Sub-pixel Technique Research Articles

Study on Sub-Pixel Techniques for Accurate Image Measurement of Displacement

The high resolving power camera was often used to improve the precision of measuring system although its price is high, because the accuracy of image measure was limited by the pixel resolving ability of camera. A method of one dimension gray level quadrature sub-pixel to detect edge was presented. This method was applied to measure the displacement of measuring head on 3-coordinate measuring machine. The data of test was shown that this system can distinguish displacement 0.001mm. it is higher accuracy than pixel level. So this method is convenient and fast , fit to track and measure the moving object. It is obvious that this method can save the cost of hardware.

A New Method for Detecting the Diameter and Spatial Location of Tiny Through-Hole

Aiming at the problem that the traditional plunged-bar method is difficult to meet the measurement requirement of spatial location of thin and small through-hole, in this paper, the digital image processing technique combined with sub-pixel detection technique is employed, and a new method is proposed to detect the tiny through-holes. The evaluating function method based on the “roundness” of the image of hole is presented to find out the posture parameters of CCD where the optical axis of CCD is parallel to the centerline of hole. Therefore, the spatial location of hole can be easily obtained by these posture parameters. Meanwhile, the diameter of hole can be achieved by means of image measuring technology at calculated posture of CCD. Owing to the non-contact measurement, this method is particularly suitable for those small through-holes drilled on the soft and easy-deformed object. The experiment results on the experimental platform illustrate the feasibility and validity of this method.

Application of adjusted subpixel method (ASM) in HRCT measurements of the bronchi in bronchial asthma patients and healthy individuals

Recently, we described a model system which included corrections of high-resolution computed tomography (HRCT) bronchial measurements based on the adjusted subpixel method (ASM). To verify the clinical application of ASM by comparing bronchial measurements obtained by means of the traditional eye-driven method, subpixel method alone and ASM in a group comprised of bronchial asthma patients and healthy individuals. The study included 30 bronchial asthma patients and the control group comprised of 20 volunteers with no symptoms of asthma. The lowest internal and external diameters of the bronchial cross-sections (ID and ED) and their derivative parameters were determined in HRCT scans using: (1) traditional eye-driven method, (2) subpixel technique, and (3) ASM. In the case of the eye-driven method, lower ID values along with lower bronchial lumen area and its percentage ratio to total bronchial area were basic parameters that differed between asthma patients and healthy controls. In the case of the subpixel method and ASM, both groups were not significantly different in terms of ID. Significant differences were observed in values of ED and total bronchial area with both parameters being significantly higher in asthma patients. Compared to ASM, the eye-driven method overstated the values of ID and ED by about 30% and 10% respectively, while understating bronchial wall thickness by about 18%. Results obtained in this study suggest that the traditional eye-driven method of HRCT-based measurement of bronchial tree components probably overstates the degree of bronchial patency in asthma patients.

Remote sensing of crop residue burning in Punjab (India): a study on burned area estimation using multi-sensor approach

The study undertaken investigates the use of multi-sensor characteristics for accurate assessment of burned areas at regular intervals for two districts of Punjab. Temporal datasets of (pre-burning and post-burning during the year 2006) LISS-III, LISS-IV, MODIS and AVHRR have been used in the quantitative estimation of burned areas. The multi-temporal image difference technique using three different indices (NDVI, NBR and GEMI3) was taken using the statistical threshold technique which has been calculated and verified by extensive ground-based measurements. The performance of the indices was evaluated using spectral separability analysis and GEMI3 was found as the best in spectral discrimination of burned and unburned surface. Moderate resolution LISS-III (23.5 m) data provides accurate estimation of burned area affected by fire, but frequent assessment is not possible due to low temporal resolution (24 days). On the other hand, MODIS (500 m) and AVHRR (1000 m), resulted in a high degree of bias in area estimation, but provide data at a high temporal rate. This bias in coarser resolution data is studied using the sub-pixel technique approach. The total burned area estimated from LISS-III data (GEMI3) is 98,697 ha and from MODIS and AVHRR data (sub-pixel) is 83,893 ha and 74,564 ha, respectively. The area estimates of LISS-III, MODIS and AVHRR were compared with LISS-IV data (aggregate to respective resolution) for the same dates in the year 2007 at selected locations. An overall regression fit was obtained for MODIS data at selected sites with a value of coefficient of determination (R 2) = 0.771. An overall linear regression fit of MODIS and AVHRR with the whole of the LISS-IV image was compared with sub-pixel estimates at MODIS (500 m), AVHRR (1000 m) and the results revealed a strong relationship with R 2 = 0.868 and R 2 = 0.817, respectively. The study suggested that for crop residue burning, a multi-sensor approach is effective for improving the accuracy of burned area estimation at coarser resolution.

Iris extraction using parametric template matching for eyegaze tracking

An eyegaze interface is one of the key technologies that serves as an input device in a ubiquitous-computing society. Recently, video-based techniques that do not require specific instruments have been studied. With these approaches, development of an accurate iris-extraction algorithm is very important to realize practical eyegaze tracking. For accurate iris extraction, it is necessary to achieve robustness, high speed, and high accuracy. Conventional iris-extraction algorithms experience difficulties in meeting all these requirements simultaneously. This study proposes an iris-extraction algorithm based on the parametric template matching method to satisfy all these requirements at the same time. The parametric template matching method achieves robustness by interpolating among some templates, and the method attains high accuracy by a subpixel matching technique. High-speed matching can be realized by coarse-to-fine matching. To verify the effectiveness of the proposed algorithm, we performed a basic experiment for eyegaze tracking. We show in this experiment that the processing time is approximately 1/900 of that of our previous method and that accuracy is acceptable with the new method. Then, we apply the proposed algorithm to an eyegaze keyboard, along with an imaging system for improving image quality, and we verify the effectiveness of this approach.

A study of mechanical and thermal properties of materials in electronic packaging: application of micro DIC

The mechanical and thermal properties of materials used in electronic packaging are of significant importance. This paper presents a novel application of Digital Image Correlation (DIC) to characterise the properties of polymeric films and solder joints used in electronic packaging. A miniature loading frame and a thermal chamber were designed to load the film and solder samples, respectively. The mechanical properties (Elastic Modulus and Poisson's ratio) of the polymeric film were estimated under uniaxial tension, while the thermal expansion of a solder ball was evaluated in a temperature chamber. Digital images of the samples were documented with a microscopic imaging system and DIC was used to evaluate the in-plane deformation. An algorithm that combined the subpixel technique, displacement fitting and correction of lens aberration was developed to improve the precision of the measurements. Results show that micro DIC is an easy-to-use technique and has strong potential as a characterisation methodology for materials and structures in electronic packaging.

Precisionin situvolume measurement of micro droplets

This research presents an in situ droplet volume measurement system which is applied to the one drop fill (ODF) process of liquid crystal display (LCD) manufacture. The system developed utilizes a stroboscopic technique to synchronize the triggering of a strobe light and a CCD camera. A steady image of the droplet flying in free space can be captured in situ by the CCD camera. The method of precise volume estimation is based on a rotationally symmetric model of the droplet's shape. Polynomial fitting is used to reconstruct the droplet profile. The image resolution can thus be enhanced by a subpixel technique. Compared to a precision electronic balance, the total weight measured by this system has an error within ± 0.3%, and the computation time for each droplet is about 0.4 s. This satisfies the actual ODF requirements.

Displacement/strain measurements using an optical microscope and digital image correlation

We conduct displacement/strain measurements on the micro- scale using light microscopy and digital image correlation DIC. Errors in the measurements attributed to the optical arrangement and aberration induced at high magnification are identified using a warping function. Coefficients of the warping function are determined using a simple tech- nique that employs a precisely made orthogonal cross-grating plate. By acquiring images of the grating and identifying the nodes using subpixel techniques, a relationship between the object and the image planes is established. Thus, the displacement/strain derived by means of DIC is corrected by converting the displacement components in the image plane to the coordinate system existing on the object's surface. The approach is validated through a determination of the elastic properties of common metals; errors in estimation of the elastic modulus were within 4%. Although surface preparation generally plays a critical role in suc- cessful application of DIC, it is found to be of minimal importance under high magnification. Instead, the natural surface texture can be used with adjustment of the light incident angle. Results of the study show that DIC is a powerful tool in performing displacement/strain measurements on the microscale using a light microscope provided that an adequate cor- rection is employed for image distortion. © 2006 Society of Photo-Optical Instru-

Deformation measurements using mutual information: principle and applications

The paper presents a new method applied to measure displacement fields using mutual information concept. Based on analysis of digital image sequences, we propose the formulation derived from the mutual information between subsets in the un-deformed and deformed image. The quantity of the mutual information between two subsets establishes a criterion of their mutual dependence based on the notion of information connection between them. We can obtain the integer pixel displacement for the corresponding subset. And the accurate displacement field is obtained by using sub-pixel technique. In the experiments, the method is validated and the resulting solution can show accuracy to 0.02 pixels. This method was also applied successfully to determine the displacement fields of laminated composites of AS4/PEEK[0/±45/90] 7s under uniaxial compression.

New Experimental Technique for Material Instability Study

The paper presents a new method applied to measure displacement fields using probability concept. Based on analysis of digital image sequences, we propose the formulation derived from the information of probability between subsets in the un-deformed image and deformed image. The quantity of this information between two subsets establishes a criterion of their mutual dependence based on the maximum a posteriori (MAP) estimate between them. So the subset in deformed image that maximizes the quantity is the corresponding subset of that in un-deformed image. After get the corresponding subset, we can obtain the integer pixel displacement. And we can get accurate displacement field using sub-pixel technique. In the experiments, the method is validated and the resulting solution can show accuracy to 0.02 pixels. This method was also applied successfully to determine the displacement fields of laminated composites under uniaxial compression. The elastic-plastic mechanical behavior and instability of the composites is studied.

Sub-pixel image correlation: an alternative to SAM and dye penetrant for crack detection and mechanical stress localisation in semiconductor packages

Sub-pixel image correlation has been applied to the measurement of surface deformation, in particular to the measurement of thermally induced strain in microchips. A Fourier shift technique coupled with successive approximation is used to determine the sub-pixel component of the deformation. This reduces the effects of systematic errors on data associated with interpolation or curve-fitting present in other sub-pixel techniques. For all image correlation techniques, defocus errors can have serious effects on the accuracy of the technique. These errors are eliminated in this case through use of a set of images at different axial positions, where only the in focus information is used. This allows determination of the out-of-plane component of the displacement to within roughly 1/40 of the depth of focus (250 nm at ×10 magnification). An in-plane deformation/displacement uncertainty of roughly 2% of a pixel (<15 nm at ×10 magnification) is achievable on real-world samples.

25.4: Color and Luminance Management for High‐Resolution Liquid‐Crystal Displays

AbstractA new method of color management is described which takes advantage of the high pixel density achievable with TFTLCDs. In this method, a calibration 10‐bit look‐up‐table can be loaded into the monitor and implemented as a 2×2 spatial dither block to provide a 10‐bit color palette for 8‐bit color drive. Other subpixel dithering techniques are also described for monochrome and color high‐resolution TFTLCDs. These techniques can create a very large palette, and combined with a 10‐bit digital data source to achieve precise luminance and color calibration.

Subpixel microscopic deformation analysis using correlation and artificial neural networks

Microscopic deformation analysis has been performed using digital image correlation and artificial neural networks (ANNs). Cross-correlations of small image regions before and after deformation contain a peak, the position of which indicates the displacement to pixel accuracy. Subpixel resolution has been achieved here by nonintegral pixel shifting and by training ANNs to estimate the fractional part of the displacement. Results from displaced and thermally stressed microelectronic devices indicate these techniques can achieve comparable accuracies to other subpixel techniques and that the use of ANNs can facilitate very fast analysis without knowledge of the analytical form of the image correlation function.

Non-contact laser inspection for the inner wall surface of a pipe

A non-contact laser sensor based on the ring optical cutting image method to measure the size and profile of the inner wall of a pipe is developed. The sensor consists of a laser diode light source, an optical ring pattern generator and a CCD camera. The optical ring pattern from the optical ring pattern generator is projected onto the inner wall of the pipe, which is then viewed by the CCD camera. Reasonable parameters according to the theory of light scattering and reflection are chosen to simulate and optimize the measurement system. The adaptive weighted average value filter and the subpixel technique on several-step computing and half Gaussian fitting are deployed to obtain the edge and the centre of the ring image in order to filter the noise of the image and raise the resolution of the measurement system. The experimental results show that the principle is correct and the techniques are realizable.

Interpolation-free subpixel motion estimation techniques in DCT domain

Currently existing subpixel motion estimation algorithms require interpolation of interpixel values which undesirably increases the overall complexity and data flow and deteriorates the estimation accuracy. We develop discrete cosine transform (DCT)-based techniques to estimate subpel motion at different desired subpel levels of accuracy in the DCT domain without interpolation. We show that subpixel motion information is preserved in the DCT of a shifted signal under some condition in the form of pseudophases, and we establish subpel sinusoidal orthogonal principles to extract this information. The proposed subpixel techniques are flexible and scalable in terms of estimation accuracy with very low computational complexity O(N/sup 2/) compared to O(N/sup 4/) for the full-search block-matching approach and its subpixel versions. Above all, motion estimation in the DCT domain instead of the spatial domain simplifies the conventional hybrid DCT-based video coder, especially the heavily loaded feedback loop in the conventional design, resulting in a fully DCT-based high-throughput video codec. In addition, the computation of pseudophases is local, and thus a highly parallel architecture is feasible for the DCT-based algorithms. Finally, simulation on video sequences of different characteristics shows comparable performance of the proposed algorithms to block-matching approaches.

Sub-pixel non-parametric PSF estimation for image enhancement

Applying standard resolution enhancement and sub-pixel measurement techniques to an imaging system is problematic when the system characteristics are not known. The importance of precise system characterisation is often underestimated in resolution enhancement and sub-pixel measurement. The methods presented allow accurate sub-pixel measurements of system characteristics to be made with minimal assumptions. The non-parametric technique developed accurately characterises the properties of an imaging system. This is demonstrated by measuring the point spread function (PSF), along with static and dynamic distortions, for a high precision thermal imaging system to sub-pixel accuracy. The PSF is estimated to ±0.1 of a pixel and imaging system errors to the order of ±0.1 of a pixel are identified. The improved precision of PSF estimation is shown to benefit resolution enhancement. A novel feature of the method used to estimate the PSF (and to enhance the image) is that the estimation of the spatially invariant sub-pixel PSF and of geometric distortion are performed independently.

Aliasing reduction in staring infrared imagers utilizing subpixel techniques

We introduce and analyze techniques for the reduction of aliased signal energy in a staring infrared imaging system. A standard staring system uses a fixed two-dimensional detector array that corresponds to a fixed spatial sampling frequency determined by the detector pitch or spacing. Aliasing will occur when sampling a scene containing spatial frequencies exceeding half the sampling frequency. This aliasing can significantly degrade the image quality. The aliasing reduction schemes presented here, referred to as microscanning, exploit subpixel shifts between time frames of an image sequence. These multiple images are used to reconstruct a single frame with reduced aliasing. If the shifts are controlled, using a mirror or beam steerer for example, one can obtain a uniformly sampled microscanned image. The reconstruction in this case can be accomplished by a straightforward interlacing of the time frames. If the shifts are uncontrolled, the effective sampling may be nonuniform and reconstruction becomes more complex. A sampling model is developed and the aliased signal energy is analyzed for the microscanning techniques. Finally, a number of experimental results are presented that illustrate the perlormance of the microscanning methods.