JPH0831960B2 - Still image coding method and apparatus - Google Patents

Description

The present invention relates to a method for encoding and decoding still images by connecting a still image encoding device and a moving image decoding device to each other, and a method thereof. It relates to a device to be implemented.

(Prior Art) Conventionally, in the communication of a still image in a teleconference or the like, a still image communication station and a still image communication station communicate with each other by a still image encoding device and a still image decoding device. . Alternatively, between the moving image communication stations, communication is performed in a still image mode prepared in advance in both the moving image encoding device and the moving image decoding device.

(Problems to be Solved by the Invention) However, in still image communication in a conventional teleconference or the like, since the encoding processing methods of the still image encoding device and the moving image decoding device are different, the still image communication station is The still picture communication station and the moving picture communication station are carried out in the closed areas of the moving picture communication station and the moving picture communication station, respectively, and communication across both the still picture station and the moving picture station is infeasible, which is very inconvenient.

In view of the above-mentioned drawbacks, a technical problem of the present invention is to provide a still image coding method and apparatus for realizing communication between a still image encoder and a moving image decoder.

(Means for Solving the Problem) According to the present invention, intraframe coding is performed on a still image by n lines for each frame, and it is shown that regions other than the n lines are invalid lines between frames. A still image encoding method is obtained, which is characterized in that encoding is performed by substituting for a code.

That is, according to the first invention of the present application, in still image coded transmission, an area determined at every arbitrary time is coded using correlation in the screen, and the area other than the coded area is coded. There is provided a still image coding method characterized in that coding is performed in a state where there is no change when the correlation between screens is used.

Further, according to the second invention of the present application, in encoding a still image, a unit for storing the first still image and n for each frame based on the correlation in the screen with respect to the output of the unit for storing the still image. Intra-frame encoding means for moving line by line and encoding, first code conversion means for converting the intra-frame encoded signal so as to reduce redundancy, and intra-frame encoding not performed in the screen For a region other than the n-th line, a second code conversion unit that generates a code indicating that there is no change between screens, or one of the outputs of the first code conversion unit and the second code conversion unit is displayed. There is provided a still image coding device comprising: a selecting unit for selecting; and a controlling unit for controlling the operation of the selecting unit and the unit for storing the still image.

(Outline of the Invention) As shown in FIG. 1, a still image encoding device 40 and a moving image decoding device 41 include a transmission path 42 for a still image having a low transmission rate.
Tied with. When the still image to be transmitted is input, the still image encoding device 40 encodes the input image little by little, and gradually passes the encoded data to the transmission path 42. This is because the transmission rate of the still image transmission path 42 is very low, and a large amount of data cannot be instantaneously passed.

On the other hand, a moving image encoding device (not shown). In order to remove the influence of noise and distortion caused by encoding, or code error on the transmission path, periodic image rewriting (refreshing) is performed. As shown in FIG. 2, refreshing is performed by intra-frame coding using intra-frame correlation while moving n lines by a predetermined screen (every time), and a new image is written in the frame memory. Get caught. In the areas other than the refresh area, inter-frame coding is performed using the correlation between screens.

Therefore, in the still image encoding according to the present invention, the above-mentioned refresh mode is used to perform the encoding so that the moving image decoder can perform the decoding.

That is, when encoding a still image, the still image to be transmitted is written in the frame memory 1 that stores the still image as shown in FIG. Then, the intra-frame encoder 2 using the correlation in the screen performs coding while moving n lines for each frame. The intra-frame encoded signal b,
The first code converter 4 further reduces redundancy by using an efficient code such as Huffman code. In the areas other than the n-line in which the intra-frame coding is not performed, the second area is used to express that there is no change between the screens.
In the code converter 5, it is replaced with a code indicating an invalid line between frames. When encoding,
The control circuit 3 includes a frame memory 1, an intraframe encoder 2,
By controlling the second code converter 5 and the selector 6, the following operation is performed.

The control circuit 3 gives the frame memory 1 a read command c for controlling the reading of the image to be encoded.
The frame memory 1 reads the image signal a only when the read command c instructs reading of the image signal a. The control circuit 3 further provides the intra-frame encoder 2 and the second transcoder 5 with an encoding execution stop signal d for controlling the execution stop of the intra-frame encoding. Intraframe encoder 2
Performs intra-frame encoding when the encoding execution stop signal d given from the control circuit 3 indicates the execution of encoding. When the encoding execution stop signal indicates that the encoding is stopped, the intraframe encoder 2 does nothing and enters the stopped state. The second code converter 5 generates a code e indicating an invalid line between frames corresponding to the coding execution stop signal and supplies the code e to the selector 6. Control circuit 3
The coding execution stop signal d given by the above-mentioned code moves by n lines for each frame. Further, when the control circuit 3 gives a signal indicating execution of intraframe coding to the intraframe encoder 2, it gives the selector 6 a switching signal f for selecting the output of the first code converter 4, and the intraframe code. Then, the signal g which has been coded and code-converted is selected. When the intra-frame coding is stopped, the switching signal f for selecting the output of the second code converter 5 is given to the selector 6.

In this way, the intra-frame encoding is performed for each n lines for each frame, and the regions other than the n lines are replaced with the codes indicating the invalid lines between the frames to perform the encoding. This can be equivalent to the case where encoding is performed with a moving image encoder using the correlation of.

On the other hand, on the receiving side, the image portion that is rewritten when it receives the above code can be decoded by the refresh mode using the intraframe decoding of the moving image decoding apparatus.

As the decoding device, as shown in FIG. 4, a normal moving image decoding device 41 using the correlation between screens and the correlation within the screen can be used.

The code transmitted from the transmitting side is subjected to inverse code conversion by the inverse code converter 7 and sent to the inverse quantizer 8. Further, the inverse code converter 7 generates a selection signal (flag) indicating whether the line has been intra-frame coded or inter-frame coded and selected as the selection signal h of the decoder. Supply to the vessel 12. The differential signal i inversely quantized by the inverse quantizer 8 is added with the prediction signal j given from the selector 12 by the adder 9 to become a decoded signal k. Decoded signal k
Is output as the output of the decoding device and is also sent to the intraframe decoder 10 and the interframe decoder 11. The intra-frame decoder 10 generates a prediction signal l _-1 from an encoded signal such as the previous pixel or the previous line in the screen, and the selector 12
Give to. The interframe decoder 11 delays the decoded signal k sent from the adder 9 for one frame time and _supplies it to the selector 12 as an interframe prediction signal l _-2 . The selector 12 selects the prediction signals l _-1 and l _-2 according to the selection signal h supplied from the inverse sign converter 7.

In this way, for example, at the time t in FIG. 2, the refreshed area is subjected to interframe coding at the time t + m, and the refresh line moves to the next area. However, since the line on which the inter-frame coding is executed is replaced with the invalid data when the coded data is coded, the inter-frame predicted signal l _-2 becomes the output signal of the decoding device as it is. Therefore, at time t + m, the signal refreshed at time t stored in the interframe encoder becomes the output of the decoding device as it is. Then, the refresh area at time t + m is added. In the line for decoding between frames in this way, since the differential signal i sent from the transmitting side is invalid data, a signal refreshed up to the previous frame is output.
Then, the signal refreshed in this frame is added, the refresh area is moved by n lines for each frame, the area of the refreshed new image is gradually expanded, and this is repeated to obtain one image. To form.

When the intra-frame encoder 2 uses transform coding such as orthogonal transform, the decoding device 41 may have a configuration as shown in FIG. Inverse code converter 7 and inverse quantizer 8
Operates in the same manner as described above. The output of the inverse quantizer 8 is given to the adder 9 and the intraframe decoder 10. The output of the adder 9 is given to one input of the selector 12.
The output of the intraframe decoder 10 is supplied to the other input of the selector 12. The selector 12 selects either the output of the intraframe decoder 10 or the output of the adder 9 according to the selection signal h given from the inverse code converter 7. Selector 12
The output signal of is output as the output of the decoding device 41 and is given to the interframe decoder 11. The interframe decoder 11 delays the signal given from the selector 12 by one frame and sends it to the adder 9. In-frame decoder in this case
10 is an intraframe encoder used on the transmitting side (see FIG. 3)
Inverse conversion of 2.

As described above, the still image encoding device 40 performs intra-frame encoding while moving n lines for each frame, and indicates that areas other than n lines in the screen are invalid lines between frames. By substituting with the code and performing the encoding, the receiving side can perform the decoding in the refresh mode using the intra-frame decoding of the moving image decoding apparatus 41.

(Example) Next, an example of the present invention will be described in detail.

FIG. 6 is a block diagram of the encoder of this embodiment. The input image signal is supplied to the frame memory 1 via the line 100. The frame memory 1 reads out the image data only when the read control signal c supplied from the control circuit 3 through the line 31 instructs the reading of the image,
It is supplied to the intraframe encoder 2 via 12.

When the intraframe encoder 2 uses the predictive coding method, the configuration is as shown in FIG. The image signal a read from the frame memory 1 according to the image reading instruction is supplied to the subtractor 21 via the line 12. Subtractor 21
Subtracts the image signal a supplied from the frame memory 1 and the intra-frame prediction signal p supplied from the intra-frame predictor 23 to obtain the intra-frame difference signal Q. Subtractor
The intraframe difference signal Q obtained in 21 is supplied to the quantizer 22. The quantizer 22 quantizes the intraframe difference signal Q supplied from the subtractor 21 and supplies it to the code converter 4 via the line 24 as an output of the intraframe predictor and to the intraframe predictor 23. Supply. In-frame predictor
23 generates an intra-frame prediction signal p from a pixel in the vicinity of the pixel to be encoded, for example, a previous pixel or a previous line pixel, and supplies the intra-frame prediction signal p to the subtractor 21. The quantizer 22 and the intra-frame predictor 23 execute their respective functions when the encoding execution stop signal d supplied from the control circuit 3 via the line 32 indicates the execution of encoding. When the encoding execution stop signal indicates the stop of encoding, each function is stopped. That is, the quantizer 22
And the intra-frame predictor 23 sets the output to zero.

Next, the control circuit 3 will be described with reference to FIG.

The clock oscillator 300 generates a reference clock and supplies it to the line counter 310. The line counter 310 divides the frequency of the clock supplied from the clock oscillator 300 and counts the line number. For example, if the number of pixels per screen is 256 samples × 240 lines, the line number is updated by 1 every 256 clocks and counted, and when counting up to 240 lines, it returns to the first line number. The line number obtained by the line counter 310 is supplied to the address of the lower bit of the ROM (Read Only Memory) 330 via the line 3133. Further, the line counter 310 generates a carry once for every 240 lines and supplies it to the frame counter 320 via the line 3132.

Frame counter 320 is line counter 310 to line 31
Each time a carry signal is supplied via 32, the frame number is updated by 1 and counted up. The frame number obtained by the frame counter 320 is supplied to the upper bit address of the ROM 330 via the line 3233. The ROM 330 generates a control signal for executing intraframe coding. In order to perform the intra-frame encoding while moving by n lines for each frame, a line to be encoded is determined in advance for each frame and a signal for executing the intra-frame encoding, for example, 1 is written at the address. The intra-frame coding execution signal moves to the line determined for each frame. The area of the screen where intra-frame coding is not performed is the address 0 of that line.
Is written. The intra-frame encoding execution signal thus generated is supplied to the frame memory 1 via the line 31 as the read control signal c for the frame memory. Further, the intra-frame coding execution signal generated in the ROM 330 is supplied to the delay 340. The delay 340 is a delay corresponding to the delay time from when the read control signal c is supplied to the frame memory 1 to when the data is supplied to the intraframe encoder 2 with respect to the intraframe encoding execution signal supplied from the ROM 330. Make compensation. The output signal d of the delay 340 is supplied to the intraframe encoder 2 and the code converter 5 as a coding execution stop signal via the line 32, and is also supplied to the delay 350. The delay 350 is a delay time from the coding execution stop signal is supplied to the intraframe encoder 2 to the output of the data in which the intraframe coding is executed, with respect to the coding execution stop signal, The code converter 4 compensates for a delay corresponding to the delay time required for code conversion. The output of the delay 350 is the line 3 as the selection signal f of the first and second transcoders 4 and 5.
It is supplied to the selector 6 via 6.

Returning to FIG. 6, the first code converter 4 performs code conversion of the quantized intra-frame differential signal b supplied from the intra-frame encoder 2 using an efficient code such as Huffman code. Then, it is supplied to the selector 6 via the line 46. Second
When the coding execution stop signal d supplied via the line 32 indicates the stop of the coding, the code converter 5 always uses the efficient code such as the run-length code and invalidates it between the frames. The code e indicating that it is a line is generated. The output of the transcoder 5 is supplied via line 56 to the selector 6. The selector 6 selects the first and second code converters 4 and 5 according to the selection signal f supplied from the control circuit 3. When the selection signal f supplied from the control circuit 3 instructs to select the signal g which is code-converted by performing the intra-frame coding at 1, the output signal of the first code converter 4 is changed. select. When the selection signal is 0 and the selection of the code e indicating the invalid line between frames is instructed, the output of the second code converter 5 is selected. Selector 6
The output of is supplied to the transmission line via line 60.

Next, the decoding device will be described with reference to FIG.

The decoding device shown in FIG. 9 is a normal moving image decoding device 41 that utilizes intra-picture correlation and inter-picture correlation.

The signal sent from the transmitting side is supplied to the inverse code converter 7 via the line 700. The inverse sign converter 7 performs inverse sign conversion and supplies the inversely converted signal to the inverse quantizer 8.
Further, the inverse code converter 7 generates a signal h indicating whether the signal has undergone intra-frame coding or inter-frame coding from the code, and the selection signal of the decoders 10 and 11 is generated. Is supplied to selector 12 via line 712. The inverse quantizer 8 inversely quantizes the signal supplied from the inverse code converter 7, and supplies the obtained difference signal i to the adder 9. The adder 9 adds the difference signal i supplied from the dequantizer 8 and the prediction signal i supplied from the selector 12 to obtain a decoded signal k.
Get. The decoded signal k output from the adder 9 is supplied to the intraframe decoder 10 and the interframe decoder 11. Also,
The decoded signal k output from the adder 9 is output via line 900 as the output of the decoding device. The intra-frame decoder 10 temporarily stores the decoded signal k supplied from the adder 9 and predicts an intra-frame prediction signal from a pixel in the vicinity of the pixel to be decoded, for example, the previous pixel or the previous line pixel. l _-1
Is generated and supplied to the selector 12 via the line 1012. The prediction function of the intraframe decoder 10 is the same as that of the intraframe encoder 2. The interframe decoder 11 includes an adder 9
The decoded signal k supplied from (1) is delayed by one frame and is supplied to the selector 12 via the line 112 as an inter-frame predicted signal l _-2 . The selector 12 selects a prediction signal according to the selection signal h supplied from the inverse code converter 7. The prediction signal i output from the selector 12 is supplied to the adder 9.

In the above description, the predictive coding method is used as the intra-frame encoder 2, but of course other methods such as orthogonal transform can be applied. At this time,
The function of the intra-frame predictor 23 and the function of the subtracter 21 included in the intra-frame encoder 2 may be deleted, and instead, a conversion circuit may be provided for the input signal and the conversion result may be quantized. As the decoding device, a decoding device as shown in FIG. 5 may be used. The conversion method is not limited to Hadamard conversion, DCT, and others.

(Effects of the Invention) As described above, by using the still image coding method or coding device of the present invention, decoding can be performed by a normal moving image decoder, and a still image encoder and a moving image can be used. Communication with the image decoder is possible. Therefore, the still image station can be expanded to a still image station, and the moving image station can be expanded to a moving image station.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a connection relationship between a still image encoding device and a moving image decoding device of the present invention, FIG. 2 is a conceptual diagram showing periodical image refresh of the present invention, and FIG. 3 is a book. FIG. 4 is a block diagram showing the concept of the invention, FIG. 4 is a block conceptual diagram of an ordinary moving image decoding apparatus, FIG. 5 is an ordinary decoding apparatus used when transform coding is used as an intraframe encoder, and FIG. 6 is FIG. 7 is a block conceptual diagram according to an embodiment of the present invention, FIG.
FIG. 8 is a block conceptual diagram of an intra-frame encoder when the predictive coding system of the embodiment shown in FIG. 8 is used, FIG. 8 is a block conceptual diagram of a control circuit of the embodiment shown in FIG. 6, and FIG. 9 is an implementation shown in FIG. It is a block conceptual diagram of the normal moving image decoding apparatus used for an example. 1 ... Frame memory, 2 ... In-frame encoder, 3 ...
... control circuit, 4 ... second code converter, 5 ... second code converter, 6 ... selector, 7 ... inverse code converter, 8 ... inverse quantizer, 9 ... adder, 10 ... In-frame decoder, 11 ...
… Frame intercompositor, 12 …… Selector, 21 …… Subtractor, 22
... Quantizer, 23 ... intra-frame predictor, 300 ... clock oscillator, 310 ... line counter, 320 ... frame counter, 330 ... ROM, 340 ... delay, 350 ... delay.

Claims (2)

[Claims] 1. A still image is intra-frame-encoded by n lines for each frame, and the region other than the n lines is replaced with a code indicating an invalid line between the frames for encoding. A method for encoding a still image, which is characterized by being performed. 2. In encoding a still image, a means (1) for storing a first still image and n lines for each frame based on the correlation in the screen with respect to the output of the means (1) for storing the still image. An intra-frame encoding means (2) for moving and encoding each frame, a first code conversion means (4) for converting the intra-frame encoded signal so as to reduce redundancy, and an intra-frame code in the screen. The second code conversion means (5), which generates a code indicating that there is no change between screens, in the areas other than the n lines that have not been encoded, the first code conversion means (4), and the first code conversion means (4). A still image coding device, comprising: a selection unit (6) for selecting one of the outputs of the second code conversion unit (5).