Re: Matrix, LUT, XYZ
Re: Matrix, LUT, XYZ
- Subject: Re: Matrix, LUT, XYZ
- From: Steve Upton <email@hidden>
- Date: Thu, 14 Mar 2002 01:00:56 -0800
At 1:31 AM +0100 3/14/02, Helmut wrote:
>
I am using successfully colormanagement with Adobe and Heidelberg products. However two questions puzzle me always if I hear about monitor profiling:
>
>
1. What is a Matrix and a LUT-based Profile ?
A matrix-based profile is the form most monitor profiles take. It is a very simple beast with a collection of color coordinates for the colorants (RGB phosphors in the case of a monitor), the curves (gamma) for each channel, the white point and a few other bits.
Very simple. And in the case of the monitor profile, totally dependant on the calibration of the monitor - which is supposed to bring it into the correct state - and the CMM.
LUT-based profiles are multidimensional lookup tables filled with values that map colors throughout the color space. An easy way to visualize it is to think of the Lab->CMYK table as a 3D cube of points. At any location is an entry for CMYK that should describe the closest (or best) formulation to get the color at that location.
The real strength is the ability for the tables to effectively swirl and bend numerically in an attempt to conform to the strange behavior of a printer. We hand them nice orderly Lab colors and they contort the CMYK numbers to squeeze the desired colors out of a printer. The stranger the behavior of the printer (inkjets and diesubs can be pretty whacked) the more corrections have to be in the table. And also the greater value in having a table with more grid points.
>
>
2. The space "XYZ" or "xyY". What is defined by which letter? (I understand LAB, LCH, RGB...)
They are different spaces.
XYZ is an early color space created in 1931 based on human perception experiments. Useful numerically it is difficult to imagine and not perceptually uniform. Lab is a derivative created in 1976 that is better at these tasks. The colorimetric (PCS) side of a profile can either output/input XYZ or Lab.
xyY or Yxy is also a derivative of XYZ and the basis of the popular horseshoe-shaped chromaticity diagram. There are volumes written on it but I think the most popular uses are the graphing of gamuts in 2D and also in the specification of colors in matrix profiles - such as those entered in Photoshop to define working spaces.
(I used the linguistic meaning of the word 'derivative' here - as in 'created from'. sorry if I offended any math types)
Regards,
Steve
________________________________________________________________________
o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX
o email@hidden 206.985.6837
________________________________________________________________________
--
_______________________________________________
colorsync-users mailing list | email@hidden
Help/Unsubscribe/Archives:
http://www.lists.apple.com/mailman/listinfo/colorsync-users
Do not post admin requests to the list. They will be ignored.