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

• US 20020101543A1
• Filed: 01/23/2002
• Published: 08/01/2002
• Est. Priority Date: 01/26/2001
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips N.V.
• Inventors: Ojo, Olukayode Anthony, Kwaaitaal-Spassova, Tatiana Georgieva, Eland, Rudolf
• Granted Patent: US 7,034,892 B2
• Time in Patent Office: Days
• 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) according to this invention 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) comprising 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 (100), provided with a sigma filter (112), to reduce the noise in images, characterized in that the sigma filter (112) comprises one filter kernel (107) designed to operate on pixels from both a current image and from the output (118) of the spatio-temporal filter unit, being a temporally recursive filtered image.

2. A spatio-temporal filter unit (100) as claimed in claim 1, characterized in that it comprises:

a spatial pixel buffer (104) to store pixels of the current image;

a spatial pixel selector (106) to select pixels from the spatial pixel buffer (104);

a temporal pixel buffer (108) to buffer pixels from the output (118) of the spatio-temporal filter unit, being a temporally recursive filtered image;

a temporal pixel selector (110) to select pixels from the temporal pixel buffer (108); and

the sigma filter (112) comprising one filter kernel (107) designed to operate on the pixels from both the spatial pixel selector (106) and the temporal pixel selector (110).

3. A spatio-temporal filter unit (100) as claimed in claim 2, characterized in that it comprises an adaptive sigma filter (112).

4. A spatio-temporal filter unit (100) as claimed in claim 3, characterized in that of at least one of the pixel selectors, being the temporal pixel selector (110) and the spatial pixel selector (106), the aperture can be adjusted.

5. A spatio-temporal filter unit (100) as claimed in claim 4, characterized in that at least one of the pixel selectors, being the temporal pixel selector (110) and the spatial pixel selector (106), is designed such that the distance between the selected pixels is adjustable.

6. A spatio-temporal filter unit (200) as claimed in claim 4, characterized in that it comprises a motion detector (224) designed to detect motion and to control the aperture of the temporal pixel selector (210) based on detected motion.

7. A spatio-temporal filter unit (200) as claimed in claim 4, characterized in that it comprises a motion estimator (222) designed to supply motion vectors and to control the position of the temporal pixel selector (210) related to the temporal pixel buffer (208), based on the motion vectors supplied by the motion estimator (222).

8. A spatio-temporal filter unit (200) as claimed in claim 4, characterized in that it comprises a noise estimator (220) designed to estimate a noise level in the current image and to control the aperture of at least one of the pixel selectors, being the temporal pixel selector (210) and the spatial pixel selector (206), based on the estimated noise level.

9. A spatio-temporal filter unit (200) as claimed in claim 4, characterized in that it comprises a noise estimator (220) designed to estimate a noise level in the current image and to control thresholds of the adaptive sigma filter (212), based on the estimated noise level.

10. An image display apparatus (300) comprising:

receiving means (302) for receiving a signal representing images;

a display device (306) for displaying the images; and

a spatio-temporal filter unit (100), provided with a sigma filter (112), to reduce the noise in the images, characterized in the sigma filter (112) comprises one filter kernel (107) designed to operate on pixels from both a current image and from the output (118) of the spatio-temporal filter unit, being a temporally recursive filtered image.

11. An image display apparatus (300) comprising:

receiving means (302) for receiving a signal representing images;

a display device (306) for displaying the images; and

a spatio-temporal filter unit (100), provided with a sigma filter (112), to reduce the noise in the images, characterized in that it comprises;

a spatial pixel buffer (104) to store pixels of a current image;

a spatial pixel selector (106) to select pixels from the spatial pixel buffer (104);

a temporal pixel buffer (108) to buffer pixels from the output (118) of the spatio-temporal filter unit, being a temporally recursive filtered image;

a temporal pixel selector (110) to select pixels from the temporal pixel buffer (108); and

the sigma filter (112) being an adaptive sigma filter comprising one filter kernel (107) designed to operate on the pixels from both the spatial pixel selector (106) and the temporal