3D Slit Scanning with Planar Constraints★

We present a planarity constraint and a novel three‐dimensional (3D) point reconstruction algorithm for a multiview laser range slit scanner. The constraint is based on the fact that all observed points on a projected laser line lie on the same plane of laser light in 3D. The parameters of the plane of laser light linearly parametrize a homography between a pair of images of the laser points. This homography can be recovered from point correspondences derived from epipolar geometry. The use of the planar constraint reduces outliers in the reconstruction and allows for the reconstruction of points seen in only one view. We derive an optimal reconstruction of points subject to the planar constraint and compare the accuracy to the suboptimal approach in prior work. We also construct a catadioptric stereo rig with high quality optical components to remove error due to camera synchronization and non‐uniform laser projection. The reconstruction results are compared to prior work that uses inexpensive optics and two cameras.     

Noise deconvolution for area fraction measurements

Abstract

A novel approach to area fraction measurement is developed to deal with the limitations of the segmentation method. The new approach takes advantage of the statistical nature of the noise within an image to deconvolute the image histogram and calculate, by means of fitting, the area fractions. Both segmentation and noise deconvolution approaches are critically discussed, and their limitations and advantages tested using two extreme backscattered electron images of a metal matrix composite. The deconvolution approach is shown to produce accurate results in a situation in which the segmentation approach fails.     

Experimental assessment on the performance of hot wire anemometry in and around a permeable medium by comparison with Particle Image Velocimetry

The air flow through a test section partially obstructed by a permeable array of wires was measured simultaneously by Hot Wire Anemometry (HWA) and Particle Image Velocimetry. The objective of the study was the assessment of the suitability of HWA for the measurement of flow velocities amid and adjacent to groups of small obstacles. In the present case the obstacles are set in a regular array configuring a highly permeable structure. The probe was placed at three characteristic positions: in the free flow close to the wire array, inside the permeable medium, and at the interface between the permeable structure and the free flow. The measurements were performed with the hot wire operating under natural convection and mixed convection heat transfer, and operating the hot wire at different overheat ratios. Natural convection plumes extending over several permeable volume elements were detected when the hot wire was under natural convection, in some cases reaching velocities up to 60 mm/s downstream from the hot wire position. For low velocity flows, natural convection can be regarded as a flow velocity offset, which becomes negligible at local velocities higher than 0.03 m/s. For higher velocities, in the mixed convection regime, the intrusivity of the HWA probe becomes relevant. Furthermore, the flow in the test section used in the study presents a linear instability that produces velocity fluctuations. Availing ourselves of this phenomenon we verified the dynamic response of the HWA at the lowest velocity where the flow shows periodic fluctuations; for a local mean velocity of (0.131 ± 0.012) m/s the HWA showed a satisfactory dynamic response up to 20 Hz.     

Instant Propagation of Sparse Edits on Images and Videos

The ability to quickly and intuitively edit digital contents has become increasingly important in our everyday life. We propose a novel method for propagating a sparse set of user edits (e.g., changes in color, brightness, contrast, etc.) expressed as casual strokes to nearby regions in an image or video with similar appearances. Existing methods for edit propagation are typically based on optimization, whose computational cost can be prohibitive for large inputs. We re‐formulate propagation as a function interpolation problem in a high‐dimensional space, which we solve very efficiently using radial basis functions. While simple to implement, our method significantly improves the speed and space cost of existing methods, and provides instant feedback of propagation results even on large images and videos.     

Vision-Based Task-Level Control of a Flexible-Link Manipulator

This paper discusses a vision-based approach to implement task-level control in flexible-link manipulators. The proposed approach emphasizes the advantage of using vision in the control of flexible manipulators. It is pointed out that taking advantage of the inherent robustness, implementation of an image-based visual servo can be regarded as a synthetic solution to precise task-level control of flexible manipulators. This approach is implemented in a three-dimensional flexible-link manipulator. The implementation makes good use of filters in decoupling task-level control and vibration suppression control. Moreover, we point out that although the robustness of the approach can help to overcome the difficulty in control resulting from the complex measurement of the link's elastic deformation, it lacks in capability of tip trajectory specification. This problem is analyzed in this research and it leads to the proposal for the integration of the image interpolation technique. This technique makes the proposed approach adequate for tasks involved with complex tip trajectories. For flexible-link manipulators, the proposed approach with the remedy is the first vision-based synthetic solution that attempts to make a flexible manipulator usable for a practical task.     

Neural network face detection

Abstract

Analysing a video sequence is a challenge, because faces are constantly in dynamic motion, presenting many different possible rotational and illumination conditions. While solutions to the task of face detection have been presented, the detection performances of many systems are heavily dependent upon a strictly constrained environment. This paper presents the results of an image-based neural network face detection system which seeks to address the problem of detecting faces under gross variations.     

The Photographic Lens in Medical Photography

The author reports on a number of specific applications of photography in medicine for which the normally available lenses for amateur cameras do not suffice. To begin with, the problems involved in ultra-violet and infra-red photography are dealt with. In ultra-violet photography the spectral transmission of the lenses is of importance whereas in infra-red photography the chromatic correction is decisive. Further, attention is drawn to the rble stereo-photography is playing in medical tuition. To conclude, the reasons are given for the superiority of lens-optical systems in radiography.     

Half-Tone Reproduction on Diazo Materials

A simplified screening method providing an easy means of producing good quality screened masters. A general consideration of half-tone diazo printing.     

IMAGE仪器2LHR采集单元PA板的维修

祝彩霞，王泰昆．IMAGE仪器2LHR采集单元PA板的维修．物探装备，2006，16（4）：268-269 本文针对2LHR型采集单元PA板维修难度大的情况，对PA板的电路结构和使用器件进行了分析，找出了PA板单道指标超限的故障原因，并对CMOS器件进行分析，根据其特性，提出维修过程中应注意的事项，以确保维修质量和效率。     

Time–frequency diagram applied to stability analysis in gas metal arc welding based on acoustic emission

Abstract

Time–frequency diagram is applied to estimating the stability of gas metal arc welding process. A methodology has been developed to obtain indexes based on image processing of the spectrogram in order to evaluate the relationship between the spectrogram and the stability of process. The acoustic emission (AE) signals have been processed and characterised to obtain the spectrogram of the acoustic signals generated by arc. Statistical analysis of image generated by spectrogram and temporal parameters of AE signals has been used as a tool to obtain a method for stability evaluation. As a main result of the research, it demonstrates the effectiveness of the application of image processing of the time–frequency diagram for evaluating the stability in the welding processes. The results demonstrate the validity of this method to characterise the stability using the image characterisation.