Printing System Models - Control of Color Imaging Systems: Analysis and Design - page 604

Transfer
model

Developed mass
on PR

TMA

(DMA)

V a

Model parameters

FIGURE 10.47 Transferred image on the paper.

transfer model is the output of the development process and the output is the TMA
on the paper for all the CMYK separations (Figure 10.47).
Fusing and paper MTFs can also be incorporated based on the need to approxi-
mate the actual spatial response of the printed image to the model output. The paper
MTFs are particularly useful for modeling the appearance of high-resolution images,
since the images are strongly affected by the diffusion of light through the paper.
Light scattering effects in xerographic images is modelled in Ref. [34]. Coleman and
Li [35] present an approach to model the paper MTF using an experimentally
determined paper light-spread function to describe the scattering phenomenon.

10.4 TONE REPRODUCTION CURVE
The tone reproduction curve (TRC) of a printer is the relationship between the input
pixel value and the tone level that appears at various points in the imaging process.
The TRC at the end of the development process refers to the function of the toner
mass deposited with respect to the input pixel value represented in terms of the
requested gray level or area coverage. Ideally, this graph should be linear for a linear
development. Due to various printer nonlinearities like laser spreading in the expos-
ure process, dot spreading in the development process, light diffusion and scattering
on paper, etc., the TRC is a nonlinear function. The curve also depends on various
process parameters. TRCs can be computed for various halftoning schemes using the
printer model described in this chapter by creating a step change in gray levels
(Figure 10.48). Figure 10.49 shows TRC functions for cyan separation for two
different halftoning schemes.

Bayer

Blue noise

Virtual printer
model

Error diffusion

Contone patch 10%-100% K
ramp

FIGURE 10.48 Schematic for computing the TRC.