[argyllcms] Re: Calibrate to BT.2100 PQ curve?
- From: "Roger Breton" <graxx@xxxxxxxxxxxx>
- To: <argyllcms@xxxxxxxxxxxxx>
- Date: Fri, 23 Feb 2018 13:39:47 -0500
Hi Florian,
Can your cLUT be used with external TV boxes?
/ Roger
-----Original Message-----
From: argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-bounce@xxxxxxxxxxxxx]
On Behalf Of Florian Höch
Sent: Friday, February 23, 2018 12:46 PM
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Re: Calibrate to BT.2100 PQ curve?
Hi Niklas,
Am 23.02.2018 um 18:20 schrieb Niklas Haas:
That also raises a question: do we want to calibrate to "raw" PQ (i.e.
anything above the highest supported brightness level gets
hard-clipped to 1.0), or do we want to include some sort of "knee"
function to automatically roll-off the response near the display's peak
brightness?
Cue BT.2390, which is an attempt at such a roll-off function (and seems to
work quite well in practice).
My five cents on 1D (desktop) calibration with PQ: It seems not that useful
in a general sense, because operating systems would have to actively
re-encode their graphical widgets into Rec.2020 with PQ (or rather DCI-P3
encoded with a Rec.2020 container and PQ transfer) before sending it to a PQ
display, otherwise desktop elements could end up much too bright and color
detail clipped. It seems more useful for already PQ encoded content (= HDR
motion video).
Also, even with the roll-off, unless you also do a saturation adjustment
(like the one mandated in BT.2390), the resulting color on screen would not
maintain hue and saturation (as far as possible).
This basically requires a color managed approach that not just involves
shaper curves (and possibly a matrix), but a full 3D lookup table, i.e.
the use of cLUT profiles.
Attempts at such implementations exist (tooting my own horn here, e.g.
DisplayCAL has the ability to create input cLUT profiles with PQ transfer
function, including roll-off with saturation adjustment, as well as 3D LUTs
in various non-ICC formats, and madVR also has built-in support for PQ via
shaders).
Florian.
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