Image analysis – Image compression or coding – Adaptive coding
Reexamination Certificate
2001-05-01
2002-12-03
Chen, Wenpeng (Department: 2624)
Image analysis
Image compression or coding
Adaptive coding
C382S236000, C382S243000, C375S240250
Reexamination Certificate
active
06490373
ABSTRACT:
BACKGROUND ART
When compositing images, there are cases where information called an alpha value indicating the overlay area and the degree of transparency of an object is appended in addition to the luminance of the object. The alpha value is determined for each pixel, an alpha value of 1 indicating complete opacity or occlusion and an alpha value of 0 complete transparency or nonocclusion. Alpha values become necessary when overlaying an image of an object onto a background image. Hereinafter, an image represented only by such alpha values is called an alpha plane.
In the case of a cloud, frosted glass, etc., an alpha value intermediate between [0, 1] may be used to represent the image, but there are cases where two values {0, 1} are sufficient.
For the encoding of a conventional binary alpha plane, binary image coding techniques such as MR and MMR, defined in CCITT's international standards traditionally used for facsimile systems, etc., or coding techniques standardized by JBIG can be used. These coding schemes are referred to generically as binary still image coding. In binary still image coding, efficient coding can be achieved by predicting a low order pixel from a high order pixel in the scanning direction and by entropy-encoding the difference between them.
In a binary moving image, such as two successive alpha planes of a moving image, correlation between successive frames can be utilized. That is, efficient coding can be achieved by predicting a pixel to be encoded, from a previously obtained binary image having high correlation, and by encoding the difference between them, rather than predicting a low-order pixel from a high-order pixel in the scanning direction and encoding the difference between them.
However, binary still image coding in the prior art has exploited only the correlation between the high-order and low-order pixels in the scanning direction even when a binary image having high correlation with the binary image to be encoded or decoded is obtained at the encoder or decoder, and hence the prior art has had the problem that a large number of code bits are required.
For the encoding of a conventional alpha plane, waveform coding is used, as is done in the JPEG coding scheme.
However, many alpha planes have the property that most portions are uniform and intermediate values are distributed along the boundary.
Since such alpha planes contain high frequency components along the boundary, the waveform coding as employed in the prior art has had the problem that efficient coding is difficult to achieve.
DISCLOSURE OF THE INVENTION
In view of the above-described problems of the prior art, it is an object of the present invention to provide an image encoding apparatus, an image decoding apparatus, an image encoding method, an image decoding method, and a medium having recorded thereon a program which causes a computer to carry out their processing operations, wherein a pixel to be encoded is predicted from a previously obtained binary image having high correlation, and the difference between them is encoded, thereby achieving more efficient encoding and decoding than can be achieved with the binary image encoding and decoding techniques used in the prior art.
In view of the above-described problems, it is also an object of the present invention to provide an image encoding apparatus and its corresponding decoding apparatus, an image encoding method and its corresponding decoding method, and media storing their execution programs, wherein the distribution of intermediate values is analyzed, and a smoothing function approximating the distribution and a binary base image having only two values, a maximum value and a minimum value, are encoded respectively, thereby achieving more efficient coding than the prior art.
The present invention is an image encoding apparatus comprising: blocking means
1
for taking as an input a target binary image to be encoded, and for obtaining a target block by dividing said target binary image into blocks each containing a plurality of pixels; blocking means
2
for obtaining a reference block by dividing a previously obtained reference binary image into blocks each containing a plurality of pixels;
exclusive OR block constructing means for constructing an exclusive OR block by sequentially scanning said target block and said reference block and by exclusive-ORing pixel values between said two blocks; and exclusive OR encoding means for generating a coded sequence representative of the results of said exclusive-ORing, and for outputting the same as encoded data.
Another invention is an image decoding apparatus comprising: blocking means
2
for obtaining a reference block by dividing a previously obtained reference binary image into blocks each containing a plurality of pixels; exclusive OR decoding means for recovering said exclusive OR block by decoding the encoded data encoded by the image encoding apparatus one embodiment; and target block constructing means for constructing a target block by combining said exclusive OR block with said reference block.
Still another invention is an image encoding apparatus comprising: blocking means
1
for taking as an input a target binary image to be encoded, and for obtaining a target block by dividing said target binary image into blocks each containing a plurality of pixels; blocking means
2
for obtaining a reference block by dividing a previously obtained reference binary image into blocks each containing a plurality of pixels;
statistical model selecting means for selecting a statistical model from among a plurality of statistical models, based on the states of pixels surrounding a reference pixel in said reference block, said reference pixel corresponding to a target pixel in said target block; and entropy encoding means for entropy-encoding said target pixel based on said selected statistical model, and for outputting the same as encoded data.
Still another invention is an image decoding apparatus comprising: blocking means
2
for obtaining a reference block by dividing a previously obtained reference binary image into blocks each containing a plurality of pixels; statistical model selecting means for selecting a statistical model from among a plurality of statistical models, based on the states of pixels surrounding a reference pixel in said reference block, said reference pixel corresponding to a target pixel in said target block; and entropy decoding means for recovering said target block by entropy-decoding, based on said selected statistical model, the encoded data output from the image encoding apparatus of one embodiment.
Still another invention is an image encoding apparatus according to one embodiment, further comprising: motion estimating means for searching through said reference binary image for a block that most resembles said target block, and for obtaining motion information from the result of said searching, and wherein: said blocking means
2
is a motion compensated blocking means
2
which obtains a reference block by applying motion compensation to said reference binary image using said motion information, and said motion information also is output from said image encoding apparatus.
Still another invention is an image decoding apparatus according to one embodiment, wherein said blocking means 2 is a motion compensated blocking means
2
which obtains a reference block by applying motion compensation to said previously obtained reference binary image using the motion information output from the image encoding apparatus of another embodiment.
The present invention of claim
16
is an image encoding apparatus according to claim
9
, further comprising: reference block adoption determining means for comparing said target block with said reference block, and for determining, based on the result of said comparison, whether said reference block is to be adopted or not, and thereby switching the remainder of processing between various means; and target pixel encoding means for generating a coded sequence representative of pixel values in said
Ankei Takeshi
Etoh Minoru
Hata Koichi
Chen Wenpeng
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
LandOfFree
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