Scan Distortion Research Articles

Orientation Modulation for Data Hiding in Clustered-Dot Halftone Prints

We present a new framework for data hiding in images printed with clustered dot halftones. Our application scenario, like other hardcopy embedding methods, encounters fundamental challenges due to extreme bilevel quantization inherent in halftoning, the stringent requirements of image fidelity, and other unavoidable printing and scanning distortions. To overcome these challenges, while still allowing for automated extraction of the embedded data and a high embedding capacity, we propose a number of innovations. First, we perform the embedding jointly with the halftoning by employing an analytical halftone threshold function that allows steering of the halftone spot orientation within each halftone cell based upon embedded data. In this process, image fidelity is emphasized and, if necessary, the capability to recover individual data values is sacrificed resulting in unavoidable erasures and errors. To overcome these and other sources of errors, we propose a suitable data detection and error control methodology based upon a statistical representation for the print-scan channel that effectively models the channel dependence upon the cover image gray-level. To combat the geometric distortion inherent in the print-scan process, we exploit the periodic halftone structure to recover from global scaling and rotation and propose a novel decision directed synchronization technique that counters locally varying printing distortion. Experimental results demonstrate the power of the proposed framework: we achieve high operational rates while preserving halftone image quality.

A Hybrid Nonlinear Adaptive Tracking Controller for a Resonating Fiber Microscanner

A robust hybrid tracking controller for a nonlinear resonating fiber microscanner is developed and implemented to remove scan distortions—toroid and swirl. Using offline batch feedback, a nonlinear search, and simulated regulation, an adaptive controller iteratively finds system parameters that cause an online open-loop feedback linearized plant-inversion controller to robustly and accurately track a spiral scan with a high-speed flyback region. This offline adaptive feedback/online open-loop hybrid approach removes the need for miniature sensors and high-speed real-time controllers in situ.

Transtomography for implant placement guidance in non-invasive surgical procedures

To illustrate the use of transtomography for the placement of implants using a radiopaque radiographic guide and to evaluate the accuracy of transtomography. The study included 11 implants inserted with minimally invasive procedures. Pre-operative, intraoperative and post-operative examinations were performed with a ProMax panoramic unit implemented with transtomographic technique (Planmeca Oy, Helsinki, Finland). At each implant site, cross-sectional and longitudinal intraoperative transtomograms were taken through a radiopaque reference guide to control and adjust the drilling axis. The effective axis on post-operative transtomograms was compared with the planned axis correction estimated on intraoperative images. Radiopaque guides, used as the gold standard, were measured on intraoperative cross-sectional slices to evaluate image distortion. Intraoperative transtomograms, with the reference guide inserted in the bone, gave clear images of the cortical plates and accurate information of drilling length and axis, which allowed the surgeon to adjust pilot drilling axis in 6 sites (54.5%) out of 11 sites, including sites with narrow bone ridges. The implant axis on the post-operative tomogram compared with the planned axis correction showed an angle difference ranging from 0.8 degrees to 3.4 degrees. The image distortion on cross-sectional slices ranged from 0.03 mm to 0.52 mm, resulting in a distortion ratio ranging from 0% to 6% when expressed in percentages. Transtomographic examination performed with a radiographic reference guide during implant surgery can provide the necessary and accurate information for implant placement. Transtomography distortion appears to be less important than in other conventional tomographic systems and comparable with CT scan distortion.

An Error Space Controller for a Resonating Fiber Scanner: Simulation and Implementation

A robust error-space controller for an amplitude modulated resonating fiber scanner is developed and implemented. Using a nonlinear dynamics model, the system’s open loop temporal response for a spiral scan pattern is simulated and compared to experiments to understand scan distortions, such as, toroid, swirl, and beating. A feedback linearized linear quadratic regulator based on error dynamics drives the tracking error to zero. Controller simulations determine robustness limits, and effects of fiber nonlinearities and actuator time delay. Using real-time hardware, the controller asymptotically tracks and is capable of removing the scan distortions. Image acquisition with the controlled scanner produces nearly pixel accurate images.

A Nonlinear State-Space Model of a Resonating Single Fiber Scanner for Tracking Control: Theory and Experiment

A nonlinear state-space dynamic model of a resonating single fiber scanner is developed to understand scan distortion—jump, whirl, amplitude dependent amplitude and phase shifts—and as the basis for controllers to remove those distortions. The non-planar nonlinear continuum dynamics of a resonating base excited cantilever are reduced to a set of state-space coupled Duffing equations with centripetal acceleration. Methods for experimentally determining the model parameters are developed. The analytic frequency responses for raster, spiral and propeller scans are derived, and match experimental frequency responses for all three scan patterns, for various amplitudes, and using the same model parameters.

Ocular scanning and perceptual size distortion in hemispatial neglect: effects of prism adaptation and sequential stimulus presentation.

When asked to compare two lateralized shapes for horizontal size, neglect patients often indicate the left stimulus to be smaller. Gainotti and Tiacci (1971) hypothesized that this phenomenon might be related to a rightward bias in the patients' gaze. This study aimed to assess the relation between this size underestimation and oculomotor asymmetries. Eye movements were recorded while three neglect patients judged the horizontal extent of two rectangles. Two experimental manipulations were performed to increase the likelihood of symmetrical scanning of the stimulus display. The first manipulation entailed a sequential, rather than simultaneous presentation of the two rectangles. The second required adaptation to rightward displacing prisms, which is known to reduce many manifestations of neglect. All patients consistently underestimated the left rectangle, but the pattern of verbal responses and eye movements suggested different underlying causes. These include a distortion of space perception without ocular asymmetry, a failure to view the full leftward extent of the left stimulus, and a high-level response bias. Sequential presentation of the rectangles and prism adaptation reduced ocular asymmetries without affecting size underestimation. Overall, the results suggest that leftward size underestimation in neglect can arise for a number of different reasons. Incomplete leftward scanning may perhaps be sufficient to induce perceptual size distortion, but it is not a necessary prerequisite.

54.3: Modeling and Control of the Resonant Fiber Scanner for Laser Scanning Display or Acquisition

AbstractThe resonant fiber scanner produces a flying laser spot scan for display or image acquisition purposes. Dynamic nonlinearities during large amplitude vibrations of the resonant fiber scanner result in distortions in the two‐dimensional scan pattern and the acquired images. A dynamic model which includes the fibers dynamic nonlinearities has been developed to understand the nonlinear behavior and as the basis of a controller to remove the scan distortion. A robust state‐space controller has been implemented to force the resonant fiber scanner to follow a spiral scan pattern. Acquired images at 250×250 pixel resolution demonstrate improved image fidelity over previous images taken with open‐loop scanning.

Use and Verification of Digital Image Correlation for Automated 3-D Surface Characterization in the Scanning Electron Microscope

In this article a technique for automatically characterizing the three-dimensional geometry of fracture surfaces is presented. The technique described utilizes digital image correlation (DIC) to provide an accurate and fast method of digitally reconstructing fracture surfaces from stereo pairs produced in the scanning electron microscope (SEM). Accuracy of photogrammetric relationships, based on the geometry of image formation in the SEM, and errors due to scan distortions are quantified. The technique is used to measure features of known geometry and then applied to a turbine blade, for surface roughness measurement, and a fatigue fracture surface for profile analysis.

Computer Simulation of the AFM/LFM Imaging Process: Hexagonal versus Honeycomb Structure on Graphite

Although the atoms in cleavage planes of graphite are arranged in a honeycomb structure, it is well known from experimental work that atomic force microscopy (AFM) yields a hexagonal structure, a phenomenon that has not been understood so far. Here, computer simulations of the atomic-scale imaging process on graphite by AFM are reported, showing that this behaviour can be explained within a simple model of elastic tip–sample interaction. Both the topographic (AFM) images and the friction force or lateral force microscopy (LFM) images were simulated as a function of the scanning direction relative to the graphite lattice and as a function of the cantilever force constant. The scan distortions and the skipped area due to the AFM/LFM imaging process were evaluated. Simulations were performed both in the presence and in the absence of atomic-scale stick–slip processes. It is shown that neither stick–slip processes nor an inequivalence of the A- and B-sites of graphite is necessary to generate a hexagonal AFM image when scanning an atomic honeycomb structure. Rather, the simulations demonstrate that due to the two-dimensional elastic lateral displacement of the cantilever, the potential maxima—which correspond to the positions of the honeycomb lattice—are avoided by the scanning path of the tip apex, resulting in a hexagonal structure of the AFM and LFM images.© 1997 John Wiley & Sons, Ltd.

Computer Simulation of the AFM/LFM Imaging Process: Hexagonal versus Honeycomb Structure on Graphite

Although the atoms in cleavage planes of graphite are arranged in a honeycomb structure, it is well known from experimental work that atomic force microscopy (AFM) yields a hexagonal structure, a phenomenon that has not been understood so far. Here, computer simulations of the atomic-scale imaging process on graphite by AFM are reported, showing that this behaviour can be explained within a simple model of elastic tip-sample interaction. Both the topographic (AFM) images and the friction force or lateral force microscopy (LFM) images were simulated as a function of the scanning direction relative to the graphite lattice and as a function of the cantilever force constant. The scan distortions and the skipped area due to the AFM/LFM imaging process were evaluated. Simulations were performed both in the presence and in the absence of atomic-scale stick-slip processes. It is shown that neither stick-slip processes nor an inequivalence of the A- and B-sites of graphite is necessary to generate a hexagonal AFM image when scanning an atomic honeycomb structure. Rather, the simulations demonstrate that due to the two-dimensional elastic lateral displacement of the cantilever, the potential maxima-which correspond to the positions of the honeycomb lattice-are avoided by the scanning path of the tip apex, resulting in a hexagonal structure of the AFM and LFM images.

Simulation of ship wakes image by an along-track interferometric SAR

Abstract A mathematical model that allows simulations of the image of waves in ship wakes by either regular or interferometric airborne Synthetic Aperture Radar (SAR or INSAR) is described. The three-component velocity field induced at the ocean surface by a moving ship serves as the input to the model. The simulations take into account the effect of temporal variations of the wave field in the wake on the INSAR imaging by the velocity bunching mechanism. The model also accounts for the scanning distortion of the image. The developed algorithm allows study of the visibility of the ship wave wake by a regular SAR or by INSAR for arbitrary imaging parameters, as well as for different ship sizes and ship velocity vectors relative to the platform flight track. Various patterns of ship wake images obtained by numerical simulations are presented.

Simulation of an interferometric synthetic aperture radar imagery of an ocean system consisting of a current and a monochromatic wave

A model which simulates azimuthal imaging of a monochromatic ocean wave and current by an interferometric synthetic aperture radar (INSAR) is developed. The model allows one to obtain simulation of a regular synthetic aperture radar (SAR) as a particular case. The effects of velocity bunching and scanning distortion, as well as the dependence of the output on wave propagation direction, are considered. SAR and INSAR imaging of a monochromatic wave is compared both qualitatively and quantitatively for a wide range of governing parameters. Analytical expressions for both SAR and INSAR outputs were obtained for small values of the velocity‐bunching parameter. The accuracy of these analytical approximations was checked numerically.

Comparison of aircraft synthetic aperture radar and buoy spectra during the Norwegian Continental Shelf Experiment of 1988

Aircraft synthetic aperture radar (SAR) measurements from seven flight paths at two different altitudes were acquired over a trimodal ocean wave system off the coast of Norway on March 11, 1988. These three wave systems traveling in different directions were also measured by a directional buoy with the buoy spectra rotated into the radar coordinates for comparison with SAR spectra. Fifteen subspectra were averaged to obtain the measured SAR spectra, and sixteen spectral bands were averaged to obtain the measured buoy spectra. The seven flight paths in conjunction with the three wave systems resulted in a nearly uniform distribution of azimuth peak directions varying from 0° to 83° and R/V varying from 28 to 110. The comparison of the SAR‐ and buoy‐derived peak wavelength and direction shows some scatter. We consider the scatter to be due primarily to the statistical uncertainty in the spectral estimates, the wave number resolution, and differences in the temporal and spatial averaging. Scanning distortion is shown to cause significant bias in the SAR and buoy comparison for slow‐flying aircraft imaging ocean wave swell. Correction of the SAR spectra for this special radar‐ocean condition gives significant improvement in the SAR‐buoy comparison. We investigate the relative importance of the motion‐related mechanisms (velocity bunching, velocity smearing, and scanning distortion), and the tilt contributions using four nondimensional imaging parameters.

Optical scan-correction system applied to atomic force microscopy

Nonlinearities inherent in the piezoelectric actuators used in high-resolution scanning probe microscopies limit the usefulness of the instruments for precision dimensional measurements of submicrometer to micrometer scale structures. These nonlinearities can result in images where the scale changes by over 40% from one region of the image to another. This paper describes a simple two-axis optical beam displacement sensor that is used to accurately measure the (x,y) position of a piezoelectric tube scanner used in an atomic force microscope. This sensor has a noise level of 6.1 Årms over a frequency range of 0.5 Hz–1 kHz and a stability of about 200 Å over a 30-min period. Two different methods were used to correct the scans: postimaging software image correction and real-time feedback scan correction. The software method allows fast imaging and does not alter the control of the microscope, but requires postimaging image processing. It also loses some image information because of interpolation errors and the necessity of cropping the image to recover a rectangular image area. Feedback correction uses the sensor and a control system to accurately position the scanner for each data point of the image. This method eliminates the postprocessing of the images as well as interpolation errors, but limits the achievable scan speed and also adds the noise of the sensor and control system to the scan itself. Finally, both scan-correction systems reduce imaging errors dramatically over conventional open-loop piezoelectric scanners. Both linear and quadratic scan distortion are reduced to about 1%–2% of the image size.

Airborne SAR imagery of ocean surface waves obtained during LEWEX: some initial results

The potential and the difficulties of using airborne synthetic-aperture radar (SAR) to study ocean surface waves are presented. Airborne C-band SAR imagery obtained with the real-time SAR processor on the Canada Centre for Remote Sensing (CCRS) Convair 580 during the Labrador Extreme Waves Experiment (LEWEX) shows waves propagating through the marginal ice zone as well as through open water regions. Examples are chosen to illustrate both coherent and noncoherent scene motion effects. Coherent scene motion effects include velocity bunching. acceleration defocus, and coherence time limitations. Noncoherent scene motion effects include scanning distortion and look misregistration. The slow platform velocity of airborne SAR precludes replication of spaceborne observations, largely due to coherent motion effects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An efficient technique of characterising calibration grids in e-beam lithography tools

Electron beam lithography systems are used to overlay a pattern over previous levels exposed by optical means or other electron beam machines. This requires the calibration of machine deflection to a nominal reference. A specially designed calibration grid of gold bars on silicon is permanently mounted in the system. Deflection errors are calibrated to these grids by scanning the grid with the writing deflection. The higher-frequency calibration grid errors can be filtered out mathematically. The deflection scan distortion is determined by using a best fit spline function to the measured data of the beam scan position over the calibration grid. Results of this filtering method indicate a repeatability and accuracy of grid characterisation of 0.15 mu m (3 sigma).

Microdiffraction in Dedicated STEM

Microdiffraction in dedicated STEM instruments has shown considerable promise as a source of microanalytical information. A major problem has been the relatively inefficient sequential methods used to obtain the diffraction pattern. The apparatus shown schematically in Fig. 1 has facilitated parallel viewing and recording of diffraction patterns in the HB5 STEM. The equipment is robust, low cost and can be installed with no modifications to the microscope.A series of diffraction patterns were recorded under identical conditions at a (110) zone axis in an Al-4% Cu foil shown in Fig. 2(a) to allow direct comparison of sequential and parallel recording methods. The thickness in this part of the foil was ∼220 nm as measured from the projected widths of θ' plates. The selected area “rocking beam” images in Figs. 2(b) and (d) are clearly noisy, suffer from scan distortions and their usefulness for phase identification and crystal orientation is severely limited.

Laser printer scanning system with a parabolic mirror

A high quality nonimpact printer at a speed of 10,000 1/min is realized by a new laser scanning system and an electrophotographic process. The laser scanning system uses a parabolic mirror for correcting line scanning distortion. When a polygonal mirror facet is placed on the axis of the parabolic mirror at about two-thirds of the focal length from the mirror surface, and the focus of the parabolic mirror is on a photosensitive drum surface. The scanning velocity distortion is reduced to less than 0.1% over +/-30 degrees of the scanning angle. The confusion circle induced by the parabolic mirror is 1 order of magnitude smaller than the spot size determined by diffraction limit. The tolerance of the length from the rotating mirror to the parabolic mirror for 0.1% distortion over +/-30 degrees scanning angle is 10% of focal length. This high speed laser printer has demonstrated the high quality printing of 10-dots/mm resolution.

Laser printer scanning system with a parabolic mirror

A high quality nonimpact printer at a speed of 10,000 1/min is realized by a new laser scanning system and an electrophotographic process. The laser scanning system uses a parabolic mirror for correcting line scanning distortion. When a polygonal mirror facet is placed on the axis of the parabolic mirror at about two-thirds of the focal length from the mirror surface, and the focus of the parabolic mirror is on a photosensitive drum surface. The scanning velocity distortion is reduced to less than 0.1% over ±30° of the scanning angle. The confusion circle induced by the parabolic mirror is 1 order of magnitude smaller than the spot size determined by diffraction limit. The tolerance of the length from the rotating mirror to the parabolic mirror for 0.1% distortion over ±30° scanning angle is 10% of focal length. This high speed laser printer has demonstrated the high quality printing of 10-dots/mm resolution.

The Correcting Method of Beam Scanning Distortion Using the Parabolic Mirror

The Correcting Method of Beam Scanning Distortion Using the Parabolic Mirror