Jean-Pierre Van de Capelle

Two-dimensional transforms for device color calibration

Color device calibration is traditionally performed using one-dimensional per-channel tone-response corrections (TRCs). While one-dimensional TRCs are attractive in view of their low implementation complexity and efficient real-time processing of color images, their use severely restricts the degree of control that can be exercised along various device axes. A typical example is that 1-D TRCs in a printer can be used to either ensure gray balance along the C = M = Y axis or to provide a linear response in ΔE units along each of the individual (C, M and Y) axis but not both. This paper proposes a novel two-dimensional calibration architecture for color device calibration that enables significantly more control over the device color gamut with a modest increase in implementation cost. Results show significant improvement in calibration accuracy and stability when compared to traditional 1-D calibration.

Color Management in the Future

Todays color management in the commercial printing community is dominated by two types of workflows: ICC workflows [1] and more traditional, “device CMYK” workflows. In many cases the device CMYK workflows use ICC color management in the prepress arena to convert digital RGB images to CMYK. Consequently, one could argue that ICC workflows actually dominate the space. For many applications, ICCbased color management fulfills most of the needs of the typical CMYK printing used by a large number of commercial printers, irrespective of how the print-stream data is formatted or which color space is used within that print stream. As such, one should realize that the incremental economic value of diff erent, future color management systems will be relatively small for this market. One can argue that most of the needs of the commercial printer were already fulfilled with the ICC version 2 or version 3 specifications, and that the incremental value of the version 4 specification is rather small. This version provided some clarification as well as rendering intents for input and display devices. This does not mean that todays color management has no problems. The remaining problems are often of a very fundamental nature, such as device color stability, significantly diff erent device color gamut, or the influence of the illuminant on the color rendition of the printed material, which can include metamerism and fluorescence. Metamerism is a psychophysical phenomenon commonly defined as a situation in which two samples of a color match under one illumination condition, but fail to match under another condition

Usage of the Chameleon accelerator for color transformations

A hardware color transformation accelerator, in CMOS ASIC form, and its usage are described. The CHAMELEON ASIC performs multi-dimensional tetrahedral interpolations at a speed of 10 Million (32 bit) pixels per second. The achieved accuracy of the color transformation is a major topic, which strongly depends upon the kind of interpolation used. A report is made on the application of this ASIC in different fields of the graphics industry and the achieved results are compared to the desired market needs.