Practical Methods for Characterizing the Optical Performance of Digital Camera-Based Imaging Systems: Image Processing Application Using ImageJ

Practical Methods for Characterizing the Optical Performance of Digital Camera-Based Imaging Systems: Image Processing Application Using ImageJ

Sami D. Alaruri (Independent Researcher, USA)
DOI: 10.4018/IJECME.2020010103

Abstract

In this paper, practical and simple methods for characterizing the optical performance of a digital CCD camera equipped with a zoom lens using test targets projected by a Newtonian collimator coupled to an integrating sphere and a halogen light source are presented. The presented methods include the evaluation of the CCD camera system modulation transfer function (MTF), uniformity, dynamic range, linearity, and signal-to-noise ratio (S/N) properties in the visible region of the spectrum. Through out this work image processing for the recorded target images is performed using ImageJ. In addition, the paper presents a comparison between MTF measurements collected with a 1951-USAF resolution test target and a slanted edge test target. Finally, simple mathematical expressions for the measured optical system performance properties are provided. The presented optical system characterization methods can provide researchers with the needed data when a CCD or CMOS digital camera is integrated with a lens system.
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2. Experimental Setup

The Newtonian collimator based experimental setup used to characterize the CCD camera system is shown schematically in Figure 1. The collimator (Chrzanowski 2007) optics incorporates an off-axis parabola (OAP) having surface accuracy equal to λ/8 (P-V at 632 nm), reflectance > 93% (3 to 14 µm), clear aperture = 30.5 cm, and focal length = 152.4 cm. A motorized target wheel, integrating sphere and a halogen lamp integrated with the collimator allow for the back uniform illumination of the selected test target. Furthermore, an adjustable halogen lamp power supply allows for the test target to be illuminated between 10 − 5 and 103 lux. The test target is projected to the camera system by the collimator optics and is mounted on a manual range simulation stage connected to a micrometer that can be used for varying the test target range between infinity and 1000 meters. Figure 2 illustrates the collimator simulated range versus the micrometer translation in millimeters. Moreover, the test targets used for evaluating the imaging system optical performance are: 1) 1951 USAF resolution test target (Edmund Optics, p/n 54690); 2) Edmund Optics-EIA Gray Scale 20:1 Logarithmic (SN 52358); and 3) a slanted edge test target. It is worth noting here that the CCD digital camera used in this work is equipped with 87 mm focal length zoom lens and is placed approximately 100 cm from the collimator exit end. Additionally, the CCD camera incorporates a Sony Imager ICX267 (1.45 M pixel, 4.65 μm pixel size, 14 bit depth CCD imager, ½” format, interline CCD, 30 frames/s, Silicon substrate). Finally, the captured target images are transferred via IEEE 1394B-800 Mb/s interface to a P.C. equipped with an image grabber board for image processing.

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