Television – Image signal processing circuitry specific to television – Noise or undesired signal reduction
Reexamination Certificate
1998-07-31
2002-07-16
Miller, John W. (Department: 2614)
Television
Image signal processing circuitry specific to television
Noise or undesired signal reduction
C348S608000, C348S612000, C348S624000, C348S226100, C348S241000, C348S242000, C382S250000, C382S261000, C382S236000, C382S172000
Reexamination Certificate
active
06421097
ABSTRACT:
BACKGROUND
1. Field
The present invention relates to video image processing, and more particularly, to reducing flicker in a video image sequence.
2. Background Information
FIG. 1
is a schematic diagram illustrating an arrangement for a typical video conferencing system. In this diagram, a user/subject is positioned in front of a camera
110
while looking at a computer monitor
120
. The area or room is illuminated by a light source
130
. Camera
110
is designed to reduce flicker due to light source
130
. This may be accomplished by setting the aperture time of the camera to capture a whole number of illumination cycles for light source
130
. In this context, aperture time refers to the length of time during which the camera is sensitive to incident light. Illumination cycle refers to the multiplicative inverse of the frequency of the variation of the intensity of the light source. This may also be accomplished by setting the camera frame rate such that the frame exposure starts at approximately the same point in the illumination cycle for each frame.
For the situation illustrated in
FIG. 1
, computer monitor
120
acts as a second light source. The refresh rate on the computer monitor depends on many variables and, quite possibly, does not correspond to one of the frequencies handled by the camera using the previously described methods. Due to this frequency mismatch, some frames, such as in an image sequence displaying the scene illustrated in
FIG. 1
, may get more illumination than other frames, resulting in flickering in the video sequence that may be annoying to a human observer. A need, therefore, exists for a technique to reduce flicker for video image sequences displaying situations or scenes involving a second light source, such as a computer monitor, for example.
SUMMARY
Briefly, in accordance with one embodiment of the invention, a method of reducing flicker in a video image sequence includes the following. Successive video images are temporally filtered. The filter length is adjusted so as to reduce the amount of filtering across temporal discontinuities in the video image sequence.
Briefly, in accordance with another embodiment of the invention, a method of reducing flicker in a video image sequence includes the following. Successive video images are temporally filtered. The filter length is dynamically adjusted.
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Hentschel, et al., Comparison between median filtering and vertical edge controlled interpolation of flicker reduction, Jun. 1989 IEEE, pp. 279-289.
Intel Corporation
Kacvinsky John
Miller John W.
Natnael Paulos
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