colorSpec (version 0.5-2)

calibrate: make a linear modification to a colorSpec responder

Description

make a linear modification to a colorSpec responder so a specific single spectrum (the stimulus) creates a given specific response. The options are complicated, but in all cases the returned object is multiply(x,mat) where mat is an internally calculated MxM matrix. Stated another way, the spectra in the output are linear combinations of spectra in the input x. In case of ERROR, a message is logged and the original x is returned.

Usage

## S3 method for class 'colorSpec':
calibrate( x, stimulus=NULL, response=NULL, method=NULL )

Arguments

x

a colorSpec responder with M spectra. The type must be 'responsivity.light' or 'responsivity.material'. The wavelength sequence of x must be regular.

stimulus

a colorSpec object with a single spectrum, with type 'light' or 'material' to match x. The wavelength sequence of stimulus must be equal to that of x. If st

response

an M-vector, or a scalar which is replicated to length M. All entries in response must be positive. If response is NULL, then an appropriate default may be chosen, see Details.

method

an MxM adaption matrix. method can also be 'scaling' and it is then set to the MxM identity matrix, which scales each responsivity spectrum in x independently. If M=3, method can also be

Value

• a colorSpec object equal to multiply(x,mat) where mat is an internally calculated MxM matrix. The quantity and wavelength are preserved. Note that mat is not the same as the the MxM adaption matrix. To inspect mat execute summary on the returned object. If method is 'scaling' then mat is diagonal and the diagonal entries are the M gain factors needed to achieve the calibration.

Details

If stimulus is NULL, it is set to illuminantE or neutralMaterial to match x. If response is NULL and the response of x is electrical or action, then response is set to an M-vector of all 1s. If response is NULL and the response of x is neural, then this is an ERROR and the user is prompted to supply a specific response. If method is NULL and M=3 and the response of x is neural, then method is set to the 3x3 Bradford matrix. Otherwise method is set to the MxM identity matrix, which scales each responsivity spectrum in x independently.

References

Edward J. Giorgianni and Thomas E. Madden. Digital Color Management: Encoding Solutions. 2nd Edition John Wiley. 2009. Chapter 15 - Myths and Misconceptions.

See Also

is.regular, quantity, wavelength, colorSpec, summary, illuminantE, neutralMaterial, product

Examples

# make an art gallery illuminated by illuminant A
gallery = product( A.1nm, 'artwork', xyz1931.1nm, wave='auto')      
# chromatically adapt the output XYZs to D50 white point, using Bradford matrix
gallery.D50 = calibrate( gallery, response=officialXYZ('D50') )
gallery.D50

# make a flatbead scanner from illuminant F11 and a Flea2 camera
scanner = product( subset(Fs.5nm,'F11'), 'paper', Flea2.RGB, wave='auto')  
# adjust RGB gain factors so the perfect reflecting diffuser yields RGB=(1,1,1)
scanner = calibrate( scanner )
scanner

# same flatbead scanner, but this time with some "white headroom"
scanner = product( subset(Fs.5nm,'F11'), 'paper', Flea2.RGB, wave='auto' )  
scanner = calibrate( scanner, response=0.95 )
scanner