Television – Format conversion – Line doublers type
Reexamination Certificate
1999-08-11
2002-12-03
Kostak, Victor R. (Department: 2711)
Television
Format conversion
Line doublers type
C348S448000
Reexamination Certificate
active
06489998
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the processing of video images and, more particularly, to techniques for deinterlacing video images.
2. Description of the Related Art
All major television standards use a raster scanning technique known as “interlacing” or “interlace scanning.” Interlace scanning draws horizontal scan lines from the top of the screen to the bottom of the screen in two passes. Each pass is known as a field. In the National Television System Committee (NTSC) standard used in North America, each field takes approximately {fraction (1/60)}
th
of a second to draw.
Interlace scanning depends of the ability of the cathode ray tube (CRT) phosphors to retain an image for a few milliseconds, in effect acting like a “memory” to retain the previous field while the newer interleaved field is being scanned. Interlace scanning provides a benefit in television systems by doubling the vertical resolution of the system without increasing broadcast bandwidth.
FIG. 1
shows a number of parallel horizontal scan lines
10
on a conventional television display. A first set of horizontal lines
12
is scanned in a first field period and then a second set of horizontal lines
14
is scanned in a second field period. Thus, the first field is temporarily shifted by {fraction (1/60)}
th
of a second from the second field. When rapidly changing images are being displayed, an object in motion may appear to be fuzzy due to the temporal displacement between the two fields.
This temporal displacement typically does not create a problem on conventional television displays, primarily because the image of the “older” field quickly fades in intensity as the light output of the phosphors decays. A secondary reason is that the spatial displacement in the images caused by motion results in a fine detail that television displays resolve well. For these reasons, interlace scanning of motion pictures works acceptably well on conventional television displays.
FIG. 2
shows a set of progressively scanned horizontal lines
16
. In progressive scanning, all horizontal lines
16
, are scanned out in one vertical pass
18
, so there is no time displacement of adjacent lines as in interlace scan. Progressive scanning requires a much higher bandwidth signal. Consequently, progressive scanning is typically used for applications where improved image quality and higher resolution are required, relative to conventional television systems. Progressive scanning is widely used in computer CRTs and liquid crystal displays (LCD).
If a motion picture formatted for an interlaced monitor device as in
FIG. 1
is to be displayed on a progressively scanned device as in
FIG. 2
, then it must be converted from the interlaced format to the progressive format. This format conversion is known as deinterlacing.
FIG. 3
is a flow diagram of a deinterlace process
19
of the prior art. A first series of interlaced video fields
20
is generated by a video source (not illustrated) at {fraction (1/60)}
th
second intervals.
In this example, each of the video fields
20
has a spatial resolution of 720 horizontal by 240 vertical pixels. Each field contains half the vertical resolution of a complete video image. The first series of video fields
20
are input to a deinterlace processor
22
, which converts the 720 by 240 interlaced format to a second series of video fields
24
. In this example, each of the second series of video fields
24
may have 720 by 480 pixels where the fields are displayed at 60 frames per second.
FIG. 4
shows a prior art method
25
of deinterlace processing. A video field
26
containing scan lines
30
, and a previous video field
28
containing scan lines
32
is fed into a field combination deinterlace processor
34
. The result is a combined frame
36
with scan lines
38
sourced from video field
26
and scan lines
40
sourced from video field
28
. When this simple deinterlacing of the prior art is performed, and a motion picture formatted for an interlace display is converted to a progressive format, a noticeable “artifact” or error arises because the image content of vertically adjacent lines is time shifted by {fraction (1/60)}
th
second as noted previously. The error is most visible around the edges of objects that are in motion.
FIG. 5
shows a deinterlaced image
42
with a stationary object
43
that is rendered without distortion.
FIG. 6
shows an image
44
with the object
43
′ in motion. The edges of object
43
′ create artifacts
45
on the edges of the image
44
because of the aforementioned temporal shift. These artifacts
45
are introduced into the image by the conventional field combination deinterlacing method
25
of FIG.
4
.
FIG. 7
is an illustration of an alternative prior art method
46
to deinterlace an image using a single reference field rather than two fields. The method
46
interpolates or doubles the number of lines of one field to produce a progressive frame. A video field
48
is scanned from an image to contain a half set of lines
50
. The half set of lines
50
is deinterlaced by line interpolation in a deinterlacing interpolator
52
.
The resulting frame
54
will have all the lines
50
of the original video field
48
. The remaining lines
56
are created by interpolation of lines
50
. The resultant image will not have motion artifacts because all the lines in the image will be created from lines
50
that are time correlated. This alternative method
46
of deinterlacing does not produce motion artifacts, but the vertical resolution of the image is reduced by half.
In summary, deinterlacing by combining two fields into a single frame preserves the vertical resolution in an image, but may result in motion artifacts. Deinterlacing by interpolation of a single field to produce a frame eliminates the motion artifacts, but discards half the vertical resolution of the original image. In view of the forgoing, it is desirable to have a method of deinterlacing that provides for preservation of the full resolution of an image, while at the same time eliminating motion artifacts.
SUMMARY OF THE INVENTION
The present invention fills these needs by providing a method and apparatus for deinterlacing a video input stream while reducing motion artifacts and maintaining vertical resolution in the deinterlaced video stream. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device or a method. Several inventive embodiments of the present invention are described below.
In one embodiment of the present invention, a digital image processor is provided. The digital image processor includes a deinterlacing processor that is implemented upon a digital processing unit. The deinterlacing processor is coupled to an input operable to receive an interlaced video stream, a digital memory for storing portions of the interlaced video signal, and an output operable to transmit a deinterlaced video stream. The deinterlacing processor is operable to perform frequency analysis upon the received interlaced video stream in order to generate the deinterlaced video stream having reduced motion artifacts.
In another embodiment of the present invention, a method for deinterlacing an interlaced video stream is provided. The method includes receiving a video frame including a number of pixels from an input of the interlaced video stream. The video frame is analyzed for frequency information inherent to the video frame in order to detect motion artifacts. A number of motion artifact detection values is determined for each of the pixels in the video frame. An ultimate detection value is then determined for each motion artifact detection values. The ultimate detection value corresponding to each pixel is mixed with a set of spatially corresponding pixels to generate an output pixel.
In yet another embodiment of the present invention, a method for deinterlacing an interlaced video stream is provided. The method includes receiving a first
Adams Dale R.
Thompson Laurence A.
DVDO, Inc.
Kostak Victor R.
Perkins Coie LLP
LandOfFree
Method and apparatus for deinterlacing digital video images does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for deinterlacing digital video images, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for deinterlacing digital video images will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2992900