Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 115 for “"Spatial Frequency"”.
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Camera Spatial Frequency Response Derived from Pictorial Natural Scenes
… the ISO12233:2017 for measuring the edge-based Spatial Frequency Response (e-SFR), a sister measure of the MTF designed for measuring discrete systems. Many modern camera systems incorporate non-linear, highly adaptive image signal processing (ISP) to improve image quality. As a result, system …
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DISCRETE TRANSFORMS WITH GOOD TIME-FREQUENCY AND SPATIAL-FREQUENCY LOCALIZATION
<p>Discrete orthonormal time-frequency basis functions are described and used for both analysis and synthesis of complex-valued signals. We derive expressions for complex-valued expansion coefficients in time-frequency lattices in the discrete one dimensional case. This derivation is based on …
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Spatial frequency based closed-loop control of sheet metal forming
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1987.
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Minimizing high spatial frequency residual in active space telescope mirrors
… correction limit and the three predominant high spatial frequency mirror surface residual components: actuation-induced dimpling, manufacturing-induced print-through, and disturbance-induced uncorrectable error. The methods for simulating each effect are discussed, and an objective function is …
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Numerical modeling and ray tracing of SPatIal Frequency modulation for Imaging
… performance of a simple system that implements SPatIal Frequency modulation for Imaging (SPIFI). SPIFI utilizes a chirped frequency mask that modulates the intensity of light along a single axis at a linear frequency sweep giving each lateral position a unique spatial frequency. By taking the …
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Two-dimensional spatial frequency content and confusions among dot matrix characters
… dot matrix characters to the two-dimensional spatial frequency similarity of these characters. During the first phase of the study, subjects were shown single alphanumeric characters from four different dot matrix fonts. In addition to the font variable, the size of the character was varied. …
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Effects of luminance, color, and spatial frequency variations on perceived image quality
… of varying levels of luminance, color, and spatial frequency content on the perceived image quality of a soft-copy color image. A secondary objective was to test the robustness of selected image quality metrics (MTFA, SQRI, and ICS) to the color variations as measured by the change in …
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Ultra-high precision scanning beam interference lithography and its application : spatial frequency multiplication
… low-pass filter is utilized to reduce high spatial-frequency noise in the stage mirror non-flatness measurement. A factor that causes another kind of the mirror measurement error, which is an apparent location-dependent mirror non-flatness measurement, has been determined. A corresponding …
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Investigation of high and low spatial frequency laser induced periodic surface structures on metals
Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-03-28 without embargo terms
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Manipulating spatial frequency to understand global and local information processing in 7-month-old infants
… filter real life objects of their high and low spatial frequencies. High spatial frequencies provide information about the smaller parts where as low spatial frequencies provide information about the larger ones. By removing high or low spatial frequency we can control the coarseness of their …
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A psychophysical investigation of human visual perceptual memory. A study of the retention of colour, spatial frequency and motion visual information by human visual short term memory mechanisms.
… term memory, with special interest in colour, spatial frequency and velocity. Previous studies of VSTM have indicated the existence of specific memory mechanisms for visual attributes such as orientation, spatial frequency, velocity, contrast and colour. The retention of information in visual …
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Improving ultrasound display by retrieving high-frequency sonographic information
… which is obtained at high transmission frequency, has limited depth of penetration because of tissue attenuation. The goal of this dissertation is to optimize the ultrasound axial resolution by applying all of the information available in the received echo signal. Recent results by …
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Prediction of modulation detectability thresholds for line-scan displays
… 2 replications at every combination of 10 spatial frequencies, 2 target orientations, and 5 noise amplitudes. Line rates were 525, 945, and 1,225 lines per frame; the spatial frequencies were between 1 and 20 c/deg; and the gratings were oriented vertically (perpendicular to the video …
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Detection and elimination of rock face vegetation from terrestrial LIDAR data using the virtual articulating conical probe algorithm
… to the overlying vegetation which has a high spatial frequency. On the other hand, with most TLS systems, the width of the lidar laser beam is very small, and the data acquisition hardware supports only first-return signals. For the case where vegetation is covering a rock face, the underlying …
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Fast Fourier transform square wave voltammetry
… the effect of experimental parameters in the spatial frequency domain. A new method was developed to determine truncation frequencies. A₀, the first spatial frequency, was shown to be an effective measure of peak height and its use in calibration curves was demonstrated. The real and imaginary …
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Examining Visual Masking in Target Aquisition Uning Two-dimensional Fourier Analysis Techniques
Spatial vision refers to a general class of perceptual capabilities that allows people to see the structure of objects within an image or visual scene. For example, spatial vision underlies people's abilities to discriminate important objects (or so-called "targets") from less important …
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The Venetian blind effect: Contrast disparity modulation in irradiation stereoscopy
… venetian blind effect for a square-wave carrier spatial frequency of 3.14 c/deg and square-wave modulation spatial frequencies of 0.26, 0.39, 0.79, and 1.57 c/deg.</p><p>In Experiment 2 we increased the spatial frequencies. We measured contrast disparity thresholds for the perception of slant for …
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Differences in image properties across facial expressions: effects on perceived contrast, stimulus efficacy and oculomotor responses
… for fearful expressions are driven by their low spatial frequency content. Unaddressed by this account, however, is the extent that expressions of fear compared to other faces differ in terms of the statistical image properties that define facial stimuli (their Fourier amplitude spectra), and the …
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Experiments and numerical analysis on air bearing slumping of segmented thin-shell mirrors for X-ray telescopes
… long thermal cycles and produces mid-range spatial frequency errors due to the anti-stick mandrel coatings. Over the last few years, MIT Space Nanotechnology Lab has developed a non-contact slumping process differentiating from the preceding contact slumping, which utilizes a pair of porous …
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