DIGITAL IMAGE PROCESSORS

A digital image processors (digital signal processor) are a valuable tool for increasing the contrast, smoothness, and signal-to-noise ratio of the raw microscopy image and for performing complex operations such as background subtraction and enhancement of image contrast. This unit (a dedicated computer) is positioned between the zoom microscope and the TV monitor and other recording devices. The processor converts the raw image into digital form by an A/D converter, performs image processing operations digitally, and reconverts the processed signal back to analogue form through a D/A converter.

The final processed image can be displayed on a TV monitor or sent to other devices such as a thermal printer, VCR, or computer, which print, record, or receive the processed analogue signal. Available image processing operations are displayed in a menu on the TV screen and are activated by clicking on them with a computer mouse. The current processors are quite sophisticated and perform many of the functions contained in computer software programs used for processing and analyzing images from digital cameras. Although they are expensive, image processors are indispensable for many video applications. The operations performed by a high-end digital image processor include the following:

Live: Displays the live raw image.

Real-time background subtraction: A background image containing image artifacts such as dust, scratches, and uneven illumination is captured and stored in memory. The background frame is subtracted from each incoming raw image frame, and the corrected background-subtracted frame is displayed in real time (30 frames/s) on the TV monitor.

Frame averaging: Improves the S/N ratio and smoothness of the image. The designated number of frames to be averaged is held in a frame buffer, and the average is computed and displayed at video rate. At each calculation/display cycle, a new frame enters the buffer and the oldest frame is discarded.

Frame accumulation: Accumulates the signals of the designated number of frames into a single image frame to produce a clearer image (higher S/N ratio). Subtraction: Does a simple subtraction of the input image from a memorized image.

CCD on-chip integration: Integrates the image for the designated number of frame equivalents instead of accumulating or averaging individual 1/30 second frames. This procedure gives a clearer picture of low-light specimens.

Background subtraction plus accumulation: Combines the functions of background subtraction and frame accumulation.

Sequential subtraction: Removes those features that remain stationary in a stack with a designated number of frames. Only moving objects are displayed.

Rapid transition isolation: Removes image features from the processed image that remain stationary or do not change in intensity, leaving an image representing features that exhibit rapid change.

Spatial filtering: Enhances high or low spatial frequency information. Masks composed of various pixel matrices are used for edge enhancement, shadow enhancement, sharpening, or smoothing of the image.

Image trace: Traces the trajectories of moving objects.

Maximum density trace: Traces the pathways of moving objects that are brighter than the background.

Minimum density trace: Traces the pathways of moving objects that are darker than the background.

The image display commands of the processor are also versatile and include contrast adjustment with image histogram display, with adjustments for setting the white and black end points; _ adjustment for differential adjustment of bright and dark features; real-time edge sharpening; split-screen display; pseudocolor; superimposition of a real-time image over an image stored in memory; real-time zooming; superimposed display of scale bar, typed comment, and timer/clock.

Image processors also provide image analysis features for measuring lengths of traced lines, areas, particle counts, interpoint distances, and velocities. Intensity analysis commands allow you to measure intensities of points and average intensities within areas; you can also obtain intensity profiles along a line through an image, an image histogram of a designated region of interest, and a three-dimensional profile of intensity levels within a defined region of interest.