O
> The definitions in the article are sound.
>
Some, but not all. Like the bit about using data in the Saturation
intent
to make in-gamut colors more vivid. Sorry, but, that's not in the ICC
spec. So that part of the IBM definitions (which are specific for this
printer; you're not quoting from an ICC spec, you're quoting from a
specific IBM document for a specific printer with a specific profile
and a specific kind of printing configuration, i.e. CMYK laser).
> Maybe not how it is said in
> "inkjetspeak", but true to the concepts of rendering. FYI, here is
> how the
> International Color Consortium (for you plebes, that's what icc means)
> defines "Saturation Intent":
>
> "3.1.3 Saturation Intent
> The exact gamut mapping of the saturation intent is vendor specific
> and
> involves compromises such as trading off preservation of hue in
> order to
> preserve the vividness of pure colors. It is useful for images which
> contain
> objects such as charts or diagrams."
>
> Source:
> http://www.color.org/iccprofile.xalter
>
> I guess maybe they're still using that "same old line" as well.....
>
>
Only if you misread what the ICC has written. Let's parse it more
exactly...:-)
See where it says "vendor specific"?
That means: it's vendor specific; meaning, a vendor can decide to do
whatever
they want here, in order to "preserve the vividness of pure colors" by
using
"compromises such as the trading off of the preservation of hue".
Maybe this isn't clear enough, so (a bit peevishly...:-), but also in
good
humor, and with all due respect), I'll just point it out again.
Vendor-specific.
There is no "rule" in the ICC spec that suggests what may, or should, be
done here, or exactly how to go about accomplishing it by calculating
data and
putting it into the Saturation intent.
Vendor-specific.
Means: the vendor can be creative (or not); skillful (or not); put
whatever
data they feel is appropriate into the Saturation intent; to
accomplish the
general goal stated here: to preserve the vividness of pure colors.
(Pure
being taken to mean: highly saturated colors, and in particular, the
RGBCMY
primaries and the other colors that are near them as well).
Vendor-specific means: your mileage will vary, depending on the vendor
that
you're using to build your profiles. Like us...:-) Or "them", whoever
"them"
may be. (Epson, Canon, HP, and/or whatever other vendor-specific
software
is being used to build the profiles). The results are expected to vary
from
vendor to vendor, because all vendor profiling algorithms will be
different.
There's no inkjetspeak involved here. There is one nice, small,
cleanly-written
paragraph in the ICC spec that you've presented here and this is
exactly what
it says.
"The exact gamut mapping is vendor-specific",
and that means the exact methods used to map out-of-gamut colors for the
Saturation intent are based on the profiling algorithms of specific
vendors.
There is no rule or law about how the Saturation intent behaves; only
the
suggestion that the user will expect to get the best possible saturation
when they use it. (Not re-adjusted saturation for in-gamut colors; or
over-saturation, as much older ICC profiles produced with the Saturation
intent, years ago; just the best saturation for Pure colors)
***
That final line, about "useful for images which contain objects such
as charts
or diagrams" does NOT say that this technique should make the
Saturation intent
unfit for printing photographic images. It simply means that by mapping
out-of-gamut colors (which will tend to include the "Pure" colors that
are
typically used in charts and diagrams, for vividness and contrast) as
vividly
as possible, the Saturation intent can be particularly useful for
printing
images which contain highly saturated, out-of-gamut colors (while at
the same
time, it recognizes that from a technical standpoint, there may be a
trade-off
in preservation of hue for those out-of-gamut colors.)
You'll note that, unlike the IBM document that started this
discussion, there
is -no mention- in this paragraph from the ICC spec of any concept of
changing
the mapping of IN-GAMUT colors to also make them more vivid, which is
where I
really started to take objection to the IBM document.
***
Conclusion:
The Saturation intent data is vendor-specific, meaning: different
vendors
can choose to implement this any way they like.
The overall concept of the Saturation intent is to produce the most
vivid
colors in the print for out-of-gamut colors.
The ICC spec has no suggestions or requirements to make adjustments to
in-gamut
colors for the Saturation intent.
The Saturation intent will give you the most saturated colors in your
print, if you just so happen to be printing things like charts and
diagrams which contain "pure" colors.
For in-gamut colors, the data in our Saturation intent is perfectly
appropriate for making photographic prints as well.
David Miller
Senior Software Developer, Digital Color Solutions
Datacolor