adaptation {spacesXYZ}

Chromatic Adaptation Transforms (CATs)

Description

Construct transforms from a source viewing enviroment with a given illuminant, to a target viewing environment with a different illuminant. Some standard linear von-Kries-based CAT methods are available.

Usage

CAT( source.XYZ, target.XYZ, method="Bradford" )

Arguments

source.XYZ

the XYZ of the illuminant in the source viewing environment. source.XYZ can also be a string with the name of a standard illuminant as in the function standardXYZ().

target.XYZ

the XYZ of the illuminant in the target viewing environment. target.XYZ can also be a string with the name of a standard illuminant as in the function standardXYZ().

method

the method used for the chromatic adaptation. Available methods are: "Bradford", "VonKries", "MCAT02", "Bianco+Schettini", and "scaling"; see References. Partial matching is enabled, and matching is case-insensitive.
method can also be a 3x3 matrix, which is the cone response matrix used to construct a von-Kries-based CAT. The matrix must be invertible and map both source.XYZ and target.XYZ to the positive octant.

Value

CAT() returns an object with S3 class CAT, which can be passed to adaptXYZ(), adaptxyY(), adaptLab(), or adaptLuv().

An object with S3 class CAT is a list with the following items:

method

full name of the adaptation method, as in Arguments. If argument method is a 3x3 matrix, then this method is NA.

Ma

3x3 cone response matrix M_A for the method, as defined in Lindbloom

source.XYZ

XYZ of the illuminant in the source viewing environment

source.xyY

xyY of the illuminant in the source viewing environment

target.XYZ

XYZ of the illuminant in the target viewing environment

target.xyY

xyY of the illuminant in the target viewing environment

M

3x3 matrix defining the CAT. The matrix is written on the left and the source XYZ is written as a column vector on the right. This matrix depends continuously on source.XYZ and target.XYZ, and when these are equal, M is the identity. Therefore, when source.XYZ and target.XYZ are close, M is close to the identity. Compare with Lindbloom.

Note

Chromatic adaptation can be viewed as an Aristotelian Analogy of Proportions. For more about this, see the vignette Chromatic Adaptation.

References

Bianco, Simone and Raimondo Schettini. Two new von Kries based chromatic adaptation transforms found by numerical optimization. Color Research & Application. v. 35. i. 3. Jan 2010.

Hunt, R. W. G. The Reproduction of Colour. 6th Edition. John Wiley & Sons. 2004.

International Color Consortium. ICC.1:2001-04. File Format for Color Profiles. 2001.

Lindbloom, Bruce. Chromatic Adaptation. http://brucelindbloom.com/Eqn_ChromAdapt.html

Pascale, Danny. A Review of RGB Color Spaces ...from xyY to R'G'B'. https://babelcolor.com/index_htm_files/A%20review%20of%20RGB%20color%20spaces.pdf 2003.

Wikipedia. CIECAM02. https://en.wikipedia.org/wiki/CIECAM02

See Also

standardXYZ(), adaptXYZ(), adaptxyY(), adaptLab(), adaptLuv()

Examples

D65toC = CAT( 'D65', 'C' )
D65toC

##  $method
##  [1] "Bradford"
##  
##  $Ma
##          X       Y       Z
##  L  0.8951  0.2664 -0.1614
##  M -0.7502  1.7135  0.0367
##  S  0.0389 -0.0685  1.0296
##  
##  $source.XYZ
##            X Y       Z
##  D65 0.95047 1 1.08883
##  
##  $source.xyY
##              x         y Y
##  D65 0.3127266 0.3290231 1
##  
##  $target.XYZ
##          X Y       Z
##  C 0.98074 1 1.18232
##  
##  $target.xyY
##            x         y Y
##  C 0.3100605 0.3161496 1
##  
##  $M
##              X            Y           Z
##  X 1.009778519  0.007041913 0.012797129
##  Y 0.012311347  0.984709398 0.003296232
##  Z 0.003828375 -0.007233061 1.089163878
##  
##  attr(,"class")
##  [1] "CAT"  "list"


adaptXYZ( D65toC, c(1,1,0.5) )
##              X         Y         Z
##  [1,] 1.023219 0.9986689 0.5411773