Image processing apparatus including a partitioned low pass channel

Claim 2

Electronic image processing apparatus in which an image signal representing a predetermined array of picture elements, or pels, is applied to a high pass filter acting as an image feature detector whose signal output is added to the output of a low pass filter to provide a feature-enhanced output signal, characterised in that the low pass filter is also arranged to act as an image feature detector and includes a prefilter arranged to filter said image signal and a sampling filter arranged to subsample the prefiltered image signal according to a sparse sampling pattern having non-zero pel weightings regularly spaced at locations that are nonadjacent other non-zero weightings.

Claim 3

Electronic image processing apparatus in which an image signal representing a predetermined array of picture elements, or pels, is applied to a high pass electronic filter acting as an image feature detector whose signal output is added to the output of a low pass electronic filter to provide a feature-enhanced output signal, characterised in that the low pass electronic filter comprises a pair of subsidiary filters operating one in a band pass channel and the other in a narrow band low pass channel, each subsidiary filter including a subsidiary low pass filter arranged to prefilter said image signal and a subsidiary sampling filter based on a sparse array of non-zero pel weightings arranged at regularly spaced, nonadjacent locations along each dimension of the array to effect a sub-sampling of the prefiltered image signal, the sampling filter operating in the band pass channel comprising at least one filter forming a subchannel that acts as a detector of a selected image feature and connected so that its output is cored before being combined together with the output of the subsidiary filter operating in the narrow band low pass channel to form a feature enhanced output of the low pass channel.

Claim 4

Electronic image processing apparatus in which an image signal representing a predetermined array of picture elements, or pels, is applied to a high pass electronic filter acting as an image feature detector whose signal output is added to the output of a low pass electronic filter to provide a feature-enhanced output signal, characterised in that the low pass electronic filter comprises a pair of subsidiary filters operating one in a band pass channel and the other in a narrow band low pass channel, each subsidiary filter including a subsidiary low pass filter arranged to prefilter said image signal and a subsidiary sampling filter based on a sparse array of non-zero pel weightings arranged at regularly spaced, nonadjacent locations along each dimension of the array to effect a sub-sampling of the prefiltered image signal, the sampling filter operating in the band pass channel comprising at least one filter forming a subchannel that acts as a detector of a selected image feature and connected so that its output is cored before being combined together with the output of the subsidiary filter operating in the narrow band low pass channel to form a feature enhanced output of the low pass channel.

Claim 5

Apparatus as claimed in claim 2 wherein the subsidiary filter operating in the narrow band low pass channel comprises a further pair of subsidiary filters operating in a second band pass channel and a second narrow band low pass channel that are both partitioned from said narrow band low pass channel.

Claim 6

In electronic image processing apparatus of the kind in which an image signal representing the brightness of a predetermined array of picture elements, or pels, is applied to high pass and low pass electronic filters operating in respective high pass and broad band low pass channels, the improvement wherein said low pass electronic filter comprises a pair of secondary filters operating in respective band pass and narrow band low pass channels to generate a signal in said broad band low pass channel, each secondary filter including (a) a low pass prefilter based on a low pass array of pel weightings so chosen as to generate a low pass signal from the image signals and (b) a sampling filter based on a sparse sampling array having nonadjacent pel weightings spaced at regular row and column intervals that are directly related to the size of the low pass prefilter array.

Claim 7

In electronic image processing apparatus of the kind in which an image signal representing the brightness of a predetermined array of picture elements, or pels, is applied to high pass and low pass electronic filters operating in respective high pass and broad band low pass channels, the improvement wherein said low pass electronic filter comprises a pair of secondary filters operating in respective band pass and narrow band low pass channels to generate a signal in said broad band low pass channel, each secondary filter including (a) a low pass prefilter based on a low pass array of pel weightings so chosen as to generate a low pass signal from the image signals and (b) a sampling filter based on a sparse sampling array having nonadjacent pel weightings spaced at regular row and column intervals that are directly related to the size of the low pass prefilter array.

Claim 8

Apparatus as claimed in claim 4 in which the sampling filter operating in the narrow band low pass channel is based on a sparse array of pel weightings so chosen as to generate a low pass signal from the prefiltered image signal.

Claim 9

Apparatus as claimed in claim 4, in which the sampling filter operating in the band pass channel is based on a sparse array of pel weightings so chosen as to generate an image feature signal from the prefiltered image signal.

Claim 10

Electronic image processing apparatus responsive to sampled brightness data for generating a filtered image signal representative of an enhanced image, said sampled brightness data being derived from elemental portions of an image, said electronic image processing apparatus comprising: a high pass filter responsive to the brightness data for generating a high pass signal representative of small scale brightness fluctuations in the image; a low pass filter for generating a low pass signal representative of large scale brightness fluctuations in the image, said low pass filter comprising a narrow band low pass filter for generating a narrow band low pass signal representative of the larger brightness fluctuations in the low pass image signal, a band pass filter for generating a band pass signal representative of brightness fluctuations within a particular spatial pass band of the image, both said narrow band low pass and said band pass filters comprising (a) low pass means for generating a prefiltered image signal from a set of filter coefficients arranged as an array of filter weights and (b) sub-sampling means for generating a subsampled signal by processing the prefiltered image signal with a set of filter coefficients arranged as a sparse array of filter weights having regularly-spaced non-zero weights at nonadjacent locations along each dimension of the array.

Claim 11

Electronic image processing apparatus responsive to sampled brightness data for generating a filtered image signal representative of an enhanced image, said sampled brightness data being derived from elemental portions of an image, said electronic image processing apparatus comprising: a high pass filter responsive to the brightness data for generating a high pass signal representative of small scale brightness fluctuations in the image; a low pass filter for generating a low pass signal representative of large scale brightness fluctuations in the image, said low pass filter comprising a narrow band low pass filter for generating a narrow band low pass signal representative of the larger brightness fluctuations in the low pass image signal, a band pass filter for generating a band pass signal representative of brightness fluctuations within a particular spatial pass band of the image, both said narrow band low pass and said band pass filters comprising (a) low pass means for generating a prefiltered image signal from a set of filter coefficients arranged as an array of filter weights and (b) sub-sampling means for generating a subsampled signal by processing the prefiltered image signal with a set of filter coefficients arranged as a sparse array of filter weights having regularly-spaced non-zero weights at nonadjacent locations along each dimension of the array.

Claim 12

In electronic image processing apparatus of the kind in which an image signal representing the brightness of a predetermined array of picture elements, or pels, is applied to a low pass filter operating in a low pass channel and the output thereof is a filtered image signal representative of the low-frequency portion of an enhanced image, the improvement wherein the low pass channel is partitioned into a narrow band low pass channel and a band pass channel, said partitioning effected by a pair of filters operating in said low pass channel, each filter of said pair including (a) a subsidiary low pass filter arranged to prefilter the image signal and (b) a sampling filter arranged to sample the prefiltered image signal according to a sparse sampling matrix having non-zero elements at locations nonadjacent other non-zero elements.

Claim 13

In electronic image processing apparatus of the kind in which an image signal representing the brightness of a predetermined array of picture elements, or pels, is applied to a low pass filter operating in a low pass channel and the output thereof is a filtered image signal representative of the low-frequency portion of an enhanced image, the improvement wherein the low pass channel is partitioned into a narrow band low pass channel and a band pass channel, said partitioning effected by a pair of filters operating in said low pass channel, each filter of said pair including (a) a subsidiary low pass filter arranged to prefilter the image signal and (b) a sampling filter arranged to sample the prefiltered image signal according to a sparse sampling matrix having non-zero elements at locations nonadjacent other non-zero elements.