There are several candidate parameters to describe feature size. The area, determined by counting pixels and often expressed as the “equivalent diameter” (the diameter of a circle with the same area), is widely used. But for some applications other diameters, such as that of the largest inscribed or smallest circumscribed circle, may be more appropriate. Length is usually determined as the greatest distance between any two points in the object, but for a long, curved object like a fiber the length of the skeleton is more meaningful, and there are a great many alternative definitions for breadth. The perimeter of objects is difficult to determine because (except for some smooth objects such as those bound by a membrane or surface tension) the resolved perimeter usually increases in length with magnification.

Whatever measure of size is chosen, determining the values is typically performed on a binary (black and white) image after any necessary processing such as filling of holes, morphological smoothing, rejection of small features due to dirt or noise, watershed separation, and so on. Calibration may be performed by imaging a stage micrometer. Statistical analysis is often performed on the resulting data. This interactive tutorial illustrates typical procedures for measuring the sizes of objects, as well as typical sequences by which data are obtained and presented.

The tutorial initializes with a randomly selected specimen imaged in the microscope appearing in the Specimen Image window. The Choose A Specimen pull-down menu provides a selection of images, in addition to the initial randomly chosen one. The Original button shows the original image. The Calibration button adds a scale bar. The Thresholded button shows the binary image produced by brightness thresholding, while the Processed button shows the result of morphological processing to remove noise, fill holes, separate touching features, etc. as required by each image. The Measured button shows lines showing the measurements performed on the features in each case, and the Report button shows these lines superimposed on the original image for reference. The Results button shows a statistical summary of the measurement results.

---

BACK TO INTRODUCTION TO DIGITAL IMAGE PROCESSING AND ANALYSIS

BACK TO MICROSCOPY PRIMER HOME

Questions or comments? Send us an email.

© 1998-2009 by Michael W. Davidson, John Russ, Olympus America Inc., and The Florida State University. All Rights Reserved. No images, graphics, scripts, or applets may be reproduced or used in any manner without permission from the copyright holders. Use of this website means you agree to all of the Legal Terms and Conditions set forth by the owners.

This website is maintained by our
Graphics & Web Programming Team
in collaboration with Optical Microscopy at the
National High Magnetic Field Laboratory.

Last modification: Tuesday, Sep 11, 2018 at 01:48 PM

Access Count Since July 20, 2006: 7664

For more information on microscope manufacturers,
use the buttons below to navigate to their websites: