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Re: HiRes color correction



Greetings All

I am sorry I missed the initial comments on Hi-Res Colour Correction I have
to make the sad admission that I left the Country without taking my trusty
portable computer with me. It won't happen again !!!

Firstly let me say that I absolutely agree with all of you about the real
time nature of the controls.
We have observed colour correction suites where the colour corrector feeds
a noise reducer [usually a DVNR with all the advanced options installed]
resulting in a total delay of maybe 8 frames between the time the colourist
turns a knob and the time that the resulting change appears on the monitor.
Even in this situation it becomes surprisingly difficult to make subtle
changes to the colour balance of the image. There is always a tendency to
turn the control too far in the first place and then over compensate when
backing it off. Eventually you get to the right setting but it feels like
hard work.

Subtle colour correction relies very heavily on hand-eye co-ordination and
as with any control circuit too much delay introduced into the feedback
loop causes the output to 'ring' or oscillate. It can also  be  compared to
playing a musical instrument when you only hear the other musicians in the
band several seconds after they have all played their notes - the result
would either be complete chaos [or perhaps some very early Pink Floyd --
tuning up under the influence of several exotic herbs.]

If we agree to disregard the concept of running a colour processor in slow
motion or using a software based 'photoshop' approach we perhaps have two
solutions. Neither of which are simple or ideal.

1] Work real time with low resolution proxy images and then 'render' the
full res files slowly.
--- This I beleive is the DaVinci Resolve approach

2] Build a mainly hardware based solution that works quickly enough to do
the job in one go.
--- More like our MegaDEF system.

The big problem with [1] , as pointed out by Mr Grace, is that it is too
easy to produce an image that looks OK at low resolution but will exhibit
obvious edges or noise effects when magnified several times. If subtle and
generally overall grades are required then maybe you could get away with
this however as we all like to use regional colour corrections and often
very large alterations for specific objects within the scene I suspect that
there would be some horrible accidents.

As for [2] - It is unfortunate that the programable devices that Howie
Burch mentions are not fully up to the job.
We at Pandora have been using programable gate arrays FPGA's and EPLD's for
many years and I suspect the designers at DaVinci are using the same parts.
Unfortunately the one function that is very very difficult to provide in a
programmable device of any type is a simple multiplier which happens to be
the most common element required for any DSP algorithm [for example our ESR
card uses around two hundred multipliers]
Yes  there are many work arounds especially where you only need to multiply
by a constant value [i.e. in a FIR filter algorithm] however none are
really efficient in terms of performance or real estate on the device and
therefore eventually cost. This problem has tended to limit the use of
fully programmable solutions [such as the Atlightspeed card for example]
for advanced colour correction processes.
It is therefore not easy to build a universal colour corrector for very
high resolution images although we are fairly confident that we have found
a way.

I do not want to promote advertising on this site or any  product wars
between us and DV however I suggest that anyone interested in this subject
should consult both our web site [http://pogle.pandora-int.com] for a full
technical description of MegaDef and also the DaVinci site for a
description of Resolve.

Now that the Spirit DataCine is begining to get established we are
effectively entering the beginning of a new ERA in colour correction and
film processing. I for one would welcome any discussion comments or
suggestions on this subject either directly to me or via the user group.

At the risk of sounding INCREDIBLY big headed about the whole subject I
could comment that in some small way your future is in our [and DaVinci's ]
hands so please don't hold back !!!!!


Steve Brett.