206 results about "Nyquist frequency" patented technology

A variety of optical arrangements and methods of modifying or enhancing the optical characteristics and functionality of these optical arrangements are provided. The optical arrangements being specifically designed to operate with camera arrays that incorporate an imaging device that is formed of a plurality of imagers that each include a plurality of pixels. The plurality of imagers include a first imager having a first imaging characteristics and a second imager having a second imaging characteristics. The images generated by the plurality of imagers are processed to obtain an enhanced image compared to images captured by the imagers. In many optical arrangements the MTF characteristics of the optics allow for contrast at spatial frequencies that are at least as great as the desired resolution of the high resolution images synthesized by the array camera, and significantly greater than the Nyquist frequency of the pixel pitch of the pixels on the focal plane, which in some cases may be 1.5, 2 or 3 times the Nyquist frequency.

Embodiments of methods and/or apparatus for 3-D volume image reconstruction of a subject, executed at least in part on a computer for use with a digital radiographic apparatus can obtain image data for 2-D projection images over a range of scan angles. For each of the plurality of projection images, an enhanced projection image can be generated. In one embodiment, through the application of a resolution increasing interpolator, a prescribed CBCT routine scanning mode with preset binning can increase a spatial resolution, Nyquist frequency or MTF.

The invention discloses a self-adoptive correcting device of mismatch error of time-interleaved analog-digital converter, comprising an M channel TIADC, a signal recombination, a digital reference signal memorizer, a simulated reference signal generator, a self-adaptive reconstruction filter bank, a clock generation circuit and a subtraction device. Signals after passages are reconstructed are used to correct each passage instead of single correction on each passage, thereby solving the problem that when an input signal bandwidth is larger than the Nyquist frequency of each passage ADC, the time error can not be corrected due to aliasing. Each self-adoptive reconstruction filter is divided into a plurality of sub-filters for concurrent working, thereby not improving the requirement of thetreatment speed for a self-adoptive correcting filter while realizing the effect of signal recombination and ensuring the practicability of the hardware of the structure of the invention. A digital reference signal is internally installed in the device and is taken as a target to carry out the self-adoptive correction, pre-measuring or calculating a passage mismatch error is not needed, and the source of the error is not needed to be discriminated so that various mismatch errors can be corrected.

A method and apparatus are provided for reducing distortion in a dynamically delayed digital sample stream of an imaging system. The method includes the steps of delta-sigma modulating an input analog signal of the imaging system at a frequency above the Nyquist frequency of the input analog signal to generate a digital sample stream and changing a length of the sample stream to delay a portion of the sample stream while maintaining synchronism between a delta-sigma modulator and a demodulator of the system.

A radio communication device for receiving a single-carrier signal transmitted in a partial spectrum of Nyquist frequency band, includes: an interference eliminator for eliminating interference from a received signal by spectrum reproduction of non-transmitted spectra using a symbol replica, to output an interference eliminated signal, wherein the interference includes intersymbol interference which is caused by symbols which are more than a predetermined distance away from a decision symbol point; a symbol sequence estimator for estimating a transmission symbol sequence by separating nearby intersymbol interference within the predetermined distance of the decision symbol point based on the interference eliminated signal, to output a decision signal; and a replica generator for generating the symbol replica from decoding result of the decision signal, wherein the symbol replica is fed back to the frequency-domain interference eliminator.

A method and apparatus are provided for reducing distortion in a dynamically delayed digital sample stream of an imaging system. The method includes the steps of delta-sigma modulating an input analog signal of the imaging system at a frequency above the Nyquist frequency of the input analog signal to generate a digital sample stream and changing a length of the sample stream to delay a portion of the sample stream while maintaining synchronism between a delta-sigma modulator and a demodulator of the system.

A digital camera includes: a lens unit that forms a subject image on an imaging plane; an image sensor that includes color filters each disposed at one of pixels disposed in a lattice-like pattern over pixel intervals (a, b) along two directions, an x direction and a y direction, extending perpendicular to each other, with color filters corresponding to a first color component among first through nth (n≧2) color components, disposed in a checkered pattern at pixels amounting to at least half an entire color filter density and color filters corresponding to remaining color components disposed at other pixels, and outputs image signals expressing the subject image; and an optical low pass filter unit at which light having passed through the lens unit and yet to enter the image sensor undergoes light beam separation along two diagonal directions ((1/2)a, (1/2)b)×(√2/α) and ((1/2)a, −(1/2)b)×(√2/α) relative to (x, y) coordinate axes, so as to achieve frequency modulation for the subject image to become extinct at a band formed by connecting spatial frequencies (α/(2a), 0) and (0, α/(2b)) at positions calculated by multiplying, by a multiplier α, a Nyquist frequency 1/(2a) and a Nyquist frequency 1/(2b) at the image sensor assumed respectively along the x direction and the y direction. When the pixel intervals (a, b) assumed along the two directions at the image sensor are both within a 2.5˜5 μm/pixel range, a position of an extinction frequency band is set for the optical low pass filter by setting the multiplier α for the Nyquist frequencies at the image sensor within a range of 1.5≦α≦3.5.

An interlace motion artifact detector which identifies video image spatial frequencies characteristic of motion artifacts. The detected frequency is the maximum which can be represented by the vertical sampling rate of the video format (i.e., the Nyquist frequency). This frequency is detected by a pair of partial Discrete Fourier Transforms (DFT) which each calculate only the frequency component of interest. Additional vertical frequency components at one half and one quarter the interlace motion artifact frequency are also detected via a partial DFT. The presence of these lower frequencies acts as an indication of an erroneous motion artifact detection. Additionally, the dynamic range and maximum level of the video data is used as an indication of when to boost the frequency detection levels in areas of low brightness and/or contrast.

The method of manufacturing a conductive sheet of the present invention is provided with: a creation step for creating image data that indicates a meshed pattern; and an outputting step for outputting and forming wire materials on a base body on the basis of the created image data, and manufacturing a conductive sheet having the meshed pattern. The image data has, in convolution integration of a power spectrum of the image data and standard vision responsiveness of human beings, a characteristic of having each of the integration values at a spatial frequency band that is not less than 1/4 and not more than 1/2 of a Nyquist frequency corresponding to the image data to be greater than integration values at a null-space frequency.

The invention discloses a method for estimating OFDM rapid-varying channels in low-density pilot distribution. The method comprises: multiplexing Gaussian-distribution pilot-frequency data and to-be-transmitted data at a transmitting end according to a time-frequency random insertion mode; performing random down-sampling and multiplexing at a receiving end on a frequency far below Nyquist frequency; transmitting received pilot-frequency data which is obtained through multiplexing and corresponds to a pilot-frequency position to perform compressed sensing channel reconstruction; obtaining S nonzero channel values in a channel delay-Doppler sparse domain; and obtaining the channel parameters of all sub-carriers in a frequency domain through channel coefficient zero padding excepting S nonzero positions, as well as delay-Doppler sparse domain inverse transformation processing. The method has the advantages of performing random down-sampling on the frequency far below Nyquist frequency, utilizing the compressed sensing channel reconstruction to filter noise so as to improve the parameter estimation precision of OFDM rapid-varying channels under pilot-frequency distribution conditions low in signal-to-noise ratio and density and realizing high-precision channel parameter estimation and tracking, along with low estimation-calculation complexity and low bit error rate.

A wide band analog-to-digital converter used in a frequency multiplexed communication system. The converter includes a plurality, M, of time-interleaved analog-to-digital converter subunits (ADC subunits). The sampling rate, FS1, of the M ADC subunits is selected to locate one or more integer multiples of a Nyquist frequency of a respective subunit ADC in one or more guard bands, and/or such that one or more integer multiples of FS1 are also located in the guard bands.

The invention discloses a two-dimensional sub-pixel sampling-based super-resolution display method and a two-dimensional sub-pixel sampling-based super-resolution display device. Based on the characteristic of diversity of R, G and B primary color sub-pixel arrangement of flat panel display equipment, a Nyquist frequency limiting region of each primary color sub-pixel arrangement is calculated, and a group of R, G and B primary color anti-aliasing filters is designed on the basis of the calculated Nyquist frequency limiting region of each primary color sub-pixel arrangement, so that the aim of weakening and even eliminating the aliasing introduced by sub-pixel sampling is fulfilled while a high image sensing resolution is kept. According to the method and the device, corresponding anti-aliasing filtering is applied to R, G and B primary color components of an original image respectively, and then sub-pixel sampling is performed on the filtered image according to the spatial position structure of the two-dimensional sub-pixel arrangement of the display equipment. The visual perception resolution of the flat panel display equipment is improved at a lower cost on the premise of not changing any physical attribute, super-resolution display of the display equipment is realized, and meanwhile, the method is simple and easy to implement.

The invention discloses a signal collecting method with a sampling frequency lower than the Nyquist frequency. Firstly, an appropriate conversion basis matrix is selected for an input signal, sparsity expression is performed on the signal with the conversion basis matrix so as to determine the sparsity k of the signal, the sampling times M of compressive sampling are calculated with the sparsity, M channels are divided for respectively performing sampling on the signal in a fNTQ/M mode, integration is performed on the sampling value of each channel so as to obtain M measured values, and a reconstruction end reconstructs an original signal by solving the optimization problem. According to the signal collecting method with the sampling frequency lower than the Nyquist frequency, the compressed sensing principle serves as a basis so as to perform compressive sampling on sparse signals or signals capable of being expressed in a sparse mode with the frequency far lower than the Nyquist frequency, and limitation on the sampling frequency by the classic Nyquist sampling theorem is broken. Meanwhile, the signal collecting method with the sampling frequency lower than the Nyquist frequency is easy to carry out and reduces pressure in collecting, storing, transmitting and processing data.

A technique for generating coefficients for a digital filter. A gain control signal with a value of reference gain and a frequency control signal with a value of reference frequency are provided. A plurality of gain and/or frequency points are calculated, according to a model of the frequency/gain characteristic of a prototype analog filter, at frequencies equal to and less than a Nyquist frequency (where the Nyquist frequency is half the sampling frequency of the digital frequency) and which match corresponds to gain and/or frequency points in the corresponding digital filter characteristic. Pre-warped parameters of a model of the analogue filter are calculated from the calculating points and a transform is applied to the resulting pre-warped analogue model, thus, converting the pre-warped analog model into the digital domain. Coefficients from the transformed model are generated and applied to the filter, thereby generating the coefficients of the digital filter.

A two-channel time-interleaved analog-to-digital converter (TIADC) system that provides for estimation and correction of offset, gain, and sample-time errors. Error in the offsets of the two ADCs that form the TIADC produces a spurious signal at the Nyquist frequency that can be used to minimize the difference of offsets of the ADCs. The difference in gain between the two ADCs produces spurious signals reflected around the Nyquist frequency whose magnitudes can be reduced by minimizing the difference in signal power between the two ADCs. An Automatic Gain Control loop corrects the scaling of the input signal due to the average of the gains of the ADCs. Phase error produces spurious signals reflected around the Nyquist frequency that are π/2 out of phase with those due to the gain error. Minimizing the difference between the correlation of consecutive signals from the ADCs reduces the magnitude of these image tones.

The invention discloses a method for processing seismic data by using high-precision single-channel spectrum analysis technology in petroleum geophysical exploration data processing. The method comprises the following steps of: labeling and selecting data, partitioning an analyzed time window segment into data segments, adding linear slopes at two ends of a time window and filling zero to the channel length of the primary data, performing Fourier transformation on the data of the disturbed m time window segments to obtain an amplitude spectrum, storing the amplitude spectrum into a seismic channel, determining an Nyquist frequency, arranging the calculated spectral values into a seismic data format to obtain a data frequency distribution rule, and selecting a processing method and a processing parameter according to the determined data frequency distribution rule to obtain a high-precision stratum section and determine the position of an oil-containing stratum. The method can quickly reflect the frequency characteristics of the seismic data at different processing stages, and can clearly display the problems so that the processing measure has pertinence.