PDA

View Full Version : LUT (Lookup Table)


auras
12-02-2003, 10:09 AM
Hello folks,

Here, i have some questions for you. I am doing a color grading for some materials in Combustion 2 on MAC OS X with 23 inch Cinema HD Display. On Combustion 2, there's a function call view "LUT". I don't know which is the most appropriate setting to use. And if you can, plase explain to me more in detail about this function and how to use it as well (don't bother about it if it's too troublesome). My color grading is going to be sent for film transfer on 35mm.

Any ideas ?

Thanks
TwoMints

Jack Pfeiffer
12-02-2003, 12:06 PM
Hi...

A lot of people have asked about LUTs.
At this time, there is no tutorial that I know of to help give hands on.
But, here is some helpful background info for you to better understand what a LUT is and how it is used...

Regards,
JACK

Using "View Look Up Tables" (LUTs) - Defined: Computer monitors can only display 8 bits per channel. This setting results from the monitor's display adapter and settings. Usually, you would set the display adapter to "True Color", or a 16, 777, 216 color palette. This number equals a bit depth of 8 for the three color channels. When you want to use the monitor to display a higher bit depth for such files as Cineon and DPX, you use a view LUT to display the higher bit depth in the 8-bit color space by mapping the colors. The image data is not affected by the conversion. Using the view LUT is also useful for leaving footage in logarithmic color space from input to output (import to rendering) while displaying the data in a linear way in the viewport. Specifically, this lets you work with Cineon and DPX files without converting from logarithmic color space. You can use a view LUT to also calibrate a monitor. To help you with this, the View LUT panel includes a feature for
displaying test patterns.

Simply put, Output Look Up Tables help maps the 8 bit intensity information onto 24 bit false colour space.



There is a good definition, compete with images here :
http://www.sli.unimelb.edu.au/envis/automap/colordepth.html

and here:
http://www.udayton.edu/~cps/cps560/notes/clown/


I am going to TRY to "help" you... But, please be aware that I personally have NOT worked directly with Film and LUTs (Look Up Tables...) I used them ONCE in a Discreet Class i attended, but that's it! So, Quite honestly, I am a "video-guy" for the last 25 years, and NOT film....

However, since I do a lot of Combustion training, I have tried to educate myself on the essential basics, such that when my students ask me questions, I can at least try to provide semi-intelligent answers ...

As you may already know, the conept of LUTs applies to the problems faced by the conversion of 10 bit Log Film to 8 bit Linear or Video Data... Video simply does NOT have the color depth necessary. Therefore, an interm4diate file, quite often a Cineon file, is created. Next, a LUT is used by video-based programs such as Combustion to best view the results and achieve a resemblance of color accurate viewing...

What are Cineon Files? Definition of Cineon Image File Format: The Cineon image file format is a subset of the ANSI/SMPTE DPX file format. Read More Here: http://www.cineon.com/file_format.php

There is an On-Line Technical definition of the Cineon file format here:
http://www.cineon.com/ff_draft.php

How do you convert 10 bit log images to 8 bit linear images? Answer: Read the lengthy article here:
http://www.cineon.com/conv_10to8bit.html

As for Combustion:

Basically, combustion 2.1 has "Film Tools" -- specifically grain, color management and LUTS.
The Grain and Color Tools are compatible with Discreet's other effects systems including flame and inferno. The combustion 2.1 add grain tools include settings for most common Kodak film stocks, as well as full parameter control for automatically matching to any film type used in production. combustion 2.1 can basically remove grain by using some pretty sophisticated math (algorithms) that reduce grain in an image, all without sacrificing image clarity.

LUTs: Combustion 2.1 has Look Up tables, which are a set of controls that describes specific pixel values to be used in image display or conversion. These tools provide controls on a per-footage level (histogram, separate RGB controls), as well as tools to preview results of LUT operations on the monitor without having to use external utilities. The LUT files are compatible with flame and inferno and support similar editing, import and export functions to generic ASCII LUT files.

Here's some more websites with additional info:

http://www.dai.ed.ac.uk/HIPR2/colmap.htm

http://www.sgi.com/software/opengl/advanced97/notes/node131.html

http://www.cee.hw.ac.uk/hipr/html/colmap.html

http://www.etl.go.jp/~matsui/eus/manual/node141.html

-end-

Jack Pfeiffer
12-17-2003, 08:46 AM
There is now a LUT / Cineon Tutorial...

see the post dated 17-dec entitled
"New C Tutorial: 2K Cineon Files and LUTs" . . .

bye,

jack

CGTalk Moderation
01-16-2006, 07:00 PM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.