Adaptive zonal coder

• US 5,063,608 A
• Filed: 11/03/1989
• Issued: 11/05/1991
• Est. Priority Date: 11/03/1989
• Status: Expired due to Term

• Current Assignee: Datacube, Inc.
• Original Assignee: Datacube, Inc.
• Inventors: Siegel, Shepard L.
• Primary Examiner(s): Razavi, Michael
• Assistant Examiner(s): COUSO, YON JUNG
• Application Number:
  US07/431,548
• Time in Patent Office: 732 Days
• Field of Search: 382/56, 382/49, 382/27, 382/50, 382/52, 358/133, 358/261.1, 358/261.3, 358/432, 358/135, 358/136
• US Class Current: 382/239
• CPC Class Codes: H04N 19/13 Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/146 Data rate or code amount at the encoder output
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/60 using transform coding
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

The invention provides a method and apparatus for performing image data compression. Initially, a two-dimensional block of image data in a spatial domain is transformed by a transform coder, resulting in a two-dimensional array of activity coefficients in a frequency domain. The array is then serialized and quantized, yielding a one-dimensional array of coefficients with a leading coefficient and an original trailing coefficient. Next, a portion of the array is selected by choosing a new trailing coefficient based on a setable ratio of the energy of the new short array to the energy of the original array. Lastly, an end-of-block symbol is appended after the new trailing coefficient, and the selected portion of the array is encoded using an entropy coder. The invention allows image data to enjoy enhanced compression with good image fidelity, and allows image fidelity to degrade gracefully in trade for higher degrees of image compression.

Claims

1. A method for image data compression comprising the steps of:

transforming a two-dimensional block of image data in a spatial domain to resulting data in a frequency domain represented as a two-dimensional array of activity coefficients;

serializing said entire two-dimensional array of coefficients, yielding a one-dimensional array of coefficients with a leading coefficient and an original trailing coefficient;

quantizing said one-dimensional array of coefficients;

selecting a portion of said one-dimensional array of coefficients beginning with said leading coefficient and ending with a new trailing coefficient that is closer to the leading coefficient than said original trailing coefficient, wherein said portion is selected by a process comprising the steps of;

obtaining a measure of total activity of said one-dimensional array of coefficients,

determining in real time a measure of activity of successive sub-portions of said one-dimensional array, and adding said measure of activity to a running total,

performing a comparison in real time of said running total to a setable level based on said measure of total activity, and

designating a new trailing coefficient according to said comparison;

appending an end-of-block symbol after said new trailing coefficient; and

encoding only said portion with an entropy coder.

2. The method of claim 1, wherein said sub-portions are single coefficients.

3. The method of claim 1, wherein said setable level is also based on a degree of desired image quality.

4. Apparatus for image data compression comprising:

a transform coder for transforming a two-dimensional block of image data in a spatial domain to resulting data in a frequency domain represented as a two-dimensional array of activity coefficients;

a serializer for serializing said entire two-dimensional array of coefficients, yielding a one-dimensional array of coefficients with a leading coefficient and an original trailing coefficient;

a quantizer for quantizing said one-dimensional array of coefficients;

a selector for selecting a portion of said one-dimensional array of coefficients beginning with said leading coefficient and ending with a new trailing coefficient that is closer to the leading coefficient than said original trailing coefficient, said selector including;

a measurer for measuring total activity of said one-dimensional array of coefficients,

a measurer for obtaining a measure of activity in real time of successive sub-portions of said one-dimensional array, and for adding said measure of activity to a running total,

a comparer for performing a comparison in real time of said running total to a setable level based on said measure of total activity, and

a designator for designating a new trailing coefficient according to said comparison;

an appendor for appending an end-of-block symbol after said new trailing coefficient; and

an entropy encoder for encoding only said portion.

5. The apparatus of claim 4, wherein said sub-portions are single coefficients.

6. Apparatus for inclusion in an image data compression pipeline that includes a transform coder, a serializer, a quantizer and an entropy coder comprising:

a memory connected to said quantizer and said entropy coder with an input and an output adapted to store and delay at least a block of transformed, serialized and quantized image data, and adapted to provide an entropy coder with successive sub-portions of said block of image data;

a first measurer connected to said quantizer for measuring the total activity of said block of image data;

a second measurer connected to said output of said memory for measuring the activity of successive sub-portions of said image data and computing a running total of said activity;

a control law unit connected to the first and second measurers, and to an entropy coder, adapted to compare said running total provided by said second measurer to a level based in part on said total activity provided by said first measurer, and sending an end-of-block signal to said entropy encoder;

wherein said entropy coder is adapted to encode only a portion of said block of image data based on when it receives an end-of-block signal.

7. A method for image data compression comprising the steps of:

transforming a two-dimensional block of image data from a spatial domain to a frequency domain, wherein said resulting block of image data in the frequency domain is represented by a two-dimensional array of activity coefficients;

serializing said entire two-dimensional array of coefficients, yielding a one-dimensional array of coefficients;

quantizing said one-dimensional array of coefficients;

selecting a visually significant portion of said one-dimensional array of coefficients, said step of selecting including the steps of;

obtaining a measure of total activity of the one-dimensional array of coefficients,

determining in real time a running total of the activity of successive portions of said one-dimensional array as they enter the entropy coder,

performing in real time a comparison of successive values of said running total to a setable level based on said measure of total activity of the one-dimensional array of coefficients, and

demarking a trailing end of said one-dimensional array according to said comparison;

appending a symbol at a trailing end of the selected portion for indicating the end of said portion; and

encoding said portion with an entropy coder.

8. Apparatus for use in an image processing pipeline including a transform coder, a serializer, and a quantizer, said apparatus comprising:

first means for obtaining a measure of total activity of a two-dimensional block of image data represented as a one-dimensional array of quantized activity coefficients;

second means for determining in real time a running total of successive activity coefficients of said one-dimensional array as said activity coefficients are received by an entropy coder;

third means connected to said first means, said second means and said entropy coder for performing a comparison of said running total to a settable level based on said measure of total activity, and

for demarking an activity coefficient of said one-dimensional array as a trailing end of said one-dimensional array according to said comparison.

9. The apparatus of claim 8, further comprising memory means connected to said entropy encoder for allowing a block of image data to dwell momentarily while said first means measures its total activity.