JP3072901B2 - Still image transmitter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a still image transmitter suitable for use in a terminal device such as a still image transmission system or a videotex.

[Summary of the Invention]

The present invention is suitable for use in a terminal device such as a still image transmission system or videotex, for example, in a still image transmitter adapted to compress and transmit an original digital image signal and transmit the compressed digital image signal from outside in this compression encoding. Setting means for setting a compression rate, compression encoding means for compressing and encoding the original digital image signal at the set compression rate, and decoding means for decoding the digital image signal compressed and encoded by the compression encoding means Display means for displaying the digital image signal decoded by the decoding means and the original digital image signal simultaneously or alternately, and the relationship between the decoded digital image signal and the original digital image signal displayed on the display means Compression ratio determining means operated when the compression ratio is determined based on Transmitting means for transmitting a digital image signal compressed and encoded by the compression encoding means at the determined compression ratio after the determination, and the digital image signal decoded by the decoding means and the original digital image signal Display means for displaying simultaneously or alternately, and a compression rate determination operated when the compression rate is determined based on the relationship between the decoded digital image signal and the original digital image signal displayed on the display means. With the means, it is possible to check in advance on the transmission side whether or not the image quality of the image that has been compression-encoded and transmitted and decoded by reception measurement is satisfactory.

[Conventional technology]

As the transmission bit rate in telephone lines and the like has been improved, image data of still images with a large amount of information can be transmitted in a relatively short time. Are being developed.
FIG. 3 shows a videotex (interactive character / graphics information system) constructed on a digital telephone network as an example of a system using such a terminal device. In FIG. (2) is a communication line, (3a), (3b), and ‥‥ are digital telephones, respectively (4)
a), (4b), and ‥‥ are terminal devices, (5a), (5b),
‥‥ indicates a still image input / output source such as a video tape recorder, and (6) and (7) indicate information centers.

In the videotex on the digital telephone network, the transmission bit rate can be used up to 64 kbps in both the upstream and downstream directions.
a), (4b), and (4) Not only the compressed and encoded image information is transmitted, but also the terminal devices (4a), (4b), and (2) can exchange the compressed and encoded image information in a short time. It can be carried out.

Generally, transmission of image data (especially color image data) requires a long time, but according to the compression encoding, image data that almost reproduces an original image can be transmitted in a relatively short time. ABTC (Ad
aptive Block Truncation Coding (hereinafter referred to as block coding) or ADCT (Adaptive Discrete Coding).
A Cosine Transform method is known.

In the block coding method among these compression coding methods, as shown in FIG. 4, for example, 768 dots (pixels) in the horizontal direction × 4 pixels in the vertical direction displayed on the monitor of the terminal device.
The image (8) consisting of 80 dots is divided into basic blocks Bij (1 ≦ i ≦ M, 1 ≦ j ≦ N) of 8 dots × 8 dots. Then, the transmitting the screen data is first transmitted by compression coding the basic block B _11, the basic block B ₁₂ in the following, ‥‥ B _1N, B _21, and transmits the ‥‥ the respective compression coding. In order to compress and encode each basic block, 1/4 obtained by dividing the basic block (FIG. 5A) into four parts is obtained.
After introducing the concept of a block (4 × 4 block) (FIG. 5B) and a 1/16 block (2 × 2 block) (FIG. 5C) obtained by dividing the basic block into 16 blocks, The encoding modes shown in the table are used in combination.

Also, the processing block unit in the basic block is represented by “mn”, where m indicates an m × m block,
n indicates a position in the basic block shown in FIG. 8B. When the encoding of each encoding mode in Table 1 is performed on the processing block "mn", a "mode flag" shown in FIG. 6A is added before the data information of the basic block. The receiving side can decode the image data based on the "mode flag" information.

FIG. 7 shows a coding algorithm of a conventional block coding method for performing compression coding of an 8 × 8 basic block by combining the above-described coding modes. In Figure 7, epsilon ₁ and epsilon ₂ shows the standard deviation of the data values of all pixels of each processing block, the threshold value E ₁ and E ₂ represent the value of each standard deviation. A ₀ and a ₁ are the data values of the pixels at the upper left corner and upper right corner of the processing block divided into four equal parts, respectively, d ₁ and d ₂
And d ₃ are respectively a ₁ −a ₀ , that is, a kind of variation of data values,
The thresholds D ₁ , D _2, and D ₃ each indicate an allowable value of data variation. Therefore, when both the standard deviation ε ₁ and the variation d ₁ are smaller than the allowable value, the process proceeds from step (100) to step (104) and is processed in the A8 mode, and the values of 64 pixels of the basic block are all the same value ( (For example, an average value). When the standard deviation ε ₁ or the variation d ₁ is larger than the allowable value, the process shifts to the step (105) and the 4 ×
It advances each step (108) or less, or to step (112) or less in accordance with the 4 or standard deviation epsilon ₂ blocks or greater less than the threshold value E _2. Step (112) The following shows the decoding of the 2 × 2 block, first after obtaining the variation d ₃ in step (113), when the variation d ₃ is less than the threshold D ₃ from step (114) to the step (115) Proceed,
When the variation d ₃ is the threshold value D ₃ or proceeds from step (114) to the step (116).

In the above-described block coding method, the compression ratio of the image data can be changed by changing the respective values of the thresholds D _{1 to} D ₃ and E ₁ and E ₂ . For example, when the values of the thresholds E ₁ and E ₂ are set to be small and the value of the threshold D ₃ is set to be large, the compression encoding is easily performed in the A2 mode. In this A2 mode, the original image data of the basic block Bij shown in FIG. 8A is compression-coded and transmitted, and the image data of the basic block Bij when decoded on the receiving side is as shown in FIG. 8B.

Further, for example, a threshold E ₂ by setting a small threshold value E _1, D ₂
When the value of is set to a large value, the compression encoding
It is easier to do in A4 mode. The image data of the basic block Bij when the original image data shown in FIG. 8A is compressed and transmitted in the A4 mode and decoded on the receiving side is shown in FIG.
It becomes as shown in.

[Problems to be solved by the invention]

In general, when performing compression encoding, the transmission time is shortened as the compression rate of image data is increased, but the image quality on the receiving side is degraded as the compression rate is increased. When transmitting, there is a possibility that the person cannot be identified. Therefore, it is preferable that the compression ratio of the image data is set to a maximum value as long as the image quality on the receiving side can be maintained at a satisfactory level.

However, conventionally, since the transmitting side cannot confirm the image quality of the image corresponding to the compression-encoded image data, there has been an inconvenience that the compression rate of the image data cannot be set to an optimal value corresponding to the original image data. .

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to enable a transmission side to confirm in advance whether or not the image quality of an image that has been compressed and transmitted and decoded at a reception side is satisfactory.

[Means for solving the problem]

As shown in FIG. 1, for example, in a still picture transmitter according to the present invention, in a still picture transmitter adapted to compress and encode an original digital image signal and transmit the same, a setting for setting a compression rate in this compression and encoding from outside is performed. Means, compression encoding means for compressing and encoding the original digital image signal at the set compression ratio, decoding means for decoding the digital image signal compressed and encoded by the compression encoding means, and decoding means Display means for simultaneously or alternately displaying the decoded digital image signal and the original digital image signal; and a compression ratio based on the relationship between the decoded digital image signal and the original digital image signal displayed on the display means. Compression ratio determining means operated when the compression ratio is determined, and the compression ratio determined after the compression ratio is determined by the compression ratio determination means. And transmission means for transmitting a digital image signal compression-coded by the compression coding means compression ratio provided, in which so as to display the image based on the decoded image signal.

[Action]

According to the present invention, after the setting means (14) sets the compression rate in the compression coding to a predetermined degree, the image signal obtained by compression coding the original digital image signal at the compression rate and then decoding Can be displayed on the transmission side. Therefore, it is possible to confirm in advance whether the image quality of the image decoded on the receiving side is satisfactory or not on the transmitting side.

〔Example〕

Hereinafter, an embodiment of a still picture transmitter according to the present invention will be described with reference to FIGS. 1 and 2. FIG. In this example, the present invention is applied to a terminal device of a still image transmission system using a communication line.

FIG. 1 shows a terminal device of this example. In FIG. 1, (9) is a microcomputer composed of a central processing unit (CPU) (10), a ROM (11) and a RAM (12).
Reference numeral 3) denotes a system bus of the CPU (10) including a data bus, an address bus, a control bus, and the like. A ROM (11) and a RAM (12) are connected to the system bus (13). The microcomputer (9) controls each part of the terminal device (8a) via the system bus (13).

Also, (2) is a communication line, and this communication line (2)
ISDN (Integrated Services, Inc.
Digital network), high-speed digital line, analog telephone line, DDX (digital data exchange)
A network (there are two types, DDXC and DDXP) and a dedicated line are assumed. Further, instead of the communication line (2), a wireless transmission path using a communication satellite or the like can be used.

(16) is for the first video signal composed of a frame memory
RAMs (VRAM1) and (17) denote a second video signal RAM (VRAM2) also composed of a frame memory, (18) a write / read control circuit, and a microcomputer (9) via a system bus (13). Then, the write / read control circuit (18) is controlled to generate a write / read signal, and the write / read signal is supplied to respective write enable terminals of VRAM1 (16) and VRAM2 (17). Also, (19)
Indicates an address signal generation circuit, and (20) indicates a timing circuit. The timing circuit (20) generates a clock signal and signals corresponding to a vertical synchronization signal and a horizontal synchronization signal of a video signal, respectively, and generates an address signal generation circuit (19). To supply. The microcomputer (9) controls an address signal generating circuit (19) via a system bus (13) to generate an address signal for designating horizontal and vertical pixel positions for writing or reading. , This address signal is VR
It is supplied to the respective address signal input terminals of AM1 (16) and VRAM2 (17).

The input / output terminals of VRAM1 (16) and VRAM2 (17) are connected to the system bus (13), and the output terminal of VRAM1 (16) is connected to one fixed contact (21a) of the switch circuit (21). , VRAM2 (17) output terminal to its switch circuit (2
Connect to the other fixed contact (21b) in 1). The switch circuit (21) can be opened and closed by the microcomputer (9) via the system bus (13), and the movable contact (21c) of the switch circuit (21) is digital / analog (D / A).
Connect to the digital signal input terminal of the converter (22),
An analog image signal generated by the A converter (22) is supplied to a monitor (23). Therefore, the switch circuit (2
By switching the movable contact (21c) of 1), VRAM1
(16) or an image corresponding to the digital image signal stored in the VRAM2 (17) is displayed on the monitor (23).

Also, (14) is a keyboard, (15) is a keyboard (1
I / O circuit that connects 4) to the system bus (13), (2
Reference numeral 4) denotes a communication control circuit. This communication control circuit (24) adds a protocol suitable for the communication circuit (2) to data for transmission and then transmits the communication circuit (2) at a predetermined transmission rate.
And converts the data received via the communication circuit (2) into a format that can be easily processed by the microcomputer (9).

Reference numeral (25) denotes an input terminal. An analog video signal (video signal, etc.) corresponding to a still image is input to the input terminal (25) from a still image input / output source such as an electronic still camera and a video tape recorder. Supply. The analog video signal is further supplied to a decoding circuit (26) to generate an image signal composed of, for example, a luminance signal and a chrominance signal and an image signal composed of three primary color signals. Supply to converter (27). The digital image signal (image data) generated by the A / D converter (27) is input to the input terminal of the VRAM2 (17) and the input / output circuit (28).
Are supplied to the input terminals respectively. The input / output circuit (28) sends the image data itself or a synchronization signal or the like corresponding to the image data to the microcomputer (9) or the like via the system bus (13).

In this example, as will be described later, after the microcomputer (9) compresses and encodes the image data stored in the VRAM2 (17), the microcomputer 9 decodes the compressed and encoded image data and writes it to the VRAM1 (16). I have to. However, a DSP (Digital Signal Processor) (29) which is a kind of microcomputer dedicated to compression encoding and decoding may be used. In this case, as indicated by the broken line in FIG.
2 between the output terminal of (17) and the system bus (13)
The SP (29) is connected so that the operation of the DSP (29) is controlled by the microcomputer (9).

In the terminal device shown in FIG. 1, one frame of image data corresponding to one still image stored in the VRAM2 (17) is compression-encoded, and the compression-encoded image data is transmitted to a communication line (2). 2 will be described with reference to FIG. 2. In this example, the block encoding method (AB
TC method).

First, in step (120) of FIG. 2, a video signal for one frame supplied to an input terminal (25) is decoded by a decoding circuit (26), and the decoded video signal is converted to an A / D converter. The image data is converted into digital image data by (27), and the converted digital image data for one frame is written to the VRAM2 (17). Then, step (12
In 1), the image data written in the VRAM 2 (17) is supplied as it is to the monitor (23) via the D / A converter (22), and the image corresponding to the image data is displayed on the monitor (2).
3) Projection. Therefore, in this case, the switch circuit (2
The movable contact (21c) in 1) is switched to the fixed contact (21b).

Next, in steps (122) and (123), the operator of the terminal device operated the "confirmation key" provided on the keyboard (14) to instruct the transmitting side to previously confirm the compression-encoded image. Later, the keyboard (1
4) Input a parameter indicating "degree of compression ratio" when performing compression encoding of image data. Specifically, the seventh
The threshold values D _{1 to} D ₃ and the threshold values E ₁ and E
Enter the initial value of each value of ₂ . In this example, the compression rate is initially increased to generate a coarse image, and the compression rate is gradually reduced to generate an image close to the original image. Are determined to be satisfactory, the values of those parameters are fixed. Therefore, the values of these parameters are initially set to relatively large values and are gradually reduced.

When the degree of the compression ratio is set in step (123), the operation of the microcomputer (9) proceeds to step (12).
Moving to 4), the image data stored in the VRAM2 (17) is compression-coded according to the designated compression ratio in accordance with the procedure of FIG. Then, the microcomputer (9) decodes the compression-encoded image data, and writes the decoded image data to the VRAM1 (16) (step (12)
5), (126)). Then the microcomputer (9)
Switches the movable contact (21c) of the switch circuit (21) to the fixed contact (21a) side in step (127), and
The image data of (16) is supplied to a monitor (23) via a D / A converter (22). As a result, an image corresponding to the compression-encoded image data is displayed on the monitor (23). The operator observes the image displayed on the monitor (23), and operates the key indicating “OK” on the keyboard (14) if the image quality of the image is satisfactory, and adjusts the image quality of the image. If it is not satisfactory, the user operates the key indicating "NG" (step (128)). In this case, for example, assuming that the original image data stored in the VRAM2 (17) corresponds to the face of a person, it is determined that the image quality of the compression-coded image is good. Means that the face of the person corresponding to the image has the image quality of an attitude that can be recognized as the face of the same person as the face of the person in the original image data.

When the key indicating "NG" is operated in step (128), the operation returns to step (123), and the operator inputs a smaller value of the parameter indicating the degree of compression ratio of the image data from the keyboard (14). I do. Then, by repeating steps (124) to (127), an image having an image quality closer to the original image is displayed on the monitor (23). If you are not satisfied with this image quality, go to step (12
8) Return to step (123) again.

When the key indicating "OK" is operated in step (128), the operation proceeds to step (129), and the microcomputer (9) compresses and encodes the image data in the VRAM2 (17) in accordance with the set compression ratio. In step (130), the compression-encoded image data is transmitted to the communication line (2) via the communication control circuit (24).
As a result, image data corresponding to an image whose image quality is satisfactory is transmitted to the communication terminal of the other party after the data is compressed and encoded to reduce the transmission time. As described above, according to this example, there is an advantage that the transmission side can confirm in advance whether the image quality of the image that has been compressed and transmitted and decoded at the reception side is satisfactory.

In the above embodiment, the original image and the image after compression encoding are alternately displayed on the monitor (23). For example, the original image is displayed on the right side of the monitor (23). The images after compression encoding may be displayed simultaneously, or the images may be printed out. Also, instead of using a frame memory as the VRAM1 (16), a normal working RAM can be used instead.

Step (128) in the procedure shown in FIG.
, And monitors the image corresponding to the compressed and encoded image data stored in VRAM1 (16) (23)
At the same time, the image data may be transmitted to the other terminal device via the communication line (2).
Even in this case, there is an advantage that the operator on the transmission side can check the quality of the compression-encoded image transmitted to the terminal apparatus on the other side. The compression coding method is not limited to the block coding method, and may be applied to any method capable of changing the degree of data compression, such as an ADCT (Adaptive Discrete Cosine Transform) method.

As described above, the present invention is not limited to the above-described embodiment, and may adopt various configurations without departing from the spirit of the present invention.

〔The invention's effect〕

According to the present invention, display means for simultaneously or alternately displaying the digital image signal decoded by the decoding means and the original digital image signal, the decoded digital image signal and the original digital image signal displayed on the display means Compression rate determining means operated when the compression rate is determined based on the relationship between the compression rate determination means and the compression rate determination means. And transmitting means for transmitting the compressed and coded digital image signal. Therefore, the compression ratio is determined based on the relationship between the decoded digital image signal displayed on the display means and the original digital image signal. It can be performed promptly, and when the compression ratio is determined, the digital image signal that has been compression-encoded can be transmitted immediately. There is.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
FIG. 3 is a block diagram showing an example of videotex, FIG. 4 is a diagram showing a screen structure according to a conventional block coding method, and FIGS. 5 and 6 are block codes. FIG. 7 is a flowchart showing an algorithm of the block coding method, and FIG. 8 is a diagram showing an example of coding according to the example of FIG. (2) is a communication line, (9) is a microcomputer,
(14) is the keyboard, (16) is the first video signal RA
M, (17) is a second video signal RAM.

Continuation of the front page (56) References JP-A-63-299478 (JP, A) JP-A-62-108686 (JP, A) JP-A-1-25693 (JP, A)

Claims (1)

(57) [Claims] 1. A still picture transmitter for compressing and encoding an original digital image signal and transmitting the same, wherein a setting means for externally setting a compression rate in the compression and encoding; Compression encoding means for compressing and encoding the original digital image signal; decoding means for decoding the digital image signal compressed and encoded by the compression encoding means; digital image signal decoded by the decoding means; Display means for displaying image signals simultaneously or alternately; and operating when the compression ratio is determined based on a relationship between the decoded digital image signal displayed on the display means and the original digital image signal. After the compression ratio is determined by the compression ratio determination unit, the compression ratio is determined by the compression ratio determination unit. Still picture transmitter, characterized in that it comprises a transmission means for transmitting the digital image signal compression-coded by the compression coding means.