Thuy Tuong Nguyen

Structured Light-Based 3D Reconstruction System for Plants

Camera-based 3D reconstruction of physical objects is one of the most popular computer vision trends in recent years. Many systems have been built to model different real-world subjects, but there is lack of a completely robust system for plants.This paper presents a full 3D reconstruction system that incorporates both hardware structures (including the proposed structured light system to enhance textures on object surfaces) and software algorithms (including the proposed 3D point cloud registration and plant feature measurement). This paper demonstrates the ability to produce 3D models of whole plants created from multiple pairs of stereo images taken at different viewing angles, without the need to destructively cut away any parts of a plant. The ability to accurately predict phenotyping features, such as the number of leaves, plant height, leaf size and internode distances, is also demonstrated. Experimental results show that, for plants having a range of leaf sizes and a distance between leaves appropriate for the hardware design, the algorithms successfully predict phenotyping features in the target crops, with a recall of 0.97 and a precision of 0.89 for leaf detection and less than a 13-mm error for plant size, leaf size and internode distance.

Plant phenotyping using multi-view stereo vision with structured lights

A multi-view stereo vision system for true 3D reconstruction, modeling and phenotyping of plants was created that successfully resolves many of the shortcomings of traditional camera-based 3D plant phenotyping systems. This novel system incorporates several features including: computer algorithms, including camera calibration, excessive-green based plant segmentation, semi-global stereo block matching, disparity bilateral filtering, 3D point cloud processing, and 3D feature extraction, and hardware consisting of a hemispherical superstructure designed to hold five stereo pairs of cameras and a custom designed structured light pattern illumination system. This system is nondestructive and can extract 3D features of whole plants modeled from multiple pairs of stereo images taken at different view angles. The study characterizes the systems phenotyping performance for 3D plant features: plant height, total leaf area, and total leaf shading area. For plants having specified leaf spacing and size, the algorithms used in our system yielded satisfactory experimental results and demonstrated the ability to study plant development where the same plants were repeatedly imaged and phenotyped over the time.

Automated Mobile System for Accurate Outdoor Tree Crop Enumeration Using an Uncalibrated Camera

This paper demonstrates an automated computer vision system for outdoor tree crop enumeration in a seedling nursery. The complete system incorporates both hardware components (including an embedded microcontroller, an odometry encoder, and an uncalibrated digital color camera) and software algorithms (including microcontroller algorithms and the proposed algorithm for tree crop enumeration) required to obtain robust performance in a natural outdoor environment. The enumeration system uses a three-step image analysis process based upon: (1) an orthographic plant projection method integrating a perspective transform with automatic parameter estimation; (2) a plant counting method based on projection histograms; and (3) a double-counting avoidance method based on a homography transform. Experimental results demonstrate the ability to count large numbers of plants automatically with no human effort. Results show that, for tree seedlings having a height up to 40 cm and a within-row tree spacing of approximately 10 cm, the algorithms successfully estimated the number of plants with an average accuracy of 95.2% for trees within a single image and 98% for counting of the whole plant population in a large sequence of images.

Development of Wideband and High IIP3 Millimeter-Wave Mixers

This paper presents the design and development of highly linear, wide bandwidth mixers. We propose a linearization technique that combines the optimum drain bias condition and multiple-gated transistors for resistive mixers. An on-chip three-line edge-coupled Marchand balun is designed to have low phase and amplitude imbalance for canceling out the even order intermodulation products. Two mixer prototypes: a single-balanced (SB) mixer and a double-balanced (DB) mixer are designed to prove the concepts. The experimental results demonstrate that the SB prototype mixer has a measured conversion loss of less than 11 dB and third-order input intercept point (IIP3) range of 27–33 dBm at 15-dBm LO drive from 7 to 34 GHz. The DB mixer exhibits a conversion loss of less than 11 dB and IIP3 range of 31–35 dBm from 7–26 GHz at 17-dBm LO drive. Both prototypes achieve a high port-to-port isolation of over 30 dB within the operation bandwidth. To the best of our knowledge, the mixers have the highest linearity over the widest bandwidth ever reported.

Robust dose-response curve estimation applied to high content screening data analysis

Background and methodSuccessfully automated sigmoidal curve fitting is highly challenging when applied to large data sets. In this paper, we describe a robust algorithm for fitting sigmoid dose-response curves by estimating four parameters (floor, window, shift, and slope), together with the detection of outliers. We propose two improvements over current methods for curve fitting. The first one is the detection of outliers which is performed during the initialization step with correspondent adjustments of the derivative and error estimation functions. The second aspect is the enhancement of the weighting quality of data points using mean calculation in Tukey’s biweight function.Results and conclusionAutomatic curve fitting of 19,236 dose-response experiments shows that our proposed method outperforms the current fitting methods provided by MATLAB®;’s nlinfit nlinfit function and GraphPad’s Prism software.

A 7–42 GHz dual-mode reconfigurable mixer with an integrated active IF balun

This paper presents a novel, dual-mode, reconfigurable, fully integrated double-balanced ring mixer. The change in DC bias of the mixer core leads to two operation modes: a passive mixer and an active mixer with variable conversion gain. In addition, an active IF balun using a DC-coupled differential pair configuration is designed to cover IF frequency from DC to 4 GHz. The measurement results show that the conversion gain can change from −6 dB to 6 dB over RF frequency range of 742 GHz. The measured input third order intercept point (HP3) is 5 dBm and the measured input 1-dB compression point (IP1dB) is 5 dBm at the highest conversion gain mode with 4-dBm LO drive. At the lowest conversion gain mode, the HP3 is 20 dBm and IP1dB is 12 dBm with 13-dBm LO drive.

Development of a double-octave (7-34 GHz), highly linear single balanced resistive HEMT mixer using device linearization techniques

We present the design and development of a highly linear, wide bandwidth single balanced resistive mixer (SBRM). We propose a linearization technique that combines the optimum drain bias condition and multiple gated transistors for resistive mixers. The experimental results demonstrate that the prototype mixer has a conversion loss of less than 11 dB, third-order input intercept point (IIP3) range of 27-33 dBm at 15 dBm LO drive, and a high port-to-port isolation of over 40 dB from 7 to 34GHz. To the best of our knowledge, this mixer has the highest linearity over a 27GHz bandwidth ever reported.