Printing System Models - Control of Color Imaging Systems: Analysis and Design - page 609

the increase in TC, the volume of the gamut has increased by a signi cant amount.

In Figure 10.55, the two gamuts are created by using different media. This
is achieved by plugging in the re ectance spectrum of the substrate (R s ( l )) in

Equation 10.54.

10.7 VIRTUAL PRINTER MODEL TUNING
TO AN EXPERIMENTAL PRINTER
High-volume digital color printers designed with image-on-image EP technology
perform recharge and exposure (several times) on the developed toner layer. Accord-
ingly, light exposure depends on the optical transmissivity of multiple toner layers.
The voltage across a previously developed toner layer, development suppression due
to image voltage, etc. are other contributing factors that play an important role in the
actual response of the printer. In a real printer, these physical processes interact in a
more complicated way as compared with the processes modeled by the virtual printer
and are speci c to a particular architecture of the print engine. To make the models

more representative of the physical process, a few key parameters can be tuned to
generate colors similar to the real printer. A few important steps used in tuning the
parameters of the virtual printer models are as follows:

(1) Use realistic values for the process parameters = actuators like voltage levels,

media optical properties, etc. for a nominal print engine.
(2) Tune the toner master curves using experimental data that represent the
absorption spectra of each of the C, M, and Y toners.
(3) Tune the single separation coef

PR = toner =

cients in the color model for each of the

C, M, Y, and K separations.
(4) Tune the color mixing coef cients for C, M, and Y separations.

(5) Match the channel-wise TRCs, assuming each separations of the real printer
is linearized with a TRC.

10.7.1 T UNING T ONER M ASTER C URVES
In the main equation of the re ectance spectral model (Equation 10.54), assume the

transmittance from air through toner to paper equals the return transmittance from
paper through toner to air (i.e., ¼ t 0 (m i ;

t (m i ; l ) l )). Equation 10.54 can then be

simpli ed as

2

R ( m i , g; l) ¼ p 0 ( g ) þ [ 1 p 1 ( n 1 , n 2 , i )]t ( m i ; l) R s (l) ( 10 : 69 )

The total FSR term, p 1 (n 1 , n 2 , i), depends on the refractive indices n 1 and n 2 of the air
and toner layer as well as the angle of incidence of light. The measurable FSR term,
p 0 (g), depends on the total FSR and gloss, which (again) is a function of the fusing
temperature and transferred mass on the substrate. For our tuning purpose, all
the above terms are assumed constant for a single toner. So let p 0 (g)

¼ C 1 and

1 p 1 (n 1 , n 2 , i) ¼ C 2 .