>>Because their gamut and whitepoint already match your display device
a simple 1D transform will give you a viewable result.
<<[...]
>>And part of that is divorcing the primaries from either the input
device or output device.
Those were the bits that hadn't quite clicked yet, thanks Alex!
On 3/7/14, 5:51 AM, Alex Fry wrote:
The ACES values are scene linear.
The difference with scene linear files you would have previously been
working with, is that whilst they would have been scene linear in
their intensity, but their primaries are effectively display referred
(either Rec709 primaries or P3). Because their gamut and whitepoint
already match your display device a simple 1D transform will give you
a viewable result.
ACES stores values using the much wider primaries shown below, they
are wide enough that they cover all of the visible colours in the
horseshoe of the spectral locus.
When you look at the Yxy diagram below, you have to remember that big
Y/brightness (the intensity of the pixel) is collapsed into the Z
axis, so you have to imagine it coming out of the screen towards you.
The scene linear files you would have used in the past can only
represent colour within the green or blue triangles, ACES can
represent colours across the entire spectral locus (plus some
imaginary colours outside the horseshoe but within the ACES triangle).
But the total sum brightness, and its linearity relative to light
levels in the scene remain the same.
I was under the impression that one of the main points of ACES is
to use the linear light state as the common ground for all colour
qworkflows
It is.
And part of that is divorcing the primaries from either the input
device or output device.
Inline image 1
On Thu, Mar 6, 2014 at 10:19 AM, Frank Rueter <[email protected]
<mailto:[email protected]>> wrote:
Thanks.
Using OCIO and RRT (sRGB) yields the expected result. I guess my
confusion was/is with the fact that ACES linear does not produce
the result I expected from scene referred linear data, and I was
under the impression that one of the main points of ACES is to use
the linear light state as the common ground for all colour
qworkflows, as it should represent the light data captured on set
irrelevant of input output signals.
In other words, I would a have expected ACES linear to be a lot
closer to the linear light images I have been working with over
the years.
It may just be a case of un-learning things to be able to
understand this fully.
Cheers,
frank
On 3/6/14, 8:17 AM, hxpro wrote:
On 03/03/2014 19:52, Frank Rueter wrote:
Actually, scratch that, ACES linear followed by
rec709>linear in Nuke
doesn't look like anything I see in RawViewer in terms of
saturation.
The gamma looks reasonable though.
Any more hints?
ACES uses very saturated primaries (in chromaticity terms),
this means that just performing a 1D colour space conversion
will result in desaturated looking images. You need to use
something like the RRT+ODT to convert to something 'filmic',
or at least you need to map from the ACES primaries into the
rec709 primaries somehow. You'd need to be careful doing so
due to gamut missmatches, which is where a lot of the
challenges are.
Kevin
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