The Color Transformation Language
The Color Transformation Language, or CTL, is a programming language for digital color management.
Digital color management requires translating digital images between different representations or color spaces. For example, the pixels in an image may encode the colors that should be seen when the image is displayed on a video monitor. Printing this image on paper, or recording it on motion picture film requires transforming the pixels to an appropriate representation: Video, inks on paper and film all have different color gamuts and dynamic ranges. Color mixing is additive for video, but subtractive for inks and film. Video and film typically use three color channels, while four or more inks are used for printing on paper. A color management system must transform each pixel in the original image to corresponding amounts of ink or film density values.
The details of how each pixel is transformed can be fairly complex, and they are often subject to artistic decisions. When images are exchanged between different parties, it is desirable to exchange exact descriptions of appropriate color transforms along with the digital image files. Two people in different geographical locations may each have a copy of the same digital image file. When one of them prints the image on paper, he or she wants to be sure that the result is the same as as for the other person. In order to achieve identical results, the two must agree on details of the printing process (for example, inks and paper), and they must agree on the transform that converts pixels in the file into amounts of ink on paper. Of course, this requires a description of the transform.
The Color Transformation Language, or CTL, is a small programming language that was designed to serve as a building block for digital color management systems. CTL allows users to describe color transforms in a concise and unambiguous way by expressing them as programs. In order to apply a given transform to an image, the color management system instructs a CTL interpreter to load and run the CTL program that describes the transform. The original and the transformed image constitute the CTL program's input and output.
Color transforms can be shared by distributing CTL programs. Two parties with the same CTL program can apply the same transform to an image.
License
CTL is distributed under the following License:
Copyright © 2006 Academy of Motion Picture Arts and Sciences
("A.M.P.A.S."). Portions contributed by others as indicated.
All rights reserved.
A world-wide, royalty-free, non-exclusive right to distribute, copy,
modify, create derivatives, and use, in source and binary forms, is
hereby granted, subject to acceptance of this license. Performance of
any of the aforementioned acts indicates acceptance to be bound by the
following terms and conditions:
* Redistributions of source code must retain the above copyright
notice, this list of conditions and the Disclaimer of Warranty.
* Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the Disclaimer of Warranty
in the documentation and/or other materials provided with the
distribution.
* Nothing in this license shall be deemed to grant any rights to
trademarks, copyrights, patents, trade secrets or any other
intellectual property of A.M.P.A.S. or any contributors, except
as expressly stated herein, and neither the name of A.M.P.A.S.
nor of any other contributors to this software, may be used to
endorse or promote products derived from this software without
specific prior written permission of A.M.P.A.S. or contributor,
as appropriate.
This license shall be governed by the laws of the State of California,
and subject to the jurisdiction of the courts therein.
Disclaimer of Warranty: THIS SOFTWARE IS PROVIDED BY A.M.P.A.S. AND
CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT ARE DISCLAIMED. IN NO
EVENT SHALL A.M.P.A.S., ANY CONTRIBUTORS OR DISTRIBUTORS BE LIABLE FOR
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Manual
Downloads
Source code for the CTL interpreter:
The CTL interpreter depends on the IlmBase software package, which can be downloaded from here:
If you want to use CTL together with the OpenEXR image file format, you should download the OpenEXR and OpenEXR_CTL packages:
The OpenEXR_Viewers package contains source code and documentation for two OpenEXR image viewing programs. Both programs rely on CTL to perform color rendering.
CTL Project at Source Forge
The CTL project is hosted by Source Forge; you can find it at