[Tig] Care and Feeding of LUTs

Jim Houston 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.

Jim Houston
Starwatcher Digital
Pasadena, CA

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