Re: Fwd: Monitor calibration/profiling for video applications
Re: Fwd: Monitor calibration/profiling for video applications
- Subject: Re: Fwd: Monitor calibration/profiling for video applications
- From: Graeme Gill <email@hidden>
- Date: Fri, 17 Aug 2012 09:53:53 +1000
Steve Kale wrote:
Hi,
> My take on this is that the video guys 'hard-tune' devices to a specific primary/gamma set (to
> use terms loosely) whereas the ICC approach has a much higher degree of flexibility in that each
> device is profiled and each piece of media carries with it a profile that, in effect, contains
> expectations as to how that content should look.
Not really. The ICC approach breaks the task down into components, so that there
is the flexibility to mix and match. Hence devices are characterised, and then
the CMM links profiles to create an emulation (or adaptation) of one colorspace
to another. The typical Video approach jumps directly to a single target,
the desired response of the display, and then used more add-hock methods
to calibrate the display so that it emulates the desired response. When the display
and the target response are both additive, it's not too hard to break this
down into hitting the desired primary chromaticities and per channel responses.
If the device (say) is not close to additive, then this approach doesn't
work too well, nor does it provide any mechanism to control out of gamut
mapping (typically out of gamut colors will be clipped in some crude fashion,
although the aim will be to avoid this by ensuring that the display has
a greater gamut than the target response). In this case it's necessary
to use an ICC like approach of calibrating the display to get it close
and have sufficient gamut, characterise it and then link the desired
response with the display characterisation to compute a device link (3D Lut)
that implements the emulation.
One of the advantages having a single specific target in mind has is that
some fine tuning can be applied over the whole system, whereas the normal
ICC approach puts up with any slight errors introduced in the separate
characterisation of the input and output devices and the linking process.
> display. It would seem much more sensible to me for the video industry to move to an ICC-profile
> type setup where recording devices are profiled (perhaps less important because of post
> processing), displays are profiled and each video (however processed for effect) comes with a
> profile that aids a CMM to deliver the correct look on any display.
Ideally, but I can very well understand this approach not being practical in the real
world at present. The ICC approach has struggled (and still struggles) to work in a
practical sense of profiles and systems being available, whereas fixed standards such
as sRGB and the typical Video industry approach around Rec. 709 etc. are relatively
simple and practical. They do straight jacket technical development though, resulting
in great struggles when things like wider gamut displays or higher dynamic range are
introduced.
The utopia of Video being tagged with a profile would rely on most displays
having 3D cLUT mapping hardware (or the equivalent), some reasonable
"smart" CMM like linking and gamut mapping in every display, and a reasonably
accurate profile of the display itself. This is a perfectly doable scheme that
would work, the greatest obstacle being getting industry agreement,
standardisation and a feely usable reference implementation. I guess it could
happen in the future, but I suspect many people in the Video industry don't
know enough about color to know that they don't know everything about color,
and the current arrangements work "well enough".
> Is this a fair view of the world? (says someone who has just profiled his computer monitor with
> i1Profiler while reading Poynton's "Digital Video and HD" and about to recalibrate my plasma
> display with HCFR)
It is, but the world is a messy place.
Graeme Gill.
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