Image decoding apparatus for persistently storing reference images

Abstract

An image coding apparatus which includes a frame memory selecting unit (35) for selecting, in response to a selection signal, an image to be continuously stored in a plurality of frame memories (9, 10) as a background image and storing the background image into the plurality of frame memories (9, 10), and a background motion compensating unit (14, 39) for performing motion compensating prediction corresponding to an input image based on the background image to generate a predicted image based on the motion compensating prediction, and an image decoding apparatus corresponding to the image coding apparatus.

Description

where “median” is an operator for calculation of a median.

Similarly, for the second frame memory,
PMV(2)=MV(2)−median (MV1(2), MV2(2), MV3(2))

FIG. 18 is a block diagram of an image coding apparatus which includes a differential vector generating unit 47 in addition to the construction of the image coding apparatus shown in FIG. 9.

For calculation of a difference vector, in addition to the operation described above, a reference motion vector PMV(3) for the third frame memory may be calculated and variable length coded.

The information generation amount of motion vectors can be supplied in such a manner as described above.

Embodiment 9

FIGS. 19 and 20 are block diagrams of decoding apparatus which correspond to the coding apparatus of the embodiment 8 described hereinabove with reference to FIGS. 16 and 18 in which a difference vector is used, respectively. Referring to FIGS. 19 and 20, reference numeral 48 denotes a motion vector adding unit. The other components are similar to those of the decoding apparatus of the embodiment 2 shown in FIG. 7, and accordingly, repetitive description of them is omitted here.

In the decoding apparatus of the present embodiment 9, a difference vector 141 variable length decoded by the variable length decoding unit 22 is added to a reference vector by the variable length decoding unit 22 to calculate a motion vector 123.

The processing following it is the same as the operation of the decoding apparatus of the embodiment 2 shown in FIG. 7, and therefore, repetitive description of it is omitted here.

Embodiment 10

While, in the coding apparatus of FIG. 1, an entire screen in a picture is used as a subject of coding, the image coding apparatus of the present embodiment 10 is constructed such that the picture type for coding is variable in units of one of a plurality of subject images (objects) which construct the screen.

Referring to FIG. 21, for example, if a screen is composed of an object 1 (fish), an object 2 (water: background picture) and an object 3 (ball) and boundaries among them are known, then those objects can be coded using different techniques from one another.

In the image coding apparatus of the present embodiment 10, such coding techniques are realized by using different picture types from one another. For example, since the object 1 exhibits a comparatively large amount of motion, the construction of picture types of FIG. 5A is used for the object 1 taking it into consideration that bidirection prediction is higher in prediction efficiency than background prediction.

On the other hand, since the object 2 is an image which exhibits little motion, it is effective to use background prediction for it. Accordingly, the construction of FIG. 5C should be used. However, if such a variation that a scene changes rapidly occurs with a certain midst picture, then the construction which includes B pictures beginning with the midst picture as seen in FIG. 5B should be employed.

FIG. 22 is a block diagram showing a concrete example of the image coding apparatus provided by the present embodiment 10. Referring to FIG. 22, reference numeral 42 denotes an object distinguishing unit, 43 a first frame memory group, 44 a second frame memory group, and 138 an object identification signal.

Operation will be described subsequently.

An input image 100 includes identification signals applied to individual objects in advance, and the identification signals are identified by the object distinguishing unit 42. The number of each of the thus identified objects is outputted as an object identification signal 138 from the object distinguishing unit 42.

The motion estimating unit 15 selects, from among the first frame memory group 43 and the second frame memory group 44, a frame memory which corresponds to the object of the subject of coding in accordance with the object identification signal 138, reads out a reference image from the selected frame memory and performs motion prediction.

Meanwhile, the motion compensation predicting unit 21 selects a frame memory corresponding to a predetermined object in accordance with a motion prediction mode 126 determined by the motion estimating unit 15 and generates a predicted image 115.

On the other hand, the frame memory selecting unit 35 writes a decoded image 108 into one of the frame memories of a predetermined one of the frame memory groups which corresponds to a predetermined object in accordance with the object identification signal 138.

Further, the object identification signal 138 is multiplexed together with other coding information by the multiplexing unit 45 and sent out as a multiplexed bit stream 139 to an external apparatus (not shown).

While, in the image coding apparatus of the present embodiment 10, the first and second memory groups are provided to realize the construction for switching of motion compensating prediction, for implementation of the hardware, a plurality of frame memories can be provided at a time by cutting a memory having a storage capacity for the plurality of frame memories based on internal addresses. As described above, with the image coding apparatus of the present embodiment 10, since a prediction structure which conforms with motion of an object can be taken, the overall prediction efficiency is improved.

Embodiment 11

A block diagram of an image decoding apparatus which corresponds to the image coding apparatus of the embodiment 10 shown in FIG. 22 is shown in FIG. 23. Referring to FIG. 23, reference numeral 46 denotes a demultiplexing unit, 43 a first frame memory group, 44 a second frame memory group, and 138 an object identification signal. The other components are similar to those of the image decoding apparatus of, for example, the embodiment 4 shown in FIG. 13, and accordingly, repetitive description of them is omitted here.

Operation will be described subsequently.

In response to an object identification signal 138 demultiplexed by the demultiplexing unit 46, the motion compensating unit 23 reads out a reference image from one of frame memories of a predetermined frame memory group which corresponds to a predetermined object, and performs motion compensation corresponding to a prediction mode to generate a predicted image 115.

In the meantime, the frame memory selecting unit 35 writes a decoded image 108 into one of the frame memories of a predetermined frame memory group which corresponds to a predetermined object in accordance with the object identification signal 138. The other processing is similar to that of the image decoding apparatus of the embodiment 4 shown in FIG. 13, and accordingly, repetitive description of it is omitted here.

Embodiment 12

FIG. 24 is a block diagram of an image coding apparatus which includes a further frame memory group in addition to the construction of the embodiment 10 described hereinabove with reference to FIG. 22 such that it may include totaling three frame memory groups. Referring to FIG. 24, reference numeral 49 denotes a third frame memory group. The other components are similar to those of the image coding apparatus of the embodiment 10 shown in FIG. 22, and accordingly, repetitive description of them is omitted here.

Subsequently, operation will be described.

An input image 100 includes identification signals applied to individual objects in advance, and the identification signals are identified by the object distinguishing unit 42. The number of each of the thus identified objects is outputted as an object identification signal 138 from the object distinguishing unit 42.

The motion estimating unit 15 selects, from among the first frame memory group 43, the second frame memory group 44 and the third frame memory group 49, a frame memory which corresponds to the object of the subject of coding in accordance with the object identification signal 138, reads out a reference image from the selected frame memory and performs motion prediction.

Meanwhile, the motion compensation predicting unit 21 selects a frame memory corresponding to a predetermined object in accordance with a motion prediction mode 126 determined by the motion estimating unit 15 and generates a predicted image 115.

On the other hand, the frame memory selecting unit 35 writes a decoded image 108 into one of the frame memories of a predetermined one of the frame memory groups which corresponds to a predetermined object in accordance with the object identification signal 138. Further, the object identification signal 138 is multiplexed together with other coding information by the multiplexing unit 45 and sent out as a multiplexed bit stream 139.

While, in the image coding apparatus of the present embodiment 12, the first, second and third memory groups are provided to realize the construction for switching of motion compensating prediction, for implementation of the hardware, a plurality of frame memories can be provided at a time by cutting a memory having a storage capacity for the plurality of frame memories based on internal addresses.

Embodiment 13

A block diagram of an image decoding apparatus corresponding to the image coding apparatus of the embodiment 12 shown in FIG. 24 is shown in FIG. 25. Referring to FIG. 25, reference numeral 49 denotes a third frame memory group. The other components are similar to those of the image decoding apparatus of, for example, the embodiment 11 shown in FIG. 23, and accordingly, repetitive description of them is omitted here.

Operation will be described subsequently.

In response to an object identification signal 138 demultiplexed by the demultiplexing unit 46, the motion compensating unit 23 reads out a reference image from one of frame memories of a predetermined frame memory group which corresponds to a predetermined object, and performs motion compensation corresponding to a prediction mode to generate a predicted image 115.

In the meantime, the frame memory selecting unit 35 writes a decoded image 108 into one of the frame memories of a predetermined frame memory group which corresponds to a predetermined object in accordance with the object identification signal 138.

The other processing is similar to that of the image decoding apparatus of the embodiment 11 shown in FIG. 23, and accordingly, repetitive description of it is omitted here.

Embodiment 14

The image coding apparatus such as embodiment 12 shown in FIG. 24 may be modified such that re-writing of image contents of a region, in which an object of a subject of coding is included, of a frame memory corresponding to the object in the second frame memory in which a decoded image of the object in the past is stored is performed after each certain interval of time or in response to a control signal from the outside.

FIG. 26 is a diagrammatic view illustrating that, for example, with a decoded image of all macroblocks including a region occupied by a certain object, image contents in a macroblock or macroblocks at the same position of a frame memory in the second frame memory group which corresponds to the object are re-written. Accordingly, in the case of FIG. 26, contents of totaling four macroblocks in two vertical columns and two horizontal rows are updated.

Further, where re-writing of image contents of a region, in which an object of a subject of coding is included, of a frame memory corresponding to the object in the third frame memory in which a decoded image of the object in the past is stored is performed after each certain interval of time or in response to a control signal from the outside, the writing operation into a frame memory in the second frame memory group in the foregoing description should be applied to the writing operation into a frame memory in the third frame memory group.

Also with a decoding apparatus which corresponds to the image coding apparatus such as embodiment 12 shown in FIG. 24 as described above, re-writing of image contents of a region, in which an object is included, of a frame memory corresponding to the object in the second frame memory group in which a decoded image of the object in the past is stored can be controllably performed after a certain interval of time or in response to a control signal from the outside.

Embodiment 15

The image coding apparatus of the embodiment 10 shown in FIG. 22 can be modified such that searching ranges of motion vector searching for a reference image from a frame memory of the first frame memory group which corresponds to an object and another reference image from another frame memory of the second frame memory group which corresponds to another object are varied for the individual objects.

For example, in the image coding apparatus of the embodiment 10 shown in FIG. 22, if a background which exhibits a comparatively small amount of motion as an object is stored in advance in a frame memory of the second frame memory group which corresponds to the object whereas an operation of successively writing a decoded image of another object which exhibits a comparatively large amount of motion at any time into another frame memory of the first frame memory group which corresponds to the object is performed, then a high prediction efficiency can be maintained for both of the objects.

Further, the image coding apparatus of the embodiment 12 shown in FIG. 24 may be modified such that searching ranges of motion vector searching for a reference image from s from memory of the first frame memory group which corresponds to an object, another reference image from another frame memory of the second frame memory group which corresponds to another object and a further reference image from a further frame memory of the third frame memory group which corresponds to a further object are varied for the individual objects.

For example, in the image coding apparatus of the embodiment 12 shown in FIG. 24, if a background which exhibits a comparatively small amount of motion as an object is stored in advance in a frame memory of the third frame memory group which corresponds to the object whereas an operation of successively writing a decoded image of another object which exhibits a comparatively large amount of motion at any time into another frame memory of the first frame memory group or the second frame memory group which corresponds to the object is performed, then a high prediction efficiency can be maintained for all of the three objects.

As described above, since searching ranges for a motion vector are set separately from each other for a plurality of frame memory groups referred to by objects. for example, for an object which exhibits a comparatively small amount of motion, the information generation amount of motion vectors can be reduced by making the searching range for a motion vector narrow.

Embodiment 16

FIG. 27 is a block diagram showing an image coding apparatus according to an embodiment 16 of the present invention. Referring to FIG. 27, reference 47 denotes a differential vector generating unit. The differential vector generating unit 47 holds motion vectors in the past obtained by referring to images of individual objects from frame memories of the first frame memory group which correspond to the objects and motion vectors in the past obtained by referring to images of the individual objects from frame memories of the second frame memory group which correspond to the objects in the image coding apparatus of the embodiment 10 shown in FIG. 22 separately for certain periods of time and calculates difference vectors separately for the individual objects. The other construction is similar to that of the image coding apparatus of the embodiment 10 shown in FIG. 22, and accordingly, repetitive description of it is omitted here.

Subsequently, operation will be described.

The motion estimating unit 15 performs motion estimation of a current image 101 of an object of a subject of coding using an image in a frame memory corresponding to the object in one of the first frame memory group and the second frame memory group selected by motion estimation as a reference image to detect a motion vector 123.

Based on the motion vector 123, the differential vector generating unit 47 selects a candidate vector (MV1, MV2 or MV3 mentioned hereinabove) from among motion vectors of the object in the past stored in the differential vector generating unit 47 and outputs a difference vector 141 of the candidate vector from the motion vector 123. The difference vector 141 is coded into a variable length codeword by the variable length coding unit 17. Accordingly, the differential vector generating unit 47 has a memory function of holding motion vectors in the past separately for certain periods of time for the individual frame memory groups.

Embodiment 17

A block diagram of a decoding apparatus corresponding to the image coding apparatus of the embodiment 16 shown in FIG. 27 is shown in FIG. 28. Referring to FIG. 28, reference numeral 48 denotes a motion vector adding unit which selects a candidate vector from among motion vectors of an object in the past stored in advance therein and adds the selected candidate vector to a difference vector 141 variable length decoded by the variable length decoding unit 22. The other construction is similar to that of the image decoding apparatus of the embodiment 11 shown in FIG. 22, and accordingly, repetitive description of it is omitted here.

Subsequently, operation will be described.

In the image decoding apparatus of the present embodiment 17, a difference vector 141 variable length coded by the variable length decoding unit 22 is supplied to the motion vector adding unit 48, by which a candidate vector is selected from among motion vectors of an object in the past stored therein and added to the difference vector 141 to regenerate a motion vector 123.

The motion vector 123 is sent to the motion compensating unit 23. The motion compensating unit 23 receives the motion vector 123, reads out an image in the memory group 43 or 44 corresponding to the object in the frame memory group selected by the frame memory selecting unit 35 as a reference image, and outputs a predicted image 115. The other processing is similar to the operation of the image decoding apparatus of the embodiment 11 shown in FIG. 23, and accordingly, repetitive description of it is omitted here.

Embodiment 18

A construction of an image coding apparatus which includes a third frame memory group 49 in addition to the construction of the image coding apparatus of the embodiment 16 shown in FIG. 27 is shown in FIG. 29. The other construction is similar to that of the image coding apparatus of the embodiment 16 shown in FIG. 27, and accordingly, repetitive description of it is omitted here.

Subsequently, operation will be described.

The motion estimating unit 15 performs motion estimation of a current image 101 of an object of a subject of coding using an image in a frame memory corresponding to the object in one of the first frame memory group, the second frame memory group and the third frame memory group selected by motion estimation as a reference image to detect a motion vector 123.

Based on the motion vector 123, the differential vector generating unit 47 selects a candidate vector (MV1, MV2 or MV3 mentioned hereinabove) from among motion vectors of the object in the past stored in the differential vector generating unit 47 and outputs a difference vector 141 of the candidate vector from the motion vector 123. The difference vector 141 is coded into a variable length codeword by the variable length coding unit 17.

Also in this instance, the differential vector generating unit 47 has a memory function of holding motion vectors in the past separately for certain periods of time for the individual frame memory groups. Since the other processing is similar to the operation of the image coding apparatus of the embodiment 16 shown in FIG. 27, repetitive description of it is omitted herein.

Embodiment 19

A construction of an image decoding apparatus corresponding to the image coding apparatus of the embodiment 18 shown in FIG. 29 is shown in FIG. 30. Referring to FIG. 30, reference numeral 49 denotes a third frame memory group. Since the other construction is similar to that of the image decoding apparatus of the embodiment 17 shown in FIG. 28, repetitive description of it is omitted here.

Subsequently, operation will be described.

A difference vector 141 variable length coded by the variable length decoding unit 22 is supplied to the motion vector adding unit 48, by which a candidate vector is selected from among motion vectors of an object in the past stored therein and added to the difference vector 141 to regenerate a motion vector 123. The motion vector 123 is sent to the motion compensating unit 23. The motion compensating unit 23 reads out a reference image in a frame memory corresponding to the object in the selected frame memory group, and outputs a predicted image 115.

As described above, if a differential vector generating unit which has a memory function of holding a number of motion vectors, which is equal to the number of the frame memory groups, in the past separately for certain periods of time for the individual frame memory groups and calculates a difference vector between a detected motion vector and a candidate vector is provided, then the information generation amount of motion vectors can be suppressed.

As described above, with the image coding apparatus of the present invention, since a background image is stored and motion compensating prediction is performed using background prediction based on the stored background image, there is an effect that coding can be performed while keeping a high prediction efficiency without being influenced by a coding sequence.

Further, with the image coding apparatus and the image decoding apparatus of the present invention, since re-writing of image contents in the individual frame memories is performed in units of a picture after a certain interval of time or in response to a control signal from the outside, there is another effect that the image contents of the frame memories can always be kept to contents with which a high prediction efficiency in background prediction can be obtained.

Further, with the image coding apparatus and the image decoding apparatus of the present invention, since re-writing of the image contents of the individual frame memories is performed in units of a macroblock after a certain interval of time or in response to a control signal from the outside, there is a further effect that the image contents of the frame memories can always be kept to contents with which a high prediction efficiency in background prediction can be obtained with a finer level.

Further, with the image coding apparatus and the image decoding apparatus of the present invention, since the searching ranges for a motion vector to be used for motion estimation are variably set for the plurality of frame memories provided in the coding apparatus, for example, when motion is to be searched for from reference to a frame memory in which a screen which involves a comparatively small amount of motion is written, a comparatively short code can be given, and accordingly, there is a still further effect that the coding information amount of motion vectors can be reduced.

Further, with the image coding apparatus and the image decoding apparatus of the present invention, since the differential vector generating unit which has a memory function of holding a number of motion vectors, which is equal to the number of the frame memories, in the past separately for a certain period of time and calculates a difference vector between a detected motion vector and a candidate vector is provided, there is a yet further effect that the information generation amount of motion vectors can be suppressed.

Further, with the image coding apparatus and the image decoding apparatus of the present invention, since motion compensating prediction is performed using the plurality of frame memories for the individual objects which construct a screen, a prediction structure conforming to motion of the objects can be taken, and consequently, there is a yet further effect that the overall prediction efficiency is improved.

Further, with the image coding apparatus and the image decoding apparatus of the present invention, since only regions of the frame memories in the frame memory groups in which an object of a subject of coding is included are re-written after a certain interval of time or in response to an external control signal, there is a yet further effect that a high efficiency in background prediction can be maintained.

Further, with the image coding apparatus and the image decoding apparatus of the present invention, since the searching ranges for a motion vector are set separately for the plurality of frame memory groups referred to by an object, there is a yet further effect that, for example, for an object which exhibits a comparatively small amount of motion, the information generation amount of motion vectors can be reduced by making the searching range for a motion vector narrow.

Furthermore, with the image coding apparatus and the image decoding apparatus of the present invention, since the differential vector generating unit which has a memory function of holding a number of motion vectors, which is equal to the number of the frame memory groups, in the past separately for certain periods of time for the individual frame memory groups and calculates a difference vector between a detected motion vector and a candidate vector is provided, there is an additional effect that the information generation amount of motion vectors can be suppressed.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

1. An image coding apparatus, comprising:

frame memories for storing a plurality of decoded images;

motion compensating prediction means for performing motion compensating prediction corresponding to an input image based on the plurality of decoded images stored in said frame memories to produce a motion vector and for generating a predicted image based on the motion compensating prediction;

prediction error calculation means for calculating a difference between the predicted image generated by said motion compensating prediction means and the input image to calculate a prediction error image;

decoding means for generating the decoded images from the prediction error image calculated by said prediction error calculation means and the predicted image;

image storage controller for determining and outputting the coding mode of the image to be predicted according to an input control signal, and allocating the type of the reference image to be stored in one of said frame memories to continuously decoded image or the stationary background image based on the selected coding mode of the image to be predicted; and

background motion compensation means for performing motion compensating prediction corresponding to the input image based on the background image to generate a motion vector and generating a predicted image based on the motion compensating prediction, wherein said image storage controller performs re-writing of image contents into said frame memories in response to a given control signal.

2. An image coding apparatus according to claim 1, wherein said frame memories includes a frame memory for storing a decoded image, and another frame memory for storing the background image.

3. An image coding apparatus according to claim 1, wherein re-writing of image contents into said storage means by said background image storage control means is performed in units of a picture after a predetermined interval of time or in response to a control signal from the outside.

4. An image coding apparatus according to claim 1, wherein re-writing of image contents into said storage means by said background image storage control means is performed in units of a macroblock after a predetermined interval of time or in response to a control signal from the outside.

5. An image coding apparatus according to claim 1, wherein said background motion compensation means has a variable searching range for a motion vector from the background images.

6. An image coding apparatus according to claim 1, further comprising differential vector generation means for holding a motion vector obtained from said motion compensation means or said background motion compensation means and calculating a difference vector between the generated motion vector and the motion vector in the past, and the difference vector is variable length coded.

7. An image coding apparatus according to claim 1, wherein said background image storage control means performs re-writing of image contents into said storage means per unit of a picture after a predetermined time-interval.

8. An image coding apparatus according to claim 1, wherein said background image storage control means performs re-writing of image contents into said storage means per unit of a macro-block after a predetermined time-interval.

9. An image coding apparatus according to claim 1, wherein said background image storage control means performs re-writing of image contents into said storage means per unit of a picture in response to an outside control signal.

10. An image coding apparatus according to claim 1, wherein said background image storage control means performs re-writing of image contents into said storage means per unit of a macro-block in response to an outside control signal.

11. An image decoding apparatus, comprising:

frame memories for storing a plurality of decoded images;

motion compensation means for performing motion compensating prediction based on the decoded images stored in said frame memories to generate a motion compensated image;

decoding means for generating coded images from the motion compensated image from said motion compensation means and a prediction error image;

an image storage controller for allocating the type of the reference image to be stored in one of said frame memories to continuously decoded image or the stationary background image based on the coding mode of the image to be decoded, which is extracted from encoded bitstream; and

background predicted image generation means for generating a background predicted image based on the background image, wherein said image storage controller performs re-writing of image contents into said frame memories in response to a given control signal.

12. An image decoding apparatus according to claim 11, wherein said frame memories includes a frame memory for storing a decoded image, and another frame memory for storing the background image.

13. An image decoding apparatus according to claim 11, wherein re-writing of image contents into said storage means by said background image storage control means is performed in units of a picture after a predetermined interval of time or in response to a control signal from the outside.

14. An image decoding apparatus according to claim 11, wherein re-writing of image contents into said storage means by said background image storage control means is performed in units of a macroblock after a predetermined interval of time or in response to a control signal from the outside.

15. An image decoding apparatus according to claim 11, further comprising a motion vector adding unit for holding a motion vector decoded in the past and adding the motion vector decoded in the past to a difference vector to regenerate a motion vector.

16. An image coding apparatus according to claim 11, wherein said background image storage control means performs re-writing of image contents into said storage means per unit of a picture after a predetermined time-interval.

17. An image coding apparatus according to claim 11, wherein said background image storage control means performs re-writing of image contents into said storage means per unit of a macro-block after a predetermined time-interval.

18. An image coding apparatus according to claim 11, wherein said background image storage control means performs re-writing of image contents into said storage means per unit of a picture in response to an outside control signal.

19. An image coding apparatus according to claim 11, wherein said background image storage control means performs re-writing of image contents into said storage means per unit of a macro-block in response to an outside control signal.

20. An image coding/decoding apparatus, comprising:

an image coding apparatus, including,

image coding frame memories for storing a plurality of decoded images;

image coding motion compensating prediction means for performing motion compensating prediction corresponding to an input image based on the plurality of decoded images stored in said image coding frame memories to produce a motion vector and for generating a predicted image based on the motion compensating prediction;

image coding prediction error calculation means for calculating a difference between the predicted image generated by said image coding motion compensating prediction means and the input image to calculate a prediction error image;

first decoding means for generating the decoded images from the prediction error image calculated by said image coding prediction error calculation means and the predicted image;

an image coding image storage controller for determining and outputting the coding mode of the image to be predicted according to an input control signal, and allocating the type of the reference image to be stored in one of said image coding frame memories to continuously decoded image or the stationary background image based on the selected coding mode of the image to be predicted; and

image coding background motion compensation means for performing motion compensating prediction corresponding to the input image based on the background image to generate a motion vector and generating a predicted image based on the motion compensating prediction; and

an image decoding apparatus, including,

image decoding frame memories for storing a plurality of decoded images;

image decoding motion compensation means for performing motion compensating prediction based on the decoded images stored in said image decoding frame memories to generate a motion compensated image;

second decoding means for generating coded images from the motion compensated image from said image decoding motion compensation means and a prediction error image;

an image decoding image storage controller for allocating the type of the reference image to be stored in one of said image decoding frame memories to continuously decoded image or the stationary background image based on the coding mode of the image to be decoded, which is extracted from encoded bitstream; and

image decoding background predicted image generation means for generating a background predicted image based on the background image,

21. An image decoding apparatus, comprising:

frame memories for storing a plurality of decoded images;

motion compensation means for performing motion compensating prediction based on the decoded images stored in said frame memories to generate a motion compensated image;

decoding means for generating decoded images from the motion compensated image from said motion compensation means and a prediction error image;

an image storage controller for allocating a type of a reference image to be stored in one of said frame memories to continuously decoded image or a stationary background image based on a coding mode of the image to be decoded, which is extracted from encoded bitstream; and

background predicted image generation means for generating a background predicted image based on the stationary background image, wherein said image storage controller performs re-writing of image contents into said frame memories in response to a given control signal.