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HSI Slicing
This interactive tutorial illustrates the use of thresholding in HSI color space to create a binary image. For color images, thresholds may be applied to each color channel, and this may be done for RGB, LAB, HSI or any other set of color coordinates. In most cases, HSI coordinates correspond best to human interpretations of color. Selecting a target color from a point on an image (as shown in the tutorial) and then adjusting tolerances to hue, saturation and intensity around that point is often a good strategy, and much simpler to understand than trying to set limits on red, green and blue.
The tutorial initializes with a randomly selected specimen appearing in the Specimen Image window. The Choose A Specimen pull-down menu provides a selection of specimen images, in addition to the initial randomly chosen one. Click on any point in the image to select a representative color, whose Hue (H), Saturation (S) and Intensity (I) values are shown at the right along with the corresponding color patch. The Hue is shown as an angle from 0 to 360 degrees, and the Saturation and Intensity are shown on an arbitrary 0 to 100 scale. The sliders are used to adjust a tolerance range for H, S and I around the values of the sampled color. Moving each slider to the right increases the tolerance range, which is shown numerically above the slider. When the Display Image setting is set to Binary by clicking on the button, the displayed image shows the pixels whose values lie within the designated ranges as white, and the background pixels 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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