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Interactive Thresholding
The most widely used thresholding methods utilize the image histogram. Manual interactive setting of thresholds on the histogram while viewing the image can be used to produce a binary image, and most programs offer this capability. This interactive tutorial illustrates the use of brightness thresholding or slicing to create a binary image.
The tutorial initializes with a randomly selected specimen imaged in the microscope appearing in the left-hand window entitled Specimen Image. The Choose A Specimen pull-down menu provides a selection of specimen images, in addition to the initial randomly chosen one. Clicking the Color Images box allows selection of color images rather than grayscale ones. Adjacent to the Specimen Image window is the Grayscale Histogram window that shows the histogram of the brightness values in the specimen image. The superimposed red lines appearing in the Grayscale Histogram window represent the upper and lower level threshold settings. These are adjusted using the Threshold Levels sliders for the Upper and Lower brightness threshold values. The Display Image buttons display on the right either the Original image, or a Masked Original (in which the pixels with brightness values between the two threshold levels are shown with their original color or brightness and the background is erased to black), or the Binary image in which the selected pixels are shown in white and the background as black.
Contributing Authors
John C. Russ - Materials Science and Engineering Dept., North Carolina State University, Raleigh, North Carolina, 27695.
Matthew Parry-Hill, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.
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