[R] package colorspace and .WhitePoint question

[Achim Zeileis]

As a follow-up to this issue:

A revised version of the "colorspace" package is now available on R-Forge 
at https://R-Forge.R-project.org/R/?group_id=20

This provides a function whitepoint() that can query and/or modify the 
whitepoint used in all color conversions within the package. To try it you 
can do:

install.packages("colorspace", repos="http://R-Forge.R-project.org")
example("whitepoint", package = "colorspace")

Glenn, it would be great if you could try this and let us know if any 
problems remain.


On Mon, 4 Jun 2018, Achim Zeileis wrote:

> Glenn,
>
> currently, this is currently not exposed in "colorspace" AFAICS. You can 
> modify it by changing .WhitePoint inside colorspace's NAMESPACE, though:
>
> R> assignInNamespace(".WhitePoint", rbind(c(95, 100, 105)),
> +    ns = "colorspace")
> R> as(XYZ(100, 100, 100), "LAB")
>       L        A        B
> [1,] 100 8.622384 3.226371
>
> I'll have another look whether this could be exposed easily (cc also Paul).
>
> Best,
> Z
>
> On Mon, 4 Jun 2018, Glenn Davis wrote:
>
>> In colorspace.R  I see:
>>
>>    setAs("color", "LAB", function(from)
>>      LAB(.Call("as_LAB", from using coords, class(from), .WhitePoint, PACKAGE = "
>> colorspace"),
>>          names = dimnames(from using coords)[[1]]))
>>    ...
>>    .WhitePoint = NULL
>> 
>> and then in colorspace.c and the function CheckWhite(),
>> I see that .WhitePoint = NULL is converted to D65.
>> 
>> I would like to pass a different .WhitePoint to
>>    as( XYZ( 100,100,100)  , "LAB" )
>> 
>> 
>> I have tried 3 methods:
>>    as( XYZ( 100,100,100)  , "LAB", .WhitePoint=XYZ(95,100,105) )
>>    .WhitePoint = XYZ(95,100,105)
>>    assign( ".WhitePoint", XYZ(95,100,105), env=as.environment('package:
>> colorspace') )
>> but all fail, for different reasons.
>> 
>> How can I transform XYZ to LAB using a whitepoint different than D65 ?
>> 
>> Thanks,
>> Glenn Davis
>> gdavis using gluonics.com
>>
>> 	[[alternative HTML version deleted]]
>> 
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>