Television – Format conversion – Line doublers type
Reexamination Certificate
1996-08-08
2001-04-24
Faile, Andrew I. (Department: 2711)
Television
Format conversion
Line doublers type
C348S459000, C345S156000, C345S182000
Reexamination Certificate
active
06222589
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to television signal processing. More particularly, the present invention relates to improved signal processing apparatus and methods for displaying video signals on high-resolution computer-type monitors substantially without motion discontinuities. The invention facilitates “mixed-signal” or “multimedia” displays of television and computer graphics signals on the same high-resolution computer-type monitor.
DESCRIPTION OF RELATED ART
In recent years the “convergence” of television and computers has received considerable attention in both the industry and the consumer media. A problem in “marrying” computers and television sets is that signal formats for computer graphics and television are incompatible.
Computer monitors typically provide a much higher resolution than do conventional television sets; they are usually progressively scanned with a relatively high frame rate (refresh” rate in computer jargon), typically at 72 Hz or more, in order to avoid flickering and eye strain. Most computer-type monitors are capable of handling a wide range of refresh rates from 60 Hz upward.
Television signals, on the other hand, are interlaced, having pairs of fields at a nominal 50 Hz rate (PAL) or a nominal 60 Hz rate (NTSC), resulting in frame rates of 25 Hz and 30 Hz, respectively.
In addition, many computer monitors are capable of displaying substantially more horizontal lines than are present in conventional interlaced television signals.
In order to overcome such incompatibilities, various techniques are known, for example, to convert progressively-scanned computer graphics VGA and SVGA signals to interlaced NTSC and PAL television signal form for display on a conventional television set. Techniques for converting interlaced NTSC and PAL television signals to progressively-scanned signals for display on computer-type monitors are also known.
The present invention is concerned with improvements in converting interlaced television signals to progressively-scanned signals for display on computer-type monitors. A problem with prior art conversion techniques has been that, in the absence of special processing, video signals displayed on a computer-type monitor have psychovisually disturbing motion discontinuities due to the differences in frame rates. For example, when a television signal is displayed on a computer-type monitor, a pendulum may appear to stop briefly or to jump during its swing. Many conversion schemes simply accept such results. Other converters employ frame averaging and/or fire interpolation techniques, adding to the complexity and cost of the converter. Simple, inexpensive techniques, such as averaging two frames, degrade picture resolution and produce double images that may be visible. Techniques causing fewer disturbing processing artifacts, such as frame interpolation, are complex and expensive.
Thus, there is an unsatisfied need for a simple, inexpensive technique, substantially free of motion discontinuities, for converting interlaced television signals to progressively-scanned signals for display on computer-type monitors.
SUMMARY OF THE INVENTION
In accordance with the present invention, a television signal is converted to a form suitable for display on a progressively-scanned variable-frame-rate high-resolution monitor of the type typically associated with a computer. A succession of progressively-scanned video frames are generated, wherein each frame is repeated at least twice in succession (i.e., the duplicated flames are identical to one another). A video frame memory stores at least two progressively-scanned video frames. Progressively-scanned video frames are written into the video frame memory at a rate derived from the timing of the progressively-scanned video frames and reading out of the video frame memory at a rate derived from the timing of the display monitor's frame rate.
A succession of progressively-scanned video flames in which each frame is repeated at least twice in succession is preferably obtained from a properly deinterlaced conventional 50 Hz or 60 Hz interlaced television signal whose source is a motion picture film (typically having a 24, 25 or 30 frames per second frame rate—25 fps for 50 Hz television and 24 or 30 fps for 60 Hz television).
In the case of a film source which has been converted to an interlaced television signal (or other progressively-scanned source which has been converted to an interlace television signal, such as a computer animated video, all of which will be referred to herein, for convenience, as a “film source”), the television signal is deinterlaced by merging opposite polarity pairs of interlaced fields derived from the same progressively scanned source frame. Each such merged pair, constituting a new deinterlaced frame, is repeated at least twice (a 3-2 pattern for 60 Hz NTSC and a 2-2 pattern for 50 Hz PAL) so that the deinterlaced signal has a frame rate the same as the original interlaced television field rate and each deinterlaced frame preferably has more horizontal scan lines than in each original interlaced television field. Field merging deinterlacers typically produce progressively-scanned frames in which there are substantially twice the number of horizontal scan lines as in each original interlaced television field. However, the number of horizontal scan lines may be increased even further, if desired. Suitable deinterlacers are known in the prior art, as described below.
The frame rate of the deinterlaced frame repeating video signal is converted to the computer-type monitor's frame rate by skipping (skipping occurs only when the monitor frame rate is less than the frame rate of the deinterlaced video) or duplicating a video frame from time to time, such that ordinarily at least two but not more than five consecutive identical deinterlaced video frames are displayed corresponding to each film source frame. The invention is primarily concerned with monitor frame rates greater than the frame rate of the deinterlaced video.
There is no requirement to synchronize either the computer-type monitor's frame rate or line rate to the frame rate or line rate, respectively, of the interlaced or deinterlaced video signals.
Frame rate conversion of the deinterlaced television signal may be accomplished by means of a two frame buffer memory in which the read-in is at the deinterlaced television signal rate and the read-out is at the frame rate of the computer-type monitor. Frames are skipped or duplicated in order to prevent memory underflow or overflow. The resulting frame repetition patterns have been found to produce motion-discontinuity-free video displays at refresh rates from 50 Hz to 100 Hz, for 50 Hz inputs, and from 60 Hz to 120 hz, for 60 Hz inputs, relatively simply and inexpensively.
In an alternative embodiment, interlaced video signals derived from “non-film” video sources (sources other than a “film source, as defined above, such as a video camera) preferably are converted to a film-source-like video signal. Deinterlaced video having a frame rate the same as the field rate of the interlaced television signal is derived using any conventional technique (e.g., line duplication, line interpolation, etc.), which increases (typically doubles) the number of lines originally in each interlaced field. An artificial film source sequence is established by repeating successive frames of line-increased progressively-scanned video so that at least 2 successive frames are identical. Although a 3-2 pattern for a 60 Hz source may be created, a 2-2 pattern for both 50 Hz and 60 Hz sources is preferred. In the case of a 2-2 pattern, every other progressively scanned frame is discarded and replaced by the repeated frame. The pseudo-film-source-like video is then applied to the double frame buffer as in the case of a film-source video signal. The resulting computer-type monitor displays are also substantially free of motion discontinuities but with the introduction of slight motion blurring (substantially as would be present if the source had actu
Dong Xu
Faroudja Yves C.
Wei Dong
Brown Reuben M.
Faile Andrew I.
Faroudja Yves C.
Gallagher Thomas A.
Gallagher & Lathrop
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