CA2088863A1 - Method and apparatus for compressing and extending an image - Google Patents
Method and apparatus for compressing and extending an imageInfo
- Publication number
- CA2088863A1 CA2088863A1 CA 2088863 CA2088863A CA2088863A1 CA 2088863 A1 CA2088863 A1 CA 2088863A1 CA 2088863 CA2088863 CA 2088863 CA 2088863 A CA2088863 A CA 2088863A CA 2088863 A1 CA2088863 A1 CA 2088863A1
- Authority
- CA
- Canada
- Prior art keywords
- image data
- compression factor
- compression
- compressing
- data
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/85—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression
- H04N19/86—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression involving reduction of coding artifacts, e.g. of blockiness
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
- H04N19/124—Quantisation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
- H04N19/154—Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
- H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
- H04N19/176—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a block, e.g. a macroblock
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
- H04N19/18—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a set of transform coefficients
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
- H04N19/182—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a pixel
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
- H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
- H04N19/51—Motion estimation or motion compensation
- H04N19/527—Global motion vector estimation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
- H04N19/146—Data rate or code amount at the encoder output
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
- H04N19/146—Data rate or code amount at the encoder output
- H04N19/152—Data rate or code amount at the encoder output by measuring the fullness of the transmission buffer
Abstract
ABSTRACT OF THE DISCLOSURE
An image evaluation circuit is connected to an image compression circuit and an image extension circuit. In the image evaluation circuit, original image data and extended image data reproduced from compressed image data are compared in each block pixel by pixel to generate block noise. The comparison is carried out twice to provide two block noises by two compression factors, and an optimum compression factor is determined in accordance with the two compression factors and the two block noises.
An image evaluation circuit is connected to an image compression circuit and an image extension circuit. In the image evaluation circuit, original image data and extended image data reproduced from compressed image data are compared in each block pixel by pixel to generate block noise. The comparison is carried out twice to provide two block noises by two compression factors, and an optimum compression factor is determined in accordance with the two compression factors and the two block noises.
Description
~886~
METHOD AND APPAR~TUS FOR COMPRESSING AND EXTENDIMG A~
I~GE
FIELD OF THE INVENTION
The invention relates to a method and an apparatus for compressing and extending an image, and ; more particularly to a method and an apparatus for evaluating an image by comparing an original image and ~ 10 an extended image.
:~ BACKGROUND OF THE INVEWTION
n a conventional facsimile or television-telephone set, transmission data is compressed and encoded so that the data transmission amount is decreased. As a method for compressing image data, an estimate encoding method and a transforma-tion encoding method are utilized conventionally. In the estimate encoding method, a signal to be next supplied is estimated in accordance with a signal which has been known by decoding an encoded signal, so that only a signal component which is different in the estimation from a correct signal is transmitted to decrease the amount of inormation to be encoded.
In the transformation encoding method, only coefficients of components, signal electric power of wh~ch converge: on a low frequency region, are encoded ~88~C~
to decrease -the amount oE informa-tion, because the signal electric power of image signals having high correlation is distrib~lted mainly on the low frequency region. That is, the correlation of the image signals is positively utilized, so that higher compression effect is ob-tained in -the transformation encoding method than in the estimation encoding method.
However, the amount of arithmetic logic processes is larger in the transformation encoding me-thod than in the estimation encoding method, so that the practical use of the transformation encoding method has been delayed as compared to the estimation encoding method.
In accordance with the development of computer technology, however, the calculation of orthogonal transformation required for the transformation encoding method has been easy in these days, so that the transformation encoding method has been widely used in the encoding of imaqes. As an orthogonal transformation to a frequency region, DCT (discrete cosine transformation) is considered to be most effective for practical uses, because DCT is superior in regard -to electric power converging on a low frequency region and the process speed of calculation algorithm. Among other orthogonal transformations than DCT, slant transformation, hurl transformation, etc. can be used in encoding images.
~ccording to the conventional image compression 2~86~
method using DCT, however, there is a disadvantage in that an optimum compression factor is difficult to be set therein. That i5, when coefficients are coarsely q~antized, a data compression factor becomes large to deteriorate the quality of image. In order wards, the process of the image compression is carried out with high speed, while block distortion which is discontinuity at boundaries of blocks is generated in reproducing images. On the other hand, when the coefficients are finely quantized, the data compression factor becomes small to decrease the block distortion, while a high speed process is hindered, and the process of pictures having fast motion is difficult to be carried out.
SUMM~RY OF THE INVENTION
Accordingly, it is an object of the invention to provide a method and an apparatus for compressing and extending an image in which an optimum compression 2~ factor is selected to maintain the quality of the image and to avoid the decrease of the process speed.
According to the first feature of the invention~
an apparatus for compressing and extending an image, comprises :
, 25 a coJnpression circuit for compressing image data to provide compressed image data by a predatermined compression factor ;
:
., 2~8~
an extension circuit for extending the compressed image data to provide reproduced image data by ex-tension data corresponding to the predetermined compression factor ; and 5an evaluation circuit for evaluating the predetermined compression fac-tor to provide an optimum compression factor in accordance with comparison between th0 image da-ta and the reproduced image data, the optimum compression factor being used in place of ; lO the predetermined compression factor ~or a subsequent compressing process by the compression circuit.
According to the other feature of the invention, a method for compressing and extending an image, comprises the steps of ;
15compressing image data to provide first compressed image data by a first compression factor ;
extending the first compressed image data to provide first reproduced image data by data corresponding to the first compression factor ; and ,~
~; 20comparing the image data and the first reproduced image data in each block pixel by pixel to provide first block noise ; and generating an optimum compression factor in accordance with the first compression factor and the first block noise, the optimum compression factor being used for subsequently compressing the image data.
5 ~88~6~
BRIEF DESCRIPTION OF THE DRAWINGS
The inven-tion will be described in more detail in conjunction with appended drawings, wherein:
Fig. 1 is a block diagram showing an image compression apparatus using DCT, and Fig. 2 is a block diagram showing an apparatus for compressing and extending an imaye of a preferred embodiment according to the inven-tion.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Before explaining a method and an apparatus for compressing and extending an image of a preferred embodiment according to the invention, the background o~ the invention will be explained.
With reference to Fig~ 1, an image data compression apparatus using a standard DCT method will be explained. The apparatus comprises a transmitter (compression circuit)l, a receiver (extension circuit) 2, and a transmission line 3, wherein image data 10 2~ which is divided into blocks each having 8 x 8 pixels (dots) is supplied to the transmitter 1, and reproduced image data 20 is supplied from the receiver 2.
In the transmitter 1, the two dimensions DCT
transformation is carried out for each block in accordance with a following transformation equation.
2r)~ 63 sl~v = l cl~ cv ~-~ ~ (~ s) cos (z x ~ cos ( Y ) v 7r ~-O~sO l6 16 In the above equation, x and y are positions of a pixel, and u and v are positions of a DCT
coefficient~ wherein cu and Cv are -~- , when u and v are zero, cu and cv are 1, when u and v are other values, Ls is 128, when a bit precision for a pixel value Pxy is of 8 bits, and Ls is 2048, when the bit ~- precision is of 12 bits.
As a result of this transformation, 64 coefficients Suv are obtained in each block, among which a coefficient Soo is called DC coefficient indicating a mean value (direct current component) of 64 pixels in a block, while the remaining coefficients ~- are called AC coefficients. In accordance with this .
transformation, 8 x 8 pixels of a block are defined by a linear coupllng of 64 DCT fundamental vectors.
In this DCT transformation, electric power of ordinary images is dlstributed mainly on a low frequency region. Bu using this property, image compression is realized to carry out quanti2ation in which a small number of bits are allocated to coefficients of a low fre~uency component, and a large number of bits are allocated to coefficients of a high ,'~
, , . : , .
,"
,, ' , 2~8~86-j7 frequency component.
The coefficient Suv is quantized at each coefficient position in a step size different from others by using a quantization table 4. When -the quantiz~tion is coarsely carried out by decreasing the number of quantiza-tion levels, the amoun-t of data can be decreased. In this case, a da-ta compression factor becomes large, while the deterioration can not be avoided in quality of images, if the coarse quantization is made without any consideration. As a result, discontinuity occurs at boundaries of blocks, and error occurs due to the drop of data. Thus, block distortion is increased in the quantization.
On the other hand, when the quantization is finely carried out to result in the decrease of the compression factor, the block distortion is decreased, while the process of motion pictures having a large amount of data is difficult to be carried out. In fact, however, a high frequency component is not included in actual images by a substantial amount.
In accordance with this tendency, the course quantization is made in the DCT method for higher order coefficients, and the fine quantization is made therein ; for lower order coeficients. Conse~uently, the encoding of data can be carried out with a high efficiency, while the quali-ty of images is not lowered.
Practically, the decision of a compression 208~
factor is made in accordance with the selection of an appropriate compression factor from plural compression factors by an operator. For this purpose, quantization tables corresponding to plural compression factors are accessed in a compression circuit to quantize coefficients of the transformation equation.
` At this time, almost all of the high frequency component is deleted.
The quantized coefficients are encoded in accordance with entropy encoding by using an encoding table 5. For this purpose, Hoffman encoding method is often used. Then, encoded data is transmitted from the transmitter 1 via the transmission line 3 to ; the receiver 2 together wi-th a parameter including information as to which table is used.
In the receiver 2, the encoded data i5 decoded to provide the quantized data by referring to the transmitted encoding table 5. The quantized data is ~
inversely quantized to provide the DCT coefficienks by referring to the transmitted quantization table 4.
In accordance with the property of the quantization, completely original DCT coefficients are not restored.
In this sense, the DCT method is defined as a non-inversible encoding method. Then, the DCT
coefficient5 are inversely transformed to the reproduced image data 20 of blocks each having 8 x 8 pixels.
2 ~ 6 ~
As described above~ the original image daka 10 is processed in the transmitter 1 -to be the compression data 30 in accordance with the orthogonal transformation, the quantization and the variable length encoding anA the compression clata 30 is extended in the receiver 2 to provide the reproduced image data in accordance with the decoding, the inverse quantization and the inverse orthogonal transformation.
Next, an apparatus for compressing and extending an image data of a preferred embodiment according to the invention will be explained in Fig. 2.
The apparatus comprises a memory 22 for storing image data 21, a compression circuit 23 for compressing image data read from the memory 22, and extension circuit 24 for extending the compressed image data, a memory 25 for storing and providing the extended image data 26, and an evaluation circuit 31 comprising a subtracter 32 for carrying out a subtraction between image data pixels of each block read from the memories 22 and 25, -20 a hold circuit 33 for holding the subtraction result as a block noise, and a decision circuit 34 for making a `~decision of an optimun compression factor in accordance with the subtraction results.
In operation, the image data 21 is stored in the memory 22, from which the image data is read to be supplied to the compression circuit 23. Then, the image data is compressed in the compression circuit 23 .
- ~
,,. '~
20~8~J
by a compression fac-tor ~. The compressed data and table data corresponding to the compression factor A
are transmitted to the extension circuit 24, and the compression factor A is supplied to be held in the hold circuit 33. In the extension circuit 24, the compressed data is extended in accordance with the transmi-tted t~ble data to provide reproduced image data which is -then stored in the memory 25.
In the evaluation circuit 31, the subtracter 32 compares pixels read from the memories 22 and 25 in each block, so that the difference is detected therein as a block noise A which is held .in the hold circuit 33. In accordance with the block noise A, a compression factor B is determined in the decision circui-t 34 to be supplied to the compression circuit 23.
In the compression circuit 23, image data read from the memory 22 is compressed by the compression factor B, and the compressed data and table data corresponding to the compression factor B are transmitted to the ex-tension circuit 24, in which the compressed data is extended by referring to the transmitted table data. The extended data is stored in the memory 25, and image data read from the memories 22 and 25 are compared in the subtracter 32 in the same manner as in the case of using the compression factor A, so that a block noise B is detected -to be stored in the 2~8~
hold circuit 33.
Then, an optimum compression fac-tor is determined in the deci~ion circui-t 3~ in accordance witll the compression factors ~ B and the block noises A B, so that the optimum compression factor thus obtained is supplied from the decision circuit 34 to the compression Gircuit 23, in which image data is compressed by the optimum compression factor.
In making the decision of the optimum compression factor by the decision circuit 34, the : compression factor B is determined to ba small, where ~ the block noise A is considerably large, because it is . considered that the compression factor A is much larger than the optimum compression factor, while the : 15 compression factor B is determined to be larger than the compression factor A, where the block noise A is small. At any rate, an error of the optimum compression factor can be small by setting the optimum compression fac-tor between the compression factors A
~` 20 and B.
~: In -the preferred embodiment, an optimum compression factor is applied to the aforementioned DCT
algorithm, so that image data becomes improved in quality by suppressing block noise providing visual ~5 problem and the encoding of image data is carried out with high efficiency.
Although the invention has been described with 2~3~3~6~
respect to specific embodiment Eor complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modification and al-terna-tive cons-tructions that may occur to one skilled in the art which fairly fall within the basic teachirly herein set forth.
~'` ' .
:, .
.
,,:
METHOD AND APPAR~TUS FOR COMPRESSING AND EXTENDIMG A~
I~GE
FIELD OF THE INVENTION
The invention relates to a method and an apparatus for compressing and extending an image, and ; more particularly to a method and an apparatus for evaluating an image by comparing an original image and ~ 10 an extended image.
:~ BACKGROUND OF THE INVEWTION
n a conventional facsimile or television-telephone set, transmission data is compressed and encoded so that the data transmission amount is decreased. As a method for compressing image data, an estimate encoding method and a transforma-tion encoding method are utilized conventionally. In the estimate encoding method, a signal to be next supplied is estimated in accordance with a signal which has been known by decoding an encoded signal, so that only a signal component which is different in the estimation from a correct signal is transmitted to decrease the amount of inormation to be encoded.
In the transformation encoding method, only coefficients of components, signal electric power of wh~ch converge: on a low frequency region, are encoded ~88~C~
to decrease -the amount oE informa-tion, because the signal electric power of image signals having high correlation is distrib~lted mainly on the low frequency region. That is, the correlation of the image signals is positively utilized, so that higher compression effect is ob-tained in -the transformation encoding method than in the estimation encoding method.
However, the amount of arithmetic logic processes is larger in the transformation encoding me-thod than in the estimation encoding method, so that the practical use of the transformation encoding method has been delayed as compared to the estimation encoding method.
In accordance with the development of computer technology, however, the calculation of orthogonal transformation required for the transformation encoding method has been easy in these days, so that the transformation encoding method has been widely used in the encoding of imaqes. As an orthogonal transformation to a frequency region, DCT (discrete cosine transformation) is considered to be most effective for practical uses, because DCT is superior in regard -to electric power converging on a low frequency region and the process speed of calculation algorithm. Among other orthogonal transformations than DCT, slant transformation, hurl transformation, etc. can be used in encoding images.
~ccording to the conventional image compression 2~86~
method using DCT, however, there is a disadvantage in that an optimum compression factor is difficult to be set therein. That i5, when coefficients are coarsely q~antized, a data compression factor becomes large to deteriorate the quality of image. In order wards, the process of the image compression is carried out with high speed, while block distortion which is discontinuity at boundaries of blocks is generated in reproducing images. On the other hand, when the coefficients are finely quantized, the data compression factor becomes small to decrease the block distortion, while a high speed process is hindered, and the process of pictures having fast motion is difficult to be carried out.
SUMM~RY OF THE INVENTION
Accordingly, it is an object of the invention to provide a method and an apparatus for compressing and extending an image in which an optimum compression 2~ factor is selected to maintain the quality of the image and to avoid the decrease of the process speed.
According to the first feature of the invention~
an apparatus for compressing and extending an image, comprises :
, 25 a coJnpression circuit for compressing image data to provide compressed image data by a predatermined compression factor ;
:
., 2~8~
an extension circuit for extending the compressed image data to provide reproduced image data by ex-tension data corresponding to the predetermined compression factor ; and 5an evaluation circuit for evaluating the predetermined compression fac-tor to provide an optimum compression factor in accordance with comparison between th0 image da-ta and the reproduced image data, the optimum compression factor being used in place of ; lO the predetermined compression factor ~or a subsequent compressing process by the compression circuit.
According to the other feature of the invention, a method for compressing and extending an image, comprises the steps of ;
15compressing image data to provide first compressed image data by a first compression factor ;
extending the first compressed image data to provide first reproduced image data by data corresponding to the first compression factor ; and ,~
~; 20comparing the image data and the first reproduced image data in each block pixel by pixel to provide first block noise ; and generating an optimum compression factor in accordance with the first compression factor and the first block noise, the optimum compression factor being used for subsequently compressing the image data.
5 ~88~6~
BRIEF DESCRIPTION OF THE DRAWINGS
The inven-tion will be described in more detail in conjunction with appended drawings, wherein:
Fig. 1 is a block diagram showing an image compression apparatus using DCT, and Fig. 2 is a block diagram showing an apparatus for compressing and extending an imaye of a preferred embodiment according to the inven-tion.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Before explaining a method and an apparatus for compressing and extending an image of a preferred embodiment according to the invention, the background o~ the invention will be explained.
With reference to Fig~ 1, an image data compression apparatus using a standard DCT method will be explained. The apparatus comprises a transmitter (compression circuit)l, a receiver (extension circuit) 2, and a transmission line 3, wherein image data 10 2~ which is divided into blocks each having 8 x 8 pixels (dots) is supplied to the transmitter 1, and reproduced image data 20 is supplied from the receiver 2.
In the transmitter 1, the two dimensions DCT
transformation is carried out for each block in accordance with a following transformation equation.
2r)~ 63 sl~v = l cl~ cv ~-~ ~ (~ s) cos (z x ~ cos ( Y ) v 7r ~-O~sO l6 16 In the above equation, x and y are positions of a pixel, and u and v are positions of a DCT
coefficient~ wherein cu and Cv are -~- , when u and v are zero, cu and cv are 1, when u and v are other values, Ls is 128, when a bit precision for a pixel value Pxy is of 8 bits, and Ls is 2048, when the bit ~- precision is of 12 bits.
As a result of this transformation, 64 coefficients Suv are obtained in each block, among which a coefficient Soo is called DC coefficient indicating a mean value (direct current component) of 64 pixels in a block, while the remaining coefficients ~- are called AC coefficients. In accordance with this .
transformation, 8 x 8 pixels of a block are defined by a linear coupllng of 64 DCT fundamental vectors.
In this DCT transformation, electric power of ordinary images is dlstributed mainly on a low frequency region. Bu using this property, image compression is realized to carry out quanti2ation in which a small number of bits are allocated to coefficients of a low fre~uency component, and a large number of bits are allocated to coefficients of a high ,'~
, , . : , .
,"
,, ' , 2~8~86-j7 frequency component.
The coefficient Suv is quantized at each coefficient position in a step size different from others by using a quantization table 4. When -the quantiz~tion is coarsely carried out by decreasing the number of quantiza-tion levels, the amoun-t of data can be decreased. In this case, a da-ta compression factor becomes large, while the deterioration can not be avoided in quality of images, if the coarse quantization is made without any consideration. As a result, discontinuity occurs at boundaries of blocks, and error occurs due to the drop of data. Thus, block distortion is increased in the quantization.
On the other hand, when the quantization is finely carried out to result in the decrease of the compression factor, the block distortion is decreased, while the process of motion pictures having a large amount of data is difficult to be carried out. In fact, however, a high frequency component is not included in actual images by a substantial amount.
In accordance with this tendency, the course quantization is made in the DCT method for higher order coefficients, and the fine quantization is made therein ; for lower order coeficients. Conse~uently, the encoding of data can be carried out with a high efficiency, while the quali-ty of images is not lowered.
Practically, the decision of a compression 208~
factor is made in accordance with the selection of an appropriate compression factor from plural compression factors by an operator. For this purpose, quantization tables corresponding to plural compression factors are accessed in a compression circuit to quantize coefficients of the transformation equation.
` At this time, almost all of the high frequency component is deleted.
The quantized coefficients are encoded in accordance with entropy encoding by using an encoding table 5. For this purpose, Hoffman encoding method is often used. Then, encoded data is transmitted from the transmitter 1 via the transmission line 3 to ; the receiver 2 together wi-th a parameter including information as to which table is used.
In the receiver 2, the encoded data i5 decoded to provide the quantized data by referring to the transmitted encoding table 5. The quantized data is ~
inversely quantized to provide the DCT coefficienks by referring to the transmitted quantization table 4.
In accordance with the property of the quantization, completely original DCT coefficients are not restored.
In this sense, the DCT method is defined as a non-inversible encoding method. Then, the DCT
coefficient5 are inversely transformed to the reproduced image data 20 of blocks each having 8 x 8 pixels.
2 ~ 6 ~
As described above~ the original image daka 10 is processed in the transmitter 1 -to be the compression data 30 in accordance with the orthogonal transformation, the quantization and the variable length encoding anA the compression clata 30 is extended in the receiver 2 to provide the reproduced image data in accordance with the decoding, the inverse quantization and the inverse orthogonal transformation.
Next, an apparatus for compressing and extending an image data of a preferred embodiment according to the invention will be explained in Fig. 2.
The apparatus comprises a memory 22 for storing image data 21, a compression circuit 23 for compressing image data read from the memory 22, and extension circuit 24 for extending the compressed image data, a memory 25 for storing and providing the extended image data 26, and an evaluation circuit 31 comprising a subtracter 32 for carrying out a subtraction between image data pixels of each block read from the memories 22 and 25, -20 a hold circuit 33 for holding the subtraction result as a block noise, and a decision circuit 34 for making a `~decision of an optimun compression factor in accordance with the subtraction results.
In operation, the image data 21 is stored in the memory 22, from which the image data is read to be supplied to the compression circuit 23. Then, the image data is compressed in the compression circuit 23 .
- ~
,,. '~
20~8~J
by a compression fac-tor ~. The compressed data and table data corresponding to the compression factor A
are transmitted to the extension circuit 24, and the compression factor A is supplied to be held in the hold circuit 33. In the extension circuit 24, the compressed data is extended in accordance with the transmi-tted t~ble data to provide reproduced image data which is -then stored in the memory 25.
In the evaluation circuit 31, the subtracter 32 compares pixels read from the memories 22 and 25 in each block, so that the difference is detected therein as a block noise A which is held .in the hold circuit 33. In accordance with the block noise A, a compression factor B is determined in the decision circui-t 34 to be supplied to the compression circuit 23.
In the compression circuit 23, image data read from the memory 22 is compressed by the compression factor B, and the compressed data and table data corresponding to the compression factor B are transmitted to the ex-tension circuit 24, in which the compressed data is extended by referring to the transmitted table data. The extended data is stored in the memory 25, and image data read from the memories 22 and 25 are compared in the subtracter 32 in the same manner as in the case of using the compression factor A, so that a block noise B is detected -to be stored in the 2~8~
hold circuit 33.
Then, an optimum compression fac-tor is determined in the deci~ion circui-t 3~ in accordance witll the compression factors ~ B and the block noises A B, so that the optimum compression factor thus obtained is supplied from the decision circuit 34 to the compression Gircuit 23, in which image data is compressed by the optimum compression factor.
In making the decision of the optimum compression factor by the decision circuit 34, the : compression factor B is determined to ba small, where ~ the block noise A is considerably large, because it is . considered that the compression factor A is much larger than the optimum compression factor, while the : 15 compression factor B is determined to be larger than the compression factor A, where the block noise A is small. At any rate, an error of the optimum compression factor can be small by setting the optimum compression fac-tor between the compression factors A
~` 20 and B.
~: In -the preferred embodiment, an optimum compression factor is applied to the aforementioned DCT
algorithm, so that image data becomes improved in quality by suppressing block noise providing visual ~5 problem and the encoding of image data is carried out with high efficiency.
Although the invention has been described with 2~3~3~6~
respect to specific embodiment Eor complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modification and al-terna-tive cons-tructions that may occur to one skilled in the art which fairly fall within the basic teachirly herein set forth.
~'` ' .
:, .
.
,,:
Claims (4)
1. An apparatus for compressing and extending an image, comprising :
a compression circuit for compressing image data to provide compressed image data by a predetermined compression factor ;
an extension circuit for extending said compressed image data to provide reproduced image data by extension data corresponding to said predetermined compression factor ; and an evaluation circuit for evaluating said predetermined compression factor to provide an optimum compression factor in accordance with comparison between said image data and said reproduced image data, said optimum compression factor being used in place of said predetermined compression factor for a subsequent compressing process by said compression circuit.
a compression circuit for compressing image data to provide compressed image data by a predetermined compression factor ;
an extension circuit for extending said compressed image data to provide reproduced image data by extension data corresponding to said predetermined compression factor ; and an evaluation circuit for evaluating said predetermined compression factor to provide an optimum compression factor in accordance with comparison between said image data and said reproduced image data, said optimum compression factor being used in place of said predetermined compression factor for a subsequent compressing process by said compression circuit.
2. An apparatus for compressing and extending an image, according to claim 1, wherein :
said compression circuit, comprises :
means for transforming said image data to provide transformed image data by using DCT ;
means for quantizing said transformed image data to provide quantized image data in accordance with quantization table data corresponding to said predetermined and optimum compression factors ;
means for encoding said quantized image data to provide encoded image data in accordance with encoding table data ; and means for transmitting said encoded image data along with said quantization and encoding table data to said extension circuit ;
said extension circuit, comprises :
means for receiving said encoded image data along with said quantization and encoding table data ;
means for decoding said encoded image data to provide said quantized image data in accordance with said encoding table data ;
means for inversely quantizing said quantized image data to provide said transformed image data in accordance with said quantization table data ; and means for inversely transforming said transformed image data to provide said reproduced image data by using said DCT ; and said evaluation circuit, comprises :
means for comparing said image data and said reproduced image data in each block pixel by pixel to provide block noise ;
means for holding said block noise ; and means for generating said optimum compression factor in accordance with said predetermined compression factor and said block noise.
said compression circuit, comprises :
means for transforming said image data to provide transformed image data by using DCT ;
means for quantizing said transformed image data to provide quantized image data in accordance with quantization table data corresponding to said predetermined and optimum compression factors ;
means for encoding said quantized image data to provide encoded image data in accordance with encoding table data ; and means for transmitting said encoded image data along with said quantization and encoding table data to said extension circuit ;
said extension circuit, comprises :
means for receiving said encoded image data along with said quantization and encoding table data ;
means for decoding said encoded image data to provide said quantized image data in accordance with said encoding table data ;
means for inversely quantizing said quantized image data to provide said transformed image data in accordance with said quantization table data ; and means for inversely transforming said transformed image data to provide said reproduced image data by using said DCT ; and said evaluation circuit, comprises :
means for comparing said image data and said reproduced image data in each block pixel by pixel to provide block noise ;
means for holding said block noise ; and means for generating said optimum compression factor in accordance with said predetermined compression factor and said block noise.
3. A method for compressing and extending an image, comprising the steps of :
compressing image data to provide first compressed image data by a first compression factor ;
extending said first compressed image data to provide first reproduced image data by data corresponding to said first compression factor ; and comparing said image data and said first reproduced image data in each block pixel by pixel to provide first block noise ; and generating an optimum compression factor in accordance with said first compression factor and said first block noise, said optimum compression factor being used for subsequently compressing said image data.
compressing image data to provide first compressed image data by a first compression factor ;
extending said first compressed image data to provide first reproduced image data by data corresponding to said first compression factor ; and comparing said image data and said first reproduced image data in each block pixel by pixel to provide first block noise ; and generating an optimum compression factor in accordance with said first compression factor and said first block noise, said optimum compression factor being used for subsequently compressing said image data.
4. A method for compressing and extending an image data, according to claim 3, wherein :
said step of compressing comprises a step of compressing said image data to provide second compressed image data by a second compression factor ;
said step of extending comprises a step of extending said second compressed image data to provide second reproduced image data by data corresponding to said second compression factor ; and said step of comparing comprises a step of comparing said image data and said second reproduced image data in each block pixel by pixel to provide second block noise ; and said step of generating comprises a step of generating said optimum compression factor in accordance with said first and second compression factors and said first and second block noises, said optimum compression factor being determined to be a value between said first and second compression factors.
said step of compressing comprises a step of compressing said image data to provide second compressed image data by a second compression factor ;
said step of extending comprises a step of extending said second compressed image data to provide second reproduced image data by data corresponding to said second compression factor ; and said step of comparing comprises a step of comparing said image data and said second reproduced image data in each block pixel by pixel to provide second block noise ; and said step of generating comprises a step of generating said optimum compression factor in accordance with said first and second compression factors and said first and second block noises, said optimum compression factor being determined to be a value between said first and second compression factors.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5600092A JPH05219385A (en) | 1992-02-07 | 1992-02-07 | Picture compression expansion method and device |
| JP4-56000 | 1992-02-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2088863A1 true CA2088863A1 (en) | 1993-08-08 |
Family
ID=13014809
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2088863 Abandoned CA2088863A1 (en) | 1992-02-07 | 1993-02-05 | Method and apparatus for compressing and extending an image |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US5357584A (en) |
| EP (1) | EP0555061B1 (en) |
| JP (1) | JPH05219385A (en) |
| CA (1) | CA2088863A1 (en) |
| DE (1) | DE69309732T2 (en) |
| TW (1) | TW279945B (en) |
Families Citing this family (19)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3442111B2 (en) * | 1993-09-14 | 2003-09-02 | 株式会社ソニー・コンピュータエンタテインメント | Image compression device, image reproduction device and drawing device |
| US5790717A (en) * | 1993-10-26 | 1998-08-04 | Bell Communications Research Inc. | Apparatus and method for predicting subjective quality of compressed images |
| JPH08186814A (en) * | 1994-12-28 | 1996-07-16 | Canon Inc | Image compressor |
| US5886743A (en) * | 1994-12-28 | 1999-03-23 | Hyundai Electronics Industries Co. Ltd. | Object-by information coding apparatus and method thereof for MPEG-4 picture instrument |
| JP2806287B2 (en) * | 1995-01-13 | 1998-09-30 | 日本電気株式会社 | Image quality evaluation device |
| US5629778A (en) * | 1995-05-15 | 1997-05-13 | Polaroid Corporation | Method and apparatus for reduction of image data compression noise |
| EP0901666A4 (en) * | 1996-03-29 | 2001-08-29 | Sarnoff Corp | Apparatus and method for optimizing encoding and performing automated steerable image compression using a perceptual metric |
| JPH1075448A (en) * | 1996-08-29 | 1998-03-17 | Asahi Optical Co Ltd | Image compressor and image expander |
| US6091773A (en) | 1997-11-12 | 2000-07-18 | Sydorenko; Mark R. | Data compression method and apparatus |
| GB9803580D0 (en) * | 1998-02-21 | 1998-04-15 | Nds Ltd | Determining visually noticeable differences between two images |
| JP3738574B2 (en) * | 1998-09-18 | 2006-01-25 | 富士ゼロックス株式会社 | Image information encoding device |
| JP3679083B2 (en) * | 2002-10-08 | 2005-08-03 | 株式会社エヌ・ティ・ティ・ドコモ | Image encoding method, image decoding method, image encoding device, image decoding device, image encoding program, image decoding program |
| US7266246B2 (en) * | 2004-04-29 | 2007-09-04 | Hewlett-Packard Development Company, L.P. | System and method for estimating compression noise in images |
| US20060034531A1 (en) * | 2004-05-10 | 2006-02-16 | Seiko Epson Corporation | Block noise level evaluation method for compressed images and control method of imaging device utilizing the evaluation method |
| US7545988B2 (en) * | 2004-08-09 | 2009-06-09 | George William Meeker | Image blocking artifact reduction via transform pair |
| US20060085541A1 (en) * | 2004-10-19 | 2006-04-20 | International Business Machines Corporation | Facilitating optimization of response time in computer networks |
| JP2009105960A (en) * | 2009-02-02 | 2009-05-14 | Seiko Epson Corp | Photographic device and program used in the same, as well as image storage method |
| EP2486517A4 (en) * | 2009-10-05 | 2014-06-11 | Icvt Ltd | Apparatus and methods for recompression of digital images |
| JPWO2014136193A1 (en) * | 2013-03-04 | 2017-02-09 | 富士通株式会社 | Base station apparatus, base station system, and IQ data compression method |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4777620A (en) * | 1985-02-20 | 1988-10-11 | Elscint Ltd. | Data compression system |
| US4754492A (en) * | 1985-06-03 | 1988-06-28 | Picturetel Corporation | Method and system for adapting a digitized signal processing system for block processing with minimal blocking artifacts |
| DE3613343A1 (en) * | 1986-04-19 | 1987-10-22 | Philips Patentverwaltung | HYBRID CODERS |
| US4903317A (en) * | 1986-06-24 | 1990-02-20 | Kabushiki Kaisha Toshiba | Image processing apparatus |
| US5020120A (en) * | 1989-12-22 | 1991-05-28 | Eastman Kodak Company | Methods for reducing quantization error in hierarchical decomposition and reconstruction schemes |
| US5021891A (en) * | 1990-02-27 | 1991-06-04 | Qualcomm, Inc. | Adaptive block size image compression method and system |
-
1992
- 1992-02-07 JP JP5600092A patent/JPH05219385A/en active Pending
- 1992-06-11 TW TW81104590A patent/TW279945B/zh active
-
1993
- 1993-02-01 US US08/011,681 patent/US5357584A/en not_active Expired - Fee Related
- 1993-02-03 DE DE1993609732 patent/DE69309732T2/en not_active Expired - Fee Related
- 1993-02-03 EP EP19930300771 patent/EP0555061B1/en not_active Expired - Lifetime
- 1993-02-05 CA CA 2088863 patent/CA2088863A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| DE69309732D1 (en) | 1997-05-22 |
| EP0555061B1 (en) | 1997-04-16 |
| US5357584A (en) | 1994-10-18 |
| JPH05219385A (en) | 1993-08-27 |
| DE69309732T2 (en) | 1997-11-13 |
| EP0555061A1 (en) | 1993-08-11 |
| TW279945B (en) | 1996-07-01 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA2088863A1 (en) | Method and apparatus for compressing and extending an image | |
| EP0399487B1 (en) | Transformation coding device | |
| EP0550012B1 (en) | Apparatus for compression encoding video signals | |
| US5475434A (en) | Blocking effect attenuation apparatus for high definition television receiver | |
| CA2011034C (en) | A highly efficient coding apparatus | |
| JPH0583696A (en) | Picture encoding device | |
| EP0716548B1 (en) | Efficient iterative decompression of standard ADCT-compressed images | |
| EP0555095B1 (en) | Method for compressing and extending an image by transforming orthogonally and encoding the image | |
| US5508745A (en) | Apparatus for controlling a quantization level to be modified by a motion vector | |
| US5734431A (en) | Video coding and decoding apparatus including corresponding nonlinear compression and expansion of a motion compensation error signal | |
| JPH0522715A (en) | Picture encoder | |
| US5675386A (en) | Method for encoding motion image and apparatus therefor | |
| JPH04373286A (en) | Picture encoder | |
| US5907636A (en) | Image signal decoder | |
| JP3271098B2 (en) | Digital image signal decoding apparatus and method | |
| JP3063380B2 (en) | High efficiency coding device | |
| JPH0244883A (en) | Moving picture transmission system | |
| US20040107399A1 (en) | Image processing apparatus and method therefor | |
| US6266448B1 (en) | Method of and apparatus for compressing and encoding digitized moving picture signals | |
| JPH0775103A (en) | Image encoder | |
| JPH06189283A (en) | Transmitting device for digital picture signal | |
| JP3517795B2 (en) | Image coding device | |
| Miyazawa et al. | Animation image coding | |
| JPH0514739A (en) | Picture encoding device | |
| JPH0670173A (en) | Picture decoding device and picture coding/decoding system |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Dead |