The DN100 camera control unit (CCU) is equipped with a series of image processing functions that enable the microscopist to quickly and easily correct imaging problems that arise from low or high contrast, poor focus, insufficient or uneven illumination, specimen shading or discoloration, and noise.

Shading, which is defined as the variation in the amplitude of the output signal current when a video sensor is uniformly illuminated, is often manifested in one side of the output image appearing brighter or darker through a continuously varying shade. Shading may result from a lack of uniformity in detector sensitivity, but the problem is often manifested or exacerbated by uneven specimen illumination. Shading correction or compensation is typically performed by increasing the signal amplitude or detector sensitivity in order to counteract the brightness variation.

The DN100 camera control unit is equipped with a shading correction function that can be used to compensate for insufficient illumination around the periphery of the image. Included in the software are five levels of compensation ranging from a relative value of 10 percent to 50 percent in steps of 10 percent. A typical example of shading correction is illustrated in Figure 1. The shading correction feature of the DN100 can be accessed through the OPTN submenu or through the Power On Setting panel of the Setup menu.

Random noise is another problem that is commonly encountered in fluorescence microscopy, due to the low light levels that often accompany this increasingly popular technique. The presence of random noise can seriously degrade the spatial resolution of a digital image. One method of remedying the situation is to average image frames in order to enhance spatial resolution while sacrificing a small degree of temporal resolution. The DN100 has a noise reduction feature that can be accessed through the OPTN submenu or through the Power On Setting panel of the Setup menu. Because image averaging tends to leave an afterimage on the television screen or computer monitor, noise reduction should be turned off when imaging a moving subject with the DN100 time-lapse software. Figure 2 illustrates the effects of image averaging in reducing noise in digital images captured using the DN100 digital camera system.

Tone or gamma is a function that is useful for improving image brightness and contrast, especially for digital images that display a reduced dynamic range. In order to allow tone adjustment that is appropriate for various types of microscopic imaging techniques, the DN100 is equipped with five different tone settings. These five tone settings are described briefly as follows:

• 1. Low: This setting is suitable for natural imaging under uniform illumination when the microscope is properly configured. In situations where the substage condenser aperture diaphragm is closed excessively, the Low setting can often compensate by reducing image contrast. However, inherent focus problems may still arise.

• 2. Mid: In this mode, the image contrast is increased, resulting in a clearer image. This is the default setting and should be utilized when the microscope is adjusted for Köhler illumination and the substage condenser aperture diaphragm is opened to achieve the correct numerical aperture.

• 3. High: When this setting is selected, the contrast is increased even more than with the Mid setting. Use this setting when the condenser aperture is wide open or when specimens lacking in contrast (transparent) are imaged under conditions that produce inherently low contrast, such as brightfield illumination.

• 4. Linear: In this setting, gamma compensation is turned off. The algorithm is appropriate for image processing. Do not use this setting for routine imaging with contrast-enhancing techniques such as phase contrast, Hoffman modulation contrast, or differential interference contrast.

• 5. Enhance: This setting is suitable for high contrast imaging, and is especially useful for imaging materials or specimens with inherently low contrast. For example, transparent specimens, such as living cells and tissues imaged in brightfield illumination will benefit from this technique. In reflected light microscopy, use the Enhance setting for highly specular materials that reflect a high degree of illumination back into the objective.

In some cases, a special effect may be applied to a digital image in order to increase the visibility of certain specimen details. For this reason, the DN100 camera control unit is capable of displaying the output image after it has been modified by any one of five different color enhancement effects. A brief description of the available effects follows (refer to the figures below for details about each setting).

• Normal: In this mode, the image is displayed in the natural color scheme that is observed in the microscope eyepieces (Figure 3). A majority of the images captured with the DN100 should be done using the Normal mode to ensure accurate reproduction of all specimen details.

  

• Nega: The Nega (an abbreviation for common photographic term Negative) displays a color-inverted form of the image, where red, green, and blue values are converted into their complementary colors (Figure 4). The technique is useful in situations when color inversion can be of benefit in exposing subtle details or in quantitative analysis of specimens.

  

• Blue Back: This mode shows the black portions of a grayscale negative image in blue (Figure 5). Often useful to reveal details in specimens having a high degree of contrast, the Blue Back filter can aid the microscopist in examining a wide spectrum of difficult specimens.

  

• B & W: An abbreviation for the term Black & White, this mode displays a grayscale form of the image (Figure 6). In many cases, digital images destined for publication in scientific journals must first be converted into black & white renditions of those captured in full color. The filter can often aid the microscopist in preparing images for publication or oral presentation.

  

• Sepia: This mode displays a sepia (brown scale) form of the image (Figure 7). Although of little utility in a majority of circumstances, the Sepia filter can often be employed to alter image color characteristics to improve the visualization of specimen detail.

Color balance is a function that enables the operator to perform an adjustment that increases or decreases the level of red, green, and/or blue in a digital image. The DN100 camera control unit is equipped with a versatile color balance function that features two different color balancing algorithms. A gain-based algorithm is provided that permits fine adjustments to the white balance, and a matrix-based algorithm is also available that allows the user to adjust red, green, and blue levels without changing the white balance of the image. Figure 8 presents an example of an image that was corrected by using color balancing.

A slightly blurred or out-of-focus image can often be corrected using the DN100's built-in sharpness control settings. Six sharpness levels are available, ranging in relative value from 0 through 5 in increasing order of the sharpness effect produced on the resulting image. Figure 9 provides an example of sharpening a blurred or out-of-focus image.

The tone, effect, color balance, and sharpness controls can be accessed from a number of different locations. Information on operating these controls is available in the following sections:

• Main Menu Features - A central feature of the DN100 network camera system main menu window is the convenient button toolbar, which provides instant 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 - Up to three custom environments for the DN100 camera control unit can be configured by the operator with this setting panel.

• Room 1 Network Client Interface - Providing a network-based remote access to the DN100's camera control unit, this virtual room allows a remote operator 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.