JPH0374066B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a transmission method for compressing and transmitting an image signal such as a facsimile signal.

As a method for transmitting facsimile signals as quickly and efficiently as possible, a data compression transmission technique that eliminates redundancy in signals is known.
In data compression transmission, a speed smoothing mechanism is essential for transmitting compressed data, which occurs temporally non-uniformly, to a constant speed transmission path. Conventionally, methods for speed smoothing have been used, such as (1) providing a variable scanning mechanism in the transmitter/receiver, and (2) providing a buffer memory in the transmitter/receiver to store and transmit data. (1) requires almost no buffer memory, but the transmitter/receiver is equipped with a variable scanning mechanism using a stepping motor, which not only complicates the device but also causes uneven scanning, which impedes high-precision image transmission. There is a drawback that For (2), the transmitting and receiving device only needs to operate at a constant speed, the scanning mechanism is simple, and high-precision image transmission is possible, but on the other hand, the transmitting and receiving device requires a buffer memory as large as one screen, and the equipment cost is high. In addition, there is a drawback that it takes a long time from the start of transmission to the completion of reception (in the case of facsimile, the completion of recording).

An object of the present invention is to provide an image data transmission method that improves the method (2) and reduces the buffer memory capacity of the receiving device, thereby reducing the device cost and shortening the time from the start of transmission to the completion of reception. be.

That is, the present invention specifies the operating speed (for example, the number of rotations of a motor) of the receiving device so that the receiving buffer memory does not become empty by calculating in advance the amount of data stored in the buffer memory of the receiving device. This is an image data transmission method characterized by transmitting image data.

In the present invention, if the receiving device is designed to be able to operate at multiple operating speeds (rotational speeds),
For one image, it is only necessary to operate at a constant speed, and there is no need to use a stepping motor, etc., and inexpensive and highly accurate reception recording is possible. Since the operating conditions are calculated and set in advance on the transmitting side, a small capacity is required, the cost is low, and the time from the start of transmission to the completion of recording is shortened.

Next, the present invention will be explained in detail using the drawings. The figure is a block diagram showing an example of an image transmission system to which the image transmission method of the present invention is applied. In the figure, reference number 10 is a transmitting device, 20 is a transmission path, and 3
0 is the receiving device. In the transmitting device, an image signal 15 generated by a facsimile transmitter 1 is compressed and encoded by a data compression device 2, and the compressed data 11 is temporarily stored in a storage device 3. On the other hand, the compressed data number 12 is sent from the compression device 2 to the calculation circuit 4, and the calculation circuit determines the operating speed of the receiving device suitable for transmitting the original (operating speed of the facsimile receiver in the receiving device: for example, the number of revolutions). ) is calculated. The transmission control device 5 receives the operating speed of the receiving device calculated by the calculation circuit through the line 13 and transmits it to the reception control device 6 through the transmission line 20, and then sequentially reads the compressed data from the storage device 3 through the line 14 and sends it to the transmission line. Send to 20. Here, there is no limit to the operating speed of the facsimile transmitter 1,
Any computer, television camera, etc. may be used as long as it has the function of generating an image signal. As the storage device 3, a magnetic tape, a magnetic disk, or other memory is used.

In the receiving device, when the receiving control device 6 receives the operating speed information designated for the receiving device, it sends a signal to the facsimile receiver 9 through the line 16 to set the receiver operating speed. Subsequently, the reception control device writes the compressed data sent through the transmission path 20 into the buffer memory 7 through the line 17. The data expansion device 8 reads the compressed data 18 from the buffer memory 7, decodes it into original image data, and sends it to the facsimile receiver 9 through a line 19 to obtain a recorded image.

Next, a method of setting the operating speed of the receiving device, which is a feature of the present invention, will be explained.

Assume that the buffer memory capacity of the receiving device is B bits, and the speed of the transmission path is V bits/second. The receiver rotation speed of the receiving device is M ₁ , M ₂ , ......M _n (M ₁ > M ₂ ...
...>M _n ) It is assumed that m types of revolutions/second can be set. However, one rotation corresponds to recording one scanning line.
In addition, the receiving device stores approximately B bits of compressed data in the buffer memory after starting data reception, and then starts decoding and recording in the decompressing device.If the receiving buffer memory is likely to overflow, the receiving device transmits the compressed data to the transmitting device. It is assumed that communication control is performed to avoid overflow of the reception buffer memory by issuing a temporary pause request or the like.

Example 1 When the number of compressed data is counted for each scanning line by the data compression device of the transmitting device, if the number of compressed data of the i-th scanning line is W _i , the first scanning line is decoded at the rotation speed M _j The receiver buffer accumulation amount b ₁ (j) is b ₁ (j)=B+V/M _j −W ₁ ...(1) However, if b 1 (j)>B, then _{b 1 (} j)=B... ...(2) is given. The first term on the right side of equation (1) is the initial value of the number of data stored in the reception buffer memory at the start of decoding, and the second term is the number of compressed data that arrives during recording of one scanning line and is written to the buffer memory. The third term is the number of data read from the buffer memory for decoding the first scanning line. Furthermore, equation (2) is a conditional equation that is controlled so that overflow of the reception buffer memory does not occur.

The receiver buffer accumulation amount b _i (j) when decoding the i-th scanning line is b _i (j)=b _i-1 (j)+V/M _j −W _i ……(1)′ However, if b _i (j)>B, then b _i (j)=B...(2') b ₀ (j)=B...(3). Therefore, if one image consists of n scanning lines, (1') for i=1, 2...n
By calculating the equation with the condition of equation (2'), the amount of data accumulated in the reception buffer memory can be checked in advance in a simulated manner.

b(j)=MIN{b _i (j)} ...(4) However, MIN{ } indicates the minimum value when i is changed from 1 to n. Here, if b(j)>0 (5) is satisfied, the reception buffer memory will not become empty, and correct decoding will be possible. In order to reduce the transmission speed as much as possible, equation (4) may be calculated by changing the rotation speed M _j and the maximum rotation speed that satisfies equation (5) may be designated as the operating speed of the receiving device. However, in an actual transmission path, the amount of buffer memory stored in the receiving device may not be as calculated by equation (4) due to the presence of transmission path errors, etc., so it is recommended to specify the rotation speed with a slight margin. It is valid.

Example 2 Under the same conditions as Example 1, the calculation can be modified as follows.

b′ _i (j)=b′ _i-1 +W _i −V/M _j ……(6) However, if b′ i (j)0, then b′ _i (j)=0 b _{′ 0} (j)= 0} ...(7) b'(j)=MAX{b _i (j)} ...(8) Here, MAX{ } indicates the maximum value when i is changed from 1 to n.

At this time, the maximum rotational speed M _j that satisfies b'(j)<B (9) for b'(j) in Equation 8 is designated as the receiving device operating speed.

Embodiment 3 When the number W _k of compressed data for multiple scanning lines, that is, K lines, is calculated, the rotation speed of the receiving device is determined by the following calculation.

b″ _k (j)=b″ _k-1 +KV/M _j −W _k ……(10) However, if b″ _k (j)＞B, then b″ _k (j)=B b″ _p (j) =B }(11) b″(j)=MIN{b″ _k (j)} ……(12) Then, for b″(j) in equation (12), b″(j)＞0 …… The maximum rotational speed M _j that satisfies (13) is designated as the receiving device operating speed.

Example 4 If one transmission image is composed of L composite images from A ₁ to _{A L} , the calculations shown in the above example may be performed by concatenating the L composite images. However, here we will show an example of another simple calculation method.

The minimum _buffer accumulation amount b _nio (l _{, j} ) (l=1,... . . L) and each partial image are transmitted individually, the final value of the buffer accumulation amount, i.e., i in equation (1') is the value b _o (l, j) (l =1,
......Calculate L). That is, for each partial image before composition, b _nio (l, j) and b _o (l,
Calculate 2m values of j) (j=1,...m).

In this case, when transmitting a composite image of A ₁ to A _L , the following calculation is performed for l=1 to L.

b(l,j)=b(l-1,j)+b _o (l,j)
...(14) b _l (j) = b (l-1, j) + b _nio (l, j)
...(15) However, b(o,j)=B b(j)=MIN{b _l (j)} ...(16) At this time, for b(j) in equation (16), b( j)>o ...(17) The maximum rotational speed M _j that satisfies the following is specified as the operating speed of the receiving device. Equation (17) indicates the condition under which the reception buffer memory does not become empty, and the above-mentioned rotation speed setting means setting the maximum rotation speed that allows correct decoding operation.

Normally, it is sufficient to prepare about three types of rotation speeds, and the minimum rotation speed at that time is set to a sufficiently low value assuming the worst case. Therefore, in the above embodiment, the top two rotational speeds
Calculate M ₁ M _2. If M ₁ satisfies the conditions, the rotation speed will be M ₁ , and if M ₂ satisfies the conditions, the rotation speed will be M _2.
If both M ₁ and M ₂ do not satisfy the conditions, reduce the rotation speed.
Just set it to _M3 .

[Brief explanation of drawings]

The figure is a block diagram showing an example of an image transmission system to which the image transmission method of the present invention is applied. 1...Facsimile transmitter, 2...Data compression device, 3...Storage device, 4...Calculation circuit, 5...
Transmission control device, 6...Reception control device, 7...Buffer memory, 8...Data decompression device, 9...Facsimile receiver.

Claims (1)

[Claims] 1. Transmit the image data to a receiving device consisting of a buffer memory that temporarily stores compressed image data, a data expansion device that decodes the image data, and a facsimile receiver that reproduces a recorded image from the decoded image data. In the image data transmission method, the operation speed of the facsimile receiver is kept constant during the image data reception, and the receiving buffer memory is emptied by calculating in advance the amount of data to be stored in the buffer memory of the receiving device. An image data transmission method, characterized in that the image data is transmitted by specifying an operating speed of the facsimile receiver so as to prevent the facsimile receiver from transmitting the image data.