Television – Format conversion – Changing number of fields for standard conversion
Patent
1994-03-24
1995-04-25
Kostak, Victor R.
Television
Format conversion
Changing number of fields for standard conversion
348441, 348699, H04N 701
Patent
active
054103584
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the frame interpolation of a moving image namely to a method and device for interpolating frames intermediate transmitted frames. The invention finds particular, but not exclusive, application to the transmission of moving images (e.g., in videophone systems).
2. Related Art
In the communication of a moving image at low bit rates for purposes such as videophone services, the necessity of making considerable cuts in the amount of information to be transmitted has frequently led to the adoption of techniques in which there is a reduction in the transmitted frame rate. However, when the frame rate is low, intermediate frames must be generated to provide a continuous image at the receiver. The intermediate frames can be obtained by repeating frames or preferably by attempting to obtain intermediate frames by interpolating from the received frames. This is illustrated in FIG. 8. A transmitter side transmits image frames Ta and Tb which are two temporally separated images of a moving input image. Frames Ta and Tb are received at a receiver side. An intermediate frame Ti is found by interpolating between frames Ta and Tb in order to produce an moving output image comprising three frames Ta, Ti and Tb instead of simply the two frames Ta and Tb.
When it is necessary to interpolate many frames between received frames it can be difficult to reproduce smooth movement at the receiver side. One known approach to solving this problem is to use motion vectors detected from the frames Ta and Tb, in the FIG. 8 example, to interpolate the missing frames at the receiver side.
In order to carry out such a method of frame interpolation of a moving image without giving rise to blurring or jerkiness, it is necessary to detect motion vectors which are visually correct. Methods which have been proposed for detecting motion vectors include: smallest predicted error power between frames; and the pixel values.
In these methods, the detection range is restricted to a 2-dimensional plane. Moreover, the unit of detection is frequently comparatively small for example a rectangular block 8 pixels.times.8 lines. An explanation will now be given of such a frame interpolation system based on block units, the assumed application being to videophones.
Referring to FIGS. 9 and 10 a frame interpolation method is shown which is based on motion vector detection in rectangular block units. In FIG. 9, encoded data is received at a decoding part 2, the decoded frame being passed to first frame memory 3 after the previously decoded frame stored in this first frame memory 3 has been moved into a second frame memory 4. Motion vectors are also received at the receiver which with the frames in frame memories 2 and 3 are the used to interpolate an intermediate frame Ti as will now be described with reference to FIG. 10.
In FIG. 10, Ta is the frame which has been transmitted from the transmitter side at the immediately preceding point in time, Tb is the frame at the current point in time, and Ti is a frame which is to be interpolated between transmitted frames Ta and Tb. Consider that the frame to be interpolated is temporally spaced between the frames Ta and Tb in the ratio a: (1-a) as shown in FIG. 10.
The frames Ta and Tb are considered to be composed of blocks B'(I) and B'(I), respectively with a set of motion vectors Vab denoting the displacements of blocks B'(I) between frames Ta and Tb. This is illustrated in FIG. 10.
A block B(I) of the interpolated frame Ti is obtained by the interpolation part 5 of FIG. 9 by means of the following equation: associated with the block B'(I).
A detailed description of a specific method may be found in an article by Wada: Masahiro WADA, "System for motion-compensated frame interpolation of colour moving image signals", Denshi Joho Tsushin Gakkai Ronbunshi, (B-I), Vol. J72 B I, No. 5, pp. 446-455.
U.S. Pat. No. 4,672,442 published on 9th Jun. 1987 describes a moving picture frame rate conversion system which converts the first picture signa
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Hatori Yoshinori
Kaneko Masahide
Koike Atsushi
Shackleton Mark A.
Welsh William J.
British Telecommunications public limited company
Kokusai Denshin Denwa Co. (KDD)
Kostak Victor R.
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