Pulse or digital communications – Testing
Patent
1996-10-15
1999-08-03
Chin, Stephen
Pulse or digital communications
Testing
375249, 375247, 348353, H04B 346
Patent
active
059334517
DESCRIPTION:
BRIEF SUMMARY
The present application relates to apparatus for determining the complexity of a data signal; in particular, complexity determining apparatus in a data processing system using a constant bit rate encoder.
BACKGROUND OF THE INVENTION
It is sometimes useful to have an indication of the complexity of a data signal. For example, it has been proposed to multiplex a plurality of coded video signals, each encoded using a constant bit rate (CBR) encoder. The bit rate allocated to each of the CBR encoders is dynamically varied, based on both the coding complexity of the video signal being encoded, and the combined complexities of all of the video signals being multiplexed. In such a system, video signals having relatively high coding complexity are allocated a higher bit rate than those having relatively low coding complexity.
One known measure of the complexity of a data signal is the number of bits necessary to encode the signal using a variable bit rate (VBR) encoder: more bits indicate higher complexity, and conversely, fewer bits indicate lower complexity. A VBR encoder is a complex electronic system, however, and adding a VBR encoder for each signal to be multiplexed to determine the complexity of that signal is expensive and results in lowered reliability due to the added complex circuitry. It is desirable to provide an indication of the complexity of an input data signal, without the added expense and decreased reliability of a complex electronic system.
BRIEF SUMMARY OF THE INVENTION
The inventors have realized that CBR encoders maintain a constant bit rate by varying the quantization step size of the signal being encoded. In general, more complex signals require more bits to encode than less complex signals. However, in a CBR encoder, more complex signals are encoded with a larger quantization step size (or fewer quantizing levels), and less complex signals are encoded with a smaller quantization step size (or more quantization levels). Fewer quantization levels require fewer bits to encode them, which offsets the increased bits which would be necessary to encode the higher complexity signal and allows the signal to be encoded at the allocated constant bit rate.
The inventors have further realized that the relationship between the quantization step size and the resulting number of bits in the coded signal is approximately inversely linear. I.e. doubling the quantizing step size reduces the bit count by half. If a data signal having a given complexity is supplied to a CBR encoder to be encoded at a first predetermined bit rate, the CBR encoder will calculate and apply an appropriate quantization step size to produce an encoded signal at that first bit rate. If the same signal is to be encoded, but at a second predetermined bit rate twice the first predetermined bit rate, the quantization step size calculated by the CBR encoder will be half the quantization step size determined for the first predetermined bit rate. Thus, the product of the quantization step size and the resulting number of bits into which the signal is encoded is constant for a signal of a given complexity.
If a second data signal, having a higher complexity than the above data signal, is supplied to the CBR encoder to be encoded at the above first predetermined bit rate, the calculated quantization step size will be larger than that for the above data signal in order to maintain the first predetermined bit rate. The product of the quantization step size and resulting number of bits will, thus, be greater than that for the above, less complex data signal. However, for this second data signal, this product will be constant, regardless of the allocated bit rate. The inventors, thus, have recognized that the product of the quantization step size and the resulting number of bits in the coded signal varies with the complexity of the data signal, but is independent of the bit rate allocated to the CBR to encode that signal.
In accordance with principles of the present invention, apparatus for determining a complexity measure of a data signa
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Girons Regis Saint
Ozkan Mehmet Kemal
Chin Stephen
Herrmann Eric P.
Kurdyla Ronald H.
Liu Shuwang
Thomson Consumer Electronics Inc.
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