One-Dimensional, Two-Dimensional, and Spot-Color Management and Control Methods - Control of Color Imaging Systems: Analysis and Design - page 452

The shadow regions of most TRCs also have low quality characteristics such as
non-smooth development or contours. Adding more toner does not change the color
much at the saturation region because it is nearly saturated. Here, full saturation is
based on the physical device. Note that it is possible for a person to specify a color
that is more saturated than the physical device can deliver. TRCs in the shadow
region can be low quality because of the physical device, gray-balance algorithms
such as smoothing algorithms, and the user speci cations. If the TRCs are not

smooth and well behaved in the shadow region, unwanted contours can occur in
dark saturated colors. In this section, we show how to produce TRCs that work well
for highlights and shadow regions.

8.6.2.1 Highlight Corrections

We illustrate highlight corrections using the highlight region of the cyan gray-balance
TRC, which is shown in Figure 8.19. In this figure, active control patches near the

highlight region are at cyan digital input values of C in ¼

13 and C in ¼

30. After gray

balance, their corresponding outputs are C out ¼ 20 and C out ¼ 46. The passive control

patches are at C in ¼ 0andC in ¼ 1 digital counts. The active control patch is used

during iterations to find its C out value with control-based gray-balance calibration. The

passive shadow control patch is not directly used during iteration. The C out value for
the passive shadow patch is assigned (or user selected). We can have more than one
passive control patches. Nodes are included in Figure 8.19 for the four C in values
mentioned above. The variation in digital count appears as development on the paper
for all active control patches. If nothing is done to compensate for the highlights, then,
for this example, the lightest printable highlight input values are near C in ¼ 13. The

passive control patch with the input highlight value of C in ¼ 1 is a value that is well

within the highlight region and is not developable. In other words, a value of 1 can be

50

Smooth TRC
Control patch e s

45

40

35

30

25

20

15

10

5

0

0 5 10 15 20 25 30 35

C in

FIGURE 8.19 Highlight region of cyan gray-balanced TRC.