System and method for utilizing a two-dimensional adaptive filter for reducing flicker in interlaced television images converted from non-interlaced computer graphics data

• US 6,094,226 A
• Filed: 07/12/1999
• Issued: 07/25/2000
• Est. Priority Date: 06/30/1997
• Status: Expired due to Fees

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Lutz, Juergen M., Ke, Ligang
• Primary Examiner(s): Kostak, Victor R.
• Application Number:
  US09/351,552
• Time in Patent Office: 379 Days
• Field of Search: 348/447, 348/910, 348/446, 348/458, 348/627, 348/625, 348/607, 348/613
• US Class Current: 348/446
• CPC Class Codes: G06T 3/40 Scaling of whole images or parts thereof, e.g. expanding or contracting
• CPC Class Codes: G09G 2310/0224 Details of interlacing
• CPC Class Codes: G09G 2340/0414 Vertical resolution change
• CPC Class Codes: G09G 2340/0421 Horizontal resolution change
• CPC Class Codes: G09G 5/04 using circuits for interfacing with colour displays
• CPC Class Codes: H04N 9/641 Multi-purpose receivers, e.g. for auxiliary information H04N9/642 takes precedence
• CPC Class Codes: Y10S 348/91 Flicker reduction

Abstract

A system and method for conversion of graphics from computer graphics formats to television formats is disclosed. More particularly, an improved scaling and flicker reduction system and method is disclosed for scaling personal computer (PC) graphics formats into different resolution television (TV) formats and for reducing flicker due to the conversion process of interlacing non-interlaced PC graphics to match interlaced TV formats. The scaling implementation reduces line buffer requirements by using a conditional scaling technique for converting graphics from a PC resolution format to a TV resolution format. The flicker reduction implementation provides a two-dimensional adaptive filter that selects between multiple filters so that different parts of an image may have different flicker reduction and different levels of trade off between flicker reduction and resolution. The system and method disclosed are more generally applicable to converting images from one resolution to another and to reducing flicker in images converted from a non-interlaced format to an interlaced format.

Claims

1. A flicker reduction system for reducing flicker in non-interlaced images converted to interlaced images, comprising:

a flicker reduction filter receiving image data representative of pixel values within a single image, said flicker reduction filter having at least two selectable filters with each filter providing a different frequency response for said flicker reduction filter; and

filter selection circuitry receiving image data representative of pixel values from at least two lines within said single image and having a filter selection signal as an output, said filter selection signal being dependent upon an analysis of pixel values from at least two lines of said single image and being applied to said flicker reduction filter to adaptively select from among said at least two selectable filters to process said image data within said single image;

wherein said filter selection circuitry utilizes horizontal and vertical pixel conditions within a two-dimensional window around a currently processed pixel to provide a two-dimensional adaptive filter selection.

2. The flicker reduction system of claim 1, wherein said two-dimensional window is not centered around said currently processed pixel.

3. The flicker reduction system of claim 2, wherein said two-dimensional window is a horizontally sliding two-dimensional window such that different pixels may be in different positions within the two-dimensional window when being the currently processed pixel.

4. The flicker reduction system of claim 1, further comprising a current buffer storing pixel values from a line currently being input, and at least one line buffer storing pixel values from previous lines, said current buffer and said at least one line buffer providing said image data representative of pixel values from at least two lines to said flicker reduction filter and to said filter selection circuitry.

5. The flicker reduction system of claim 4, wherein said filter selection circuitry requires a propagation time period to produce said filter selection signal, and wherein said flicker reduction filter receives said image data in a time delayed manner to account for said propagation time.

6. The flicker reduction system of claim 1, wherein said image data comprises non-interlaced computer graphics data.

7. The flicker reduction system of claim 6, wherein said non-interlaced computer graphics data is a luma (Y) component of YCbCr data converted from RGB graphics data.

8. The flicker reduction system of claim 1, wherein said at least two filters include a first filter for portions of an image having sharp changes between adjacent pixel values, and a second filter for portions of an image having smooth changes between adjacent pixel values.

9. The flicker reduction system of claim 4, wherein said flicker reduction filter is a 5-tap FIR filter having four selectable sets of filter coefficients to provide four different selectable filters with differing frequency responses.

10. The flicker reduction system of claim 9, wherein one of said sets of filter coefficients is a pass-through filter.

11. The flicker reduction system of claim 1, wherein said flicker reduction filter comprises a 3-tap FIR filter having three selectable sets of filter coefficients and a base FIR filter coupled to said 3-tap FIR filter.

12. The flicker reduction system of claim 1, wherein said filter selection circuitry provides said filter selection signal on a per-pixel basis to adaptively select a set of filter parameters on a per-pixel basis.

13. A method for reducing flicker in non-interlaced images converted to interlaced images, comprising:

receiving image data representative of pixel values within a single image;

providing a flicker reduction filter having at least two selectable filters with each filter providing a different frequency response for said flicker reduction filter;

adaptively selecting from among said at least two selectable filters based upon pixel values from at least two lines of said single image utilizing a two-dimensional window around a currently processed pixel to select one of said at least two selectable filters; and

processing said image data within said single image with said flicker reduction filter to produce output pixel data that is dependent upon said adaptive filter selection.

14. The method of claim 13, wherein said providing step comprises providing a flicker reduction filter having four sets of selectable filter parameters to provide four selectable filters.

15. The method of claim 14, wherein said selecting step comprises:

comparing a vertically adjacent pixel pair from a second subsequent line and a first subsequent line;

storing a value corresponding to a result of said comparison;

comparing a vertically adjacent pixel pair from said first subsequent line and a currently processed line;

storing a value corresponding to a result of said comparison;

comparing a vertically adjacent pixel pair from said currently processed line and a first previous line;

storing a value corresponding to a result of said comparison;

comparing a vertically adjacent pixel pair from said first previous line and a second previous line;

storing a value corresponding to a result of said comparison;

repeating said comparing and said storing steps for a number of pixels horizontally across said image; and

choosing one of said four sets of selectable filter parameters based upon said comparisons and said stored values.

16. The method of claim 13, wherein said two-dimensional window is not centered around said currently processed pixel.

17. The method of claim 16, wherein said two-dimensional window is a horizontally sliding two-dimensional window such that different pixels may be in different positions within the two-dimensional window when being the currently processed pixel.

18. A graphics processing system for use in converting computer formatted images into television formatted images, comprising:

an input interface having computer graphics data as an input;

an adaptive flicker reduction filter coupled to said input interface to receive said computer graphics data and having flicker reduced image data as an output, said flicker reduction filter having at least two sets of selectable filter parameters dependent upon conditions related to values of vertically and horizontally adjacent pixel values within a two-dimensional window around a currently processed pixel to provide a two-dimensional adaptive filter selection;

a rate converter having said flicker reduced image data as an input and having line rate adjusted data as an output, said line rate adjusted data being substantially compatible with a line rate for a desired television format; and

a television output interface having said line rate adjusted data as an input and having television output data as an output, said television output data being substantially compatible with said desired television format.

19. The graphics processing system of claim 18, wherein said computer graphics data is a progressive scan format and said desired television format is an interlaced format.

20. The graphics processing system of claim 18, wherein said computer graphics data is a RGB computer graphics format.

21. The graphics processing system of claim 20, further comprising a RGB to YCbCr converter having said computer graphics data in said RGB computer graphics format as an input and having YCbCr data as an output.

22. The method of claim 18, wherein said two-dimensional window is not centered around said currently processed pixel.

23. The method of claim 22, wherein said two-dimensional window is a horizontally sliding two-dimensional window such that different pixels may be in different positions within the two-dimensional window when being the currently processed pixel.

24. A personal computer system providing an image output compatible with a television format, comprising:

a central processing unit, a memory, an input device, and a storage device connected to each other through an internal bus; and

a graphics processing system connected to said internal bus converting non-interlaced computer graphics data to a desired interlaced television format, said graphics processing system including;

adaptive flicker reduction circuitry applying one set of at least two selectable sets of filter parameters dependent upon two-dimensional conditions related to pixel values within said image utilizing a two-dimensional window around a currently processed pixel to provide a two-dimensional adaptive filter selection.

25. The method of claim 24, wherein said two-dimensional window is not centered around said currently processed pixel.

26. The method of claim 25, wherein said two-dimensional window is a horizontally sliding two-dimensional window such that different pixels may be in different positions within the two-dimensional window when being the currently processed pixel.

27. A method for converting computer formatted images into television formatted images for graphics processing, comprising:

receiving computer graphics data representative of an image;

applying a flicker reduction filter to said computer graphics data with filter parameters dependent upon values of vertically and horizontally adjacent pixel values within said image utilizing a two-dimensional window around a currently processed pixel to provide a two-dimensional adaptive filter selection; and

outputting converted image data in said desired television format.

28. The method of claim 27, wherein said two-dimensional window is not centered around said currently processed pixel.

29. The method of claim 28, wherein said two-dimensional window is a horizontally sliding two-dimensional window such that different pixels may be in different positions within the two-dimensional window when being the currently processed pixel.