OpenWindows Advanced User's Guide

10.5.1 Monitor Calibration Concepts

Every color device, such as a scanner, monitor or printer, has a set of color reproduction characteristics. The KCMS software uses a set of characterization data for a particular make and model of a color device. Gathering characterization data of a scanner or a monitor requires highly specialized instruments and is called characterization. Characterization results in a file called a nominal profile that contains detailed, machine-readable color reproduction information. A collection of nominal profiles are provided with the KCMS product. Nominal is an average color response derived from measurements taken from several samples of each type of device.

Note -

Currently only monitors can be characterized; scanners and printers cannot be characterized.

The nominal profile represents the color reproduction of a device at known settings and in a known environment. Nominal profiles are adequate for most workstation users. But the reproduction characteristics of a color device change due to age, media, and temperature. To obtain accurate color reproduction, you should adjust the nominal profile to reflect the actual reproduction characteristics of your device in your viewing environment. The process of adjusting the nominal profile is called calibration. For more information on adjusting your viewing environment, see "10.5.2 Adjusting Your Viewing Environment". For more information on calibrated profiles, see " Calibrated Profiles and Visuals".

Although scanner and printer calibration is difficult, video monitor calibration is accomplished by displaying a programmed sequence of test colors and measuring the output of the display by a puck. The KCMS library then computes the correction factors necessary to compensate for the inaccuracies of the monitor. This process is monitor calibration. The KCMS Calibrator Tool performs monitor calibration. See "10.5.4 Running Calibrator Tool"for instructions on how to calibrate your monitor with Calibrator Tool.

If you adjust any of your monitor's front-panel controls (such as Brightness, Contrast, Picture or Black Level) you need to recalibrate to update the color reproduction of your monitor. If you are a critical user of color, you should recalibrate whenever you adjust any of these settings or once every two weeks. You must recalibrate if you replace your monitor or your framebuffer.

Application programs can access the KCMS library directly through the KCMS application programming interface (API). If you purchased the Software Developer's Kit (SDK), see the KCMS Application Developer's Guide for detailed information on the KCMS API. Calibrated Profiles and Visuals

When Calibrator Tool calibrates your monitor it produces one calibrated profile for each frame buffer's visual. When images are displayed on a monitor, two conditions may exist that affect whether the resultant color appears the same on two different devices: the slow shifting of color and the use of X visuals.

Recalibrating corrects the slow shifting of color. Your frame buffer's hardware gamma lookup table (LUT) corrects X visuals. A visual is a data structure describing the display format a display device supports. The visual describes the display characteristics for each pixel in the window. In other words, a window's visual instructs the display device's hardware gamma LUT how to interpret the value of the window's pixels. When the visual goes through the gamma LUT, it is then corrected.

If the KCMS software calibrates a corrected X visual, the resultant color will not appear the same on two different devices because the visual will be gamma corrected twice. The KCMS software determines if the X visual has been corrected with a hardware gamma LUT to ensure color consistency. For more information on X visuals and hardware gamma LUTs, see the xgetvisualinfo(3) and xsolarisgetvisualgamma(3) man pages.

The calibrated profile that describes your monitor is copied to the /etc/openwin/devdata/profiles directory. Read-only nominal profiles are in /usr/openwin/etc/devdata/profiles.

A copy of the profile you select with Calibrator Tool (see " To Select a Monitor") is made for each type of color visual supported by your frame buffer. GrayScale or StaticGray visuals are not considered because they are not color visuals. If your frame buffer supports both PseudoColor and TrueColor visuals, two or more sets of measurements will be taken by Calibrator Tool.