Resolution downscaling of video images

• US 20020181592A1
• Filed: 04/25/2002
• Published: 12/05/2002
• Est. Priority Date: 05/22/2001
• Status: Active Grant

• Current Assignee: Funai Electric Co., Ltd. (Funai Electric Holdings Company Limited)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Van Zon, Kees, Gagarin, Konstantin Y.
• Granted Patent: US 7,215,708 B2
• Time in Patent Office: Days
• US Class Current: 375/240.18
• CPC Class Codes: G06T 3/4084 in the transform domain, e.g. fast Fourier transform [FFT] domain scaling
• 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 19/48 using compressed domain processing techniques other than decoding, e.g. modification of transform coefficients, variable length coding [VLC] data or run-length data motion estimation in a transform domain H04N19/547; processing of decoded motion vectors H04N19/513
• CPC Class Codes: H04N 19/51 Motion estimation or motion compensation
• CPC Class Codes: H04N 19/59 involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
• CPC Class Codes: H04N 19/80 Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation H04N19/635, H04N19/86 take precedence
• CPC Class Codes: H04N 19/90 using coding techniques not provided for in groups H04N19/10-H04N19/85, e.g. fractals
• CPC Class Codes: H04N 7/0125 one of the standards being a high definition standard

Abstract

A method and apparatus for downscaling video images to a lower resolution (e.g. from HDTV to SDTV) is presented. The method comprising the steps of frequency domain anti-aliasing filtering and downscaling the first video signal in a first direction corresponding with a line direction in the first video signal to obtain a downscaled video signal, and spatial domain downscaling the downscaled video signal in a second direction perpendicular to the first direction to obtain the second video signal. The method and apparatus of the invention are suitable for efficient and high quality decoding both progressive and any-type encoded interlaced signals.

Claims

1. A method for downscaling a spatial resolution of a first video signal to obtain a second video signal at a lower spatial resolution than the spatial resolution of the first video signal, said method comprising the steps of:

frequency domain anti-aliasing filtering and downscaling the first video signal in a first direction corresponding with a line direction in the first video signal to obtain a downscaled video signal, and

spatial domain downscaling the downscaled video signal in a second direction perpendicular to the first direction to obtain the second video signal.

2. A method as claimed in claim 1, wherein the downscaling is performed prior to or during an inverse transform operation such as an inverse DCT.

3. A method as claimed in claim 2, wherein the inverse transform operation is followed by an inverse motion compensation prior to the spatial domain downscaling.

4. A method as claimed in claim 2, wherein the inverse transform operation is followed by the spatial domain downscaling prior to an inverse motion compensation.

5. A method as claimed in any of the previous claims, wherein the first video signal comprises groups of pixels and wherein the method is performed per group of pixels.

6. A method as claimed in claim 5, wherein the groups of pixels are included in sequences of mixed field/frame-type encoded groups of pixels and wherein the field-type encoded groups of pixels are frequency domain anti-aliasing filtered in both the first direction and the second direction whereas the frame-type encoded groups of pixels are frequency domain anti-aliasing filtered in the first direction and spatial domain anti-aliasing filtered in the second direction.

7. A method as claimed in claim any of the preceding claims, wherein the first video signal comprises quantized frequency transform coefficients, wherein the method further comprises inverse quantizing the quantized frequency transform coefficients to obtain frequency transform coefficients, wherein the anti-aliasing filtering is performed on the frequency transform coefficients, and

wherein said inverse quantizing step and said filtering step are performed by using a combined matrix which is a combination of a quantization matrix and a filter matrix.

8. An apparatus for downscaling a spatial resolution of a first video signal to obtain a second video signal at a lower spatial resolution than the spatial resolution of the first video signal, said apparatus comprising:

means for frequency domain anti-aliasing filtering and for downscaling the first video signal in a first direction corresponding with a line direction in the first video signal to obtain a downscaled video signal, and means for spatial domain downscaling the downscaled video signal in

a second direction perpendicular to the first direction to obtain the second video signal.