Browsing by Author "Cheng, Chu-Ming"

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Accessing Refractive Errors via Eccentric Infrared Photorefraction Based on Deep Learning
(2019-01-01)
Yang, Chia-Chi
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Su, Jian-Jia
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Li, Jie-En
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Zhu, Zhi-Yu
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Tseng, Jin-Shing
Eccentric infrared photorefraction is an attractive vision screening method which is widely used for uncooperative subjects, such as infants and toddlers. Unlike conventional slope-based photorefraction, a deep neural network is used to predict refractive error in this study. Total 1216 ocular image were collected by a homemade photorefraction device, whose corresponding refractive error was measured by a commercial autorefractor device, to create a series of dataset for our deep neural network. The mean squared error of the preliminary result is +/- 0.9 diopter, which indicates its feasibility and can be improved with bigger database.
Design of a dual-f-number illumination system and its application to DMD (TM) projection displays
(2006-09-01)
Cheng, Chu-Ming
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Chern, Jyh-Long
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光電工程學系
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Department of Photonics
A dual-f/# optical system is evaluated and considered for illumination. Etendue theory has been employed to increase the optical throughput and collection efficiency. A classical Cooke triplet with a dual f/# is included for illustration. As a demonstration of the potential application to projection displays, an elliptically shaped illumination-pupil system is proposed to increase the optical collection efficiency in the DMD(TM) (Digital Micromirror Device(TM))-based projection system. With a dual-f/# configuration, this design can eliminate the f/2.4 constraint that was caused by the light-steering action of the narrow +/- 12 degrees tilt angles on the DMD(TM). The percentage of increase in the optical collection efficiency is 6.2% in the dual f/2.0 x f/2.4 optical projection system by using ray-tracing simulation. This method enables a lower than f/2.4 optical design with a high brightness and an adequate contrast ratio in the DMD(TM)-based projectors.
Illuminance formation and color difference of mixed-color light emitting diodes in a rectangular light pipe: an analytical approach
(2008-01-20)
Cheng, Chu-Ming
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Chern, Jyh-Long
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光電工程學系
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Department of Photonics
We developed an analytical method of illuminance formation for mixed-color LEDs in a rectangular light pipe in order to derive American National Standards Institute (ANSI) light uniformity, ANSI color uniformity, and color difference of light output using photometry, nonimaging, and colorimetry. The analytical results indicate that the distributions of illuminance and color difference vary with different geometric structures of light pipes and the location of the light sources. It was found that both the ANSI light and the ANSI color uniformity on the exit plane of the light pipe are reduced exponentially with the increase in length of the light pipe. It is evident that a length scale L/A greater than unity assures that the mixed-color LED sources on the entrance plane are uniformly illuminated with acceptable uniform brightness and color on the exit plane of the rectangular light pipe, where L is the length of the light pipe, and A is a constant, which is a geometric parameter for the scale unit of the light pipe's input face. Furthermore, the ANSI light uniformity can be minimized, and the ANSI color uniformity can be maximized under the condition of multilight-source locations P = Q = +/- A/4, where P and Q are the coordinates along the long axis and the short axis, respectively, with one being the entrance plane of the light pipe. We can conclude that the optimum form factor of the light pipe is a square shaped cross section, with the length scale L/A being equal to unity and with multilight sources located individually on positions of A/4 in order to achieve very uniform illuminations with the highest light efficiency and compact package for the optical system with mixed-color LEDs, where L is the length of the light pipe. (C) 2008 Optical Society of America.
Optical transfer functions for specific-shaped apertures generated by illumination with a rectangular light pipe
(2006-12-01)
Cheng, Chu-Ming
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Chern, Jyh-Long
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光電工程學系
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Department of Photonics
We investigated the pupil functions of specific-shaped apertures generated by Lambertian illumination with a rectangular light pipe to derive the corresponding optical transfer functions (OTFs) in aberration-free and defocused optical systems. The semianalytical results indicate that the curves of the OTF of the optical system vary with the form of the shaped apertures that are generated by illumination with different geometric structures of light pipes and light sources. It was found that the OTF values of even-peak frequencies decrease when the Lambertian light source decreases. If there are a total of n X n individual apertures within a pupil, then n near-periodical peaks will appear on the OTF curve. It is evident that the values of the OTF remain almost unchanged even when the lengths of the light pipes are different. Furthermore, the geometric structure of the light pipe does not affect the resolution limit of the optical system, and under the condition of a larger defocused coefficient omega(20), the results of the defocused system can coincide with those of the aberration-free systems. (c) 2006 Optical Society of America.
Programmable apodizer in incoherent imaging systems using a digital micromirror device
(2010-02-01)
Cheng, Chu-Ming
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Chern, Jyh-Long
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光電工程學系
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Department of Photonics
We propose a programmable apodizer using a digital micromirror device and the total-internal-reflection prism subsystem for incoherent imaging systems. It is shown that the proposed programmable apodizer can extend the depth of focus with the specific shaped aperture generated by the digital micromirror device. With a scale ratio of K <= 0.05, one can achieve almost the same level of imaging quality as provided by the conventional annular apodizer, where K represents the ratio between the integer multiple of the micromirror's square pixel size and the diameter of the effective aperture stop. (C) 2010 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3314306]
Projection quality improvement with embedded illumination modulator in projector system
(2010-06-01)
Cheng, Chu-Ming
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Chern, Jyh-Long
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光電工程學系
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Department of Photonics
We demonstrate an approach for improving the image quality for a projector system with a shape-programmable pupil, which could be generated by an illumination modular in which a digital micromirror device is embedded. Essentially, the shaped pupil from the illumination modulator is developed with a dynamically programmable approach to provide aberration compensation for the projection system. By analyzing the optical transfer function, the resolution limit of an imaging system with specific defocus, spherical aberration and coma are shown to be improved significantly with a binary-shaped pupil. It is found that the improvement of the projection quality could be characterized by the scale ratio of K = c/D, defined as the ratio between the resolution scale of structured light, c, and the size scale of the aperture stop, D. When K is equal to 0.05, the low-frequency components of the image could be improved, while if K is equal to 0.3, the imaging quality of the image at high-frequency components can be enhanced in a defocused system. Furthermore, as K ranges from 0.05 to 0.3, the imaging performance of the optical contrast could be enhanced in a projector system with large coefficients of defocused, spherical aberration and coma. (c) 2010 Optical Society of America