Image analysis – Image compression or coding – Gray level to binary coding
Reexamination Certificate
2000-05-19
2004-01-20
Patel, Jayanti K. (Department: 2624)
Image analysis
Image compression or coding
Gray level to binary coding
C358S003060
Reexamination Certificate
active
06681049
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image encoding method and apparatus, and more particularly to a binary image encoding method for compressing data of binary images for use in data output devices such as a printer, a copier, a facsimile, and so on, a binary image encoding apparatus which implements the method, and a recording medium for executing the method.
2. Description of Related Art
In recent years, the improvements in the resolution and the image quality as well as the ability of processing colored images in the data output devices such as a printer, a copier, a facsimile and so on make the data compression technology (particularly, the compression technology directed to binary image data for preventing a degraded image quality) more and more important in order to reduce the storage capacity and the transmission time. As the compression technology suitable for the binary image data, there have been known the reversible compression techniques such as the arithmetic coding, the Huffman coding, the MH (Modified Huffman) coding, the entropy coding such as the MR (Modified READ (Relative Element Address Designate)) coding, the method which combines these coding techniques with differential coding, and so on. However, these compression techniques encounter the difficulties in realizing the sufficient compression ratio for a pseudo-gray scale binary image which is produced by converting the gradation of a multi-value image in which a natural image is mixed. To compensate for the insufficient compression ratio, conventionally, the binary image is predicted, a data sequence representative of a hit or miss for the prediction is formed into blocks for extending information source, and the blocked data is subjected to the Huffman block encoding. In the following, description will be made on a conventional technique implementing a method of encoding a pseudo-gray scale binary image produced by converting the gradation of a multi-value image in which a natural image is mixed.
FIG. 11
is a block diagram illustrating a conventional binary image encoding apparatus which employs a conventional method of encoding a pseudo-gray scale binary image.
In
FIG. 11
, reference numeral
1
designates a control unit,
2
a data input unit,
3
a prediction unit,
4
a prediction table,
5
a blocking unit,
6
a Huffman block encoding unit,
7
a Huffman table, and
8
a data output unit.
The following description focuses the operation and so on of the binary image encoding apparatus configured as illustrated.
Referring to
FIG. 11
, the control unit
1
receives from the data input unit
2
a binary image data which is an input image, and transfers the binary image data to the prediction unit
3
. The prediction unit
3
performs the prediction of the received data from information on the surrounding already-encoded pixels using the prediction table
4
. The prediction unit
3
converts the received data to a data sequence in which data is equal to “0” for a pixel the prediction of which is hit and data is equal to “1” for a pixel the prediction of which is miss. Subsequently, the control unit
1
transfers the data sequence indicative of the prediction hit or miss to the blocking unit
5
. The blocking unit
5
converts the received data to the blocked data which consists of M×N pixels. The Huffman block encoding unit
6
utilizes the Huffman table
7
to perform the Huffman block encoding on the blocked data received from the blocking unit
5
through the control unit
1
, and outputs the compressed data resulting from the encoding. The control unit
1
transfers the compressed data from the Huffman block encoding unit
6
to the data output unit
8
, and outputs the compressed data from the data output unit
8
.
FIGS. 12A and 12B
are diagrams for explaining the prediction of the binary image. When the prediction is performed using four reference pixels X
1
, X
2
, X
3
and X
4
shown in
FIG. 12A
, there are 2
4
=16 possible states for the four pixels, and the prediction function f(X
1
, X
2
, X
3
, X
4
) is determined for each state in the following manner.
(1) f(X
1
, X
2
, X
3
, X
4
)=1 for a pattern which has the higher probability that the encoding-target pixel X is equal to “1”; and
(2) f(X
1
, X
2
, X
3
, X
4
)=0 for a pattern which has the higher probability that the encoding-target pixel X is equal to “0”.
As shown in
FIG. 12B
, the prediction function f(X
1
, X
2
, X
3
, X
4
) is used to predict a binary image to output “1” for a prediction-miss pixel and “0” for a prediction-hit pixel. The prediction function f(X
1
, X
2
, X
3
, X
4
) may take the form of a table, as shown by the prediction table
4
in FIG.
11
.
FIG. 13
is a diagram for explaining the blocking procedure. As a blocking method, it is contemplated, for example as shown in
FIG. 13
, that a binary image is blocked into blocks of 4×4 pixels. In this event, since one block consists of 16 pixels, the blocked data is outputted as a 16-bit data sequence.
However, the foregoing conventional binary image encoding method and binary image encoding apparatus, due to the same Huffman block encoding uniformly applied on entire image data, has a problem in that the efficient encoding cannot be accomplished because it cannot sufficiently make use of the feature of image data which presents different correlation between adjacent pixels for each region.
In addition, since the reduction in the redundancy of image data due to the prediction coding is insufficient, there is a problem that it is impossible to perform the efficient encoding.
Thus, a need exists for realizing a higher compression ratio in the conventional binary image encoding method and binary image encoding apparatus, and accordingly a need exists for a recording medium which has recorded thereon this binary image encoding method for execution on a computer.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a binary image encoding method for realizing a higher compression ratio, a binary image encoding apparatus which is capable of realizing a higher compression ratio, and a recording medium having recorded thereon this binary image encoding method for execution on a computer.
In order to solve the problems mentioned above, a binary image encoding method according to the present invention comprises: a predicting step of predicting a binary image; a blocking step of blocking a data sequence into blocks to produce blocked data, the data sequence indicating whether a prediction at the predicting step is hit or miss; and an encoding step of switching a Huffman table in accordance with the blocked data around a Huffman-block-encoding-target block to apply a Huffman block encoding to the Huffman-block-encoding-target block.
Thereby, it is possible to provide a binary image encoding method for realizing the higher compression ratio.
In order to solve the problems mentioned above, a binary image encoding apparatus according to the present invention comprises: a prediction unit for predicting a binary image; a blocking unit for blocking a data sequence into blocks to produce blocked data, the data sequence indicating whether the predictions in the prediction unit are hit or miss; a Huffman block encoding unit for switching a Huffman table in accordance with the blocked data around a Huffman-block-encoding-target block to apply the Huffman block encoding to the target block; and a control unit for controlling the binary image encoding apparatus.
Thereby, it is possible to provide the binary image encoding apparatus for realizing the higher compression ratio.
In order to solve the problems mentioned above, a recording medium according to the present invention has a program recorded thereon, the program causing a computer to execute the steps of: predicting a binary image; blocking a data sequence into blocks to produce blocked data, the data sequence indicating whether a prediction at the predicting step is hit or miss; and switching a Huffman table in accordance
Hiratsuka Seiichiro
Kobayashi Masa-aki
Azarian Seyed
Matsushita Electric - Industrial Co., Ltd.
Patel Jayanti K.
Stevens, Davis, Miller & Mosher, LLP.
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