This is a very new tag used for HDR content. The only files I know that
use it are the jpegs on https://ccameron-chromium.github.io/hdr-jpeg/
But they have an invalid ICC creation date, so `icc` can't process them.
(Commenting out the check for that does allow to print them.)
If the CIPC tag is present, it takes precedence about the actual data
in the profile and from what I understand, the ICC profile is
basically ignored. See https://www.color.org/events/HDR_experts.xalter
for background, in particular
https://www.color.org/hdr/02-Luke_Wallis.pdf (but the other talks
are very interesting too).
(PNG also has a cICP chunk that's supposed to take precedence over
iCCP.)
This isn't used by any mandatory tags, and it's not terribly useful.
But jpegs exported by Lightroom Classic write the 'tech' tag, and
it seems nice to be able to dump its contents.
signatureType stores a single u32 which for different tags with this
type means different things.
In each case, the value is one from a short table of valid values,
suggesting this should be a per-tag enum class instead of a
per-tag DistinctFourCC, per the comment at the top of DistincFourCC.h.
On the other hand, 3 of the 4 tables have an explicit "It is possible
that the ICC will define other signature values in the future" note,
which suggests the FourCC might actually be the way to go.
For now, just punt on that and manually dump the u32 in fourcc style
in icc.cpp and don't add any to_string() methods that return a readable
string based on the contents of these tables.
This is the type of namedColor2Tag, which is a required tag in
NamedColor profiles.
The implementation is pretty basic for now and only exposes the
numbers stored in the file directly (after endian conversion).
s15Fixed16Number and XYZNumber are somewhat awkwardly duplicated
in both Profile.cpp and TagTypes.cpp. Other than that, this is a
pure code move.
No behavior change.
The spec names are still a bit cryptic ("deviceMfgDescTag"
for "device manufacturer description"), but less cryptic than
just the fourcc.
There's a private tag area, so this will only print the spec name
of tags in the current spec. Private tags are in active use, e.g.:
$ icc /Library/ColorSync/Profiles/WebSafeColors.icc
...
Unknown tag ('dscm'): type 'mluc', offset 312, size 1490
(That's a v2 file. In v2, 'desc' has that strange textDescriptionType.
In v4, 'desc' has type 'mluc' -- but in v2, it didn't yet, so Apple
invented the private 'dscm' tag which has the description as an 'mluc'.)
When several tags refer to the same TagData object, we now only print
it the first time, and print "(see 'foob' above)" the following times,
where `foob` is the tag identifier where we printed it the first time.
This is used in v2 profiles for the required 'desc' tag. In v2
profiles, it's also used by the 'dmnd', 'dmdd', 'scrd', 'vued' tags.
In v4 profiles, these all use 'mluc' instead (except for 'scrd', which
is no longer part of the spec in v4).
The idea is that we'll have one type for each tag type.
For now, this treats all tag types as unknown, but it puts most
of the infrastructure for reading tags in place.
This trims the input bytes to the profile size stored in the file.
Alternatively, we could reject files where the stored size doesn't
match the handed in size. But ICC profiles can be embedded in other
files, and those could conceivably pad the ICC profile data some.
There's a small, old-timey list of platforms in the spec, but as far
as I can tell nobody is using additional platforms on Linux or Android
or what. So let's try going with an enum class instead of the FourCC
machinery for now.
Namely:
- preferred CMM type
- device manufacturer
- device model
- profile creator
These all have in common that they can take arbitrary values, so I added
a FourCC class to deal with them, instead of using an enum class.
I made distinct types for each of them, so that they aren't accidentally
mixed up.
These flags are always 0 in practice in all profiles I've seen so far,
but hey, probably nice to dump them anyways.
And hey, it's just 86 lines to print 4 bits.
Always computing computing the md5 takes some time, but most
icc profiles are small. So that's probably fine.
If this ends up being a perf problem in the future, or if it ends up
rejecting tons of embedded proiles from images, we can row it back.
But let's see if we can get away with this first.
This is a bit messy: The spec says that PCSXYZ and PCSLAB are the only
valid profile connection spaces -- except for DeviceLink profles, where
all data color spaces are valid.
So this uses the existing ColorSpace enum for profile connection spaces
instead of adding a dedicated enum, to not duplicate all the color space
parsing and printing code. That matches what the spec does, too.
This saves about 100 lines of code, at the expense of less type
safety -- but further down the line we probably want to be able to
compare data color spaces and profile connection spaces, so the type
safety would likely get in the way then. (But if not, we can change
things around once we get to that point.)
