Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1998-06-10
2001-09-25
Chung, Phung M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
Reexamination Certificate
active
06295624
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a data compression system and to concealing errors in compressed data. An embodiment of the invention concerns concealing errors in compressed data reproduced from a recording apparatus. In a preferred embodiment the data is transformed by a two dimensional spatial frequency transform such as a wavelet transform. The background to the present invention, and the present invention are described herein, by way of example, with reference to wavelet transformed video data.
2. Description of the Prior Art
The wavelet transform is known. Referring to
FIG. 1
, data subjected to the transform occupies a plurality of two-dimensional spatial frequency bands. In the example of
FIG. 1
there are seven bands denoted 0 to 6. There may be other numbers of bands e.g. 9 or more. The wavelet transform transforms the data such that the video data in bands 4, 5 and 6 is sub-sampled horizontally and vertically by ½ and so represent ¼ size images. The video data bands 0, 1, 2 and 3 is sub-sampled horizontally and vertically by ¼ and so represents {fraction (1/16)} size images. Horizontal spatial frequency increases generally from left to right as indicated by arrow H and vertical spatial frequency increases generally from top to bottom as indicated by arrow V. It is found that typically the most significant image data is in the lowest frequency band 0 and the least significant image data is in the highest frequency band 6.
Video data, as very well known, may be recorded on a medium such as tape. The recording may introduce errors in the data, due to a variety of factors including tape defects and head failure for example. It is known to detect the errors and to conceal them. Concealment is generally done by replacing data in error by some form of average of adjacent data: that is a form of low pass filtering.
The wavelet transform has the property that data in bands 1 to 6 is frequency inverted after transformation. Low pass filtering does not always produce the best replacement value for data errors when applied to wavelet transformed data having frequency inverted data.
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided a method of concealing errors in data encoded to occupy a plurality of two-dimensional spatial frequency bands, data in at least one band being frequency inverted and data in at least one other band being frequency uninverted, wherein the frequency inverted data is filtered by a high pass spatial filter to conceal errors and the frequency uninverted data is filtered by a low pass spatial filter to conceal errors.
The said one aspect of the invention also provides apparatus for concealing errors in data encoded to occupy a plurality of two-dimensional spatial frequency bands, data in at least one band being frequency inverted and data in at least one other band being frequency uninverted, comprising means for detecting data errors and the spatial frequency band of the data in error, and filter means responsive to the detecting means to high pass filter the frequency inverted data to conceal errors therein and to low pass filter the frequency uninverted data to conceal errors therein.
It is known to conceal video data errors by a variety of concealment techniques. The techniques includes:
a) replacing a data item in error by its nearest neighbouring data item. The neighbouring item may be horizontally, vertically or diagonally adjacent:
b) replacing a data item in error by the weighted sum of neighbours each side of the error as in:
negative diagonal concealment;
positive diagonal concealment;
horizontal concealment;
vertical concealment; and
c) temporal concealment using data from an adjacent field or frame.
It has been found that in wavelet transformed data different concealment techniques are appropriate for different spatial frequencies.
According to another aspect of the present invention there is provided a method of processing compressed data in which method the data may be subject to errors, the method including the step of providing, in association with the compressed data, concealment data indicating the form of error concealment to be used to conceal any errors which arise.
The said another aspect of the invention also provides apparatus for compressing data, comprising means for compressing data and means for producing concealment data indicative of the form of error concealment to be used to conceal any data errors which arise in the compressed data, and for associating the concealment data with the compressed data.
Providing the concealment data simplifies and improves the concealment of data errors because the concealment of a data error takes place in the most appropriate manner as determined by the concealment data without the need to determine and compare a plurality of different concealment values as part of the concealment process. In an embodiment of said another aspect of the invention, data indicating a plurality of different forms of concealment is provided in association with respective different items of compressed data.
Referring again to
FIG. 1
, there are many bands, (e.g. seven bands 0-6) each representing an image. The concealment has to be appropriate to the particular band. Thus for seven bands, with potentially different forms of concealment appropriate to different data items in each band, the amount of concealment data can become considerable and thus a significant overhead on the compressed data stream.
In accordance with a further aspect of the present invention the data is transformed by a two dimensional spatial frequency transform, the data occupying a plurality of different two dimensional spatial frequency bands, different forms of concealment data being provided, bands having like spatial frequency properties being associated with like forms of concealment data.
The further aspect also provides apparatus for compressing data wherein the compressing means transforms the data by a two dimensional spatial frequency transform, the data occupying a plurality of different two dimensional spatial frequency bands, and the concealment data producing means produces different forms of concealment data, bands having like spatial frequency properties being associated with like forms of concealment data.
Preferably the wavelet bands are grouped together into e.g. 4 groups having similar spatial properties. The same concealment data is used for all the bands in a group. This reduces the amount of concealment data which is required to be transmitted.
One of the purposes of providing concealment data is to simplify the process of concealing errors which may be introduced by the process of recording compressed data on a recording medium such as tape due to e.g. tape defects. However if the concealment data is transmitted with the compressed data, it is liable to be subject to errors for the same reasons as errors occur in the compressed data.
According to yet another aspect of the invention, there is provided a method of recording the data in tracks on a recording medium including the step of recording concealment data in tracks different from those of the compressed data with which the concealment data is associated.
The yet another aspect of the invention also provides means for recording the data in tracks on a recording medium wherein the recording means records concealment data in tracks different from those of the compressed data with which the concealment data is associated.
In an embodiment where the data is recorded using a video data recorder in which data is recorded in a plurality of tracks by a plurality of video recording heads, the concealment data is recorded via a different head to the compressed data to which it relates. This reduces the likelihood of simultaneous loss of compressed data and the associated concealment data.
The above, and other objects, features and advantages of this invention will be apparent from the following detailed description of illustrative embodiments which is to be read
Chung Phung M.
Frommer William S.
Frommer & Lawrence & Haug LLP
Kessler Gordon
Sony United Kingdom Limited
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