Color & Print Quality

With our acknowledged expertise in color print quality, we are pleased to provide a complete overview of color imaging issues.

• The Nature of Color

  Fire engines aren't red—they only look that way.
  Color is a perception. When you stand outside and look at a fire engine light travels from the sun and bounces off the fire engine into your eye. To see color, both the light and your eye are as essential as the object. We start with the electromagnetic spectrum—the gamut of visible light—and its perception by the human visual system. Then we look at differences between additive and subtractive printing colors, transmissive color, opponent-process theory, colored media effects, etc.

  Measuring Color

  What is a color space and why is it of value? During this we relate the spectrum to Hue, Saturation, & Lightness and CIE-based standards of XYZ; xyY; L*a*b* and LCH. We explain why ΔE and new versions are important. As well as gamut differences and gamut mapping strategies.

  Color Management

  After an overview of color management, we discuss characterization and calibration, source vs. target color spaces, InterColor profiles, color space conversions, and PostScript color management, including Color Rendering Dictionaries (CRDs).

  Printer Technology Quality Factors

  The key technical quality factors of printer technology—resolution and addressability, color depth, screening, and image enhancement, and the tradeoff between color depth and screen frequency, are explained. We briefly look at the issues of resolution and color depth from the digital camera and scanner side to better understand the importance and interrelationship of these issues. Screening and graphic arts issues discussed are:

  • Rational screen angles
  • moiré
  • supercell screening
  • Screening with partial color depth
  • Sub-dot "contone" screening
  • Stochastic screening
  • De-screening
  • Sharpening and smoothing image enhancement options
  • Gray component replacement (GCR)
  • Undercolor removal (UCR)
  • Undercover addition (UCA)
  • and Trapping

  Printer Architecture & Technology

  Review color printer architecture and the range of print engine technologies—liquid and solid inkjet, xerography and its cousins, thermal transfer and dye diffusion, and some novel photographic and digital offset technologies. After briefly looking at some key color printers representing various technologies and market segments, representative color printers are selected for actual print quality comparison. Print quality comparisons emphasize the level of device-independent color rendition achieved with PostScript, including a variety of technologies, comparisons within the xerography, and alternative gamut mapping strategies. A few key cost-per-copy issues may be briefly discussed.