Signal data processing using equal importance packetization

Details Signal data processing using equal importance packetization Signal data processing using equal importance packetization

1998-03-24

2001-04-10

Chin, Wellington (Department: 2664)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S422000, C375S240000

Reexamination Certificate

active

06215787

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to techniques for transmitting, storing, or otherwise processing image data or other types of signal data.
BACKGROUND OF THE INVENTION
In many data transmission applications, it is common for data to “hop” over network links of different capacities. For example, a typical scenario might involve a high-capacity network link switching over to a wireless link. Networks in which such hopping occurs are generally referred to as heterogenous networks. In heterogenous networks, packets may have to be dropped to accommodate a hop to a lower-capacity link. Packets could also be lost in the network due to transmission errors or congestions. If packet retransmission is not a viable option, due to real-time transmission constraints or other limitations, it is still important to provide the receiver with the most meaningful information possible despite the packet loss.
For applications in which image data is transmitted, a conventional approach to alleviating the packet loss problem is to send the images in a layered, multiresolution manner. This approach separates the data into parts of unequal importance. Packets are then labeled with an indication of the priority of the data contained therein. Thus, in a scenario in which a packet needs to be dropped, a network control mechanism may be used to discard the lowest priority packets first. At the receiver, the image is reconstructed from the high-priority essential information carried in packets which were labeled as such and therefore not dropped. A similar technique used in video data transmission is described in G. Karlsson and M. Vetterli, “Three-Dimensional Subband Coding of Video,” Proc. IEEE Int. Conf. Acoust., Speech and Signal Proc., pp. 1100-1103, New York, N.Y., April 1988. Although this technique does not require the introduction of additional data, it does require the additional complexity of examining the contents of each packet to determine priority. In addition, it is generally not applicable to transmission over the Internet, which is based on the Internet Protocol (IP) and does not provide priority levels, and transmission over broadband networks based on asynchronous transfer mode (ATM), which can accommodate only two priority levels. These and other important networks may therefore require packet retransmission, redundant packet transmission or other inefficient techniques in order to ensure a desired quality level for the image reconstructed at the receiver. Similar problems arise in processing compressed image data as well as other types of compressed and uncompressed data.
Other data processing applications in which conventional techniques are inadequate include the storage and retrieval of image data or other types of data in multiple resolutions. For example, conventional techniques for storing images in multiple resolutions generally require a user to keep track of which stored files correspond to which resolutions. This unduly complicates the data storage, retrieval, reconstruction and viewing process.
SUMMARY OF THE INVENTION
The invention provides improved processing of image data and other types of signal data by representing the signal data in such a way that, when separated into packets, all packets are of approximately the same importance. As a result, if some of the packets are, for example, randomly lost in a lossy packet network, the resulting degradation in the reconstructed signal is substantially uniform regardless of which packets are lost. The techniques are suitable for use in conjunction with data transmission over a wide variety of lossy packet networks, including the Internet and broadband ATM networks, and may be used with raw or compressed image data, as well as video, audio and other types of signal data. Moreover, the invention can be used to facilitate the processing of signal data in multiresolution storage applications.
A signal transmission system configured in accordance with an illustrative embodiment of the invention assigns portions of an image signal to packets such that each of the packets has an approximately equal cumulative image signal energy. The energy-equalized packets are then individually quantized and encoded to generate compressed packets which are transmitted over the network. At the receiving end, the received compressed packets are individually decoded and inverse quantized, and then used to generate a reconstructed version of the original image. Another possible implementation of the transmission system includes a scrambler for scrambling the image such that pixels in the image are mapped to different spatial positions. This produces a whitened image which is subsequently separated into subbands. The use of the whitened image allows the subbands to be assigned deterministically to the packets, which can then be compressed and transmitted as in the energy equalization implementation. Both of these illustrative implementations provide graceful degradation in reconstructed image quality in the presence of packet loss. Alternative embodiments may be configured to process video, audio, speech and other types of signal data.
In accordance with another aspect of the invention, an image processing system may be configured to generate packets of substantially equal importance, and to store the packets in a storage device rather than directly transmitting them over a network. For example, an original image may be separated into packets of substantially equal importance using the above-noted energy equalization or whitening techniques, or other suitable techniques. The resulting packets are then stored in the storage device in the form of a number of same-resolution files, each corresponding generally to one or more of the packets. A given same-resolution file upon retrieval from the storage device is processed to obtain a reconstructed image of a given resolution. This storage and retrieval arrangement allows a user to view a coarse-resolution reconstructed image by retrieving any one of the stored same-resolution files. The user therefore need not keep track of the resolutions of particular stored files, as in conventional multi-resolution storage techniques. In order to obtain higher-resolution reconstructed images, the user retrieves one or more additional same-resolution files from the storage device. As these additional files are retrieved, the reconstructed image quality will improve until the highest resolution reconstructed image is obtained. Similar techniques may be used to provide multiresolution processing for a variety of other types of signal data.


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