The present invention relates to evaluating the accuracy of a color printing system.
It is conventional in the electronic printing industry to desire to print documents so that the colors from a printing press match the colors from a client's desktop color printer. The traditional approach has been for the printing press company to repeatedly make slight adjustments to the printing process until the colors from the printing press match the colors from a client's desktop color printer. This approach is expensive due to the time spent by skilled operators and the expensive equipment required to make the adjustments.
An emerging approach is to manage colors from their creation to the printer, to compensate for differences in computer monitors, desktop printers, and printing presses. The International Color Consortium promotes standardization of color management, centered around representing colors in a profile connection space (PCS). Each printer in a color managed workflow is described by a color profile, which defines how colors in the PCS control how much printer-specific colorant is used to print that color accurately. Different printers will be given slightly different color values for a particular color to compensate for the slight differences in each printer, so that ideally, the same color will be printed by all of the printers. The workflow can be described by a job definition format (JDF) file that can be associated with any printer definition language, such as the Adobe® portable document format (PDF), Adobe® PostScript® language, or Hewlett-Packard® printer control language (PCL).
Color profiles may also be used to display accurate colors, despite variances in computer monitors. Different computer monitors have different color profiles in a color managed workflow. Each such profile defines how colors in the PCS control how much monitor-specific phosphor is used to accurately display that color. Different monitors will be given slightly different color values for a particular color to compensate for slight differences in each monitor, so that ideally, the same color will be displayed by all the monitors.
Similar profiles can also be used to define characteristics of scanners and other color devices.
In a typical workflow, the user creates a color in some application color space using some color-managed application. One common application color space is L*a*b*, which has an algebraic relationship with a standard PCS. Another common application color space is RGB, which must be associated with a color profile in a color managed workflow. The RGB color profile is typically a monitor profile or scanner profile. The RGB color space combined with its color profile defines the relationship to the PCS.
In the most common workflow, color-managed documents are printed to printers or printing presses (output devices) that understand the PostScript language. Each of these output devices has a built-in printer profile that defines how colors in a particular PCS control how much printer-specific colorant is used to accurately print the color. One such PCS is the XYZ color space, which has been defined by the Commission International de l'Éclairage (CIE). To print colors in a document, the application and the driver together transform colors according to each associated application color space and generate a file of PostScript language commands. These commands, when executed by the output device, request colors in the XYZ color space. Using the built-in printer profile (called a color rendering dictionary or CRD in PostScript), these colors in XYZ color space are converted into device colors, which control how much colorant is used.