National Institute of Standards and Technology

Simultaneous Calibration of Multiple Microscopes using an iPhone

Summary

The iPhone liquid crystal display (LCD) allows efficient and accurate calibration of an inexpensive array of handheld microscopes for measuring microscopic dynamic events over a large field of view (FOV).

How does one build an inexpensive array of handheld microscopes for measuring microscopic dynamic events over a large FOV? The challenges of building such an instrument lie in estimating spatial, temporal, and color properties of each handheld microscope, as well as in integrating individual FOV into a large FOV seamlessly. Figure 1 illustrates the use of traditional objects for color, spatial, and pose calibrations in comparison with the iPhone LCD used for calibrations.

iPhone calibration
Traditional objects used for color (A), spatial (B), and pose (C) calibrations. These objects are replaced by an iPhone LCD and the rendering of a virtual object (D).

Description

To explore the above calibration challenges with arrays of microscopes, we first assembled a linear array of two digital handheld microscopes (Dino X Lite AM-413MT5, 12 frames per second, 1280 x 1024 image pixel dimensions), and then connected them to a computer via USB. These microscopes are currently used primarily for skin and scalp dermatology, and printed circuit board inspection. Although the calibration methodologies at a macro-scale can be applied at a micro-scale, the calibration objects cannot be used because the microscopic resolution imposes much higher quality specification at a much higher costs. We used traditional calibration objects (i.e., Gretag Mcbeth color chart, a stage micrometer for pixel-to-millimeter conversion, and a set of prior known shapes and their locations for pose estimation) for comparison purposes to alternative calibration objects (see Figure 1).

Next, we developed calibration methods to perform pixel-to-millimeter conversion, red-green-blue color normalization, and microscope pose estimation using the high resolution LCD of an iPhone. The iPhone LCD is placed under an array of microscopes as illustrated in Figure 1 (D). It renders temporally varying pixel intensities that represent a dynamic virtual calibration object.

Major Accomplishments

The paper: Peter Bajcsy, Jacob Siegel, Mary Brady, “Calibrating multiple microscopes with a smartphone,” SPIE Newsroom, 1 April 2014, SPIE Newsroom. DOI: 10.1117/2.1201403.005223, https://spie.org/x106863.xml.(download pdf)

Lead Organizational Unit:

ITL

Staff:

ITL-Software and Systems Division
Information Systems Group

Publications:

Peter Bajcsy, Jacob Siegel, Mary Brady, “Calibrating multiple microscopes with a smartphone,” SPIE Newsroom, 1 April 2014, SPIE Newsroom. DOI: 10.1117/2.1201403.005223, https://spie.org/x106863.xml.(download pdf)

Contact:

Date created: April 10, 2014 | Last updated: