1. Field of the Invention
The present invention relates to the generation of color models which characterize display devices.
2. Description of the Related Art
Typically, display devices, such as liquid crystal displays (LCD) or cathode-ray tubes (CRT), produce colors on a screen by combining different amounts of red, blue and green light. The actual color produced from specific combinations of RGB light varies from display device to display device. Therefore, in order to consistently reproduce colors on different displays, manufacturers of display devices create color models that characterize the output of a particular display device in terms of a standard color coordinate system. For instance, Commission Internationale de l'Enclairage (CIE) XYZ color coordinates are often used.
Conventionally, a display device characterization is represented by the following equation:
      [                            X                                      Y                                      Z                      ]    =            [      M      ]        ·          [                                                  R              ′                                                                          G              ′                                                                          B              ′                                          ]      R′G′B′ are radiometric scalar values that are related to device RGB values according to generally non-linear relationships commonly called “gamma curves.” The matrix M is a 3×3 tristimulus matrix which relates the linear R′G′B′ values to XYZ values.
Conventionally, the tristimulus matrix M is populated according to the following equation:
  M  =      [                                        X                          r              ,              max                                                            X                          g              ,              max                                                            X                          b              ,              max                                                                        Y                          r              ,              max                                                            Y                          g              ,              max                                                            Y                          b              ,              max                                                                        Z                          r              ,              max                                                            Z                          g              ,              max                                                            Z                          b              ,              max                                            ]  Each X, Y, and Z value in matrix M corresponds to a measured XYZ value when the maximum R, G and B values are applied to the device. Once determined, the tristimulus matrix M maps any linearized R′G′B′ value used by the display device to the actual XYZ color that the display device is expected to reproduce.
This conventional model for characterizing display devices is built upon the assumption that the measurements are done in a dim environment where ambient lighting has little effect on the measurements. This assumption may not always prove true. For example, many display devices will produce a non-zero amount of light when displaying the color black. This black point measurement is often called flare. In addition, a non-zero flare value can be caused by higher than optimal ambient lighting. In either case, the flare skews the results of the measurements.
Attempts to measure or estimate flare, and correct for its effect, are well-known in the art. However, these attempts have generally been unsatisfactory. For instance, the effect of flare has been built into a general gain-offset-gamma-offset (GOGO) model for gamma curves. This model attempts to correct for the effects of flare in gamma curves. However, the effect of this model is limited since each gamma curve can only act on each channel independently. Other efforts have been made to correct for flare in the tristimulus matrix, but these efforts still utilize the conventional formula for populating the matrix.
As such, the conventional method does not fully address problems associated with flare, since only measurements at maximum RGB values are used to populate the tristimulus matrix. Even if flare is accounted for, the measurements themselves may be inaccurate, and therefore, the resulting tristimulus matrix may not provide the most accurate device characterization.