Television – Format conversion – Line doublers type
Reexamination Certificate
1999-09-30
2001-12-11
Eisenzopf, Reinhard J. (Department: 2614)
Television
Format conversion
Line doublers type
C348S443000, C348S448000, C348S451000, C348S458000
Reexamination Certificate
active
06330032
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to apparatus and methods for filtering motion effects from a de-interlaced image. More particularly, the invention relates to an apparatus and method for reducing motion artifacts on a pixel-by-pixel basis keying from the surrounding region of a progressive image formed by the combination by two or more interlaced images.
Conventional televisions use an interlaced technology whereby in a first image field the odd horizontal lines of an image are refreshed. Subsequently, in the next video field the even lines are refreshed. Thus, providing that the fields are refreshed at a sufficiently fast rate, the image appears to a viewer as being a single image and as the fields are refreshed the images can clearly show motion. However, on a progressive television there is no interlacing. Thus, all odd and even lines are displayed simultaneously and refreshed sequentially.
Progressive televisions are becoming more popular. However, television broadcasts are designed for use with conventional interlaced televisions. Therefore, there is a need for progressive televisions to be able to adapt to use interlaced images and to be able to display those images. One problem with merging such images into a progressive image is when fast motion appears in the image sequence.
One solution has been to interpolate the even lines in the field having the odd lines, and vice versa. However, since only half of the input lines make up each of the resultant output images the usable vertical frequency response is also halved. The merged image has merging artifacts that are particularly noticeable when the image sequence incorporates motion. A better solution would fix these merging artifacts. The prior art image sequence of
FIGS. 1A-1C
illustrates two images from an interlaced video sequence followed by a resulting de-interlaced image, respectively.
As can be seen in
FIG. 1A
, a vertical bar
12
is displayed on a first interlaced image
10
. The vertical bar
12
is displayed on the right side of reference line
20
. In the next interlaced image
14
the vertical line
12
has been horizontally shifted. This is due to horizontal motion of the vertical line in the image sequence. If subsequent interlaced images were shown it would be likely that the vertical line
12
would again be displaced along the X-axis of each of the images
10
,
14
. Taking these two interlaced images
10
,
14
and merging the two interlaced images
10
,
14
without any filtering would create a de-interlaced image
16
having a merged bar
18
. The merged bar
18
is a combination of the two images of the vertical bar
12
where the vertical bar
12
is displaced horizontally due to the motion. Thus, the merged bar
18
would look similar to a zipper as shown in FIG.
1
C. It is for this reason that prior art filters for motion artifacts of this type are referred to as zipper filters, or motion filters.
Conventional motion filters remove the zipper artifacts by buffering the first interlaced image
10
and the second interlaced image
14
and then comparing those two images to determine motion. However, this requires a great deal of frame memory (at least two fields), which can be costly. Accordingly, it is an object of this invention to provide a filter which minimizes motion defects.
It is another object of this invention to provide a filter that minimizes additional hardware requirements.
It is still another object of this invention to provide a filter which operates on pixel-by-pixel basis keying from a local region of an image.
These and other objects of the invention will be obvious and will appear hereinafter.
SUMMARY
The aforementioned and other objects are achieved by the invention which provides a method for filtering motion effects from a de-interlaced image and an apparatus associated therewith. The method assumes that the de-interlaced image is formed by a combination of a first interlaced image and a second interlaced image. An example of the application of such a device is taking standard television images and combining them for display on a progressive television.
A first step in the method is to create an interpolated line between two horizontal lines in a region of the first interlaced image. The first interlaced image is made of multiple horizontal lines.
A variance value is then determined between the interpolated line and a corresponding line in a corresponding region of the second interlaced image. The variance calculation results in a variance value that is indicative of an interrelationship between the two lines.
A threshold value will have been predetermined in the system and the variance value is compared against that threshold value. If the variance value is less than the threshold value, then the correlation is strong and the corresponding line is displayed in the de-interlaced image. Otherwise if the variance value exceeds the threshold value, then the interpolated line is displayed. This process is repeated for each pixel until the entire screen is displayed. This allows a window to be moved across the screen allowing the motion defects to be determined in a relatively small region and thus creating a detailed image whenever possible. In the preferred embodiment, the region is
11
pixels wide and
3
pixels in height.
The invention can also incorporate an alpha blender. The alpha blender operates between a lower limit and an upper limit to soften the switching between interpolated pixels and merged pixels thereby further enhancing the image.
In further aspects, the invention provides apparatus in accord with the methods described above. The aforementioned and other aspects of the invention are evident in the drawings and in the description that follows.
REFERENCES:
patent: 5398071 (1995-03-01), Gove et al.
patent: 5446497 (1995-08-01), Keating et al.
patent: 5467138 (1995-11-01), Gove
patent: 5469217 (1995-11-01), Ibental et al.
patent: 5526053 (1996-06-01), Dorricott et al.
patent: 5784114 (1998-07-01), Borer et al.
patent: 5886745 (1999-03-01), Muraji et al.
patent: 6118488 (2000-09-01), Huang
Bedell Daniel J.
Eisenzopf Reinhard J.
FOCUS Enhancements, Inc.
Smith-Hill and Bedell
Yenke Brian P.
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