摘要:
A lattice-structured multiple description vector quantization (LSMDVQ) encoder generates M descriptions of a signal to be encoded, each of the descriptions being transmittable over a corresponding one of M channels. The encoder is configured based at least in part on a distortion measure which is a function of a central distortion and at least one side distortion. For example, if M=2, the distortion measure may be an average mean-squared error (AMSE) function of the form ƒ(D0, D1, D2), where D0 is a central distortion resulting from reconstruction based on receipt of both a first and a second description, and D1 and D2 are side distortions resulting from reconstruction using only a first description and a second description, respectively. Further performance improvements may be obtained through perturbation of the lattice points. The LSMDVQ techniques of the invention can also be extended to cases of M greater than two, for which the encoder may utilize an ordered set of M codebooks &Lgr;1, &Lgr;2, . . . , &Lgr;M of increasing size, with the coarsest codebook corresponding to a lattice. In such cases, for each number k of descriptions received, there may be a single decoding function that maps the received vector to a corresponding one of the codebooks &Lgr;k, such that reconstruction of the signal requires no more than M such decoding functions.
摘要:
A multiple description (MD) joint source-channel (JSC) encoder in accordance with the invention encodes n components of a signal for transmission over in channels of a communication medium. In illustrative embodiments, the invention provides optimal or near-optimal transforms for applications in which at least one of n and m is greater than two, and applications in which the failure probabilities of the m channels are non-independent and non-equivalent. The signal to be encoded may be a data signal, a speech signal, an audio signal, an image signal, a video signal or other type of signal, and each of the m channels may correspond to a packet or a group of packets to be transmitted over the medium. A given n×m transform implemented by the MD JSC encoder may be in the form of a cascade structure of several transforms each having dimension less than n×m. The transform may also be configured to provide a substantially equivalent rate for each of the m channels.
摘要:
A multiple description coder generates a number of different descriptions of a given portion of a signal in a wireless communication system, using multiple description scalar quantization (MDSQ) or another type of multiple description coding. The different descriptions of the given portion of the signal are then arranged into packets such that at least a first description of the given portion is placed in a first packet and a second description is placed in a second packet. Each of the packets are then transmitted using a frequency hopping modulator, and the hopping rate of the modulator is selected or otherwise configured based at least in part on the number of descriptions generated for the different portions of the signal. For example, in an embodiment in which two descriptions are generated for each portion of the signal, a first description for a current one of the portions of the signal is placed in a current packet along with a second one of the descriptions for a previous portion of the signal, and the frequency hopping rate of the modulator is doubled relative to a hopping rate used for single description transmission.
摘要:
A multiple description (MD) joint source-channel (JSC) encoder in accordance with the invention encodes n components of an image signal for transmission over m channels of a communication medium. In an illustrative embodiment which uses statistical redundancy between the different descriptions of the image signal, the encoder forms vectors from transform coefficients of the image signal separated both in frequency and in space. The vectors may be formed such that the spatial separation between the transform coefficients is maximized. A correlating transform is then applied, followed by entropy coding, grouping as a function of frequency, and application of a cascade transform. In an illustrative embodiment which uses deterministic redundancy between the different descriptions of the image signal, the encoder may apply a linear transform, followed by quantization, to generate the multiple descriptions of the image signal. For example, vectors may be formed from transform coefficients of the image signal so as to include coefficients of like frequency separated in space. The vectors are expanded by multiplication with a frame operator, and then quantized using a step size which may be a function of frequency.
摘要:
A multiple description (MD) joint source-channel (JSC) encoder in accordance with the invention encodes n components of an audio signal for transmission over m channels of a communication medium, where n and m may take on any desired values. In an illustrative embodiment, the encoder combines a multiple description transform coder with elements of a perceptual audio coder (PAC). The encoder is configured to select one or more transform parameters for a multiple description transform, based on a characteristic of the audio signal to be encoded. For example, the transform parameters may be selected such that the resulting transformed coefficients have a variance distribution of a type expected by a subsequent entropy coding operation. The components of the audio signal may be quantized coefficients separated into a number of factor bands, and the transform parameter for a given factor band may be set to a value determined based on a transform parameter from at least one other factor band, e.g., the previous factor band. As another example, the transform parameter for one or more of the factor bands may be selected based on a determination as to whether the audio signal to be encoded is of a particular predetermined type. A desired variance distribution may also be obtained for the transformed coefficients by, e.g., pairing or otherwise grouping coefficients such that the coefficients of each pair or group are required to be in the same factor band.
摘要:
Depth information about a scene of interest is acquired by illuminating the scene, capturing reflected light energy from the scene with one or more photodetectors, and processing resulting signals, in at least one embodiment, a pseudo-randomly generated series of spatial light modulation patterns is used to modulate the light pulses either before or after reflection.
摘要:
An MR imaging system uses the multiple RF coils for acquiring corresponding multiple image data sets of the slice. An image data processor comprises at least one processing device conditioned for, generating a composite MR image data set representing a single image in a single non-iterative operation by performing a weighted combination of luminance representative data of individual corresponding pixels of the multiple image data sets in providing an individual pixel luminance value of the composite MR image data set. The image data processor reduces noise in the composite MR image data set by generating a reduced set of significant components in a predetermined transform domain representation of data representing the composite image to provide a de-noised composite MR image data set. An image generator comprises at least one processing device conditioned for, generating a composite MR image using the de-noised composite MR image data set.
摘要:
Transform encoding techniques are disclosed which permit reductions in entropy coding memory requirements. In an illustrative embodiment, a selected discrete linear transform is applied to a discrete-valued version of an information signal to be encoded. The transform is selected such that it produces a transformed output that can be entropy coded using a reduced codeword memory without a substantial increase in entropy coding rate. The entropy coding may be, for example, scalar entropy coding which independently codes each of the components of the transformed discrete-valued version of the information signal, using a single entropy codebook for all of the components to be encoded. As another example, the entropy coding may utilize scalar entropy coding for a first subset of the components of the transformed discrete-valued version of the information signal, using a first codebook for each of the subset of components to be encoded, and vector entropy coding for a second subset of the components, using a second, larger codebook for each of the vectors to be encoded. Other types of entropy coding can also be improved through appropriate selection of the discrete transform.
摘要:
Diffuse image measurement system and digital image formation method. The system includes a source of light with time-varying intensity directed at a scene to be imaged. A time-resolved light meter is provided for receiving light reflected from the scene to generate time-resolved samples of the intensity of light incident at the light meter. The temporal variation in the intensity of light incident at the light meter is associated with a function of a radiometric property of the scene, such as a linear functional of reflectance, and a computer processes the samples to construct a digital image. The spatial resolution of the digital image is finer than the spatial support of the illumination on the scene and finer than the spatial support of the sensitivity of the light meter. Using appropriate light sources instead of impulsive illumination significantly improves signal-to-noise ratio and reconstruction quality.
摘要:
A system and method is provided for simultaneously designing a radiofrequency (“RF”) pulse waveform and a magnetic field gradient waveform in a magnetic resonance imaging (“MRI”) system. The method includes determining a desired pattern of RF excitation and determining, from the desired pattern of RF excitation, a plurality of k-space locations indicative of the magnetic field gradient waveform and a plurality of complex weighting factors indicative of RF energy deposited at each k-space location. The method also includes calculating, from the determined k-space locations, the magnetic field gradient waveform and calculating, from the complex weighting factors, the RF pulse waveform that will produce the desired pattern of RF excitation when produced with the calculated magnetic field gradient.