[Tig] Care and Feeding of LUTs
jdhouston at earthlink.net
Sun Feb 19 18:29:20 GMT 2012
On Feb 17, 2012, at 8:43 AM, Michael Bittle wrote:
> Hmm, I'd like to see a study that compares total time to correct (dailies through delivery) for both color correct from RAW and color correct with various LUTs, I suspect some surprising results.
LUTs are not just about imposing a look, but also should provide a
faster path to getting good results from a particular camera because
they can include subtle and time-consuming color space corrections
(3DLUTs that is). While working directly to a particular output device
without any LUTs can have advantages, mismatch in color space
primaries and white point, and odd transfer curves can cause
mismatches in the balance of hues between all of the primaries
and secondaries. These 'mismatches' are things like certain
colors being too vibrant ('neon') or too desaturated, certain hue shifts
in different luminance regions, and contamination of neutrals.
While I won't try to debate whether a colorist on a particular box
can take all of these out, I have seen for myself that it can
be very time consuming, or things are left-in that are not ideal.
There could also be a long argument about a 'video look'
versus a 'film look'. There is sometimes a strong preference
for one of these or the other. I can say that if you don't use
LUTs or tone curves, you are more likely to be favoring a 'video look' and
allowing video style color balances to remain in the image.
The 'film look' is really a 70 year experiment on how to make
pictures look nice in a dark-surround theater. In some generations
of the film look, audiences were used to certain things, so the
film look has evolved over time with recent audiences expecting
a more saturated and contrasty look.
A properly done S-shaped curve LUT is a great help in grading,
and it is also true that you may want to grade before or after a
LUT to have full control. Some LUTs are more limiting than they
should be, and some LUTs may introduce problems or noise
in the image because of the grid spacing of the LUT. But
these are often problems that can be fixed and are part
of the 'art' in making proper production LUTs. Colorists
who have encountered these implementation
problems with LUTs are more likely to shy away from
LUTs in general because it makes LUTs seemingly an
unreliable tool. And if the color pipeline is not completely
standardized at each location working on a production,
a wrongly chosen LUT can do great damage to the image
(and director confidence).
The use of the term, LUT, to represent the capture of
a 'color grade' on set also really narrows the scope of what
good LUTs are capable of. They (and their lesser cousins,
the matrix and tone curve formula) are essential for correct
conversion between color spaces. Every colorist should have
a toolbox of well-vetted LUTs as a way to speed their
work and their creativity. Working without LUTs *ever*,
is somewhat like artists who wish to grind all of their
own pigments before starting a painting. You can do
it that way, it is just more likely to take longer.
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