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Image Enhancement: Better Files, Cost Savings

(February 2013) posted on Tue Mar 12, 2013

Mandel discusses how to conserve ink and make image files easier to print by replacing CMY elements with black.


By Rick Mandel

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GCR replaces the neutral gray in CMY with black. As in UCR, there are levels of GCR that can be applied to allow the software to alter the imagery into the shadow range. In essence, higher levels have a similar affect as UCR. Black is acting as a real color now and not just shadow detail. So if the black ink has a brownish hue—many digital inks have this issue—the color shift toward a warmer (red/yellow) shadow will occur.

Figures 1-3 display a graphic with a skeleton black and optimized with UCR/GCR. The images shown are four colors, CMY colors only, and just the black channel. Within this test graphic, the shadow area displays the following:

Native file Compensated file with UCR/GCR
Cyan 82 37
Magenta 62 20
Yellow 60 19
Black (K) 91 99

The flesh-tone area shows:

Native file Compensated file with UCR/GCR
Cyan 21 0
Magenta 40 33
Yellow 53 47
Black (K) 0 20

The shadow compensation is a classic under-color removal of decreasing CMY and replacing with black. The flesh-tone data display GCR’s advantage of replacing the graying component of cyan with black. The goal is for the color to be very similar for each version, though easier to print and with ink-cost savings. L*a*b analysis is a method of measuring color without taking into account the CMYK values. Non-compensated L*a*b of the flesh area is 79, 15, 25. Compensated readings are 76, 15, 28. This is a confirmation of virtually the same color fidelity. UCR/GCR is affecting the TAC. Figure 4 shows simplistically the reduction in CMY and the addition of black.

Software
The producers of image-enhancement/optimization software would bristle at the comparison of their software to GCR/UCR. Their modifications to the file are claimed to alter the color values in a proprietary way. Print providers do want improved imagery and wider color gamut, though a reduction in ink usage is very tantalizing. With the average cost for a single liter of ink at $210, it doesn’t take long for most print operations to chalk up thousands of dollars in ink expenses.


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