RGBfromXYZ: Calculate Signal RGB from Linear RGB, XYZ, or Lab

In spacesRGB: Standard and User-Defined RGB Color Spaces, with Conversion Between RGB and CIE XYZ and Lab

Calculate Signal RGB from Linear RGB, XYZ, or Lab

Description

Calculate signal RGB from linear RGB, XYZ, or Lab

Usage

SignalRGBfromLinearRGB( RGB, space='sRGB', which='scene', TF=NULL, maxSignal=1 )

RGBfromXYZ( XYZ, space='sRGB', which='scene', TF=NULL, maxSignal=1 ) 

RGBfromLab( Lab, space='sRGB', which='scene', TF=NULL, maxSignal=1 ) 

Arguments

RGB	a numeric Nx3 matrix with linear RGB coordinates in the rows, or a vector that can be converted to such a matrix, by row. The RGB may be outside the corresponding domain box (either scene or display), see Details.
XYZ	a numeric Nx3 matrix with CIE XYZ coordinates in the rows, or a vector that can be converted to such a matrix, by row. The XYZ are assumed to be viewed under the white-point of the given RGB space.
Lab	a numeric Nx3 matrix with CIE Lab coordinates in the rows, or a vector that can be converted to such a matrix, by row.
space	the name of an installed RGB space. The name matching is partial and case-insensitive.
which	either 'scene' or 'display'. For RGBfromXYZ() which describes the input XYZ. For SignalRGBfromLinearRGB() which describes the input RGB.
TF	if not NULL, TF is a TransferFunction that overrides the appropriate transfer function of space. TF can also be a positive number. If TF=1, then TF is set to identity.TF, so the returned RGB values are actually linear, and they are not clamped to the appropriate domain box (see Value). If TF!=1 it is used to create either power.EOTF() or power.OETF() as approriate. If TF is not NULL in SignalRGBfromLinearRGB(), then space is ignored.
maxSignal	maximum value of non-linear RGB. Other common values are 100, 255, 1023, 4095, and 65535. Even when 1, they are still taken to be non-linear Signal values.

Details

In RGBfromXYZ(), the conversion is done in these steps:

• XYZ \rarrow linear RGB using the 3x3 matrix for the given space and which

• if TF is not the identity, the linear RGBs are clamped to [0,1]^3 if necessary

• linear RGB \rarrow signal RGB using SignalRGBfromLinearRGB() and all other the given arguments

In RGBfromLab(), Lab \rarrow XYZ is calculated using spacesXYZ::XYZfromLab(), with the white point (either 'scene' or 'display') of the given RGB space.

Value

a data.frame with N rows and these columns

RGB	signal RGB. If TF is not the identity, the computed linear RGBs are clamped to [0,1]^3 if necessary, which implies that the output signal RGBs are inside the cube [0,maxSignal]^3. Values are not rounded.
OutOfGamut	a logical, TRUE means one or more of the computed linear RGBs were actually clamped to [0,1].

In RGBfromLab(), if a=b=0 exactly, the R=G=B exactly.

In case of error, the functions return NULL.

References

Wikipedia. RGB color space. https://en.wikipedia.org/wiki/RGB_color_space

See Also

XYZfromRGB(), LinearRGBfromSignalRGB(), installRGB(), identity.TF, spacesXYZ::XYZfromLab()

Examples

RGBfromXYZ( c(80.310897,90.306510,84.613450, 100,100,100)/100, max=255 )
##       RGB.R    RGB.G    RGB.B OutOfGamut
##  1 230.1676 249.4122 225.2472      FALSE
##  2 255.0000 249.1125 244.4704       TRUE

spacesRGB documentation built on April 12, 2025, 1:55 a.m.