8-Color Printing: What’s Hype and What’s Real?
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Sign China 2015 - September 16-19, 2015 in Shanghai, China


8-Color Printing: What’s Hype and What’s Real?

As wide format digital production printing evolves, new technologies and paradigms are constantly being added to the continuous flow of new products.

By Judith Vandsburger

These advances have not been limited to changes in the core inkjet technology. They also encompass new concepts in color systems and color management, some of which were developed solely for the wide format domain.

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  • While just a few years ago, four-color printing was the only way to go wide format, today’s buyers are exposed to many color concepts and many different terminologies that are often used to describe the same thing. Likewise, a variety of related terms are used in conjunction with these color concepts ­ sometimes rightly and sometimes totally out of context.

    This document attempts to sort out some of this confusion. It reviews the different color concepts available today and explains each concept’s merits and disadvantages. It also explains the relationship between the different systems available and other related terms such as color gamut, color space, apparent resolution and more.

    6/8 COLORS: THE DARK/LIGHT AND HEXACHROME SYSTEMS

    Let’s review the different printing systems available today, in order to better understand the pros and cons of each.

    Digital Process 4C
    ­ 4 color CMYK printing system.

    Digital Dark/Light 6C
    ­ 6 color printing system that uses 2 diluted or “light” colors in addition to the 4 dark colors: CMYK, LC, LM

    Digital Dark/Light 8C
    ­ 8 color printing system that uses 4 diluted or “light” colors in addition to the 4 dark colors: CMYK, LC, LM, LY, LK. Digital Dark/Light systems (both 6C and 8C) enhance image quality in several aspects (as explained in the next chapter).

    Digital Hexachrome ® 6C
    ­ 6 color printing system developed by Pantone that uses Orange and Green (OG) in addition to the 4 dark CMYK colors. The Hexachrome color system attempts to match Spot Colors, also known as market-standard PMS (Pantone ® Matching System), commonly used in offset and screen printing systems.

    Note: Hi-Fi color is any printing technique that uses more than four process inks in order to expand the tonal range of the printed piece. The term Hi-Fi is commonly used when referring to any of the three printing systems described above: Digital Dark/Light 6C, Digital Dark/Light 8C, Digital Hexachrome 6C.

    The following section explains common terms used in the industry.

    6/8 COLORS: THE ADVANTAGES AND SOME “SACRED COWS”

    Color Gamut
    In the following illustration (Image 1), the three polygons, each with six points, correspond to the six primary colors: C,M,Y,R,G,B. The area inside each polygon represents all the colors that can be produced with that particular set of inks. This is the Color Gamut, also known as the Color Space, of two different color reproduction systems, and provides a handy way for color scientist to display the relationship between different gamuts.

    Color gamut differs from ink to ink due to the different ink pigmentation each company’s color lab produces. In the above illustration, the gray polygon corresponds to the market standard Chromalin, which is commonly used as a reference base. The blue polygon corresponds to one type of 4C printer and the red polygon corresponds to a different 4C printer. In this example you can see that one set of ink can deliver a wider range of greens, while the other can deliver a wider range of reds. The type of media used is another factor that contributes to color gamut.

    For instance, the better absorption characteristic of Flex media means it produces a wider “apparent” color gamut than paper. The Dark/Light system is composed of either 2 or 4 additional diluted colors, namely: LC, LM (for the 6C system) or LC, LM, LY and LK (for the 8C system), combined in printing with the traditional CMYK Dark Colors.

    Basically, the same ink pigments form the color gamuts for the 4C, 6C and 8C systems. Therefore, the outer limits of the color gamut are the same. However, the 6C and 8C systems produce a slightly wider “apparent” gamut. The alternative Hexachrome Orange and Green (OG) 6C system has an evident wider color gamut than that of the Dark/Light systems. However, the Hexachrome system has suffered - and currently still suffers - from slow market acceptance, primarily due to difficulties in customizing color management.

    6/8 Colors Reduce Graininess
    Two parameters are mainly responsible for the graininess phenomenon in digital printing, these being ink density and positioning of printed dots on media. The graininess phenomenon is most noticeable in the highlight and mid-tone areas, mainly corresponding to skin tones, pastel colors and gradient images.

    One of the goals of the 8C system is to reduce the graininess phenomenon. Using light inks means more printed dots are produced in the same printed area thereby achieving an ink density level comparable to that of 4C printing.

    By printing more dots of light ink on a specific area and enhancing gray levels, the contrast between printed dots and background is invisible to the bare eye and therefore appears less grainy All in all, this formation contributes to a much smoother, homogeneous look, resulting in photo realistic image quality without graininess. Obviously, an 8C system will produce smoother images than a 6C system, especially in areas rich in K and Y.

    Addressable and Apparent Resolution
    Print resolution is conventionally described in terms of the number of dots printed per inch, measured in DPI. This resembles an imaginary grid into which the printer deposits dots of ink. The term “Addressable Resolution” refers strictly to the number of dots that the printer can place - or address - on each linear inch of printed surface. Addressable resolution is the printer’s ability to address and produce a specific number of dots in each linear inch of printed surface.

    An 8C system produces twice as many gray levels per printed dot. It is therefore said that an image printed with a 8C system at an addressable resolution of 370 dpi, looks just as good to the human eye as the same image printed at 740 dpi from a 4C system. In other words, the human eye cannot perceive these slight nuances due to natural limitations. Hence, both prints would appear the same. One can claim that an 8C printer with an addressable resolution of 370 dpi apparently produces a printout with quality of 740 dpi, and thus has an “Apparent Resolution” of 740 dpi.

    8 COLOR PRINTING ­ WHAT’S HYPE AND WHAT’S REAL?

    When summarizing the overall benefits of the 8C system as opposed to that of the 4C system, the following conclusions can be drawn. 8C system:

    • Increases apparent resolution Produces finer details
    • Ensures smoother gradient transitions
    • Produces vivid and crisp colors
    • Reduces graininess

    The 6C system is similar in all aspects, although to a lesser extent. However, 8C printing does have some disadvantages such as extra ink consumption and lower speed.

    8C VS. 4C: TAKING A CLOSER LOOK AT THE DIFFERENCE

    Printed Samples
    The following images are samples of two similar files, one printed with an 8C printer, the other printed with a 4C printer. Take a closer look at the following nuances found in the 8C sample (left side of each image):

    Summary: The Variety of Printing Systems
    The following table describes the common 4C and 8C printing systems on the market today:

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