Robust Stereo Calibration System and Method for Accurate Digital Image Correlation Measurements


Reference #: 00612

The University of South Carolina is licensing a stereo calibration method for accurate digital image measurements in multi-media applications. This method allows users to employ standard optical equipment to measure accurately the motion and strain of an object immersed in a medium that is different from the one in which the measurement equipment is located. The method can be used with a variety of measurement systems and interfaces.


It is difficult to measure motion and strain accurately for objects that are immersed in a medium that is different from the medium in which the optical measurement system is located.  From example, measuring the deformation of biological materials, such as vascular arteries, over an extended period of time usually requires the biological material to be submerged in a bathing medium with controlled temperature and pH.  An optical measurement system, such as a camera, is often used to measure the motion and strain of the biological materials in the bathing medium. However, when light travels though different media, it refracts at the surface.  Dr. Sutton’s study and measurement of the strain errors introduced by refraction when a camera in the air measures a planar specimen submerged in water showed that strain errors rise rapidly as the angle between the optical axis and the interface changes.  When the angle is 12”, the strain is as high as 1%.  Therefore, there was a need for an accurate way to correct distortion caused by refraction and to calibrate measurement systems for use in multi-media applications.

Invention Description:

This method calibrates the shape and position of the interface when the measurement system is in one medium and the measured object is in a different medium in order to account for and correct distortion caused by refraction.  Therefore, the method produces an accurate measurement of the motion and strain for objects in media.

This method has a number of advantages.  It applies especially well to optical measurement systems, but can also be used on other measurement systems.  This method preserves the accuracy of measurements when used for multimedia applications.  Users can set up measurement systems in their preferred medium and measure what is happening in another medium without sacrificing any accuracy. The method is also not limited to a particular shape of interface.  It can be used for most interfaces including multiply curved, singly curved, and planar interfaces.  The method is not limited to applications with only two media.  Between the medium with the measurement system and the one with the object, there can be multiple media as long as the media have distinct interfaces.  The method also allows users to use standard measurement systems in applications that would normally make that impossible.  For example, standard optical systems cannot be used in environments with erosive chemicals or high temperatures, which would require specially-made measurement systems.  This method allows the user to restrict the harmful environment with a transparent material and use a standard optical measurement system.  Given that costs increase as a measurement system’s specialty increases, this method allows users to control costs while maintaining accuracy.

Potential Applications:

•    Applications where the measurement system and object to be measured are in two different media.

•    Applications where the interface is unusually shaped.

•    Applications where there are multiple media and multiple interfaces between the measurement system and the object.

•    Applications where the object to be measured is in a harmful environment that would otherwise preclude using standard measurement equipment .

Advantages and Benefits:

•    Produces accurate measurements of the motion and strain for objects in one medium when the measurement system is in a different medium.

•    Can be used with a variety of measurement systems and shapes of interfaces with accuracy.

•    Can be used in applications where there are multiple media.

•    Allows users use their preferred medium and accurately measure objects in other media.

•    Allows users to employ standard measurement systems in harmful environments, ensuring accuracy and cost effectiveness.


Patent Information:
Title App Type Country Serial No. Patent No. File Date Issued Date Expire Date Patent Status
Robust Stereo Calibration System and Method for Accurate Digital Image Correlation Measurements Utility United States 12/553,561 8,248,476 9/3/2009 8/21/2012 2/1/2031  
For Information, Contact:
Technology Commercialization
University of South Carolina
Michael Sutton
Xiaoclan Ke
Dorian Garcia
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