enough for now. See all the links
on #17714 for some more background.
This might be useful for converting data from arbitrary profiles to
sRGB.
For now, this only encodes the transfer function and puts in zero values
for chromaticities, whitepoint, and chromatic adaptation matrix.
This makes the profile unusable for now. But I've spent a very long time
reading things and need to check in some code, and it's some progress.
The encoded transfer function exactly matches the one in GIMP's built-in
sRGB ICC profile (but not the Compact-ICC-Profiles v4 one or the
RawTherapee v4 one -- I'll add a comment about why later.)
We could make UnknownTagData hold on to undecoded, raw input data and
write that back out when serializing. But for now, we don't.
On the flipside, this _does_ write unknown tags that have known types.
We could have a mode where we drop unknown tags with known types.
But for now, we don't have that either.
With this, we can for example reencode
/Library/ColorSync/Profiles/WebSafeColors.icc and icc (and other
tools) can dump the output icc file. The 'ncpi' tag with type 'ncpi'
is dropped while writing it, while the unknown tag 'dscm' with
known type 'mluc' is written to the output. (That file is a v2 file,
so 'desc' has to have type 'desc' instead of type 'mluc' which
it would have in v4 files -- 'dscm' emulates an 'mluc' description
in v2 files.)
It only implements serialization of the 7-bit ASCII string, not yet
serialization of the UCS-2 and Macintosh ScriptCode strings.
With this, matrix-based v2 profiles can be reencoded :^)
With this, common v4 profiles, such as embedded into jpgs by iPhones
(when configured to write jpegs) or Pixel phones, are identical to
the input when reexported :^)
With this, simple v4 matrix profiles using parametric curves, such as
Compact-ICC-Profiles/profiles/sRGB-v4.icc, can be completely serialized
and the serialized file can be read again by `icc` :^)
