JP2000156868A - Method and device for decoding image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to make random accesses to all pictures in a group of pictures(GOP). SOLUTION: An image decoding device is provided with a field memory group 3 for generating a forward predicting field by using a decoded picture signal in an intra-field (I pictures) obtained by the initial intra-encoding of a GOP, a variable length decoder 31 for decoding an encoded signal in a difference field, a difference signal decoder 32, and an adder 33 for adding the decoded signal of the difference filed and the signal of the forward predicting field. In the case of executing addition by the adder 33, addition of a signal of a forward predicting field to which a GOP other than the GOP including the difference field belongs is inhibited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information reproducing apparatus using a storage system moving image medium such as an optical disk or a magnetic tape, or an information receiving apparatus such as a so-called video conference system, a moving picture telephone system, and broadcasting equipment. The present invention relates to an image decoding method and an apparatus suitable for the above.

[0002]

2. Description of the Related Art The conventional motion-compensated predictive coding and its decoding method are typically represented by ISO-IEC /
JTC1 / SC2 / WG11 (MPEG: Moving P
There is a standard method (commonly referred to as MPEG1) of a moving image encoding for storage determined by an imageexperts group.

In MPEG1, a certain unit of moving picture is collectively called a GOP (Group Of Picture). FIG.
4 shows a configuration example of an OP. In FIG. 6, a picture in a GOP is an I picture (intra-coded image: Intra-co
ded picture), P picture (forward prediction coded image: Pr
edictive-coded picture), B picture (Bidirectionally Predictive-coded pictur)
e) There are three types. Here, the I picture is an intra-frame coded picture. The P picture is an inter-frame predictive coded picture. Motion prediction is performed from a recent past decoded and reproduced I picture or P picture, and the prediction error at this time is coded. The B picture is a bidirectional predictive coded picture, in which motion is predicted from both a past reproduced picture and a future reproduced picture, and a prediction error at this time is coded. A GOP is composed of one or more I-pictures and zero or more non-I-pictures. In FIG. 6, an I picture is indicated by I in the figure, a P picture is indicated by P in the figure, and a B picture is indicated by B in the figure. Further, in FIG. 6, arrows connecting the pictures indicate the direction of motion prediction.

In MPEG1, in order to enable random access (reproduction from the middle) in GOP units, as shown in FIG. 7, each GOP (GOP1, GOP1
2, GOP3,..., GOPN)
A P header (GOP header 1, GOP header 2, GOP header 3,..., GOP header N) is added. Therefore, the image decoding apparatus determines the GO of the designated GOP from the supplied encoded information (input bit stream).
By detecting the P start code and starting decoding from the first I picture of the GOP, reproduction from the middle of the moving image sequence is enabled.

[0005] Here, two flags, a closed GOP (Closed GOP) flag and a broken link (Broken Link) flag, are added to the GOP header.

The closed GOP flag is a flag that is set at the time of encoding. When predicting the first few B pictures (two frames in FIG. 6) of a GOP, the P pictures belonging to the past GOP (FIG. In the case of No. 6, this is a flag indicating that prediction from a P picture indicated by oblique lines is not used. G with closed GOP flag set
The OP is a completely independent GOP.

The broken link flag is a flag that is set when bit streams that are not closed GOPs are cut and connected by editing. Therefore, the image decoding apparatus recognizes that the first few B pictures cannot be displayed in the GOP in which the broken link flag is set.

[0008] These two flags relate to the first few B pictures of the GOP, and are designated by the designated GOP.
In the case of random access (reproduction from the middle) from, the worst case may not be able to display the first B picture, but reproduction after the I picture is possible.

The detailed bit stream code and grammar relating to the GOP are described in the MPEG1 standard.

[0010] In recent years, in MPEG2, which has been after MPEG1, in television systems NTSC and P
A method of encoding an interlaced image such as AL has been studied. In MPEG2, the unit of processing of a picture to be encoded is adaptively switched between a frame and a field, and a plurality of past decoded and reproduced frames and fields are obtained.

As in MPEG1, there are three types of pictures in a GOP in MPEG2, i.e., I pictures, P pictures, and B pictures, and each picture is allowed to have a frame or field configuration.

[0012]

Here, in the case of performing random access in GOP units in MPEG2, if the first I picture of the GOP has a field structure, the following problem occurs.

That is, as shown in FIG. 8, for example, when the current picture p13 to be coded has a field structure, motion prediction from two past decoded and reproduced fields, ie, a field p06 and a field i12, is performed. Although it can be applied, at this time, when prediction from the field p06 is used, the independence of GOP1 is lost and random access to GOP1 cannot be performed. This is because, when random access to GOP1 is performed, the field p06 to be referred to at the time of motion compensation necessary for reproducing the field p13 is not reproduced. In FIG. 8, i is an I picture, p is a P picture, and b is a B picture. In addition, the hatched dotted line in the figure indicates a GOP break.

The present invention has been made in view of the above points, and an object of the present invention is to provide an image decoding method and apparatus which enables random access to all GOPs.

[0015]

SUMMARY OF THE INVENTION An image decoding method according to the present invention has been proposed in order to achieve the above-mentioned object, and includes an intra-encoding method for grouping a plurality of fields having a field structure. The block image signal of the intra-field or the block image signal of the past forward prediction field and the block reproduction difference signal of the forward prediction field forming one frame with the intra-field are added to obtain a block reproduction signal of one field. In the image decoding method, when the intra field is the first intra field of the group,
The present invention is characterized in that addition of the intra prediction field to the block prediction difference signal of the forward prediction field belonging to the past group of the group to which the intra field belongs is prohibited.

An image decoding apparatus according to the present invention has been proposed to achieve the above-mentioned object, and is a block image of an intra-coded intra field of a group in which a plurality of fields having a field structure are put together. A signal or a block image signal of a past forward prediction field;
In an image decoding apparatus which obtains a block reproduction signal of one field by adding the intra-field and a block reproduction difference signal of a forward prediction field forming one frame by an addition unit, when the addition unit performs the addition, When the intra-field is the first intra-field of the group, the addition of the intra-field to which the forward prediction field belonging to the past group belongs to the block reproduction difference signal is prohibited.

An image decoding method according to the present invention has been proposed in order to achieve the above object, and generates a predicted image signal using only a decoded image signal of an intra-coded first field. Decoding the coded signal of the first field and the second field constituting one frame, and adding the decoded signal of the coded signal of the second field and the predicted image signal; It is characterized by.

An image decoding apparatus according to the present invention has been proposed to achieve the above object, and generates a predicted image signal using only a decoded image signal of an intra-coded first field. Predictive image generating means for performing
Decoding means for decoding the coded signal of the field of the second field and one field constituting one frame;
The present invention is characterized in that it has an adding means for adding a signal obtained by decoding the coded signal of the field (i) and the predicted image signal.

That is, according to the image decoding method and apparatus of the present invention, when encoding a P-picture belonging to a GOP in, for example, MPEG, the P-picture belonging to a past GOP is encoded.
By always prohibiting prediction from pictures, random access to all GOPs can be made possible.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

First, an image encoding method and apparatus for generating an encoded bit stream input to the image decoding method and apparatus according to the embodiment of the present invention will be described.

An image encoding method according to an embodiment of the present invention is an image encoding method that encodes a difference signal between an original image and a past decoded image, and that applies the above-described MPEG2. When encoding a P picture to which it belongs,
A random access enable flag is provided (added) to the GOP header as a flag indicating whether or not encoding has been performed using a decoded image belonging to a past GOP.

Further, in the image coding method according to the present embodiment, a forward prediction field is generated by using a locally decoded image signal of the first intra-coded intra field of the GOP, and an input field and the forward prediction field are generated. Is an image coding method for generating a difference field by taking the difference of the input field and generating a difference field. When the difference field is generated, a difference from a forward prediction field belonging to a group other than the group to which the input field belongs is generated. It is forbidden to take. In other words, in the image encoding method according to the present embodiment,
When encoding a P picture belonging to the current GOP, prediction from pictures belonging to the past GOP is always prohibited, that is, prediction is performed only from the decoded image belonging to the current GOP.

The image coding apparatus according to the present embodiment to which the image coding method according to the present embodiment is applied stores an input image supplied via a moving image input terminal 10 as shown in FIG. A field memory group 11 as storage means;
The image signal (block image signal S1) output from the field memory group 11 and a motion compensation circuit 18 described later
And a difference unit 13 for forming a difference signal (block difference signal S2) from a decoded image (block image signal S3) from the above, and converts the block difference signal S2 into a predetermined transform coefficient (DCT coefficient described later). A difference signal encoder 14 including a transforming means for transforming and a quantizing means for quantizing the transform coefficient and outputting a quantized coefficient, and an inverse quantization coefficient for inversely quantizing the quantized coefficient (coded signal S4). And a difference signal decoder 15 including inverse transform means for inversely transforming the inverse quantized coefficient to form a decoded image signal (block reproduction difference signal S5), and the block reproduction difference signal An addition circuit 16 for adding a predicted image (block image signal S3) from a motion compensation circuit 18 to be described later to S5, and a P which belongs to the current GOP together with the quantization coefficient (coded signal S4). Past of GO at the time of the Kucha of encoding
A flag indicating whether encoding is performed using the decoded image belonging to P (random access enable instruction flag S
9) and a variable-length encoder 19 for performing variable-length encoding.

First, the picture coding apparatus according to the present embodiment shown in FIG. 1 (that is, the motion compensation prediction coding apparatus to which MPEG2 is applied) will be described in detail.

In FIG. 1, an image signal input from a moving image input terminal 10 is transmitted to the field memory group 11.
Supplied to and stored. This stored image signal is
Motion prediction circuit 12 and motion compensation circuit 18 on a field basis
Sent to

The motion prediction circuit 12 calculates the motion prediction of the pixel in the image which is the current encoding target (current field) for the image signal stored in the field memory group 11 by using the past image. (Past field) and a future image (future field). here,
The motion prediction is performed by block matching between a pixel signal of a block composed of, for example, 16 × 16 pixels in a current image to be coded and a past image or a future image to be referred to. Further, the motion prediction circuit 12
The block position in the reference image when the prediction error in the block matching is minimum is supplied to the motion compensation circuit 18 as a motion vector S7.

The motion compensating circuit 18 instructs the output of a block image signal S3 located at the address specified by the motion vector S7 from a field memory group 17 in which an image already decoded and reproduced is stored. . Also, the block image signal S3 from the motion compensation circuit 18
Is an adaptive operation, and it is possible to switch from the following four modes to the optimum mode in block units.

That is, the four modes are, first, a motion compensation mode from a past reproduced image, second, a motion compensation mode from a future reproduced image, and third, from a past and future reproduced image. Motion compensation mode (the reference block from the past reproduced image and the reference block from the future reproduced image
A linear operation (for example, an average value calculation) is performed for each pixel. )When,
The fourth mode is a mode without motion compensation (that is, an intra-picture encoding mode).

At the time of switching between these modes in the motion compensation circuit 18, for example, each of the block pixel signals output in the above four types of modes and the current block pixel signal to be encoded is set for each pixel. The mode in which the sum of the absolute values of the difference values is the smallest is selected. The mode selected by this mode switching is output as the motion compensation mode signal S8.

On the other hand, the current block pixel signal S1 to be coded, supplied from the field memory group 11,
From the block pixel signal S3 supplied from the field memory group 17 via the motion compensation circuit 18 as described above, a difference value for each pixel is calculated by the differentiator 13;
The resulting block difference signal S2 is the difference signal encoder 1
4

The difference signal encoder 14 converts the block difference signal S2 into a predetermined transform coefficient, quantizes the transform coefficient, and outputs a coded signal S4.

The coded signal S4 is transmitted to the variable length encoder 19 together with the motion vector S7 from the motion prediction circuit 12 and the motion compensation mode S8 from the motion compensation circuit 18, and is output to a variable length encoder 19 such as a Huffman code. The data is subjected to long coding and output from the output terminal 20 as a bit stream.

The coded signal S4 is also supplied to a difference signal decoder 15. The difference signal encoder 15
Then, the coded signal S4 is inversely quantized, the inversely quantized coefficient is further subjected to an inverse transform corresponding to the conversion to the predetermined transform coefficient, and the encoded signal is decoded to decode the block reproduction difference signal S4.
5 is formed.

The specific configuration of the difference signal encoder 14 is as follows. The block difference signal S2 is a DCT by discrete cosine transform as a predetermined transform coefficient.
Discrete cosine converter (DC
T) and a quantizer for quantizing the output coefficient (DCT coefficient). Therefore, as a specific configuration of the difference signal decoder 15 in this case, a configuration including an inverse quantizer and an inverse discrete cosine transformer (IDCT) for inversely transforming the DCT coefficient is applied.

The block reproduction difference signal S5 from the difference signal decoder 15 is sent to the addition circuit 16. In the addition circuit 16, the block reproduction difference signal S5 and the block image signal S3 output from the motion compensation circuit 18 are added for each pixel, and as a result, the block reproduction signal S6 is output from the addition circuit 16. Is obtained. The block reproduction signal S6 is stored in the field memory group 1
7 is stored in the designated field memory.

The above is the basic configuration and operation of the image coding apparatus (motion-compensated prediction coding apparatus) according to the present embodiment.

Here, a moving image unit composed of the GOP (Group Of Picture) is applied to a moving image input to the apparatus of the present embodiment.

Hereinafter, the picture structure of the GOP is shown in FIG.
The motion compensation prediction process in the case of the GOP1 configuration indicated by X in FIG. Note that Y in FIG. 2 indicates the first stage of motion compensation prediction, and Z in FIG. 2 indicates the second stage of motion compensation prediction. Each picture is composed of a frame or a field, an I picture is indicated by i in FIG.
Pictures are indicated by p in the figure, and B pictures are indicated by b in the figure.
The definitions of the I picture, P picture, and B picture are the same as described above. Furthermore, the arrows connecting the pictures in the figure indicate the direction of motion prediction, and the dotted hatched lines in the figure indicate the GOP.
Indicates a break.

First, the first motion compensation prediction shown in Y of FIG.
In the processing of the second stage, for example, prediction is performed from an I picture or a P picture which is a past reproduced image by skipping several B pictures. In the second stage processing shown in Z of FIG. 2, the I picture or the P picture before and after reproducing the coded image in the first stage processing is referred to, and there is a gap between them. Predictive coding of the sandwiched B picture is performed.

More specifically, in the case of GOP1 of FIG. 2, for example, the picture i12 and the picture p03 are referred to at the time of motion prediction and motion compensation of the picture p13 in the first-stage processing. The picture p03 is a picture belonging to the past GOP0.

At this time, if random access to the GOP1 (reproduction from the middle) is to be enabled, reference to the picture p03 is prohibited. If random access to GOP1 is considered unnecessary, the picture p03
Use references. Note that the case of using the reference to the picture p03 is a case where the image quality is emphasized.

As another example of the GOP configuration, in the case of GOP1 shown in X of FIG. 3, for example, at the time of motion prediction and motion compensation of the picture p15 in the first stage processing shown in Y of FIG. The picture i12 and the picture p03 are referred to. The picture p03 is a picture belonging to the past GOP0. It should be noted that also in FIG.
Indicates the second-stage processing, and similarly to the above, an I picture is indicated by i in the figure, a P picture is indicated by p in the figure, and a B picture is indicated by b in the figure. The arrows connecting the pictures in the figure indicate the direction of motion prediction, and the dotted hatched lines in the figure indicate GOP breaks.

At this time, if it is desired to enable random access to the GOP1 (reproduction from the middle), reference to the picture p03 is prohibited. If random access to GOP1 is considered unnecessary, the picture p03
Use references. The case where reference to the picture p03 is used is a case where the image quality is emphasized.

The configuration and operation of the image encoding apparatus according to the present embodiment when a moving image is input in GOP units as shown in FIGS. 2 and 3 will be described.

Returning to FIG. 1, when the GOP start instruction signal S10 is inputted from the terminal 21, the GOP start code and the condition for enabling the random access to the GOP supplied via the terminal 24 are determined. The random access enable instruction flag S9 determined in advance by
The signal is input to the variable length encoder 19 via a switch 23 that is switched according to the GOP start instruction signal S10.

Therefore, in the variable length encoder 19 in this case, in addition to the motion vector S7, the motion compensation mode signal S8, and the coded signal S4, the random access enable flag S9 is also variable length coded. Output the obtained bit stream.

FIG. 4 shows the bit stream syntax (bit stream configuration method) in the GOP layer at this time.

In FIG. 4, based on the syntax (construction method) in MPEG1 described above, "closed_predi
ction_flag ”, the random access enable instruction flag S9 is output.“ reserved_bits ”is
Since group_extenstion_data is in 8-bit units,
This is because it is necessary to add 7 meaningless bits. Details of other codes are described in the MPEG1 standard.

Referring again to FIG. 1, when a GOP start instruction signal is input to the terminal 21, the picture counter 22 is reset. The picture counter 22 counts an I picture or a P picture output from the field memory group 11.

When the count value of the picture counter 22 becomes, for example, "2", a flag signal S11 is set to the motion compensation circuit 18. At this time, the motion compensation circuit 18 determines that the P picture to be currently encoded is a special P picture, in other words, 1
It is recognized that the picture is a P picture using the picture of the previous GOP as a reference picture, that is, a picture p13 in FIG. 2 and a picture p15 in FIG.

At this time, the motion compensation circuit 18 switches whether or not the prediction from the P picture belonging to the past GOP is possible according to the random access enable instruction flag S9.

Incidentally, in order to enable random access to all GOPs, prediction from P pictures belonging to past GOPs may be always prohibited. In this case, the random access enable flag S9 does not need to be added to the GOP header, and is not output from the variable length encoder 19.

The above is the description of the image coding apparatus according to the present embodiment.

Next, the image decoding method of this embodiment is as follows.
An image decoding method for decoding encoded data generated by encoding a difference signal between an original image and a past decoded image, wherein encoding of a P-picture belonging to a GOP is performed in the past. A flag (randomly accessible instruction flag) indicating whether or not the picture is coded using the decoded picture belonging to the GOP is detected from the header of the GOP, and the P picture of the current GOP is decoded to belong to the past GOP. It is to determine whether or not the image has been encoded using the encoded image.

That is, in the image decoding apparatus to which the image decoding method according to the present embodiment is applied, as shown in FIG. 5, an input mainly composed of an encoded difference signal supplied via a terminal 30 is provided. The header information added to the GOP is detected from the bit stream (the bit stream corresponding to the output from the terminal 20 in FIG. 1), and the random access enable instruction flag S26 in the header information is detected, whereby the GOP is determined. A header detector 37 for determining whether or not random access is possible, and decoding means for a variable length code to which the input bit stream is supplied when the header detector 37 determines that random access is possible And a variable length decoder 31 including an inverse quantization means for inversely quantizing an output of the decoding means and outputting an inverse quantization coefficient
A difference signal decoder 32 as an inverse transform unit for inversely transforming the inverse quantized coefficient from the variable length decoder 31 to form a decoded difference signal (block reproduction signal S21); And an addition circuit 33 for adding a decoded image signal (block image signal S22 from the motion compensation circuit 34) to be described later to the block reproduction signal S21 from the block 32.

The case where random access is performed on the image decoding apparatus side of the present embodiment shown in FIG. 5 will be described below. In the decoding device, the GOP header detector 37 first searches the input bit stream via the terminal 30 for the GOP header of the specified GOP, and adds the random access enable instruction of FIG. The random access enable instruction flag S26 corresponding to the flag S9 is checked.

The random access enable instruction flag S2
If it is determined from step 6 that random access is impossible, the search for a randomly accessible GOP temporally closest to the designated GOP is continued.

Here, when it is determined from the random access enable instruction flag S26 that random access is possible, in the case of the GOP structure like GOP1 in FIGS. 2 and 3 described above, the P picture belonging to the GOP is When encoding, it is recognized that prediction from a picture belonging to a past GOP is not used.

In this case, the input bit stream is supplied to the variable length decoder 31 via the switch 38 which is switched according to the random access enable instruction flag S26. In the variable length decoder 31, the coding difference signal S4, the motion vector S7, and the motion compensation mode signal S9 respectively corresponding to the coding difference signal S4, the motion vector S7, and the motion compensation mode signal S9 in the image coding apparatus of FIG. S25 is decrypted.

The coded difference signal S20 is sent to the next difference signal decoder 32, where it is decoded to become a block reproduction difference signal S21 corresponding to the coded signal S4 in FIG.

As a configuration of the differential signal decoder 32, a configuration including an inverse quantizer and an inverse discrete cosine transformer is applied in accordance with the above-described image encoding apparatus. However, other configurations can be applied as long as they are consistent with the image encoding device side.

The block reproduction difference signal S 21 is sent to the addition circuit 33. In the adder circuit 33, a block image signal formed by a motion compensation circuit 34 based on the motion vector S24 and the motion compensation mode signal S25 from the variable length decoder 31 and an output from a field memory group 35 described later. S22 and the block reproduction difference signal S
21 is added for each pixel, and as a result, a block reproduction signal S23 is obtained. Block reproduction signal S2
3 is sent to the field memory group 35 and stored in the designated field memory.

The reproduced image stored in the field memory group 35 is then output from the output terminal 36 and sent to, for example, an image display system.

As described above, in the image decoding apparatus (motion-compensated predictive decoding apparatus) of this embodiment, the GOP
Random access is performed in units.

Further, in the above-described embodiment,
As shown in FIG. 4, after the extension_start_code, “closed” is used as information as to whether or not the P picture is performing prediction using a picture belonging to the previous GOP.
_Prediction flag ”and“ reserved_bits ”are provided, but closed_gop may also be used.

In the image decoding method and apparatus according to the present embodiment, in order to enable random access to all GOPs, prediction from P pictures belonging to the past GOP is always prohibited. , Switch 38
Will always be closed. That is, in the image decoding method and apparatus according to the embodiment of the present invention, a block image signal of an intra-coded intra field (S22) of a GOP in which a plurality of fields having a field structure are put together or a past forward prediction field of a past is predicted. The block image signal (S22) and the block reproduction signal (S21) of the forward prediction field forming one frame with the intra field are added by the adding circuit 33 to obtain a block reproduction signal of one field. , When the intra field is the first intra field of the GOP, the GOP to which the intra field belongs
The addition of the forward prediction field belonging to the previous GOP to the block reproduction difference signal (S21) is prohibited.

Although not shown, encoded data and the like formed in the image encoding apparatus as described above are
For example, the image data can be stored in a so-called magneto-optical disk, magnetic tape, optical disk, semiconductor memory, IC card, or the like as an image recording medium, and data can be read from the image recording medium in the above-described image decoding device.

[0069]

According to the present invention, a block image signal of an intra-coded intra field or a block image signal of a past forward prediction field of a group obtained by grouping a plurality of fields having a field structure, and the intra field In the image decoding method and apparatus for obtaining a one-field block reproduction signal by adding the intra-field and the block reproduction difference signal of the forward prediction field forming one frame, the intra-field is the first intra-field of the group. Prohibiting the addition of the forward prediction field belonging to the past group of the group to which the intra field belongs to the block reproduction difference signal, that is, the image decoding side encodes the difference decoding signal of the P picture belonging to the GOP. When it belongs to the current GOP It predicted only by a decoded picture of an intra field, in other words, by always prohibited prediction from pictures which belong to a past GOP,
Random access to all GOPs is enabled.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram illustrating a schematic configuration of an image encoding device according to an embodiment.

FIG. 2 is a diagram illustrating an example of prediction according to the present embodiment.

FIG. 3 is a diagram for explaining another example of prediction in the present embodiment.

FIG. 4 is a diagram illustrating bit stream syntax in a GOP layer.

FIG. 5 is a block circuit diagram illustrating a schematic configuration of an image decoding device according to the present embodiment.

FIG. 6 is a diagram illustrating an example of an arrangement of picture types in a GOP.

FIG. 7 is a diagram for explaining a GOP header.

FIG. 8 is a diagram for explaining an example of an arrangement of picture types in a GOP when a picture structure is a field.

[Explanation of symbols]

11, 17, 35 Field memory group, 12, 34
Motion prediction circuit, 13 difference unit, 14 difference signal encoder, 15 difference signal decoder, 16, 33 addition circuit, 18, 34 motion compensation circuit, 19 variable length encoder, 22 picture counter, 23, 38
Switch, 31 variable length decoder, 32 difference signal decoder, 35 adder, 37 header detector, S
1, S3, S22 block image signal, S2 block difference signal, S4 encoded signal, S5, S21 block reproduction difference signal, S6, S23 block reproduction signal, S7, S24 motion vector, S8, S25 motion compensation mode signal, S9, S26 random access enable instruction flag, S10 GOP start instruction signal,
S11 flag signal, S20 coded difference signal

Claims (8)

[Claims] An intra-coded block image signal of an intra-field or a block image signal of a past forward prediction field of a group in which a plurality of fields having a field structure are put together, and one frame with the intra field. In the image decoding method of adding a block reproduction difference signal of a forward prediction field to obtain a block reproduction signal of one field, when the intra field is the first intra field of the group, the intra field of the group to which the intra field belongs An image decoding method, wherein addition of a forward prediction field belonging to a past group to a block reproduction difference signal is prohibited. 2. An intra-coded block image signal of an intra-field or a block image signal of a past forward prediction field of a group obtained by grouping a plurality of fields having a field structure, and one frame with the intra field. In an image decoding apparatus which obtains a block reproduction signal of one field by adding the block reproduction difference signal of the forward prediction field and the block reproduction difference signal of the forward prediction field, when the addition is performed by the addition means, the intra field is located at the head of the group. An image decoding apparatus characterized in that when an intra-field is an intra-field, addition of a forward prediction field belonging to a past group of a group to which the intra-field belongs to a block reproduction difference signal is prohibited. 3. A predicted image signal is generated using only the decoded image signal of the first field that has been intra-coded, and a second image forming one frame with the first field is generated.
An image decoding method comprising: decoding a coded signal of the field of the second field; and adding a signal obtained by decoding the coded signal of the second field and the predicted image signal. 4. The image decoding apparatus according to claim 3, wherein the signal obtained by decoding the predicted image signal and the coded signal of the second field is a signal in a block unit including a plurality of pixels. Method. 5. The first field is a first intra-coded image in a group obtained by combining a plurality of images, and the second field is a first forward prediction-coded image in the group. 4. The image decoding method according to claim 3, wherein: 6. A predicted image generating means for generating a predicted image signal using only a decoded image signal of a first field that has been intra-coded, and a second image forming one frame with the first field.
A decoding means for decoding the coded signal of the second field, and an adding means for adding the signal obtained by decoding the coded signal of the second field and the predicted image signal. apparatus. 7. The image decoding apparatus according to claim 6, wherein a signal obtained by decoding the predicted image signal and the coded signal of the second field is a block unit signal including a plurality of pixels. Device. 8. The first field is a first intra-coded image in a group in which a plurality of images are combined, and the second field is a first intra-coded image in a group in which the plurality of images are combined. The image decoding apparatus according to claim 6, wherein the image is a forward prediction encoded image.