Television – Format conversion – Line doublers type
Reexamination Certificate
1998-05-12
2001-07-24
Eisenzopf, Reinhard J. (Department: 2614)
Television
Format conversion
Line doublers type
C345S441000, C345S625000, C345S950000, C345S950000
Reexamination Certificate
active
06266092
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to digital video signal processing, and more particularly to a method and apparatus for converting an interlaced video signal to a progressively scanned format in which the perceived sharpness of moving edges is enhanced.
BACKGROUND OF THE INVENTION
Most television systems utilize signals which have been generated by scanning a source image in a 2:1 interlaced format. Many display devices are available which are capable of reproducing such images directly from the interlaced signal. For instance, in a CRT monitor, the interlaced signal may be used directly to modulate the intensity of a beam as it is swept across the screen in an interlaced raster format. Such displays, however, may suffer from artifacts such as visible line structure, flicker and twitter which are related to the interlaced nature of the scanning. In particular, these undesirable artifacts tend to become more noticeable for screens with larger diagonal sizes. It is often desirable to convert signals from an interlaced scan format to a progressive scan format in order to reduce the artifacts associated with interlaced scanning. Furthermore, some display devices are inherently progressive in nature and therefore require conversion to a progressive format before display is possible.
A number of solutions to the problem of conversion from interlaced to progressive scan format have been proposed in the prior art. One such method involves the simple merging of two interlaced video fields to produce a progressively scanned video frame in which the even lines come from the even field and the odd lines come from the odd field. This technique works well for sequences which contain little or no motion but results in objectionable artifacts when motion is present due to the simultaneous display of video data which represents the image at different points in time.
Various forms of spatial and/or temporal interpolation have also been proposed. One such method involves spatial interpolation within a single interlaced field in order to produce a progressive frame. This approach does not suffer from the motion artifacts described above but, among other problems, suffers from a loss of vertical detail since each field contains only half of the spatial picture data. Alternatively, it is also possible to generate the missing lines by means of purely temporal interpolation. This approach yields maximum vertical detail for static images but results in serious blur when motion is present. Various attempts have also been made to combine spatial and temporal interpolation in order to reap the benefits of both approaches. As described in U.S. Pat. No. 4,789,893 (Weston), it is possible to generate the missing lines as a weighted average of neighboring lines from both the current and adjacent fields. The weightings applied to each of the neighboring lines are chosen such that low vertical frequency components are contributed mainly by the current field and higher vertical frequency components are contributed partly by the current field and partly by the adjacent fields. This approach has the benefit that vertical resolution is enhanced at low temporal frequencies by the contribution from the adjacent fields, however, for higher temporal frequencies the contribution from the adjacent fields actually reduces the vertical resolution. Although this last method does not suffer from motion blur artifacts, it has been found that further enhancement of the image is possible. According to the present invention, a method is provided whereby the apparent sharpness of moving detail may be enhanced in both spatial dimensions.
The following patents are relevant as prior art relative to the present invention:
U.S. Pat. Documents
4,789,893 - Weston
Dec 6/88
Interpolating lines of video
signals
3,920,889 - Connor
Nov 18/75
Method and apparatus for
crispening video signals by
the use of temporal filters
4,792,854 - Glenn
Dec 20/88
Apparatus for temporally
processing a video signal
5,227,883 - Dischert et al.
Jul 13/93
Method and apparatus for
motion aperture correction
SUMMARY OF THE INVENTION
According to the present invention, a method and apparatus are provided for converting an interlaced video image into a progressively scanned image by way of vertical temporal processing while enhancing the apparent sharpness of moving edges. According to the invention, missing lines are generated as a weighted average of neighboring lines from both the current and adjacent fields. The weightings are chosen such that the contribution from the current field is greater than unity, the combined contribution from all adjacent fields is negative and the total combined contribution from all fields is unity. In this way, the response to high temporal frequencies is boosted which has the effect of increasing the perceived sharpness of moving edges. Whereas if the contribution of the adjacent fields were to sum to zero as in some prior art approaches, then the interpolated lines could be merged with the unmodified lines of the current field without certain unwanted motion artifacts, in the present invention it becomes necessary to replace the lines of the current field with a weighted average of neighboring lines from both the current and adjacent fields such that the total contribution from each field is the same as the total contribution from each field used to generate the missing lines.
REFERENCES:
patent: 3920889 (1975-11-01), Connor
patent: 4789893 (1988-12-01), Weston
patent: 4792854 (1988-12-01), Glenn
patent: 4837619 (1989-06-01), Tsinberg
patent: 4941045 (1990-07-01), Birch
patent: 5046164 (1991-09-01), Hurst, Jr.
patent: 5049998 (1991-09-01), Lee
patent: 5150214 (1992-09-01), Shin et al.
patent: 5227883 (1993-07-01), Dischert et al.
patent: 5446498 (1995-08-01), Boon
patent: 5475438 (1995-12-01), Bretl
patent: 5621470 (1997-04-01), Sid-Ahmed
patent: 5625421 (1997-04-01), Faroudja et al.
patent: 5668602 (1997-09-01), Sid-Ahmed
patent: 5689305 (1997-11-01), Ng et al.
patent: 5694177 (1997-12-01), Flannaghan et al.
patent: 5808688 (1998-09-01), Sung
patent: 6040869 (2000-03-01), Dischert
patent: 0 266 079 (1988-05-01), None
patent: 0 529 761 (1993-03-01), None
Dubois, Eric, “The Sampling and Reconstruction of Time-Varying Imagery with Application in Video Systems,” Proc. IEEE v.73 (4), pp. 502-522 (Apr. 1985).
Greggain Lance
Selby Steve
Wang Zhongde
Desir Jean W.
Eisenzopf Reinhard J.
Genesis Microchip Inc.
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