Method and apparatus for detecting motion between odd and even video fields

Abstract

A method for measuring motion at a horizontal and vertical position between video fields of opposite parity comprising the steps of measuring the signal values of at least two vertically adjacent pixels from a video field of one parity and at least two vertically adjacent pixels from a video field of the opposite parity such that when taken together, the pixels represent contiguous samples of an image at said horizontal and vertical position, and determining whether the signal value of any of the pixels lies between the signal values of adjacent pixels in the field of opposite parity and in response outputting a zero motion value, otherwise, outputting a motion value equal to the lowest absolute difference between any of the pixels and its closest adjacent pixel in the field of opposite parity.

Description

FIELD OF THE INVENTION[0001]This invention relates in general to digital video signal processing and more particularly to a method and apparatus whereby motion between odd and even video fields may be reliably measured despite the presence of high vertical spatial frequencies.BACKGROUND OF THE INVENTION[0002]The NTSC and PAL video standards are in widespread use throughout the world today. Both of these standards make use of interlacing in order to maximize the vertical refresh rate thereby reducing wide area flicker, while minimizing the bandwidth required for transmission. With an interlaced video format, half of the lines that make up a picture are displayed during one vertical period (i.e. the even field), while the other half are displayed during the next vertical period (i.e. the odd field) and are positioned halfway between the lines displayed during the first period. While this technique has the benefits described above, the use of interlacing can also lead to the appearance...

AI Technical Summary

Benefits of technology

"The present invention provides a method and apparatus for measuring motion between two fields with greater ability to discriminate between the presence of motion and lack thereof. The level of motion between the two fields at a specific position is determined by comparing the values of four vertically adjacent pixels, each of which having the same horizontal position. This technique minimizes false detection of motion arising from the presence of high vertical spatial frequencies and allows for actual motion to be readily detected. The resulting local measurement of motion can either be used directly or summed over an entire field in order to provide a global motion signal that is useful for determining whether an input sequence derives from a film source. The contributing pixels are chosen such that their spatial positions remain constant regardless of whether the most recent of the two fields is even or odd, thereby improving the ability to distinguish between falsely detected motion and actual motion that arises as a result of a sequence that was generated in accordance with a 2:2 pull down ratio."

Problems solved by technology

While this technique has the benefits described above, the use of interlacing can also lead to the appearance of artifacts such as line flicker and visible line structure.

Although this approach may produce acceptable results under certain conditions, the performance generally represents a trade off between vertical spatial resolution and motion artifacts.

Unfortunately, video transmission formats do not include explicit information about the type of source material being carried, such as whether the material was derived from a progressive source.

Although the quality of measurement made in this way is high, unfortunately it is of limited value.

This does not provide sufficient information to avoid artifacts under certain conditions when a film sequence is interrupted.

Also, in the case of an input sequence derived from film or CG in accordance with a 2:2 pull down ratio, no useful information is provided whatsoever.

Although this mode of measurement overcomes the limitations of the above, it is inherently a more difficult measurement to make since a spatial offset exists between fields that are of opposite parity.

This tends to increase the measured difference when there is no motion making it more difficult to reliably discriminate between when there is motion and when there is not.

This is particularly true in the presence of noise and / or limited motion.

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