Image coding system using an orthogonal transform and bit allocation method suitable therefor

• US 5,327,502 A
• Filed: 01/16/1992
• Issued: 07/05/1994
• Est. Priority Date: 01/17/1991
• Status: Expired due to Fees

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Katata, Hiroyuki, Akagi, Hiroshi, Noguchi, Yoji
• Primary Examiner(s): COUSO, YON JUNG
• Application Number:
  US07/821,221
• Time in Patent Office: 901 Days
• Field of Search: 382/56, 382/51, 382/50, 382/41, 358/133, 358/432, 358/433
• US Class Current: 382/239
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• 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 19/149 by estimating the code amount by means of a model, e.g. mathematical model or statistical model
• CPC Class Codes: H04N 19/15 by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
• CPC Class Codes: H04N 19/18 the unit being a set of transform coefficients
• CPC Class Codes: H04N 19/192 the adaptation method, adaptation tool or adaptation type being iterative or recursive
• CPC Class Codes: H04N 19/42 characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation H04N19/635 takes precedence
• CPC Class Codes: H04N 19/60 using transform coding
• CPC Class Codes: H04N 5/9264 using transform coding

Abstract

A bit allocation method which facilitate control of the number of bits to be assigned to transform coefficients and block of image data with a deviation from the functional form. An image coding system which can implement an optimal bit allocation that minimizes quantization error under a predetermined information content or amount, in carrying out bit allocations of block-adaptive type and transform coefficient-adaptive type.

Claims

1. An image coding system, comprising:

means for dividing one-screen image data of an original image into a plurality of blocks;

a transform means for determining transform coefficients for each block of the image data by performing an orthogonal transform to each of the divided image data;

a first bit-allocation means for allocating bits to the blocks depending on statistical values of the transform coefficients of respective ones of the blocks so that an amount of information for each of regions of a regular size is made constant;

a second bit-allocation means for allocating bits to the transform coefficients of each block so that the number of bits falls within a range of the number of bits having been allocated to the corresponding block;

a quantization means for quantizing each of the transform coefficients by a quantization step depending on the number of bits assigned thereto to prepare quantization indices;

an encoding means for encoding the quantization indices and transmitting the encoded quantization indices as codes along with additional information at a constant bit rate;

a decoding means for decoding the codes received from the encoding means via a transmission medium to restore the quantization indices;

a third bit-allocation means for determining the number of the bits allocated to each transform coefficient based on the corresponding restored quantization indices and the additional information;

an inverse quantization means for inversely quantizing the quantization indices of each block depending on the decoded quantization indices, the additional information, and the number of bits assigned to the corresponding one of the blocks so as to restore the transform coefficients of each block;

an inverse transform means for performing an inverse orthogonal transform to the restored transform coefficients of each block to thereby restore the picture data for each block; and

means for reconstructing an image by combining the restored image data of the blocks.

2. An image coding system, comprising:

means for dividing one-screen image data of an original image into a plurality of blocks;

a transform means for determining transform coefficients for each block of the image data by performing an orthogonal transform to each of the divided image data;

a first bit-allocation means for allocating bits to the blocks depending on statistical values of the transform coefficients of respective ones of the blocks so that an amount of information for each of regions of a regular size is made constant;

a second bit-allocation means for allocating bits to the transform coefficients of each block substantially in accordance with a function f(i) which allocates bits without limiting b(i) to an integer and which corresponds essentially to

space="preserve" listing-type="equation">A + 1nσ

(i) .sup.2 /a

where σ

(i)² is variance of the ith transform coefficient and a is a specified set value, a bit allocation directed to the ith transform coefficient being expressed as b(i) (i=0, 1, . . . , N-1), where N represents the number of transform coefficients, said bit-allocation means including means for providing a quantizing function Q(f(i)) which uniformly quantizes f(i) as a function of A and which provides a correspondingly quantized value for

N-1

Σ

b(i)

i=0

as a function of A;

said bit allocation means also including means for determining a value for A such that

N-1

Σ

b(i)=B

i=0

where B is a desired total number of bits for encoding said block and then determining b(i) by the following equation

space="preserve" listing-type="equation">b(i)=Q(f(i))=Q(A+(lnσ

(i).sup.2)/a);

a quantization means for quantizing each of the transform coefficients by a quantization step depending on the number of bits assigned thereto to prepare quantization indices;

an encoding means for encoding the quantization indices and transmitting the encoded quantization indices as codes along with additional information at a constant bit rate;

a decoding means for decoding the codes received from the encoding means via a transmission medium to restore the quantization indices;

a third bit-allocation means for determining the number of the bits allocated to each transform coefficient based on the corresponding restored quantization indices and the additional information;

an inverse quantization means for inversely quantizing the quantization indices of each block depending on the decoded quantization indices, the additional information, and the number of bits assigned to the corresponding one of the blocks so as to restore the transform coefficients of each block;

an inverse transform means for performing an inverse orthogonal transform to the restored transform coefficients of each block to thereby restore the images data for each block; and

means for reconstructing an image by combining the restored image data of the blocks.