Spatio-temporal filter unit and image display apparatus comprising such a spatio-temporal filter unit

• US 7,034,892 B2
• Filed: 01/23/2002
• Issued: 04/25/2006
• Est. Priority Date: 01/26/2001
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Ojo, Olukayode Anthony, Kwaaitaal-Spassova, Tatiana Georgieva, Eland, Rudolf
• Primary Examiner(s): Yenke, Brian P.
• Application Number:
  US10/055,390
• Publication Number:
  US 20020101543A1
• Time in Patent Office: 1,553 Days
• Field of Search: 348/607, 348618-624, 348627-629, 348/718, 348720-721, 382260-261, 382/265, 382/275, 382/205, 382/308
• US Class Current: 348/607
• CPC Class Codes: G06T 2207/20182 Noise reduction or smoothing in the temporal domain; Spatio-temporal filtering
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/50 using two or more images, e.g. averaging or subtraction
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: G06T 7/20 Analysis of motion motion estimation for coding, decoding, compressing or decompressing digital video signals H04N19/43, H04N19/51
• CPC Class Codes: H04N 5/144 Movement detection for video coding H04N19/503; analysis of motion in general G06T7/20
• CPC Class Codes: H04N 5/21 Circuitry for suppressing or minimising disturbance, e.g. moiré or halo
• CPC Class Codes: H04N 5/44 Receiver circuitry for the reception of television signals according to analogue transmission standards H04N5/14 takes precedence

Abstract

Noise reduction is an important feature in consumer television. This is realized by spatial, temporal or spatio-temporal filters. Spatial filters require pixels from within one image, while temporal filters require samples from two or more successive images. The spatio-temporal filter unit (100) integrates spatial and implicit motion-compensated temporal noise reduction in one filter. For the motion compensation, no motion vectors are required. The spatio-temporal filter unit (100) is provided with a sigma filter (112) having one filter kernel (107) designed to operate on the pixels from both a current image and from the output of the spatio-temporal filter unit, being a temporally recursive filtered image. The operation of the spatio-temporal filter unit (100) can be adjusted by varying the thresholds of the sigma filter (112) and the selection of pixels. The adjustments can be controlled by a motion estimator (222), a motion detector (224) and a noise estimator (220).

Claims

1. A spatio-temporal filter unit comprising a sigma filter for reducing noise in images, characterized in that the sigma filter comprises one filter kernel for operating on pixels from both a current image and from an output of the spatio-temporal filter unit, said output supplying a temporally recursive filtered image, characterized in that said spatio-temporal filter unit further comprises:

a spatial pixel buffer for storing pixels of the current image as supplied to the spatio-temporal filter unit;

a spatial pixel selector for selecting pixels from the spatial pixel buffer;

a temporal pixel buffer for buffering pixels from the output of the spatio-temporal filter unit; and

a temporal pixel selector for selecting pixels from the temporal pixel buffer,

wherein the sigma filter is coupled to an output of said spatial pixel selector and to an output of said temporal pixel selection, said one filter kernel operating on the pixels from both the spatial pixel selector and the temporal pixel selector.

2. The spatio-temporal filter unit as claimed in claim 1, characterized in that the sigma filter comprises an adaptive sigma filter.

3. The spatio-temporal filter unit as claimed in claim 2, characterized in that an aperture of at least one of the temporal pixel selector and the spatial pixel selector is adjustable.

4. The spatio-temporal filter unit as claimed in claim 3, characterized in that at least one of the temporal pixel selector and the spatial pixel selector is designed such that a distance between the selected pixels is adjustable.

5. The spatio-temporal filter unit as claimed in claim 3, characterized in that said spatio-temporal filter unit further comprises a motion detector for detecting motion, said motion detector controlling the aperture of the temporal pixel selector based on the detected motion.

6. The spatio-temporal filter unit as claimed in claim 3, characterized in that said spatio-temporal filter unit further comprises a motion estimator for supplying motion vectors, said motion estimator controlling a position of the temporal pixel selector relative to the temporal pixel buffer based on the motion vectors.

7. The spatio-temporal filter unit as claimed in claim 3, characterized in that said spatio-temporal filter unit further comprises a noise estimator for estimating a noise level in the current image, said noise estimator controlling the aperture of at least one of the temporal pixel selector and the spatial pixel selector based on the estimated noise level.

8. The spatio-temporal filter unit as claimed in claim 3, characterized in that said spatio-temporal filter unit further comprises a noise estimator for estimating a noise level in the current image, said noise estimator controlling thresholds of the adaptive sigma filter based on the estimated noise level.

9. An image display apparatus comprising;

receiving means for receiving a signal representing images;

a display device for displaying the images; and

a spatio-temporal filter unit comprising a sigma filter for reducing in the images, characterized in that said spatio-temporal filter unit further comprises;

a spatial pixel buffer for storing pixels of a current image as supplied to the spatio-temporal filter unit;

a spatial pixel selector for selecting pixels from the spatial pixel buffer;

a temporal pixel buffer for buffering pixels from the output of the spatio-temporal filter unit, said output supplying a temporally recursive filtered image; and

a temporal pixel selector for selecting pixels from the temporal pixel buffer,

wherein the sigma filter is an adaptive sigma filter and is coupled to an output of said spatial pixel selector and an output of said temporal pixel selector, said sigma filter comprising one filter kernel for operating on the pixels from both the spatial pixel selector and the temporal pixel selector.