DIGITAL COLOR SYSTEM AND METHOD SUMMARY OF THE INVENTION
WHICH PROVIDES A VISUAL MATCH It is an object of ^ p[esent invention to provide a system
ACROSS DIFFERENT INPUT AND OUTPUT fljat preserves the visual appearance of colors from a variety
VIEWING CONDITIONS Of mput media or color specifications with differing viewing
BACKGROUND OF THE INVENTION * environments to a variety of output media or color specifi
cations with differing viewing environments.
1. Field of the Invention A further object of the present invention is to provide a The present invention is directed to color reproduction method and means for forming an intermediate color data
systems that accept color information from multiple sources metric such that the appearance of colors from a variety of with differing media and viewing environments for editing input media or color specifications with differing viewing and layout, and then outputs the color information for environments is preserved when expressed using this interreproduction on one or more output devices using different mediate color data metric.
media and being viewed in differing viewing environments Also an object of the present invention is to provide
or for transfer to another system for additional processing consistent color reproduction across a wide variety of output
and, more particularly, to systems that provide a visual devices, media and viewing environments from an interme
match across different input media and viewing conditions diate color data metric that preserves color appearance from
and different output media and viewing conditions. a variety of inputs.
2. Description of the Related Art Another object of the present invention is to provide the Color information processing systems in which the color 20 capability for optimized color reproduction according to the
data passes through a digital intermediary allow improve- intent of the application from an intermediate color data
ments to be made using a single means which may be a metric that preserves color appearance from a variety of
digital computer. Alterations to color and tone scale of an inputs.
image can be made in a convenient and adaptable way. An object of the present invention is to provide methods
Colors for corporate logos or presentation graphics can be 25 an^ means for color data processing in the intermediate
made in a consistent fashion. Color information as images, color data metric that preserves color appearance from a
graphics, or motion video can be combined and edited in a variety of inputs.
convenient fashion. Many of these types of improvements A further object of the present invention is to provide are known to those skilled in the art. For example. U.S. Pat. methods and means for previewing on a system monitor a No. 4,500.919 entitled "COLOR REPRODUCTION 30 simulation of selected color rendering choices and effects SYSTEM", by W. F. Schreiber, discloses an image repro- which takes into account the characteristics of the output duction system of one type in which an electronic reader device, media and viewing conditions, scans an original color image, which may be in the form of The above objects can be attained by a color management a transparency or print, and converts it to an electronic system that converts or transforms color signals from an image. A computer and an interactive operator interface. 35 input device or input color specification into equivalent including a video monitor, permit an operator to edit the device-independent tristimulus values, relatable to human image by means of displaying it on a monitor. When the visuai response, relative to the input viewing environments operator has composed a desired image on the monitor, the through an analytical model of the device response. These computer causes the output writer device to make an inked input device-independent tristimulus values then may be output of the reproduced image. This system attempts to 40 converted or transformed into an intermediate color data provide image consistency by trying to preserve a tristimu- metric associated with a well-defined or reference viewing lus match between the monitor and the hard copy input and environment by the use of analytical models of human output media. This system has the limitation that the viewing chromatic adaptation mechanisms that can account for the conditions for the monitor, original and hard copy output differences between the input viewing conditions and the media must be carefully controlled to maintain the require- 45 viewing conditions associated with the intermediate color ment of identical comparison viewing conditions as required data metric. Once in the intermediate color data metric, color by a tristimulus match. A tristimulus match can only main- processing, such as color substitutions, editing, cut and paste tain the true appearance under identical viewing conditions. from different inputs, etc. may be performed according to the This is a significant limitation requiring careful attention to needs of the application. When an output device, media and the viewing environment. 50 viewing environment have been determined, the color data Another approach, as suggested by R. S. Berns (SID 92 in the intermediate color metric is first converted or transDigest page +549), is to transform all input color informa- formed into equivalent tristimulus values for the output tion into a common intermediate viewing condition inde- viewing environment again using analytical models of pendent color space using elaborate models of the human human chromatic adaptation mechanisms that can account visual system to account for the viewing environment dif- 55 for the differences between the output viewing conditions ferences between inputs and outputs. These models have the and the viewing conditions associated with the intermediate drawback that it may take up to eight color variables (R. W. color metric associated with the well defined viewing enviG. Hunt, Color Res. Appl. 16, 145-165 (1991)) to describe ronment. These tristimulus values are then converted into the appearance of color in a viewing condition independent in-gamut tristimulus values according to the intent of the manner. This approach has the further difficulty that it is very 60 application and the color gamut of the selected output difficult to invert the viewing condition independent model device. Finally the in-gamut tristimulus values are converted to obtain equivalent output device colorant values for output into device color values using an inverse analytical model of viewing conditions from the viewing condition independent the device's color response. To preview on the system variables. For many applications the complexity of the Hunt monitor the selected output rendering, the calculated output approach is not necessary and a simpler approach is needed 65 device colorant values can be transformed through an anawhich focuses on me essentials of the requirements for a lyrical model of (he device's response into tristimulus values visual match. relative to the output viewing conditions. These in turn can