Image processing apparatus including a partitioned low pass channel

• US 4,463,381 A
• Filed: 11/30/1981
• Issued: 07/31/1984
• Est. Priority Date: 04/16/1980
• Status: Expired due to Fees

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Sharman, Richard A., Powell, Philip G.
• Primary Examiner(s): Martin, John C.
• Application Number:
  US06/328,544
• Time in Patent Office: 974 Days
• Field of Search: 358/166, 358/167, 358/284, 358/96, 382/22, 382/54
• US Class Current: 348/625
• CPC Class Codes: G06V 10/28 Quantising the image, e.g. histogram thresholding for discrimination between background and foreground patterns
• CPC Class Codes: G06V 10/30 Noise filtering
• CPC Class Codes: G06V 10/36 Applying a local operator, i.e. means to operate on image points situated in the vicinity of a given point; Non-linear local filtering operations, e.g. median filtering
• CPC Class Codes: G06V 10/40 Extraction of image or video features

Abstract

An electronic image processing system, providing image enhancement and noise suppression, processes signals representing an array of picture elements, or pels. The system is of the kind providing a feature-enhanced output by the addition of outputs of a high-pass filter acting as an image-feature detector and a complementary low-pass filter. The low-pass filter, which also acts as an image-feature detector, includes a bandpass filter and a further low-pass filter. The latter filter (122) includes a prefilter (130 and FIG. 22) and a sub-sampling filter (132) based on a set of weighting patterns in the form of sparse matrices (FIG. 23). The bandpass filter (120) includes a similar prefilter (128) and a sub-sampling filter (134) based on a set of weighting patterns in the form of sparse matrices (FIGS. 26 and 27) that act as detectors of selected image features.

Claims

1. 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.

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 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.