Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-06-23
2001-05-15
Britton, Howard (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240140
Reexamination Certificate
active
06233283
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to a video encoder for coding of a video signal prior to transmission through a medium. More particularly, the present invention pertains to a technique for encoding a signal using a perceptual preprocessor for considering human vision perceptual limitations.
II. Description of the Related Art
Video information in the form of a data bit stream is typically transmitted over a medium, e.g. the internet, in a packetized stream. Such video information is obtained from a video camera which generates a video signal containing a series of successive-in-time video frames depicting video images. Each frame consists of a number of picture elements or pixels which are divided into groups to form blocks. The video signal is processed, frame-by-frame, and encoded when necessary, such as when an error signal is detected between two adjacent-in-time frames, i.e. between a present frame and a prior frame. In this manner, only data affecting a change in object motion or pixel intensity need be transmitted, thus yielding an efficient use of available transmitter communication bandwidth.
For example, in a typical video signal encoder scheme each frame is divided into macro blocks of 16×16 pixels and an error signal representing the difference between pixel intensity of a current macro block and a corresponding prior macro block is obtained. The error signal is then converted from the spatial domain to the frequency domain by a transform function, such as a discrete cosine transform device. The digitized error signal is then quantized and entropy coded for transmission to a receiver. A feedback loop is provided which uses the quantized error signal to compensate for and estimate motion of objects in a current frame by comparing the position of the objects to a position from the prior frame.
Video data transmitted in packets is usually protected by a parity check scheme as known by those having ordinary skill in the art. Thus, the majority of internet video errors results from the loss of an entire packet during, for example, network congestion and buffer overflow. Such packet loss causes single or multiple macro block losses in the decoding process which results in severe degradation in perceived quality and error propagation. To combat video signal degradation and error propagation resulting from packet loss, layered video signals are used, wherein the video signal is divided into a base layer and an enhancement layer. The enhancement layer typically provides refinement information that is added to the base layer to provide higher quality, and which is transmitted with lower priority than the base layer. A known alternative approach is to use the second or enhancement layer to transmit a redundant version of the base layer when high losses are detected. Thus, the base layer will be transmitted on two distinct data streams with the hope that at least one of the streams will be correctly received.
The drawbacks of such prior art schemes is that they fail to adequately take into account the limitations of human visual perception when viewing a video signal. For example, not all lost video information, in the form of lost data packets, is visually perceptible by a viewer. Thus, the redundant transmission of such information is an inefficient use of bandwidth, as such information is not necessary and will not result in an appreciable difference to a viewer of the video information that is contained in the redundantly transmitted data packets.
SUMMARY OF THE INVENTION
The present invention is directed to a layered video encoder which considers human video perception limitations in determining whether to re-transmit lost video packet information. The inventive encoder is a block based coder that processes a single macro block portion of a frame of a video signal at any given time by comparing intensity values of picture elements contained in a subject macro block of a current frame to intensity values of corresponding picture elements contained in the subject macro block of a prior frame adjacent-in-time to the current frame. In the event that a transmission error is detected, such as when the subject macro block is not received successfully by a receiver, it may be necessary for the subject macro block to be re-transmitted. A perceptual preprocessor is used to determine, according to a set of criteria, whether to re-transmit the subject macro block and to what priority the re-transmitted macro block should be assigned. The criteria used to determine if and how retransmission of a subject macro block should occur are based, at least in part, on limitations in human visual perception. If the information contained in the subject macro block is of the type which is highly perceivable by a human viewer, the subject macro block will be re-transmitted at a high priority by encoding the subject macro block onto a base layer and an error resilience layer of data. If the information is at a lower priority wherein the information contained in the subject macro block would be only slightly, if at all, perceived by a human viewer, then the subject macro block will be re-transmitted at a lower priority by encoding the subject macro block onto the enhancement layer, or by simply not re-transmitting the data.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.
REFERENCES:
patent: 5455629 (1995-10-01), Sun et al.
patent: 5988863 (1999-11-01), Demos
patent: 6108379 (2000-08-01), Shikakura et al.
Chiu Yi-Jen
Hartung John
Pawlyk James Steven
Britton Howard
Lucent Technologies - Inc.
LandOfFree
Layered video coding using perceptual coding criteria for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Layered video coding using perceptual coding criteria for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Layered video coding using perceptual coding criteria for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2492346