Just out of curiosity, I've look into a couple it1 file and I see for
example:
RGB_R RGB_G RGB_B XYZ_X XYZ_Y XYZ_Z
1 100.0000 100.0000 100.0000 95.10649 100.0000 108.8440 95.047 100 108.883
2 34.90846 18.70357 19.19271 6.662239 5.390882 4.420492 5.719344 4.435405
3.45356
3 53.46272 1.487180 40.57153 13.59305 7.270500 14.37423 12.71993 6.334173
13.50277
4 12.87608 12.78395 76.12723 11.79817 6.233704 52.05826 10.90296 5.285513
51.54733
5 76.48620 70.70083 83.16876 51.28491 49.63258 69.47523 50.78692 49.12363
69.13399
I was curious to see if my program (R version 3.4.2 (2017-09-28)) and the
colorspace package which uses a Matlab library would give me the same result
(XYZ).
So I use a function called RGB2XYZ from that packages and the results
differ, so I'm curious to understand why.
This function assume the following defaults and just so I don't miss any,
here is the function text:
function (RGBmatrix, illuminant = "D65", observer = 2, RefWhite =
get("XYZperfectreflectingdiffuser",
envir = environment()), RGBModel = "sRGB", RefWhiteRGB =
get("whitepointsRGB",
envir = environment()), gamma = NA, RefWhiteIllum =
get("XYZperfectreflectingdiffuser",
envir = environment()), CAT = "Bradford", CATarray =
get("ChromaticAdaptation",
envir = environment()))
{
if (is.null(dim(RGBmatrix)))
if (length(RGBmatrix) > 2)
RGBmatrix <- matrix(RGBmatrix, ncol = 3, byrow = TRUE)
CATmatrix <- CATarray[, , CAT, "direct"]
Rrgb <- RefWhiteRGB[which(RefWhiteRGB[["description"]] ==
RGBModel), ]
Rillum <- unlist(Rrgb["whitepointilluminant"])
Rgamma <- unlist(Rrgb["gamma"])
Rrgbwhitergb <- RefWhiteIllum[which(RefWhiteIllum[["Illuminant"]] ==
Rillum), ]
Rrgbwhitex <- unlist(Rrgbwhitergb[paste("X", observer, sep = "")])
Rrgbwhitey <- unlist(Rrgbwhitergb[paste("Y", observer, sep = "")])
Rrgbwhitez <- unlist(Rrgbwhitergb[paste("Z", observer, sep = "")])
if (is.na(gamma))
gamma <- Rgamma
if (RGBModel == "sRGB")
gamma <- -gamma
RGBmatrix <- apply(RGBmatrix, 1:2, function(x) InvCompand(x,
gamma))
R <- RefWhite[which(RefWhite[["Illuminant"]] == illuminant),
]
Rx <- unlist(R[paste("X", observer, sep = "")])
Ry <- unlist(R[paste("Y", observer, sep = "")])
Rz <- unlist(R[paste("Z", observer, sep = "")])
xr <- unlist(Rrgb["xRed"])
yr <- unlist(Rrgb["yRed"])
xg <- unlist(Rrgb["xGreen"])
yg <- unlist(Rrgb["yGreen"])
xb <- unlist(Rrgb["xBlue"])
yb <- unlist(Rrgb["yBlue"])
m <- matrix(c(xr/yr, xg/yg, xb/yb, 1, 1, 1, (1 - xr - yr)/yr,
(1 - xg - yg)/yg, (1 - xb - yb)/yb), 3, 3, byrow = TRUE)
mi <- solve(m)
sr <- mi %*% matrix(c(Rrgbwhitex, Rrgbwhitey, Rrgbwhitez),
3, 1)
MtxRGB2XYZ <- t(matrix(sr, 3, 3, byrow = TRUE) * m)
XYZ <- RGBmatrix %*% MtxRGB2XYZ
Adz <- CATmatrix %*% matrix(c(Rx, Ry, Rz), 3, 1, byrow = T)
Asz <- CATmatrix %*% matrix(c(Rrgbwhitex, Rrgbwhitey, Rrgbwhitez),
3, 1, byrow = T)
xyz2 <- t(apply(XYZ, 1, function(x) rowSums(matrix(x, 3,
3, byrow = T) * CATmatrix)))
xyz2 <- xyz2 * matrix(c(Adz/Asz), dim(XYZ)[1], 3, byrow = T)
XYZ <- t(apply(xyz2, 1, function(x) c(x) %*% t(solve(CATmatrix))))
XYZ
}
I suppose that my function doesn't use the same parameter as yours, I tried
a few but obviously it didn't work. Have an idea?
Thanks
