Image analysis – Image compression or coding – Gray level to binary coding
Reexamination Certificate
1998-09-18
2001-07-31
Couso, Jose L. (Department: 2721)
Image analysis
Image compression or coding
Gray level to binary coding
Reexamination Certificate
active
06269191
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 97-76413, filed Dec. 29, 1997, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to image coding, and more particularly, to a prediction image generating apparatus using a plurality of masks, and to an apparatus for coding, transmitting and decoding a binary image using the same.
2. Description of the Related Art
Documents these days include characters or tables as well as text. Also, as color displays become more developed, various color photographs or pictures are used in computing. Since printers recognize only binary images, photographs or pictures to be printed are transformed into binary images using various methods for generating binary images, such as dithering or error diffusion.
Meanwhile, in a facsimile machine, the binary image of a scanned document is formed using the above-described methods for generating binary images, and the binary image is coded and transmitted. International Telecommunications Union-Telecommunication standarization (ITU-T) determines documents frequently transmitted by facsimile as a text document, and a coding method appropriate for the document. Also, various coding tables are determined by the document of a text. Thus, images obtained by binarizing the documents including pictures or photographs do not meet the requirements of the above coding methods.
That is, in facsimile machines, a document including photographs or pictures has a coding efficiency lower than a document containing only text. A conventional facsimile image coding standard uses a modified Huffman coding method. By the Huffman coding method, a series of black pixels indicated by 1 of a binary number in Table 1 or white pixels indicated by 0 thereof is mapped with a symbol of the coding table (Table 1) to compress the image.
For instance, assuming that a bit stream of a binary image before coding is as shown in
FIG. 1A
, a process of coding the binary image with reference to the Huffman table of Table 1 is as follows. First, a series of white pixels (000000) is mapped with 0001. Second, a series of black pixels (1111) is mapped with 010. Third, a series of white pixels (000) is mapped with 001. The binary images of
FIG. 1A
coded with reference to Table 1 become binary images shown in FIG.
1
B.
TABLE 1
Black pixels
Symbol
White pixels
Symbol
1
1
1
1
2
01
2
01
3
001
3
001
4
010
4
010
5
011
5
011
6
0001
6
0001
Referring to
FIG. 1B
, the coded binary image of
FIG. 1A
which has 24 pixels requires 17 bits, whereas the uncoded binary image requires 24 bits.
By the above Huffman coding method, as the series of white or black pixels of the binary image becomes longer, the coding becomes better. A text document has large spaces between lines and at the top, bottom and sides of the page, so that the series of white pixels is long, which satisfies the above conditions. However, the binary images of photographs or pictures do not have long series of pixels.
Thus, by the Huffman coding method, the coding efficiency for the binary images of pictures deteriorates. As a result, it takes longer to transmit text including pictures than to transmit text only.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a prediction image generating apparatus using a plurality of masks in which prediction image data represents a success or failure in prediction based on pixel values of a window and element values of one of the masks in the window, of a transmitting party.
It is another object of the present invention to provide an apparatus for coding, transmitting and decoding a binary image using the prediction image generating apparatus.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the first and other objects and advantages of the present invention, there is provided a prediction image generating apparatus using a plurality of masks. The apparatus includes a maximum value searching unit, a minimum value searching unit, a mean calculation unit, a binarization unit and a comparing unit.
The maximum value searching unit searches a maximum value of element values of one of the masks corresponding to a pixel having one binary level among a plurality of pixels located in front of a current pixel having a current binary level to be predicted in a window of a predetermined size. The minimum value searching unit searches a minimum value of element values of the one mask corresponding to a pixel having the other binary level among a plurality of pixels located in front of the pixel having the current binary level to be predicted in the window of the predetermined size. The mean calculation unit takes an average of the maximum value and the minimum value searched from the maximum value searching unit and the minimum value searching unit. The binarization unit binarizes the average taken in the mean calculation unit. The comparing unit compares the binarized average with a binary level of the current pixel and outputs prediction image data indicating successful or failed prediction.
To achieve the second and other objects and advantages of the present invention, there is provided an apparatus for coding, transmitting and decoding a binary image using the prediction image generating apparatus. The apparatus includes a first prediction unit, a coding unit, a decoding unit and a second prediction unit. The first prediction unit outputs the prediction image data indicating the successful or failed prediction based on the pixel values of the window and element values of the mask in a window of the image for transmission. The coding unit codes the prediction image data output from the first prediction unit by a predetermined coding method and transmits the coded data. The decoding unit decodes the coded data transmitted from the coding unit into prediction image data before coding. The second prediction unit predicts the binary level of the current pixel from the pixel values of the window and the element values of the mask in the window of the image for reception, based upon the prediction image data decoded in the decoding unit.
REFERENCES:
patent: 5526438 (1996-06-01), Barton
patent: 5761325 (1998-06-01), Barton
patent: 5787238 (1998-07-01), Wang
patent: 5974228 (1999-10-01), Heitsch
patent: 5978554 (1999-11-01), Hakamada et al.
patent: 6020978 (2000-02-01), Cooper et al.
patent: 6064773 (2000-05-01), Yamagata et al.
Couso Jose L.
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
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