Upsampling filter and half-pixel generator for an HDTV downconversion system

• US 6,184,935 B1
• Filed: 03/29/1999
• Issued: 02/06/2001
• Est. Priority Date: 03/12/1997
• Status: Expired due to Fees

• Current Assignee: Vertex Pacific Limited (Stewart Family)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Egawa, Ren, Kim, Hee-Yong, Meyer, Edwin Robert, Iaquinto, Michael
• Primary Examiner(s): Kostak, Victor R.
• Application Number:
  US09/180,081
• Time in Patent Office: 680 Days
• Field of Search: 348/409, 348/416, 348/581, 348/458, 348/402, 348/565, 348/720, 348/714, 348/718, 348/441, 371/49.1
• US Class Current: 348/441
• CPC Class Codes: G06T 1/60 Memory management
• CPC Class Codes: G06T 3/4023 based on decimating pixels or lines of pixels; based on inserting pixels or lines of pixels
• CPC Class Codes: G06T 3/4084 in the transform domain, e.g. fast Fourier transform [FFT] domain scaling
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/162 User input
• CPC Class Codes: H04N 19/18 the unit being a set of transform coefficients
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/30 using hierarchical techniques, e.g. scalability H04N19/63 takes precedence
• CPC Class Codes: H04N 19/423 characterised by memory arrangements H04N19/433 takes precedence
• CPC Class Codes: H04N 19/428 Recompression, e.g. by spatial or temporal decimation
• CPC Class Codes: H04N 19/44 Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
• CPC Class Codes: H04N 19/523 with sub-pixel accuracy
• CPC Class Codes: H04N 19/527 Global motion vector estimation
• CPC Class Codes: H04N 19/59 involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/80 Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation H04N19/635, H04N19/86 take precedence
• CPC Class Codes: H04N 19/82 involving filtering within a prediction loop
• CPC Class Codes: H04N 19/85 using pre-processing or post-processing specially adapted for video compression
• CPC Class Codes: H04N 19/86 involving reduction of coding artifacts, e.g. of blockiness
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 5/46 : for receiving on more than one standard at will deflecting circuits of multi-standard receivers H04N3/27
• CPC Class Codes: H04N 7/0122 : the input and the output signals having different aspect ratios
• CPC Class Codes: H04N 7/0125 : one of the standards being a high definition standard
• CPC Class Codes: H04N 7/014 : involving the use of motion vectors motion estimation and compensation in video coding H04N19/51
• CPC Class Codes: H04N 7/015 : High-definition television systems
• CPC Class Codes: H04N 9/64 : Circuits for processing colour signals H04N9/77 takes precedence; camera processing pipelines for processing colour signals H04N23/84

Abstract

A video down conversion system compliant with the Advanced Television Systems Standard (ATSC) includes a decoder which decodes a Main Profile, High Level (MP@HL) image and employs a downconversion processor to produce a standard definition video signal. The system stores a subsampled image in order to reduce memory requirements and employs an upsampling filter to generate reference image data from the stored. subsampled image. The reference image data spatially correspond to the image data produced by the video decoder before it is subsampled. The upsampling filter uses different filter coefficients based on the subsampling phase of the stored image and the half-pixel indicator in the motion vector which is used to locate the downsampled reference image data in the stored subsampled image.

Claims

1. Upsampling filter circuitry for a digital video signal down conversion system which decodes a digitally encoded video signal representing a video image and decimates the decoded signal to produce a subsampled image signal that is stored for use as reference image data in decoding a subsequently received encoded image signal that is encoded as differential picture element (pixel) values relative to the earlier decoded image, the upsampling circuitry comprising:

a programmable filter having a plurality of filter coefficient values;

a coefficient memory which holds a plurality of filter coefficient sets, each coefficient set corresponding to a distinct subsampling phase;

memory access circuitry which receives a motion vector from the encoded image signal, processes the received motion vector to locate a desired segment from the stored subsampled image signal; and

control circuitry which determines the subsampling phase of the desired segment from location information provided by the memory access circuitry and programs the programmable filter with the coefficient set that corresponds to the determined subsampling phase;

wherein the programmable filter filters the retrieved desired segment to provide reference image data which corresponds to the decoded differential image data in image pixel position.

2. Upsampling filter circuitry according to claim 1, wherein:

the motion vectors in the encoded video signal define the location of the desired segment with a resolution of one-half of one pixel position;

the plurality of coefficient sets includes a number 2N coefficient sets, where N is the decimation factor applied to the decoded image to produce the subsampled image, each coefficient set corresponding to a distinct combination of subsampling phase and half pixel position;

the control circuitry determines the subsampling phase of the desired segment from the location information provided by the memory access circuitry and the half pixel position from the motion vector and programs the programmable filter with the coefficient set that corresponds to the determined sampling phase and half pixel position.

3. Upsampling filter circuitry according to claim 1, wherein:

the motion vectors in the encoded video signal define the location of the desired segment with a resolution of one-half of one pixel position; and

the filter further include a linear interpolator, responsive to the motion vector, which selectively averages adjacent pixels in the filtered desired segment to produce output pixel values which are displaced by one-half pixel position from the pixel values of the filtered desired segment.

4. Upsampling filter circuitry according to claim 1, wherein the video signal downconversion system is configured to decimate the decoded video signal by one of a plurality of decimation factors and wherein:

the filter is programmable to decimate the decoded video image by one of a plurality of decimation factors;

the coefficient memory holds multiple groups of coefficient sets, each group corresponding to one of the plurality of decimation factors;

and the control circuitry is responsive to the decimation factor and the location information provided by the memory access circuitry to program the programmable filter with the coefficient set that corresponds to the decimation factor and determined sampling phase.

5. Upsampling filter circuitry according to claim 4, wherein the decimated video signal is decimated only in the horizontal direction and the programmable filter is a one-dimensional finite impulse response (FIR) filter.

7. Upsampling filter circuitry according to claim 5, wherein the video signal downconversion system is configured to decimate the decoded video signal by one of a plurality of decimation factors:

the filter is programmable to upsample the decoded video image by one of a plurality of upsampling factors, each upsampling factor corresponding to one of the decimation factors;

the coefficient memory holds multiple-groups of coefficient sets, each group corresponding to one of the plurality of decimation factors;

and the control circuitry is responsive to the decimation factor and the location information provided by the memory access circuitry to program the programmable filter with the coefficient set that corresponds to the decimation factor and determined sampling phase.

9. A method for upsampling according to claim 7, wherein:

the motion vector defines the location of the desired image segment to one-half pixel resolution; and

the selecting step selects a pair of coefficient sets responsive to the subsampling phase, representing the subsampling phase and the subsampling phase shifted by one-half pixel position; and

the method further comprises the step of;

identifying, responsive to the motion vector, one coefficient set of the pair of coefficient sets which is to be used by the filtering step to produce the reference image data.

6. Upsampling filter circuitry for a digital video signal down conversion system which decodes a digitally encoded video signal representing a video image and decimates the decoded signal to produce a subsampled image signal that is stored for use as reference image data in decoding a subsequently received encoded image signal that is encoded as differential picture element (pixel) values relative to the earlier decoded image, the upsampling circuitry comprising:

a programmable filter having a plurality of filter coefficient values;

memory access circuitry which receives a motion vector, that defines the location of the desired segment with a resolution of one-half of one pixel position, from the encoded image signal, processes the received motion vector to locate a desired segment in the stored image, retrieves the desired segment from the stored subsampled image signal;

a coefficient memory which holds a plurality of filter coefficient sets, each coefficient set corresponding to a distinct combination of subsampling phase and half-pixel position; and

control circuitry which determines the subsampling phase of the desired segment from location information provided by the memory access circuitry and programs the programmable filter with the coefficient set that corresponds to the determined subsampling phase;

wherein the programmable filter filters the retrieved desired segment to provide reference image data which corresponds to the decoded differential image data in image pixel position.

8. A method for upsampling data representative of a stored, subsampled digital image for use in a digital video signal down conversion system which decodes a digitally encoded video signal representing a video image and decimates the decoded signal to produce the stored subsampled image, wherein the subsampled image is stored for use as reference image data in decoding a subsequently received encoded image signal which is encoded as differential picture element (pixel) values relative to the earlier decoded image before the decoded image was subsampled, the upsampling method comprising the steps of:

receiving a motion vector from the encoded image signal;

processing the received motion vector to locate a desired segment in the stored image,

retrieving the desired segment from the stored subsampled image signal; and

determining, from the location of the desired segment, a subsampling phase of the desired segment;

selecting, responsive to the determined subsampling phase of the desired segment, one set of coefficients from a plurality of coefficient sets, which one set of coefficients is to be used to filter the retrieved segment; and

filtering the retrieved desired segment using the selected set of coefficients to produce reference image data which corresponds to the decoded differential image data in image pixel position.