JP2643285B2 - Image transmission device, image reception device, image transmission system, and image transmission method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image transmission system suitable for retransmission.

2. Description of the Related Art When digitally transmitting image data using a telephone line or the like, a transmission error may occur due to noise in a transmission line or the like. An error detection code is added to the data to be transmitted in advance, and when a transmission error is detected on the receiving side, the receiving side requests retransmission of the image data from the transmitting side, and the transmitting side retransmits all the image data accordingly. When transmitting, the transmission time is more than twice as long as there is no error.

To solve this problem, conventionally, Japanese Patent Application Laid-Open No. 58-42375
As described in the publication, each horizontal scanning period of the screen corresponding to the contents of the image memory is divided into m blocks, and an address and an error detection code are added for each block and transmitted. An error is detected on the receiving side. In such a case, after receiving all the data in the image memory, the retransmission method is used in which the address of the block in which the error is detected is returned to the transmitting side, and only the data of the block corresponding to the address is retransmitted.

[Problems to be Solved by the Invention] On the other hand, when trying to transmit a natural image using a low bit rate line such as a telephone line, there is a problem that it takes a long time to transmit because of a large amount of data. For example, 1
Data compression to 3 bits per pixel, horizontal 512 pixels x vertical 2
9600 bits used for facsimile, etc. for 40 pixel images
It takes about 40 seconds to transmit in seconds.

Therefore, by processing still images hierarchically, transmitting coarse images at high speed and then gradually sending finer images,
There is a transmission method using hierarchical coding that reduces the psychological burden on the receiver. This transmission method has the following configuration, as described in Norihiko Fukinuki "Encoding of Still Images", IEICE Journal Vol. 67, No. 1, January 1984.

First, N = 2 ⁿ pixels are made into one block, and converted into frequency components by orthogonal transform such as discrete cosine transform. Next, the DC component of each block is encoded and transmitted over the entire screen. Then, by sequentially transmitting the low-frequency components to the high-frequency components in order, a coarse screen is displayed at a high speed on the receiving side at first, and the images are sequentially sharpened.

However, when the above-described retransmission scheme is applied to a transmission scheme using hierarchical coding, the following problems arise.

Blocks with transmission errors during transmission of low-frequency components are:
Even if the subsequently transmitted high-frequency component can be received without error, an image different from the original image is displayed. Since retransmission is performed after transmitting the data of the entire screen, an error-free image cannot be displayed at least until the transmission of the high-frequency component is completed. For example, when the data amount of the low-frequency component is 0.25 bits per pixel and the data amount of the high-frequency component is 2.75 bits per pixel, the transmission of the high-frequency component takes about 35 seconds. Will be seen.

An object of the present invention is to solve the above-described problems of the prior art, and to perform retransmission before transmitting a high frequency component or while transmitting a high frequency component even if there is a transmission error in transmission of a low frequency component. It is an object of the present invention to provide an image transmission system in which a receiver cannot show an abnormal screen for a long time, and an image transmission system employing this system.

[Means for Solving the Problems] In order to achieve the above object, an image transmitting apparatus according to the present invention includes a dividing unit that divides a screen into a plurality of blocks, and an image for each block decomposed by the dividing unit. A conversion unit that converts the data into data for each area; and a transmission packet formed by the converted data, the block address, and the error detection data in the block converted by the conversion unit, and transmits an image for each block to the reception side. The transmitting unit transmits the data of the low-frequency region of the image in the converted block converted by the converting unit as the data of the transmission packet for each block. A first transmission unit that transmits the block address of the transmission packet in which the error is detected from the receiving side; The data in the high-frequency region together with the data in the low-frequency region of the image of the block of the transmission packet is transmitted as the data in the transmission packet. For the transmission packet in which the error is not detected, the transmission packet in which the error is not detected. And a second transmission unit for transmitting data in a high-frequency region of the image of the block as the data of the transmission packet.

Further, another image transmitting apparatus according to the present invention includes a dividing unit that divides a screen into a plurality of blocks, a converting unit that converts an image into data for each frequency domain for each block divided by the dividing unit, A transmitting unit configured to form a transmission packet with the converted data, the block address, and the error detection data in the block converted by the unit and transmit an image to a receiving side, wherein the transmitting unit includes: An error is detected from the first transmission unit that transmits the data in the low-frequency region of the image in the converted block converted by the conversion unit as the data of the transmission packet for each block, and the reception side. When the block address of the transmitted packet is returned, the data in the low frequency region of the image of the block of the transmitted packet in which the error was detected is transmitted again. After, it is characterized in further comprising a second transmission means for transmitting the data of the high-frequency portion of the image of each block. In this case, the second transmission unit may determine that the transmission packet in which the error has been detected is:
It is desirable to repeat transmission of data in the low-frequency region of the image of the block until the error is no longer detected, and then transmit data in the high-frequency region of the image of each block.

Further, the image receiving apparatus according to the present invention is an image receiving apparatus that receives data in a low-frequency area and data in a high-frequency area for each block obtained by dividing a screen, wherein the received data is the data in the low-frequency area. Output means for outputting area information indicating whether the data is high-frequency area data and a block address of the data; holding means for holding the area information output by the output means corresponding to the block address; And determining means for determining the frequency domain of each block, which requests the transmitting side to transmit data next according to the held content held by the means. After receiving the data in the low-frequency region of the image of the block, the determination unit determines, for the block whose holding content held by the holding unit indicates unreceived, the data in the low-frequency region of the image of the block. Requesting the transmission of both data in the high-frequency area and requesting the transmission of the data in the high-frequency area when the held content held in the holding means is area information indicating the data in the low-frequency area. Requesting means. Alternatively, after receiving the data of the low-frequency area of the image of the block, for the block in which the holding content held in the holding means indicates unreceived, the determining unit determines the low-frequency area of the image of the block. Requesting means for requesting data transmission and requesting transmission of data in the high-frequency area if the held content of all blocks held in the holding means is area information indicating data in the low-frequency area; May be provided.

When the image in the block is transmitted three or more times, the high frequency region may be further divided into two or more regions.

Furthermore, the present invention provides a dividing unit that divides a screen into a plurality of blocks, a converting unit that converts an image into data for each frequency domain for each block divided by the dividing unit, and a block that is converted by the converting unit. An image transmitting apparatus including a transmission unit that forms a transmission packet with the converted data, the block address, and the error detection data and transmits an image to a receiving side, and the data in the low frequency region and the data in the high frequency region. An image transmission system comprising: an image receiving device that receives an image received by each of blocks obtained by dividing a screen.The transmission unit transmits, to the transmission packet, data in a low-frequency region of an image in a block after conversion by the conversion unit. A first transmission unit for transmitting the data as the data for each block, and a high-frequency area of an image in the converted block converted by the conversion unit. Second transmission means for transmitting the data of each block as the data of the transmission packet, and area information indicating whether the data is data of the low frequency area or data of the high frequency area. Area information adding means for adding to a transmission packet, the image receiving apparatus outputs, from the received transmission packet, the area information and the block address added to the transmission packet, and the output means Holding means for holding the area information output according to the block address corresponding to the block address, and requesting the image transmission device to transmit data in accordance with the held content held in the holding means; And a determination means for determining

According to the present invention, the first transmitting means transmits the data in the low-frequency region of the image in the block as the data of the transmission packet for each block, and the second transmitting means When the block address of the transmission packet in which the error is detected is returned from the side, the data in the high frequency region together with the data in the low frequency region of the image of the block of the transmission packet in which the error is detected, and the data of the transmission packet. As for the transmission packet in which the error is not detected, the data of the high frequency region of the image of the block of the transmission packet in which the error is not detected is transmitted as the data of the transmission packet. Therefore, the receiver can view an error-free coarse image using only the data in the low-frequency region in the block without waiting for a long time until the reception of the data in the high-frequency region in the block is completed.

According to another aspect of the present invention, the data in the low-frequency region of the image in the converted block converted by the conversion unit by the first transmission unit is transmitted as the data of the transmission packet for each block. When the block address of the transmission packet in which the error is detected is returned from the receiving side by the second transmission means, the data in the low-frequency region of the image of the block of the transmission packet in which the error is detected is transmitted again. After that, the data of the high frequency region of the image of each block is transmitted. In this case, an image different from the original image caused by incorrect data in the low-frequency area in the received block is not shown. Further, since retransmission is not repeated until no data error in the low frequency region in the block is eliminated, the total transmission time is shortened.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 8 is a block diagram of an apparatus for realizing the image transmission system represented by the present invention. FIG. 1A shows a transmitting device,
Is a transmission image memory, 2 is an encoding unit, 3 is an address addition unit, 4 is an error control code addition unit, 5 is a transmission unit, 6 is a transmission initialization unit, 7 is a retransmission address reception unit, and 8 is a transmission address memory. is there. FIG. 2B shows a receiving device.
9 is a receiving means, 10 is an error detecting means, 11 is an address extracting means, 12 is a decoding means, 13 is a receiving address memory, 14
Is retransmission address generation means, 15 is retransmission address transmission means,
16 is a retransmission address memory, 17 is a first stage data memory,
Reference numeral 18 denotes a reception image memory, 50 denotes a DCT memory, and 60 denotes reception initialization means.

FIG. 2 is a diagram showing a relationship between the transmission image memory 1 and an address. The image is decomposed into a plurality of small areas 20 to 27, and addresses A0 to A7 are assigned to each of the small areas. The reception image memory 18 has the same configuration as the transmission image memory 1.

FIG. 3A shows a configuration of the transmission address memory 8. The address column 30 stores an address to be transmitted. The area number column 31 stores the area number (described later) of each address. FIG. 3B shows the configuration of the reception address memory 13. The area number column 32 stores the area number of the received packet. Fig. 3 (c)
Shows the configuration of the retransmission address memory 16.
The address column 33 stores an address to be retransmitted. The area number column 34 stores an area number for which retransmission of each address is requested.

As shown in FIG. 7A, the small area 20 shown in FIG. 2 has luminance data X0 (0,0) in a space of 8 pixels horizontally and 8 pixels vertically.
~ X0 (7,7). Similarly, the small area 21 is X1 (0,
0) to X1 (7,7). The same applies to the small regions 22 to 27.

FIG. 7B shows the configuration of the DCT memory 50. Y0 (0,
0) to Y0 (7, 7) are the results of two-dimensional discrete cosine transform of the luminance data X0 (0, 0) to X0 (7, 7). 8
The × 8 two-dimensional discrete cosine transform and transform are defined by equations (1) and (2).

Y = AXA ^t (1) X = A ^t YA (2) The (A ^t is the transposed matrix of A) a result of the discrete cosine transform, and (0,0) consisting of only the following coefficients low frequency region D1, and a high frequency region D2 consisting coefficient (0,0) except for the following To separate. An area number D1 is assigned to the area D1, an area number D2 is assigned to the area D2, and an area number D3 is assigned to an area obtained by combining the areas D1 and D2. Each component is shown in FIG. 7 (c).

First, the outline of the operation of the image transmission apparatus of the first embodiment will be described with reference to the transmission / reception flowchart of FIG.

In the transmission / reception in the first stage, the area D1 is transmitted for all blocks constituting an image. (S10) In the second stage of transmission / reception, the remaining area D2 is transmitted for a block in which the area D1 has been transmitted without error, and the area D1 is added to the area D1 in addition to the area D2 for an error in the reception of the area D1. Is transmitted again (S11). Since the retransmission of the area D1 is performed while transmitting the area D2, the data of the erroneous area D1 can be retransmitted and corrected without waiting for the transmission of the area D2 to be completed.

In the third stage of transmission and reception, the area D2 is retransmitted for a block having an error in the reception of the area D2, and the area D1 and the area D2 are retransmitted for a block having an error in the reception of data combining the area D1 and the area D2. Is repeated until there is no reception error (S12, S13).

Next, a first-stage transmission operation of the image transmission apparatus according to the present embodiment will be described in detail.

Image data to be transmitted is written in the transmission image memory 1. The transmission initialization means 6 stores the addresses A0 to A7 of the small area to be transmitted and the area number D1 in the transmission address memory 8,
Writing is performed as shown in FIG.

The encoding means 2 first refers to the first column of the transmission address memory 8 shown in FIG.
Get D1. Next, two-dimensional discrete cosine transform is performed on the luminance data X0 (0,0) to X0 (7,7) of the small area 20 corresponding to the address A0, and the result is stored in the DCT memory 50. Next, the data string YOD1 of the area D1 of the DCT memory 50 (= Y0 (0,0))
Is output to the address adding means 3.

The address adding means 3 is a data string obtained by adding an address A0 and an area number D1 to the data string YOD1 of the area D1 of the DCT memory 50.
YO1a is output to the error control code adding means 4. The error control code adding means 4 adds a well-known CRC error control code to the data sequence YO1a, and transmits the transmission packet shown in FIG.
YO1 is generated and output to the transmitting means 5. Transmission means 5
This transmission packet YO1 is output to the telephone line. Thereafter, the encoding means 2 refers to the second column of the transmission address memory 8 shown in FIG. 4 (a) and refers to the luminance data X1 (0,0) to X1 (0) of the small area 21 corresponding to the address A1. 7,7) is converted to a two-dimensional discrete cosine transform, and the result is stored in DCT memory 50.
And the data string Y1D1 (= Y1) in the area D1 of the DCT memory 50.
(0, 0)) to the address adding means 3.

The address adding means 3 outputs the output data string Y of the DCT memory 50.
Data string Y11a with address A1 and area number D1 added to 1D1
Is output to the error control code adding means 4. The error control code adding means 4 adds a known CRC error control code to the data sequence Y11a, and outputs a transmission packet Y11 shown in FIG. The transmission means 5 transmits the transmission packet
Output Y11 to the telephone line.

The above operation is performed for all addresses written in the transmission address memory 8. Then, the transmitting means 5
Is EOS (End O) indicating that all addresses have been transmitted.
f Step) Transmit the packet.

Next, the first stage receiving operation will be described. Before starting the reception operation, the reception initialization means 6 stores the contents of the reception address memory 13 as shown in FIG.
All symbols are set to the symbol N indicating no reception.

The receiving means 9 receives the received packet Y01 from the telephone line and outputs it to the error detecting means 10. The error detection means 10
The CRC error control code is extracted from the packet Y01, and the well-known CR
The presence or absence of a reception error is determined by the C error detection method. If there is no reception error, the data string Y01a obtained by subtracting the CRC error control code from the packet Y01 is output to the address extracting means 11 and the decoding means 12. However, if there is a reception error, the receiving means 9 does not output anything.

The address extracting means 11 extracts the address A0 and the area number D1 from the data string Y01a, and outputs the data string Y0D1 and the address.
A0 and area number D1 are output to decoding means 12.

The decoding means 12 decodes the data string Y0D1 and
It is stored in the area D1 of 0. At this time, if the number of data obtained by decoding is not one in the area D1, it is regarded that there is a reception error that could not be detected by the error detection means 10, and nothing is output. If the data Y0 (0,0) is obtained without error, the address A0 of the reception address memory 13 is
The area number D1 is stored in a location corresponding to. Further, the data string Y0 (0,0) is stored in the first stage data memory 17, and the DCT is stored.
The area other than the area D1 of the memory 50 is set to 0, and the inverse discrete cosine transform is performed.
To be stored.

Since only low-order data among the discrete cosine transform coefficients is used, a fine image cannot be reproduced, but in this way, a coarse image can be viewed first using only the first stage data.

 The above operation is continued until the EOC packet is received.

FIG. 5B shows the contents of the reception address memory 13 when the EOS packet is received. In the present embodiment, it indicates that the packets of the addresses A1 and A5 could not be received.

 Next, the first stage retransmission request will be described.

In the small area where the data in area D1 could be received without error,
Since only the data in the area D2 needs to be received, only the data in the area D2 is requested. In the small area where the data in the area D1 could not be received without error, both the data in the area D1 and the data in the area D2 are required, so the data in the area D3 is requested. Therefore, the retransmission address generation means 14 is provided in the reception address memory.
Referring to FIG. 13, the address and the area number are stored in the retransmission address memory 16 as shown in FIG. The address where the reception address memory 13 shown in FIG. 5 (b) is D1 is stored together with the area number D2, and the addresses indicating non-reception (A1 and A5 in this example) are stored together with the area number D3.

Retransmission address transmission means 15 outputs the contents of retransmission address memory 16 to the telephone line.

 Next, the transmission operation in the second stage will be described.

The retransmission address receiving means 7 receives the retransmission address output by the receiving side from the telephone line and stores it in the transmission address memory 8.

When the retransmission address has been received, the contents of the transmission address memory 8 are as shown in FIG. 4 (b). Encoding means 2
As in the first stage transmission, first, the address A0 and the area number D2 are obtained by referring to the first column of the transmission address memory 8.
Next, the luminance data X0 of the small area 20 corresponding to the address A0
The two-dimensional discrete cosine transform is performed on (0,0) to X0 (7,7), and the result is stored in the DCT memory 50. Next, the data string Y0D2 of the area D2 of the DCT memory 50 corresponding to the area number D2
(= Y0 (0,0) to Y0 (7,7)) is output to the address adding means 3. The address adding means 3 is provided in the area D of the DCT memory 50.
The data string Y02a in which the address A0 and the area number D2 are added to the second data string Y0D2 is output to the error control code adding means 4.
The error control code adding means 4 adds a well-known CRC error control code to the data sequence Y02a to generate a transmission packet Y02 and outputs it to the transmitting means 5, and the transmitting means 5 is configured as shown in FIG.
Is output to the telephone line. The encoding means 2 obtains the address A1 and the area number D3 with reference to the second column of the transmission address memory 8 shown in FIG. The luminance data X1 (0,0) to X of the small area 21 corresponding to the address A0
1 (7,7) is subjected to two-dimensional discrete cosine transform, and the result is stored in the DCT memory 50.
Data string Y1D3 (= Y0 (0,0) to Y0 in area D3 of CT memory 50)
(7, 7)) to the address adding means 3.

The address adding means 3 outputs the output data string Y of the DCT memory 50.
Data example Y13a with address A1 and area number D3 added to 1D3
Is output to the error control code adding means 4. The error control code adding means 4 adds a known CRC error control code to the data sequence Y13a and outputs a transmission packet Y13 shown in FIG. The transmission means 5 transmits the transmission packet Y1
Output 3 to the telephone line.

The above operation is performed for all addresses written in the transmission address memory 8. Thereafter, the transmitting means transmits an EOS packet indicating that all addresses have been transmitted.

 Next, the reception operation in the second stage will be described.

The receiving means 9 receives the received packet Y02 from the telephone line and outputs it to the error detecting means 10.

The error detection means 10 extracts a CRC error control code from the received packet Y02 and determines the presence or absence of a reception error by a known CRC error detection method. If there is no reception error, the data string Y0 obtained by subtracting the CRC error control code from the packet Y02
2a is output to the address extracting means 11 and the decoding means 12. However, if there is a reception error, the receiving means 9 does not output anything.

The address extracting means 11 extracts the address A0 and the area number D2 from the data string Y02a, and outputs the data string Y0D2 and the address.
A0 and area number D2 are output to decoding means 12.

The decoding means 12 decodes the data string Y0D2 and
In the area D2. At this time, if the number of data obtained by decoding is not 63 in the area D2, it is regarded that there is a reception error that could not be detected by the error detection means 10, and nothing is output. Data Y0 (0,1) to Y0 (7,7)
Is obtained without error, the area number D2 is stored in the location corresponding to the address A0 in the reception address memory 13. Next, the data sequence Y0 (0, 0,
0) from the first stage data memory 17 to the area D1 of the DCT memory 50
To the data Y0 (0,0) to Y0 (7,7) in the DCT memory 50
Inverse discrete cosine transform of the received image memory to reproduce the luminance data X0 (0,0) to X0 (7,7) of the small area 20
Store in 18.

In this way, the image of the small area 20 can be reproduced on the receiving side using the data of the first stage and the data of the second stage.

Next, the receiving means 9 receives the received packet Y13 from the telephone line and outputs it to the error detecting means 10.

The error detecting means 10 extracts a CRC error control code from the received packet Y13 and determines the presence or absence of a reception error by a known CRC error detection method. If there is no reception error, the data string Y1 obtained by subtracting the CRC error control code from the packet Y13
3a is output to the address extracting means 11 and the decoding means 12. However, if there is a reception error, the receiving means 9
Produces no output.

The address extracting means 11 extracts the address A1 and the area number D3 from the data string Y13a, and outputs the data string Y1D3 and the address
A1 and area number D3 are output to decoding means 12.

The decoding means 12 decodes the data sequence Y1D3 and
In the area D3. At this time, if the number of data obtained by decoding is not 64 in the area D3, it is considered that there is a reception error that could not be detected by the error detection means 10, and nothing is output. Data Y1 (0,0) to Y1 (7,7)
Is obtained without error, the area number D3 is stored in the location corresponding to the address A1 in the reception address memory 13. DC
The data Y1 (0,0) to Y1 (7,7) in the T memory 50 are subjected to inverse discrete cosine transform, and the luminance data X1 (0,
0) to X1 (7,7) are reproduced and stored in the received image memory 18.

In this manner, even for a packet having an error in the first stage, the image of the small area 21 can be reproduced at the destination using only the packet received in the second stage.

 The above operation is continued until an EOS packet is received.

FIG. 5C shows the contents of the reception address memory 13 when the EOS packet is received. In the present embodiment, it indicates that the packets of the addresses A3 and A5 could not be received.

 Next, the second stage retransmission request will be described.

There is no need to retransmit the small area in which the data in the areas D1 and D2 or the area D3 has been received. In the small area where the data of the area D1 could be received but the data of the area D2 could not be received, it is sufficient to receive only the data of the area D2.
Request retransmission of only the data of. In the small area where the data of the area D1 has not been received, both the data of the area D1 and the data of the area D2 are necessary, so the retransmission request of the data of the area D3 is made.

Therefore, the retransmission address generation means 14 stores the address and the area number in the retransmission address memory 16 as shown in FIG. 6B with reference to the reception address memory 13 in FIG. 5C. The address (A3 in this example) in which the area number column of the reception address memory 13 is D1 is stored together with the area number D2, and the address indicating unreceived (A5 in this example) is stored together with the area number D3. Since retransmission is not required for addresses in which the area number column of the reception address memory 13 in FIG. 5C is D2 or D3, the retransmission address memory
Nothing is stored in 16.

Retransmission address transmission means 15 outputs the contents of retransmission address memory 16 to the telephone line.

 Next, the transmission operation in the third stage will be described.

As in the second stage, the retransmission address receiving means 7 receives the retransmission address output by the receiving side from the telephone line and stores it in the transmission address memory 8. When the retransmission address has been received, the contents of the transmission address memory 8 are as shown in FIG. 4 (c).

The encoding means 2 first, as in the transmission in the second stage,
The address A3 and the area number D2 are obtained by referring to the first column of the transmission address memory 8 shown in FIG. Next, the luminance data X3 (0,0) to X3 (7,7) of the small area 20 corresponding to the address A3 are
Dimensional discrete cosine transform and DCT
It is stored in the memory 50. Next, the data string Y3D2 (= Y3 (0,1) to Y3 (7,7) in the area D2 of the DCT memory 50 corresponding to the area number D2
7)) is output to the address adding means 3.

The address adding means 3 outputs to the error control code adding means 4 a data string Y32a obtained by adding the address A3 and the area number D2 to the data string Y3D2 of the area D2 of the DTC memory 50.

The error control code adding means adds a well-known CRC error control code to the data string Y32a, generates a transmission packet Y32 shown in FIG. 11 (e), and outputs the transmission packet Y32 to the transmission means 5, and the transmission means 5 Output the transmission packet Y32 to the telephone line.

Thereafter, the encoding means 2 determines whether the transmission address memory 8
The address A5 and the area number D3 are obtained by referring to the column. Next, the luminance data X5 (0,0) to X of the small area 25 corresponding to the address A5
5 (7, 7) is subjected to two-dimensional discrete cosine transform, and the result is stored in the DCT memory 50. Next, a data string Y5D3 (= Y5D3) of the area D3 of the DCT memory 50 corresponding to the area number D3
(0,0) to Y5 (7,7)) are output to the address adding means 3. The address adding means 3 outputs a data string Y5 obtained by adding an address A5 and an area number D3 to the output data string Y5D3 of the DCT memory 50.
3a is output to the error control code adding means 4. The error control code adding means 4 adds a well-known CRC error control code to the data example Y53a, and transmits the transmission packet Y5 shown in FIG. 11 (f).
3 is output to the transmitting means 5. The transmitting means 5 outputs the transmission packet Y53 to the telephone line.

Thereafter, the transmission means 5 transmits an EOS packet indicating that all the addresses have been transmitted.

 Next, the reception operation in the third stage will be described.

The receiving means 9 receives the received packet Y32 from the telephone line and outputs it to the error detecting means 10.

The error detection means 10 extracts the CRC error control code from the received packet Y32 and determines the presence or absence of a reception error by a known CRC error detection method. If there is no reception error, the data string Y3 obtained by subtracting the CRC error control code from the packet Y32
2a is output to the address extracting means 11 and the decoding means 12. However, if there is a reception error, the receiving means 9 does not output anything.

The address extracting means 11 extracts the address A3 and the area number D2 from the data string Y32a, and outputs the data string Y3D2 and the address
A3 and area number D2 are output to decoding means 12.

The decoding means 12 decodes the data string Y3D2 and
In the area D2. At this time, if the number of data obtained by decoding is not 63 in the area D2, it is regarded that there is a reception error that could not be detected by the error detection means 10, and nothing is output. Data Y3 (0,1) to Y3 (7,7)
Is obtained without error, the area number D2 is stored in the location corresponding to the address A3 in the reception address memory 13. Next, the data string Y3 (0,
0) from the first stage data memory 17 to the area D1 of the DCT memory 50
, And performs inverse discrete cosine transform of the data Y3 (0,0) to Y3 (7,7) in the DCT memory 50 to reproduce the luminance data X3 (0,0) X3 (7,7) of the small area 23 Then, it is stored in the received image memory 18.

In this way, the image of the small area 23 can be reproduced on the receiving side using the data of the first stage and the data of the third stage.

Next, the receiving means 9 receives the received packet Y53 from the telephone line and outputs it to the error detecting means 10.

The error detection means 10 extracts the CRC error control code from the packet Y53 and determines the presence or absence of a reception error by using a well-known CRC error detection method. If there is no reception error, a data string Y53a obtained by subtracting the CRC error control code from the packet Y53 is output to the address extracting means 11 and the decoding means 12.
However, if there is a reception error, the receiving means 9 does not output anything.

The address extracting means 11 outputs the data string Y53a address A5
And the area number D3, and outputs the data string Y5D3, the address A1, and the area number D3 to the decoding means 12.

The decoding means 12 decodes the data sequence Y5D3 and
It is stored in the area D3 of 0. At this time, if the number of data obtained by decoding is not 64 in the area D3, it is considered that there is a reception error that could not be detected by the error detection means 10, and nothing is output. Data Y5 (0,0) to Y5 (7,7)
Is obtained without error, the area number D3 is stored in the location corresponding to the address A5 in the reception address memory 13. DC
The data Y5 (0,0) to Y5 (7,7) in the T memory 50 are subjected to inverse discrete cosine transform, and the luminance data X5 (0,
0) to X5 (0,0) are reproduced and stored in the received image memory 18.

In this way, even for packets having errors in the first and second stages, the image of the small area can be reproduced on the receiving side using only the packets received in the third stage.

 The above operation is continued until an EOS packet is received.

 Next, the third stage retransmission request will be described.

The operation of the retransmission address generating means 14 is the same as that at the time of the second stage retransmission request. FIG. 5D shows the contents of the reception address memory 13 when the EOS packet is received. In this embodiment, since there is no need to retransmit at all addresses, the retransmission address transmitting means 15 notifies the transmitting side via the telephone line that all image data has been normally received. The transmitting side ends the transmitting operation, and the receiving side ends the receiving operation.

As described above, the image on the transmission side can be transmitted to the reception side.

In this embodiment, the image transmission is completed at the third stage,
If all image data cannot be received without error even after the completion of the third stage reception, the third stage
The transmission is repeated in the same procedure as the steps, such as the fourth step, the fifth step, and so on.

FIG. 9 shows a transmission / reception flowchart of the second embodiment.

In the second embodiment, the DCT memory 50 is divided into three areas E1 to E3. For example, in the region E1, (0,0) order,
The (0,1) order and (1,0) order are assigned to the area E2, and the remaining coefficients are assigned to the area E3. The transmission, reception, and retransmission procedures are the same as those in the first embodiment except that the procedures for the area E2 are increased. According to this embodiment, before the final fine image is obtained following the coarse image of the first embodiment, an image having an intermediate roughness can be seen in a relatively short time.

FIG. 10 shows a transmission / reception flowchart of the third embodiment. The area division of the DCT memory 50 is the same as in the first embodiment.

In the third embodiment, retransmission is repeated until there is no error in each area of the DCT memory 50. If the error is eliminated by the retransmission, or if there is no need for the retransmission, a procedure for notifying the transmitting side that all blocks have been received without error in the area is performed after the retransmission.

In the first embodiment, the retransmission of the block having an error in the transmission of the area D1 is performed at the same time as the transmission of the area D2. Therefore, it is assumed that the first retransmission of the area D1 is completed until the transmission of the area D2 is completed for all the blocks. Cannot be considered. Therefore, 2 of the area D1
The first retransmission is performed after transmitting the area D2. However, in the third embodiment, since the retransmission of the area D1 is performed using only the data of the area D1, the retransmission of the area D1 is performed before the transmission of the area D2.
Is performed for the second time. Therefore, the data in the error-free area D1 can be transmitted earlier than in the first embodiment. This is suitable for a receiver who wants to see a full screen first even on a coarse screen.

On the other hand, in the third embodiment, a procedure for requesting retransmission of a block having an error in the transmission of the area D1 is performed after the transmission of the area D1, and the transmitting side is notified that all blocks have been received without error in the area D1. Since the procedure is performed after retransmission of the area D1, even if only one block is erroneously received in the transmission of the area D1, at least two procedures are required between transmission and reception. On the other hand, in the first embodiment, the retransmission of the block having an error in the transmission of the area D1 is performed at the same time as the transmission of the area D2. Just after the transmission of the area D1, the second
If there is no error in the step transmission, no further steps are required. Therefore, the number of procedures between transmission and reception is smaller than in the third embodiment. Since image data cannot be transmitted during the procedure, the smaller the number of procedures, the shorter the total transmission time. This is suitable for receivers who want to minimize the time it takes for an error-free image to be completely transmitted.

In the embodiment, 1 packet = 1 block for simplicity, but the same effect can be obtained even when 1 packet = a plurality of blocks.

In the embodiment, the block data is divided into regions using the discrete cosine transform. However, the same effect can be obtained by dividing the block data into regions without using the discrete cosine transform.

[Effects of the Invention] According to the present invention, even if there is a transmission error in the transmission of the low frequency component, retransmission is performed before transmitting the high frequency component or while transmitting the high frequency component. No abnormal screen is shown. Also,
Since retransmission is not repeated until there is no error in some data in the block, the total transmission time is reduced.

[Brief description of the drawings]

FIG. 1 is a flowchart showing the operation of the first embodiment of the present invention, FIG. 2 is a conceptual diagram showing the configuration of a transmission image memory, and FIG. 3 is a configuration of a transmission address memory, a reception address memory and a retransmission address memory. FIG. 4 is a conceptual diagram showing a change in a transmission address memory, FIG. 5 is a conceptual diagram showing a change in a reception address memory, FIG. 6 is a conceptual diagram showing a change in a retransmission address memory, and FIG. FIG. 8 is a conceptual diagram showing the configuration of an image memory and a DCT memory, FIG. 8 is a block diagram of an apparatus for carrying out the present invention, FIG. 9 is a flowchart showing the operation of the second embodiment of the present invention, and FIG. FIG. 11 is a flowchart showing the operation of the third embodiment of the present invention, and FIG. 11 is a conceptual diagram showing the configuration of a transmission packet. 1 ... Transmission image memory, 2 ... Encoding means, 3 ... Address addition means, 4 ... Error control code addition means, 5 ... Transmission means, 6 ... Transmission initialization means, 7 ... Retransmission address reception Means 8, transmission address memory 9, reception means,
10 ... Error detection means, 11 ... Address extraction means, 12
... Decoding means, 13 reception address memory, 14 retransmission address generation means, 15 retransmission address transmission means, 16
... Retransmission address memory, 50... DCT memory, 60... Reception initialization means.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Uehara 1410 Inada, Katsuta-shi, Ibaraki Prefecture Tokai Plant, Hitachi, Ltd. (56) References JP-A-63-73786 (JP, A)

Claims (9)

(57) [Claims] A dividing unit that divides a screen into a plurality of blocks; a converting unit that converts an image of each block divided by the dividing unit into data of each frequency domain; A transmission unit configured to form a transmission packet with the converted data, the block address, and the error detection data, and transmit an image to a reception side for each block, wherein the transmission unit is configured by the conversion unit First transmission means for transmitting, in each block, data of a low-frequency region of an image in a converted block after conversion as the data of the transmission packet; and a transmission packet in which an error is detected from the reception unit. When the block address of the transmitted packet is returned, the data of the block of the transmission packet in which the error was detected is transmitted together with the data in the low frequency region of the image of the block. The data, transmitted as the data of the transmission packet, the transmission packet the error is not detected, the data of the high-frequency portion of the image of the block of the transmission packet in which the error is not detected,
And a second transmission unit for transmitting the data of the transmission packet as the data. 2. A dividing unit for dividing a screen into a plurality of blocks; a converting unit for converting an image into data for each frequency domain for each block divided by the dividing unit; A transmission unit configured to form a transmission packet with the converted data, the block address, and the error detection data and transmit an image to a reception side, wherein the transmission unit performs the conversion performed by the conversion unit. A first transmission unit that transmits low-frequency data of an image in a subsequent block as the data of the transmission packet for each block; and a block address of the transmission packet in which an error is detected is returned from the receiving side. When the data of the block of the transmission packet in which the error is detected is transmitted again, Image transmitting apparatus characterized by comprising a second transmission means for transmitting the data of the high frequency region. 3. The transmission means according to claim 2, wherein said second transmission means repeats the transmission of the data in the low-frequency region of the image of the block for the transmission packet in which the error is detected until the error is no longer detected. And transmitting the data in the high frequency region of the image of each block after the image transmission. 4. An image receiving apparatus for receiving data of a low frequency region and data of a high frequency region for each block obtained by dividing a screen, wherein the received data is the data of the low frequency region or the data of the high frequency region. Output means for outputting area information indicating whether there is any data and a block address of the data, holding means for holding the area information output by the output means corresponding to the block address, and holding by the holding means Determining means for determining the frequency domain of each block, which requests transmission of data next to the transmitting side in accordance with the held content, wherein the determining means determines whether or not the image of the block has data in the low frequency domain. For a block in which the holding content held by the holding means indicates unreceived, the data in the low-frequency region and the data in the high-frequency region of the image of the block are stored. Requesting the transmission of the data in the high-frequency area when the content held in the holding means is the area information indicating the data in the low-frequency area. An image receiving apparatus characterized by the following. 5. An image receiving apparatus for receiving data of a low frequency region and data of a high frequency region for each block obtained by dividing a screen, wherein the received data is the data of the low frequency region or the data of the high frequency region. Output means for outputting area information indicating whether there is any data and a block address of the data, holding means for holding the area information output by the output means corresponding to the block address, and holding by the holding means Determining means for determining the frequency domain of each block, which requests transmission of data next to the transmitting side in accordance with the held content, wherein the determining means determines whether or not the image of the block has data in the low frequency domain. For a block in which the held content held by the holding unit indicates unreceived, transmission of data in the low-frequency region of the image of the block is requested, When the content held for all blocks held in the holding means is area information indicating data of the low frequency area,
An image receiving apparatus requesting transmission of data in the high frequency range. 6. A division unit for dividing a screen into a plurality of blocks, a conversion unit for converting an image into data for each frequency domain for each block divided by the division unit, and an inside of the block converted by the conversion unit. An image transmission device comprising a transmission unit that forms a transmission packet from the converted data, the block address, and the error detection data and transmits an image to a reception side; and a screen that displays data in a low-frequency region and data in a high-frequency region. An image transmission system comprising: an image receiving device that receives, for each of the divided blocks, the transmission unit transmits data of a low-frequency region of an image in a block after conversion by the conversion unit, A first transmission for each block as the data
Transmitting means for transmitting the data in the high-frequency region of the image in the converted block converted by the conversion unit as the data of the transmission packet for each block.
Transmission means, and region information adding means for adding region information indicating whether the data is data in the low-frequency region or data in the high-frequency region to the transmission packet, the image receiving device, Output means for outputting the area information and the block address added to the transmission packet from the received transmission packet; and holding means for holding the area information output by the output means corresponding to the block address. Requesting the image transmission device to transmit data according to the held content held in the holding means, and determining means for determining a frequency domain of each block, wherein the determining means After the reception of the data in the low-frequency region, for a block in which the holding content held in the holding unit indicates unreceived, the image of the block is not displayed. Requesting transmission of both data in the low-frequency area and data in the high-frequency area, and when the content held in the holding means is area information indicating the data in the low-frequency area, An image transmission system, which requests transmission of area data. 7. A division unit for dividing a screen into a plurality of blocks, a conversion unit for converting an image into data for each frequency domain for each block divided by the division unit, and an inside of the block converted by the conversion unit An image transmission device comprising a transmission unit that forms a transmission packet from the converted data, the block address, and the error detection data and transmits an image to a reception side; and a screen that displays data in a low-frequency region and data in a high-frequency region. An image transmission system comprising: an image receiving device that receives, for each of the divided blocks, the transmission unit transmits data of a low-frequency region of an image in a block after conversion by the conversion unit, A first transmission for each block as the data
Transmitting means for transmitting the data in the high-frequency region of the image in the converted block converted by the conversion unit as the data of the transmission packet for each block.
Transmission means, and region information adding means for adding region information indicating whether the data is data in the low-frequency region or data in the high-frequency region to the transmission packet, the image receiving device, Output means for outputting the area information and the block address added to the transmission packet from the received transmission packet; and holding means for holding the area information output by the output means corresponding to the block address. Requesting the image transmission device to transmit data according to the held content held in the holding means, and determining means for determining a frequency domain of each block, wherein the determining means After the reception of the data in the low-frequency region, for a block in which the holding content held in the holding unit indicates unreceived, the image of the block is not displayed. Requesting transmission of data in the low-frequency area, and when the held content of all blocks held in the holding means is area information indicating data in the low-frequency area,
An image transmission system requesting transmission of data in the high-frequency region. 8. A screen is divided into a plurality of blocks, an image for each divided block is converted into data for each frequency domain, and the converted data, block address, and error detection data in the converted block are used. In the image transmission method of configuring a transmission pocket and transmitting an image for each block, the transmitting side uses, as the data of the transmission packet, data of a low frequency region of an image in the converted block after conversion. The receiving side returns a block address of a transmission packet in which the error is detected to the transmitting side when detecting a receiving error in the transmission of the data in the low frequency range. When the receiving side returns the block address of the transmission packet in which the error was detected, the image of the block of the transmission packet in which the error was detected is returned. The data in the high-frequency region is transmitted together with the data in the low-frequency region as the data of the transmission packet. For the transmission packet in which the error is not detected, the high frequency of the image of the block of the transmission packet in which the error is not detected is transmitted. An image transmission method, comprising transmitting data of an area as the data of the transmission packet. 9. A screen is divided into a plurality of blocks, an image for each divided block is converted into data for each frequency domain, and the converted data, block address, and error detection data in the converted block are used. In an image transmission method for forming a transmission packet and transmitting an image for each block, the transmission side uses, as the data of the transmission packet, data of a low frequency region of an image in the converted block after conversion. The receiving side returns a block address of a transmission packet in which the error is detected to the transmitting side when detecting a receiving error in the transmission of the data in the low frequency range. When the receiving side returns the block address of the transmission packet in which the error was detected, the image of the block of the transmission packet in which the error was detected is returned. Low after the data of the frequency region and transmission again, image transmission method characterized in that the data of the high-frequency portion of the image of each block is transmitted as the data of the transmission packet.