Differential hysteresis processing enhances image data

In applications ranging from electron microscopy to metallurgical analysis, it is necessary to extract and highlight patterns within a digital image characterized by variations in image intensity.

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In applications ranging from electron microscopy to metallurgical analysis, it is necessary to extract and highlight patterns within a digital image characterized by variations in image intensity. While many different methods have been developed to accomplish this task, a new software package, Lucis from Image Content Technology (New Britain, CT), both enhances and reveals image detail undetectable to the human eye.

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The Lucis package uses a differential-hysteresis-processing (DHP) algorithm to process the image, selectively detecting and emphasizing aspects of the visual information. Because hysteresis processing is a technique that filters out contrast variations in an image, the amount of contrast variation to be removed can be specified as a number referred to as a window size or cursor size.

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In differential hysteresis processing, if the cursor size is 20, areas of intensity variations less than 20 are filtered out but large intensity variation, such as the transition from pixel 8 to pixel 11 are maintained (top). Contrast variations less than the cursor width are removed regardless of the absolute value of the pixel's intensity. Hysteresis processing filters out the contrast variations occurring near the bottom of the contrast range, where the image is dark gray, and near the top, where the image is light. Subtracting the output of hysteresis processing from the original data preserves and enhances the small contrast variations in an image (bottom). (Photo courtesy of Brian Matsumoto/University of California.)

In operation, DHP moves this cursor across the image. As the horizontal position of the cursor moves from pixel to pixel, the vertical position of the cursor depends on whether the pixel is above, below, or inside the cursor. If the pixel is above the cursor, the cursor shifts upward. If the pixel is below, the cursor shifts downward. If the pixel is within the cursor, the cursor keeps the same intensity value as its previous value.

One way to preserve and enhance the small contrast variations in an image is to subtract the output of hysteresis processing from the original data. Since the hysteresis output removes small variations but preserves large variations, subtracting the hysteresis output from the original image effectively reduces the large variations, leaving the small variations in the image. Differential hysteresis processing is the result of performing the hysteresis-then-subtraction process on two copies of the original data, using a different cursor size for each process, and subtracting one result from the other.

PACKAGE IN USE
Optronics (Goleta, CA) already offers the Lucis package with its MagnaFire, a megapixel imaging camera system designed for scientific imaging applications costing less than $8000, the MagnaFire SP is an IEEE 1394 Firewire camera designed specifically for microscope applications. According to Optronics, Lucis operates well on brightfield, fluorescence, and other image types where poor contrast or subtle exposure elements hide image details. The camera has already been used in conjunction with the Lucis package by Brian Matsumoto, of the University of California (Santa Barbara, CA) to enhance cell images.

Another adopter of the Lucis package is Blue Ridge Pressure Castings (Lehighton, PA). That company has equipped an x-ray machine from Pantak (East Haven, CT) with the Lucis software for use in analysis of die castings. According to Andy Behler, vice president of operations, Blue Ridge uses the equipment to search for defects in samples from the production floor and can provide feedback to casting-machine operators in minutes, enabling them to optimize their processes and produce higher-quality products.

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