The color balance of a digital image produced by an optical microscope is dependent not only upon the spectrum of wavelengths transmitted through or emitted by the specimen, but also on the spectral content of the light source. In color digital cameras that utilize charge-coupled device (CCD) imaging detectors, a range of balance adjustments is often necessary in order to produce acceptable color quality in digital images.

The human eye can readily adapt to identify a white object as white even when the surrounding light intensity changes. On the other hand, digital cameras require careful adjustment of the red, green, and blue signal settings by software control in order to achieve the same end. In most digital cameras, illumination intensity and color temperature must be measured and adjusted to ensure that a white object is recorded as white. This process is often referred to as adjusting the white balance, and is a software or hardware option on many digital cameras.

Modern scientific CCD digital cameras incorporate reference circuitry that contains a digital signal processing (DSP) integrated circuit for adjusting the color balance. This circuit provides a series of look-up tables (LUT), which are utilized by the software to adjust the red, green, and blue (RGB) signal amplitudes to arrive at the proper color balance for a specific illumination intensity and color temperature. Often, the look-up tables will contain information about tungsten-halide (at a variety of color temperatures), mercury arc, and xenon arc lamps, among others. The RGB system is one of the primary color models utilized to specify and represent colors in computer-controlled cameras and software. White is produced by combining equal parts of all three colors (red, green, and blue) at levels of 100 percent.

A typical adjustment for white balance in digital photomicrography is illustrated in Figure 1, where the specimen is an octal bus switch integrated circuit housed on a wafer containing several hundred units. On the left (Figure 1(a)) is a digital image of the circuit before white balance adjustment. Note that the overall color tones are dark and have a bluish tone. After white balancing, the image appears more natural with a greater range of tonal values and reveals a greater number of circuitry details.

The DN100 digital camera system is equipped with a white balance feature that allows setting the image white balance based on the contents of the currently displayed image. If the camera head is mounted on a microscope, then the field of view should be adjusted so as not to include any specimen details before white balancing is activated. Alternatively, the specimen can be removed so that the entire viewfield is white before setting the white balance. Setting the image white balance while the display window is not empty may cause the image to take on a color cast, which can seriously impair image contrast and result in colors that deviate from those of the specimen.

There are a number of ways to activate the white balance adjustment feature of the DN100 CCU. Information on the DN100's white balance controls can be found in the following sections:

• Main Menu Features - A central feature of the DN100 network camera system main menu window is its button toolbar, which provides convenient access to a number of the most commonly used camera control functions.

• CAM Submenu Features - This important menu contains a number of features useful for measuring and calibrating image focus, controlling exposure mode and time, and adjusting camera sensitivity.

• Power On Setting Panel - This panel permits the user to configure three initial environments for the camera control unit.

• Room 1 Network Client Interface - This virtual room provides network-based remote access to the DN100's camera control unit, allowing a remote user to download live microscope images from the camera control unit. Other features include an image annotation function and an electronic zoom function. An option is also available to allow the remote user to take limited control of the camera control unit.