Television – Format conversion – Line doublers type
Patent
1995-06-28
1998-07-21
Lee, Michael H.
Television
Format conversion
Line doublers type
348448, 348443, H04N 701
Patent
active
057841144
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to video processing techniques and apparatus in which use is made of the measured motion in sequences of video images. In an important example, the invention relates to motion compensated standards conversion.
Standards conversion is the process of converting television signals between different scanning standards, particularly between European (PAL) and American (NTSC) television signals. The present invention, in this aspect, is concerned with the temporal interpolation of fields at new instants of time, rather than colour encoding and deciding which is also required for standards conversion. The description below describes processing of luminance signals; processing of the colour signals is performed in parallel in a similar manner.
Standards conversion is conventionally performed using linear filtering techniques. The techniques are, essentially, the application of a linear, vertical-temporal filter to the television signal. The quality of the conversion process, using this technique, is critically dependant on the details of the interpolation aperture (filter coefficients) which is used. The design of the filter aperture is a compromise between removing aliasing in the signal, which produces undesirable artifacts such as judder and flicker, and removing detail or blurring moving images. Although acceptable results can be achieved with this technique, the results are a compromise and picture artifacts, such as judder or blurring, can easily be seen on some types of pictures.
To avoid the problems inherent in conventional standards conversion the technique of motion compensated interpolation has been suggested. This uses information of the apparent movement of objects in television scenes to improve the conversion process.
If motion compensation can be achieved it largely eliminates the aliasing impairments which are unavoidable in conventionally standards converted pictures. Since the aliasing impairments are avoided there is no need to compromise the filter coefficients used for interpolation. Therefore, in addition to giving a picture which is free from alias impairments, the use of motion compensation allows much more of the resolution, present in the original pictures, to be retained following standards conversion.
It is an object of one aspect of this invention to provide high quality motion compensated interpolation for standards conversion. The invention is concerned in this respect with the manner in which motion vectors are used for improved interpolation of images, rather than the measurement of apparent motion in television picture. There are many known ways in which motion can be measured and suitable motion vectors fields can be derived for use with this invention.
The process of motion compensated standards conversion is, essentially, that of interpolation along the motion trajectory. The assumptions behind this type of motion compensated interpolation are that the scene comprises a number of linearly translating rigid objects. This simple model is adequate for most areas of the picture. It breaks down, however, in regions of revealed or obscured background. Care must be taken, in dealing with these areas of the image, as they can have a disproportionate effect on the overall quality of the interpolated pictures.
In order to perform motion compensated interpolation, it is necessary to displace the image of objects in the input pictures to the appropriate position in the output picture. This is achieved with the aid of what may be called a `picture shifter`. The picture shifter restructures the input image so that all the objects within it are moved to their correct position in the output image. These motion compensated input fields, can then be combined to produce an output image. By this method an output picture is produced in which there is only one, correctly positioned, image for each object. Conventional standards conversion, by contrast, generates an output picture with multiple images of each object, none of which are in the corre
REFERENCES:
patent: 4691230 (1987-09-01), Kaneko et al.
patent: 5045939 (1991-09-01), Okayama et al.
Borer Timothy John
Lyon David
Martin Philip David
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