JPH06165167A - Picture transmission system, picture transmission equipment and image receiver - Google Patents

Abstract

PURPOSE:To improve the reproduced picture quality of an image recorded at the time of absence by matching the correction variable of the picture transmitting side to a necessary value of the image receiving side. CONSTITUTION:A gamma correction circuit included in a process circuit 12b in a camera 10 is allowed to be optionally controlled at its correction variable and a system control circuit 42 controls the gamma correction variable in accordance with a request from the image receiving side. The image receiving side informs the necessity/unnecessity of gamma correction and the range of the gamma correction value when it is necessary. At the time of absence, terminated compressed images are successively recorded in a recording medium and reproduced and outputted from an intra-frame coding picture, or images are recorded in the recording medium successively from the initial terminated intra-frame coding image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image transmission system, an image transmission device and an image reception device, and more specifically,
The present invention relates to an image transmission system, an image transmission device, and an image reception device in a videophone and a video conference.

[0002]

2. Description of the Related Art Digital public communication network (so-called IS
With the spread of DN), simultaneous communication of image, voice and data has become possible, and a videophone and a video conference system have become practical. Service specifications, protocol specifications, and multimedia multiplexing frame structure specifications for audio / video services using digital lines are recommended by the International Telegraph and Telephone Consultative Committee (CCITT) Recommendation H.264. 320, H.M. 242
And H .; It has been announced as 221 mag.

H. 320 defines general system aspects of the audiovisual service. H. 221 is 64
FAS (Frame) used for exchange of frame structure and terminal capability, designation of communication mode, etc. in audio / video transmission on Kbps to 1,920 Kbps channel.
Alignment Signal) and BAS (Bi
t-rate Allocation Signal)
Specifies the coding assignment of. H. 242 defines a protocol for capability exchange between terminals and communication mode switching by BAS.

According to the above-mentioned recommendation, after the end-to-end physical connection is set up and the synchronization is established by FAS in the in-channel, the exchange sequence of the terminal capability by the BAS in the in-channel and the mode switching sequence by the designation of the communication mode are performed. Image between terminals by the procedure such as,
A method for performing multimedia communication such as voice and data is specified.

Each terminal has its own terminal capability changed according to the situation, and which communication mode is used within the range of the exchanged capability is outside the stipulated range.

Regarding the transmission speed of each information in the case of simultaneously transmitting image, voice and data, the voice is determined by the encoding system of the voice code, the data is set to a specified value, and the image is transmitted through the communication line. The remaining transmission capacity in speed is allocated.

As a compression method of image information, there has been proposed a coding method in which intra-frame coding and motion-compensated inter-frame coding are mixed so as to increase the compression rate and to suppress the propagation of transmission errors. .

[0008]

Generally, an image display device has a peculiar light emission characteristic, and in order to correctly develop an image to be displayed, a gamma correction process for matching the peculiar light emission characteristic is applied to an image signal. There is a need.

That is, the video signal has a low level in the dark portion,
The bright areas are at a high level. The brightness (optical power) is determined by the photosensitive material of the image sensor, the image display device (usually,
The fluorescent material of color CRT) and the spectral characteristics of the eye are related, and the individual input / output characteristics are non-linear characteristics mathematically expressed by a power function.

For example, the CRT picture tube has a so-called γ characteristic, which is a light emission characteristic in which the luminance of light emitted from the phosphor screen is proportional to the γth power of the video signal applied to the picture tube. In the NTSC system, normally γ = about 2.2. Therefore, a γ correction circuit that multiplies the input voltage by 1 / γ may be provided in the drive circuit of the picture tube to cancel or compensate the γ characteristic of the picture tube. However, γ correction circuits are provided for all the picture tubes. Is not economical, so
A γ correction circuit is provided on the camera side. FIG. 8 shows the γ correction characteristic.

In image measurement and the like, the total γ = 1 is preferable in that the intensity of light can be read directly, but it is usually set to γ = 0.5 to 0.7 because it becomes difficult to see dark areas. In the case of a black and white film, the negative film has γ = 0.
65, γ = 2.25 for the positive film, and γ = 1.46 in the combination of both. When the overall γ value is 1 or less, the image becomes soft, and when γ is 1 or more, the image becomes hard.

By the way, in the case of a black-and-white movie, the total γ value is set to 1.46, which is slightly high contrast, for the purpose of increasing the contrast by slightly increasing the density because there is no color.

The gamma correction functions to prevent a part of the image from being crushed when the dynamic range of brightness is wide.

In recent years, image display devices such as liquid crystal display devices and plasma display devices, which are different from CRTs, have been developed and put into practical use. In these display devices, the γ value is different from that of CRTs, and γ correction is unnecessary. There will be. When the γ values are different as described above, a new γ correction circuit is required on the display device side, and if the γ correction is originally unnecessary, a γ correction circuit for canceling the γ correction on the camera side is provided. There is a need.

The CRT of the NTSC system has a γ value of about 2.2, which is the same as that of the PAL system.
In the M type CRT, the γ value is 2.8. Therefore, PA
In the L method, the camera side applies a γ correction of 1 / 2.2 and S
In the ECAM system, the camera side applies a γ correction of 1 / 2.8. Under such circumstances, for example, when a videophone or a videoconference is conducted between a SECAM system country and an NTSC or PAL system country, the total γ value does not become 1 and the image becomes very difficult to see.

The standard γ value of a color picture tube in the NTSC system is 2.2, but there are some values of 3 to 5 due to variations depending on the type of the picture tube and the driving system.

By performing γ correction on the camera side,
The constant brightness principle does not hold, the detail decreases,
Problems such as the phenomenon of floating and the occurrence of deterioration again occur. For details, refer to Takahiko Fukibe, "Multidimensional signal processing of TV images", page 56 and after, published by Nikkan Kogyo Shimbun.

As described above, in today's image communication systems, a situation is established in which the γ correction performed on the camera side, that is, on the image transmitting side does not match the γ characteristic on the image receiving side. Due to these inconsistencies, the image is not reproduced and displayed correctly.

However, in the above-described image communication system, gamma correction is out of CCITT's recommendation, and the presence or absence of gamma correction and the correction value for correction are determined by the image transmitting side, and the image receiving side is It was not possible to know whether or not gamma correction was performed on the received image. On the contrary, the image transmission side has no way of knowing what kind of light emission characteristics the image reception side has in the image reception side, and the gamma that matches the light emission characteristics of the image display apparatus of the own terminal or the standard image display apparatus is not available. The image is output after gamma correction using the correction value.

Under such circumstances, the image display device on the image receiving side displays an image in a color different from that expected by the image transmitting side, which causes a problem in color reproducibility.

It is an object of the present invention to provide an image transmission system and an image transmission device which eliminates such inconvenience.

Also, in a normal voice-only telephone, an answering machine function for recording the voice when an incoming call is absent in a magnetic tape or a memory card is convenient, and the same applies to the above-mentioned image communication system. An answering machine function is expected.

The compressed image information may be restored and analog-recorded on the video tape. However, this not only makes the device large-scaled, but also the image quality of the reproduced image is deteriorated due to the image quality deterioration caused by the analog recording and reproduction. It gets much worse. Even if the restored image is digitally recorded, the amount of data becomes enormous.

Therefore, it is conceivable to store the received image information in a compressed state in a large-capacity storage device, for example, a hard disk. As described above, the CCIT
Recommendation H.T. In H.261, the intra-frame coded frame and the inter-frame coded frame are mixed,
In order to decode the inter-frame coded frame, the data of the previous frame to be referred to is required, and it is not possible to correctly reproduce and display by simply storing the received compressed image information in the storage device.

An object of the present invention is to provide an image receiving device which solves such a problem.

[0026]

An image receiving apparatus according to the present invention is an image receiving apparatus of an image transmitting system for compressing and transmitting image information by intra-picture coding and inter-picture coding, and is used when absent. A storage unit that stores the received image information in a compressed state, a decoding unit that decodes the compressed image information read from the storage unit, and the compressed image information that is read from the storage unit. It is characterized in that it comprises a detection means for detecting an image which has been intra-coded, and a control means for controlling the reproduction output of the restored image signal output from the decoding means according to the detection output of the detection means. .

The image receiving apparatus according to the present invention is also an image receiving apparatus of an image transmission system for compressing and transmitting image information by intra-frame coding and inter-frame coding, and compressing received image information when not present. A storage unit that stores the state, a detection unit that detects an image in which one screen is entirely encoded in the screen from the received image information when there is no presence, and one screen is displayed according to the detection output of the detection unit. It is characterized in that a control means for erasing received image information before the image which is all intra-coded from the storage means is provided.

The image transmission system according to the present invention is characterized in that the correction value of the γ correction means on the image transmission side is adjustable and the γ correction means is controlled in accordance with the request from the image reception side.

An image transmitting apparatus according to the present invention comprises a γ correcting means for γ correcting an image, a transmitting means for transmitting an output image of the γ correcting means, a control information receiving means for receiving γ correction control information, and The control information receiving unit controls the γ correction unit according to the γ correction control information received by the control information receiving unit.

[0030]

By the above means, the γ-correction (including no γ-correction) matching the γ-characteristics of the image display device on the image receiving side can be performed on the image transmitting side. As a result, color reproducibility and image quality are improved.

With regard to the answering machine function, since the image received in the absence is stored in a compressed state, the quality of the reproduced image is good and the image can be recorded in the storage means for a long time. Since reproduction output is started from an image that is all intra-frame coded, an image that is distorted at the beginning of reproduction is not displayed.

[0032]

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

FIG. 1 shows a schematic block diagram of a terminal device in an embodiment of the present invention.

In FIG. 1, reference numeral 10 denotes a camera for photographing the participants of the conference, which includes the image pickup device 12a and the image pickup device 12a.
The output of the process circuit 12b which performs camera signal processing such as white balance adjustment and gamma correction. In this embodiment, the presence / absence and the degree (gamma value) of gamma correction in the process circuit 12b can be controlled externally.

Reference numeral 14 is a document camera for photographing meeting materials such as drawings, 16 is an image display device such as a CRT or a liquid crystal display device, and 18 is an output image from the cameras 10, 14 for transmission. An image input / output circuit that selectively combines the output image and the received image of 14 and supplies them to the image display device 16.

Reference numeral 22 is an image encoding circuit for encoding the image signal to be transmitted, and 24 is an image decoding circuit for decoding the received encoded image signal.

Reference numeral 26 is a handset consisting of a microphone and a speaker, 28 is a microphone, 30 is a speaker, and 32 is a voice input / output interface for the handset 26, the microphone 28 and the speaker 30. The voice input / output interface 32 not only switches the voice input / output of the handset 26, the microphone 28, and the speaker 30, but also performs echo / cancel processing, dial tone, ring tone,
Tones such as busy tones and ring tones are generated.

Reference numeral 34 is a voice input / output interface 32.
Is a voice encoding circuit for encoding the voice signal to be transmitted from the device, and 36 is a voice decoding circuit for decoding the received encoded voice signal and outputting it to the voice input / output interface 32.

Reference numeral 38 is a data terminal device such as a personal computer, and 40 is a data interface for connecting the data terminal device 38.

Reference numeral 42 is a system control circuit for controlling the whole,
Reference numeral 44 denotes an operating device for inputting various instructions to the system control circuit 42, such as a keyboard, a touch panel,
It consists of a digitizer and a pointing device such as a mouse.

Reference numeral 46 is a communication line (for example, ISDN line).
Line interface, 48 is the image coding circuit 2
2. Information to be transmitted from the voice encoding circuit 34 and the data interface 40 and the system control circuit 42
Control information from H.264. 221 format is multiplexed and supplied to the line interface 46, and the image, audio, data and control signals are separated from the received information supplied from the line interface 46, and the image decoding circuit 24, the audio decoding circuit 36 and the data are respectively separated. A demultiplexing circuit that supplies the interface 40 and the system control circuit 42.

The flow of image signals and audio signals in the embodiment shown in FIG. 1 will be briefly described. The input image from the camera 10 and the document camera 14 is selected by the image input / output circuit 18 and applied to the image encoding circuit 22. The image encoding circuit 22 encodes the input image signal in the encoding mode according to the control signal from the system control circuit 42 and the internal determination, and outputs it to the demultiplexing / multiplexing circuit 48.

On the other hand, the input voice signal from the microphone or the microphone 28 of the handset 26 is input to the voice encoding circuit 34 via the voice input / output interface 32, is encoded here and is applied to the demultiplexing circuit 48.

Data to be transmitted from the data terminal 38 is transmitted via the data interface 40 to the demultiplexing circuit 4
Enter in 8. Further, the data to be transmitted, which is input from the operation device 44, is also input to the demultiplexing / multiplexing circuit 48 via the data interface 40.

The demultiplexing circuit 48 is the image coding circuit 2
2 and the encoded signal and data from the voice encoding circuit 34.
The data from the interface 40 and the control command from the system control circuit 42 are multiplexed and output to the line interface 46. Line interface 46
Outputs the signal from the demultiplexing / multiplexing circuit 48 to the connected communication line in a predetermined format.

The signal received from the communication line is supplied from the line interface 46 to the demultiplexing / multiplexing circuit 48. The demultiplexing circuit 48 separates the coded image signal, the coded audio signal, the data and the control command from the received signal, and the image decoding circuit 24, the audio decoding circuit 36, the data interface 40 and the system control circuit 42, respectively. Apply to.

The image decoding circuit 24 includes a demultiplexing circuit 4
The image input / output circuit 18 decodes the encoded image signal from
Apply to. The image input / output circuit 18 includes the cameras 10, 14
Image and the received image from the image decoding circuit 24 are selectively combined and applied to the image display device 16. The image input / output circuit 18 uses, for example, picture-in
It fits in the corresponding window in the picture or window display system. As a result, the input image and / or the received image is displayed on the screen of the image display device 16.

The received voice signal decoded by the voice encoding circuit 36 is applied to the speaker of the handset 26 and / or the speaker 30 via the voice input / output interface 32. As a result, the voice from the communication partner can be heard.

The received data demultiplexed by the demultiplexing / multiplexing circuit 48 is transferred from the data interface 40 to the data terminal 38.
Applied to.

A method of performing negotiation and conversion of terminal capability will be described by taking an ISDN line as an example. In the ISDN line, as shown in FIG. 2, an outband signal (that is,
Make a call using the D channel). As shown in FIG. 2, the call setup from the terminal A to the terminal B and the response from the terminal B to the terminal A enable communication on the B channel. There are other communication channels such as D channel, H0 and H1, but only the B channel will be described.

Recommendation H.264 is used by using the B channel that has become communicable in this way. According to 242, the in-band signaling procedure shown in FIG. 3 is performed on the B channel as such, thereby allocating the inside of the B channel to the data section and the control section for controlling communication. The control performed by the in-channel control unit is called in-channel control.

FIG. 4 shows a frame structure in the B channel for executing the in-channel control. FIG. 4 shows a multi-frame structure for the B channel (64 Kbps).
This multi-frame structure is 1 octet / 125μs
As shown in FIG. 4A, one frame is 8
0 octet, 1 sub-multiframe is 2 frames as shown in (b), and 1 multiframe is 8 sub-multiframes as shown in (c). In the bit direction,
Eight subchannels # 1 to # 8 of 8 Kbps are defined.

However, only the sub-channel # 8 has a transfer rate of 6.4 Kbps and FAS as a control bit.
(Frame Alignment Signal) and BAS (Bit-rate Allocation)
Signal) is inserted. The FAS and BAS enable in-channel control of the B channel.

FAS is used for frame and multi-frame synchronization. The BAS is used for exchanging information on terminal capabilities or setting capabilities necessary for determining a multiplexing method such as subchannels. In particular, the BAS can be switched every sub-multiframe (20 ms) even during data communication.

The in-band signal procedure shown in FIG. 3 will be briefly described. When the B channel becomes available for communication, terminal A,
Both Bs send FAS. The terminal capability at this time is
It is the mode 0 in the initial state (a mode only for voice and FAS and BAS). This FAS is searched by the other terminal,
H. When the condition for establishing frame synchronization defined by H.242 is satisfied, the bit structure A in the FAS shown in FIG.
0 "is transmitted. When the terminal receives A = 0,
It is confirmed that the partner terminal has established frame synchronization.
This is the so-called exchange of transmission ability.

Next, the capability information of the own terminal is transmitted to the partner terminal by BAS, and the capabilities of the partner terminals are mutually confirmed. At this point, if they can communicate with each other, data communication is started. When it is necessary to change the capability, the terminal capability is simultaneously transmitted as a command using BAS, and the data communication is started after the partner terminal completes the setting of the capability.

Data communication is independent of transmission and reception, and synchronization is established and terminal capability is set separately.
Therefore, synchronization may be lost in only one direction, or the type of data may differ between transmission and reception.

When the data communication is completed and the call is disconnected, first, the disconnecting terminal (terminal A in FIG. 4) is set to B.
Set to mode 0 using AS. As a result, the in-channel control of the B channel returns to the initial state. Next, as shown in FIG. 2, disconnection and release are performed in the D-channel out-band procedure, and all communication is completed.

FIG. 5 shows the bit structure in the FAS. Bit A indicates whether frame synchronization is lost, and E bit is C
Indicates whether an RC error has occurred. C1, C2, C3, C4
Are bits of CRC4. N1 to N5 are for multiframe numbering, and R1 to R4 are channel numbers. T
EA is a terminal device alarm, and is set to "1" when the terminal cannot respond to the received signal due to a failure inside the terminal.

FIG. 6 shows the bit structure in the BAS. As shown in FIG. 6A, the upper 3 bits represent an attribute,
The remaining 5 bits indicate the attribute value of that attribute. FIG. 6B shows the content of the attribute. The attribute value is, for example, a transfer rate value,
There are codec types, parameter values specific to each medium or information type, and the like.

FIG. 7 shows the internal structure of the process circuit 12b. For simplification of description, it is assumed that the image sensor 10a outputs color pixel signals of R (red), G (green), and B (blue) in parallel. The process circuit 12b includes R,
For each of the G and B signals, R,
White balance adjustment circuit 50R for adjusting G and B values,
.Gamma. Correction circuits 52R, 52G, which output the output signals of the circuits 50R, 50G, 50B by 50.multidot.
52B, white clip circuits 54R, 54G and 54B for adjusting the maximum white level and low pass filters (LPF) 56R, 56G and 56B for band limitation are provided.

White balance adjusting circuits 50R, 50
G, 50B and white clip circuits 54R, 54
Since the functions of G and 54B are well known, description thereof will be omitted.

The reason why the γ correction circuits 52R, 52G and 52B are installed will be briefly described.

As described above, the image receiving side has γ
Since various image display devices having different characteristics are used, even if the γ correction for the standard γ characteristics is uniformly performed on the image transmitting side, in order to hold the total γ value at a desired value (for example, 1), γ must be corrected.

Therefore, in this embodiment, the γ values of the γ correction circuits 51R, 52G, and 52B in the process circuit 12b on the image transmitting side are selectable, and the γ value at the γ value required by the image receiving side is selected.
The correction was executed. Needless to say, γ = 1 in γ correction here means no γ correction.

The γ value for γ correction requested by the image receiving side is notified to the image transmitting side as shown in FIG. 3 by using the BAS of the in-channel control of the B channel. An undefined or escape code is used as the attribute value shown in FIG. The image transmission side uses the format shown in FIG.
The upper and lower limits of its own γ correction capability are notified to the image receiving side, while the image receiving side notifies the image transmitting side of the upper and lower limits of the required γ correction value in the format shown in FIG. 9B. .

In FIG. 9A, the identifier is code information indicating the unique mode. The γ correction identifier is code information indicating that the data is for γ correction. With or without gamma correction, gamma correction is disabled on the image sending side.
That is, it indicates whether or not bypass is possible, and the γ correction value (upper limit) and the γ correction value (lower limit) indicate the range of selectable γ correction values.

In FIG. 9B, the identifier is shown in FIG.
Similar to (a), the code information indicating the unique mode and the γ correction identifier are code information indicating the data related to the γ correction. The presence / absence of γ correction indicates whether or not the γ correction on the image transmitting side is required, and the γ correction value (upper limit)
And the γ correction value (lower limit) indicate the range of the γ correction value that can be supported by the image receiving side.

When the image receiving side notifies the image transmitting side that the γ correction is unnecessary, the image transmitting side notifies the γ correction circuits 52R and 52R.
The γ value of G, 52B is set to 1, and a video signal substantially without γ correction is transmitted. When the image receiving side requests the image transmitting side for the γ correction process, and the required γ correction value is a value selectable by the image transmitting side, the image transmitting side displays the γ-corrected video signal with the requested γ correction value. To send. When the γ correction value requested by the image receiving side cannot be selected by the image transmitting side, γ correction is performed with the closest γ correction value and the video signal is transmitted.

FIG. 10 shows a circuit example in which the γ correction circuits 52R, 52G and 52B are realized by digital circuits. When the γ correction value is the upper address and the video data to be γ-corrected is the lower address, the γ-corrected video data is stored in the corresponding storage position of the ROM.

Of course, there are analog processing methods such as a method of approximating the non-linear characteristic by a broken line and a method of utilizing the non-linearity of the diode, but there is a drawback that it is weak against variations in parts and temperature fluctuations.

Although the image communication system which transmits images bidirectionally such as a videophone has been described as an example, it goes without saying that the present invention can be applied to the case where images are always transmitted unidirectionally. For example, it can be applied to a building monitoring system that monitors the inside of a building with a plurality of TV cameras, and the image receiving side can make adjustments to improve color reproducibility in dark places.

Considering the use as the measurement data, it becomes possible to obtain the image information without the γ correction, if necessary, and the convenience for the user is improved.

Next, a description will be given of an embodiment having an answering machine recording function for image information. FIG. 11 shows a schematic block diagram thereof.

In FIG. 11, 110 is a camera for photographing conference participants, 114 is a document camera for photographing conference materials such as drawings, 116 is an image display device such as a CRT or liquid crystal display device, 118 is a camera 110, An image input / output circuit that selects the output image of 114 for transmission, selectively combines the output images of the cameras 110 and 114 and the received image, and supplies them to the image display device 116.

Reference numeral 122 is an image encoding circuit for encoding the image signal to be transmitted, and 124 is an image decoding circuit for decoding the received encoded image signal.

Reference numeral 126 is a handset consisting of a microphone and a speaker, 128 is a microphone, 130 is a speaker, and 132.
Is a handset 126, a microphone 128 and a speaker 13.
0 is a voice input / output interface. The voice input / output interface 132 includes a handset 126,
Not only is the voice input / output of the microphone 128 and the speaker 130 switched, but also echo cancel processing and tone generation processing such as dial tone, ringing tone, busy tone, and ring tone are performed.

Reference numeral 134 denotes a voice input / output interface 1
A voice encoding circuit 136 for encoding the voice signal to be transmitted from 32 is a voice decoding circuit for decoding the received encoded voice signal and outputting it to the voice input / output interface 132.

Reference numeral 142 is a system control circuit for controlling the entire system, and 144 is an operating device for inputting various instructions to the system control circuit 142.
It consists of a panel, a digitizer, and a pointing device such as a mouse.

Reference numeral 146 is a line interface of a communication line (for example, ISDN line), and 148 is an H.264 information to be transmitted from the image encoding circuit 122 and the audio encoding circuit 134 and control information from the system control circuit 142.
221, which is multiplexed and supplied to the line interface 146, and the line interface 146.
This is a demultiplexing circuit that separates an image, a sound and a control signal from the received information supplied from and supplies them to the image decoding circuit 124, the sound decoding circuit 136 and the system control circuit 142, respectively.

Reference numeral 150 denotes an all-intra detection circuit for detecting whether or not all the received compressed image information in one frame is inter-frame coded. 152 is normally open, and the detection circuit 150 is provided. Circuit which is closed by the output of the control circuit 142 and the control signal of the system control circuit 142.
Reference numeral 54 is a storage device that stores the received compressed image information when the answering machine function is turned on. Gate circuit 152 and all I
The NTRA detection circuit 154 exclusively functions when reproducing the recorded image information.

Of course, as an answering machine, the received voice signal is also recorded, but the information amount of voice data is small,
Since recording can be performed with an existing inexpensive recording device, description thereof will be omitted in this embodiment. Of course, it may be stored in the storage device 154 together with the received image.

In the embodiment shown in FIG. 1, the flow of image signals and audio signals when the recorded message function is turned off will be briefly described.

The input images from the camera 110 and the document camera 114 are selected by the image input / output circuit 118 and applied to the image coding circuit 122. Image coding circuit 122
Encodes the input image signal in the encoding mode according to the control signal from the system control circuit 142 and the internal decision, and outputs it to the demultiplexing / multiplexing circuit 148.

On the other hand, the input voice signal from the microphone or microphone 128 of the handset 126 is input to the voice encoding circuit 134 via the voice input / output interface 132,
It is encoded here and applied to the demultiplexing and multiplexing circuit 148.

The demultiplexing / multiplexing circuit 148 multiplexes the coded signals from the image coding circuit 122 and the audio coding circuit 134 and the control command from the system control circuit 142, and outputs them to the line interface 146. The line interface 146 outputs the signal from the demultiplexing / multiplexing circuit 148 to the connected communication line in a predetermined format.

The signal received from the communication line is supplied from the line interface 146 to the demultiplexing / multiplexing circuit 148. The demultiplexing / multiplexing circuit 148 separates the coded image signal, the coded audio signal, the data, and the control command from the received signal, and the image decoding circuit 124 and the audio decoding circuit 1 respectively.
36 and system control circuit 142.

The image decoding circuit 124 decodes the encoded image signal from the demultiplexing / multiplexing circuit 148, and the decoded output is applied to the image input / output circuit 118 via the gate circuit 152. The image input / output circuit 118 includes the cameras 110 and 11.
The image from No. 4 and the received image from the gate circuit 152 are selectively combined and applied to the image display device 116. The image input / output circuit 118 performs, for example, picture-in-picture or fitting into a corresponding window in the window display system as a compositing process. As a result, the input image and / or the received image is displayed on the screen of the image display device 116.

The received voice signal decoded by the voice encoding circuit 136 is transmitted through the voice input / output interface 132 to the speaker of the handset 126 and / or the speaker 1.
30 is applied. As a result, the voice from the communication partner can be heard.

Since the method of negotiating and converting the terminal capability on the ISDN line is the same as that described in the embodiment shown in FIG. 1, detailed description thereof will be omitted.

H. 261 recommendation, NTSC system, PA
A common video format is defined to enable communication between multiple standards such as L-system and digital television signals. CIF format and QC
IF format. In the CIF format, the number of samples is 352 pixels × 288 lines for the luminance signal Y and 176 pixels × 144 lines for the color difference signals Cr and Cb. QCI
The F format has a quarter of the information amount of the CIF format, and the number of samples is 176 pixels × 144 lines for the luminance signal Y and 88 pixels × 72 lines for the color difference signals Cr and Cb.

The element technique of the compression method is intra-frame coding in which an image in a frame is divided into blocks of 8 pixels × 8 pixels and two-dimensional discrete cosine transform (DCT transform) is performed.
Interframe coding that performs two-dimensional DCT conversion of the difference between frames, motion compensation that reduces the amount of generated code by compensating for the motion of images between frames, and that the DCT transform coefficient generally has a zero value in the high frequency region Zero run length coding, quantization that changes the quantization step size according to the amount of data generated, short code values for frequently occurring data patterns, long code values for less frequent data patterns The variable length coding to be assigned and the frame skipping for skipping frames are adopted, and a high compression rate is achieved by these combinations, which enables moving image transmission on a low rate communication path.

Next, the transmission frame structure will be briefly described. FIG. 12 shows the structure of an error correction frame using the BCH code. 1 frame is a 1-bit error correction frame
Bit, 1-bit file identifier, 492-bit image data and 18-bit error correction parity,
There are 512 bits in total. Eight of these frames are put together to form one multi-frame.

FIG. 13 shows a multiplexed frame structure. 1
The screen is divided into 12 (in the case of CIF, in the case of QCIF, it is divided into 3 as will be described later), and one block is a group of blocks (GOB), and the frame header FH
After that, the data of each GOB is sequentially transmitted. FIG. 14 shows a GOB division method. GOB is defined as 176 pixels × 48 lines for luminance and 88 pixels × 24 lines for color differences Cr and Cb as the number of samples, and is 1/12 of CIF format and 1/3 of QCIF format.
Equivalent to. As shown in FIG. 14, GOB1 to GOB12 are sequentially numbered in the CIF format, but GOB1 and GOB1 are numbered in the QCIF format.
They are numbered GOB3 and GOB5.

FIG. 13B shows the frame header FH.
And the detailed structure of the head portion of GOB1 following this. The frame header FH includes a 20-bit frame start code PSC, a 5-bit frame number TR, and 6-bit type information PTYPE. The frame start code PSC is "0000 0000 0000 0001.
TR is a value from "1" to "30". PTYPE is split screen instruction information, document camera instruction information, screen freeze release and information source format instruction information (information indicating CIF or QCIF. ) Consists of.

There is a GOB header in the GOB area, and the required number of MB headers and coefficient data follow. One GOB consists of 33 macroblocks (MB), and 1
One macroblock (MB) consists of 8 pixels x 8 lines of 6
One block (4 luminance signals Y and 1 color difference signal Cr)
And one color difference signal Cb). The luminance signal blocks are numbered 1 to 4, and the color difference signal Cb is 5,
The color difference signal Cr is numbered 6.

The GOB header consists of a 16-bit GOB start code (GBSC), a 4-bit GOB number (GN) and 5-bit quantization characteristic information (GQUANT).
GBSC is "0000 0000 0000 000"
It is 1 ". GN takes a value from" 1 "to" 12 ". If GN is" 0 ", PSC and GO of FH
Since both GBSC + GN of B are 20 bits and the same continuous bit string is formed, "0" is not assigned to GN. GQUANT is information on the quantization step size.

The MB header includes a macroblock address (MBA) indicating the position of the macroblock (MB), macroblock type information (MTYPE), quantization characteristic information (MQUANT), motion vector information (MVD), and significant block. It is composed of pattern information (CBP).

The MBA is an absolute value for the head macroblock and a relative value (difference) for subsequent macroblocks, and has a variable length. MTYPA indicates the type of processing performed on a macroblock, such as intraframe coding (INTRA), interframe differential coding (INTER), interframe differential coding with motion compensation (MC), and filter processing (FIL). . MQUANT is G
Same as QUANT. The CBP has, as information, the number of a valid block in the four blocks of the luminance signal Y and the blocks of the color difference signals Cr and Cb of the macro block.

After the MB header, as described above, the compression-encoded image data sequentially follows the blocks of the four luminance signals and the blocks of the color difference signals Cr and Cb which are significant. There is.

PSC of frame header FH and GOB
GBSC and GN are selected to be the only data pattern so that the frame header and GOB header can be detected during demodulation.

FIG. 15 is a block diagram showing the block diagram shown in FIG.
The block diagram which extracted the main structure part of a present Example is shown. Reference numeral 160 is a BCH decoding circuit, 162 is a reception buffer, and 164 is a switching circuit for interposing a storage device 154 for the absence recording, and two switches 164.
a, 164b. Reference numeral 166 is an image frame separation circuit for separating header information, specifically, frame header FH, GOB header and MB header from the multiplexed frame shown in FIG.

Reference numeral 168 denotes an FH decoding circuit which decodes the frame header FH separated by the separation circuit 166, and includes frame number information, CIF / QCIF format information,
It outputs a freeze release command and document camera instruction information. Reference numeral 170 denotes a GOBH decoding circuit that decodes the GOB header separated by the separation circuit 166.
Output size information. An MBH decoding circuit 172 decodes the MB header separated by the separation circuit 166. The MBH decoding circuit 172 has intra-frame coding (INTRA) or inter-frame coding (ITRA).
NTER) and the motion vector are output.

Reference numeral 174 is a variable length decoding circuit for variable length decoding the compressed image data from the image frame separation circuit 166, 176 is a dequantization circuit for dequantizing the output of the modulation decoding circuit 174, and 177 is GOBH decoding. A quantization value setting circuit 178, which sets the quantization step size of the inverse quantization circuit 176 according to the quantization value information from the circuit 170 and the MBH decoding circuit 172, outputs the output of the inverse quantization circuit 176 to the inverse discrete cosine transform ( It is an inverse DCT conversion circuit that performs DCT conversion). The output of the inverse DCT conversion circuit 178 is decoded image data or difference data between frames.

Reference numeral 180 denotes an arithmetic circuit for outputting the output of the inverse DCT conversion circuit 178 as it is or by adding the pixel values of the previous frame and outputting the two switches 180a, 180b.
And an adder 180c. Switches 180a, 180
b is the INTER output from the MBH decoding circuit 172
/ INTRA identification signal is switched in conjunction with
In the case of NTRA, both are connected to the contact a and output the output of the inverse DCT conversion circuit 178 as it is, and in the case of INTER, both are connected to the contact b and added to the output of the inverse DCT conversion circuit 178 with the pixel value of the previous frame and output. To do.

Reference numeral 182 denotes a frame memory for storing the image data output from the arithmetic circuit 180 for two screens (frames) of the current frame and the previous frame, and 184 denotes CIF / QCIF information from the FH decoding circuit 168 and the MBH decoding circuit. A memory control circuit for controlling the frame memory 182 according to the motion vector information from 172. Reference numeral 186 is a filter for band-limiting the decoded image data from the previous frame storage area of the frame memory 182 and applying it to the adder 180c.

The storage device 154 is a large capacity memory 188.
And a memory control circuit 190 that controls writing and reading of the memory 188. Of course, a solid-state memory, a magnetic disk, an optical disk, a magneto-optical disk or the like can be used as the storage medium.

The system control circuit 142 receives frame number information, CIF / QCIF format information, freeze release instruction, document camera instruction information, etc. from the FH decoding circuit 168. All INTRA detection circuits 150 are F
The frame number information is received from the H decoding circuit 168, and the MBH
Upon receiving the INTER / INTRA identification information from the decoding circuit 172, it outputs an opening / closing control signal for the gate circuit 152.

The operation of FIG. 15 in the absence mode, that is, when the answering machine function is activated will be described. When there is an incoming call in unattended mode, the call is connected as described above and B
The CH decoding circuit 160 decodes the BCH frame shown in FIG. 12 and outputs the received data in the image data multiplexing frame structure shown in FIG. Its output is receive buffer 1
It is applied to the switching circuit 164 via 62. The system control circuit 142 switches the switching circuit 164 according to the connection of the call.
Switch 164b is connected to the a contact. This allows
The received data having the image data multiplexing frame structure shown in FIG. 13 is applied to the storage device 154. The system control circuit 142 controls the writing area on the memory 188 by the memory control circuit 190.

There is a call disconnection request or the storage device 15
When the received data stored in the memory 188 of No. 4 reaches a predetermined amount, the system control circuit 142 disconnects the call and enters the state of preparation for the next incoming call.

The operation of reproducing the image information recorded in this way will be described. In response to the reproduction instruction, the system control circuit 142 first closes the gate circuit 152 and connects both the switches 164a and 164b to the b contact. And
The received data stored in the memory 188 of the storage device 154 is read and transferred to the image frame separation circuit 166 via the switching circuit 164.

The image frame separation circuit 166 extracts the frame header F from the input image data multiplexing frame structure.
The H, GOB header and MB header are separated, and the separated header information is applied to the FH decoding circuit 168, GOBH decoding circuit 170 and MB decoding circuit 172, respectively, and the compressed image data itself is applied to the variable length decoding circuit 174. . F
The H decoding circuit 168, GOBH decoding circuit 170 and MB decoding circuit 172 decode the respective header information.

That is, the FH decoding circuit 168
The format (CIF or QCIF) of the frame currently being processed is identified from PTYPE in the header, and the identification information is used as the identification information.
Output to. The circuit 168 also identifies, from the TR information, the frame number currently being processed, and the entire INTRA detection circuit 1
Output to 50.

The GOBH decoding circuit 170 uses the GQUANT
From the information, the GOB macroblock (M
B) The quantized value (Q value) is read and the quantized value setting circuit 1
Supply to 77. The MB decoding circuit 172 determines from the MTYPE information of the MB header whether the macro block currently being processed is intra-frame encoded (INTRA) or inter-frame encoded (INTER), and
The identification information of A / INTER is input to the arithmetic circuit 180 and all IN
It is supplied to the TRA detection circuit 150. MB decoding circuit 172
Also, the presence or absence of motion compensation (MC) is read from the MTYPE information, and when motion compensation is performed, the motion vector is supplied to the memory control circuit 184.

The image information separated by the image frame separation circuit 166 is variable length decoded by the variable length decoding circuit 174 and applied to the inverse quantization circuit 176. Inverse quantization circuit 1
76 is a quantization step by the quantization value setting circuit 177.
Dequantize the output of circuit 174 by size. Inverse DCT
The conversion circuit 178 converts the output of the inverse quantization circuit 176 into an inverse DCT.
Convert.

When intra-frame coded (INTRA), the output of the inverse DCT conversion circuit 178 passes through the arithmetic circuit 180 and is applied to the frame memory 182 to be sequentially written in the storage area for the current frame.

When inter-frame coded (INTER), the output of the inverse DCT conversion circuit 178 is the inter-frame difference data, and the arithmetic circuit 180 responds to the INTER / INTRA identification signal from the MBH decoding circuit 172. The switches 180a and 180b are connected to the b contact.
As a result, the adder 180c causes the inverse DCT conversion circuit 17
The image data of the previous frame from the previous frame area of the frame memory 182 is added to the difference data output from the frame memory 182.

In the MC (motion compensation) mode, the memory control circuit 184 reads the image data of the previous frame from the position shifted by the amount of the motion vector according to the motion vector information from the MBH decoding circuit 172 and sets the filter 186. It is applied to the adder 180c via the. In addition, MC
In the mode, the filter 186 is turned on / off based on the MTYPE information.

In this way, while the decoded image data is being written in the current frame storage area of the frame memory 182, the entire INTRA detection circuit 150 displays one screen (frame) by the frame number and the INTER / INTRA information. It is checked whether or not all are in INTRA mode. If all are in INTRA mode, the gate circuit 152 is opened and the image input / output circuit 118 from the frame memory 182 is opened.
Allows image data supply to. As a result, one screen is displayed on the image display device 116 from the completely restored image.

Interframe coding (INTER) even for one copy
The displayed frame (screen) cannot be correctly restored without proper data of the previous frame, and if it is displayed as an image, it will be a disordered screen. However, in the present embodiment, the image display is started from an image in which one screen is all in the INTRA mode, that is, an image that can be completely restored only by the screen, so that the distorted image is not displayed on the screen.

FIG. 16 shows a schematic block diagram of another embodiment of the present invention, and FIG. 17 shows a schematic block diagram of its characteristic portion. FIG. 17 corresponds to FIG. Figure 11
The same components as those in FIG. 15 are designated by the same reference numerals.

In FIG. 16, reference numeral 202 is an all-INTRA detection circuit, 204 is a memory device for answering machine recording, 206 is an FH decoding circuit for decoding a frame header at the time of answering machine recording, and 208.
Is a system control circuit for controlling the whole. As shown in FIG. 17, the storage device 204 stores the memory 210, the decoding result of the FH decoding circuit 206 (in particular, the frame number), and the memory 210 according to the instruction from the system control circuit 208.
Control circuit 212 for controlling writing and reading of data
Consists of.

In the embodiments shown in FIGS. 11 and 15, the received image information is recorded in the storage device without changing the image data multiplexed frame structure. However, in the embodiments shown in FIGS. 16 and 17, the frame header is not recorded. The received image information is stored for each frame. As a result, the storage capacity of the storage device 204 is substantially increased. As the storage medium of the memory 210, like the memory 188, a solid-state memory, a magnetic disk,
Optical disks, magneto-optical disks, etc. can be used.

Next, the operation in the absence mode (absent recording) will be described. When there is an incoming call in the absence mode, the call is connected as described above, and the BCH decoding circuit 160 is
The BCH frame shown in FIG. 2 is decoded, and the reception data is output with the image data multiplexing frame structure shown in FIG. The output is sent to the switching circuit 164 via the receiving buffer 162.
Applied to. The system control circuit 208 switches the switches 164a and 164b of the switching circuit 164 according to the call connection.
Are both connected to the a contact. As a result, the received data having the image data multiplexing frame structure shown in FIG. 13 is sent to the image frame separation circuit 166 via the switch 164a, and to the storage device 204 and FH via the switch 164b.
It is applied to the decoding circuit 206.

The FH decoding circuit 206 is connected to the FH decoding circuit 168.
Similarly, the frame header is decoded, the head of the frame is notified to the memory control circuit 212, and the frame number information is supplied to the system control circuit 208 and the memory control circuit 212. The memory control circuit 212 writes the received data from the switch 164b in the memory 210 in response to the notification of the beginning of the frame. System control circuit 2
8 stores the image information currently stored in the memory 210 and the frame number from the FH decoding circuit 206 in a linked manner.

In this way, the system control circuit 2 stores the received data in the memory 210 frame by frame.
08 stores the frame number linked to the storage position information.

The image frame separation circuit 166 separates each header information and supplies it to the decoding circuits 168, 170 and 172. In this embodiment, it is only necessary to detect a coded frame in which one frame is not all frames, and it is not necessary for the circuit 174 and thereafter to be operating.

Decoding circuits 168, 170 and 172 decode the header information as described above, and FH decoding circuit 168.
Supplies the frame number information to all INTRA detection circuits 202 and the system control circuit 208, and the MBH decoding circuit 17
2 shows all INTER / INTRA identification information
It is supplied to the detection circuit 202. All INTRA detection circuit 20
2 checks from the frame number information and the INTER / INTRA identification information whether or not all of the one frame is intra-frame coded, and when detecting all the intra-frame coded frames, the frame number is determined by the system control circuit. Notify 208.

The system control circuit 208 uses all INTRA
The frame number that matches the frame number notified from the detection circuit 202 is traced back from the frame numbers of the received data stored in the storage device 204, and all the information stored before the stored information of the matched frame number is checked. ,
Delete from memory 210. Since the first frame of the received data stored in the storage device 204 in this way is guaranteed to be the compressed image data of all INTRA, it is read by the sequential decoding circuit 124 to be decoded,
An image may be displayed on the image display device 116.

In the embodiments described after FIG. 11, since the received data is recorded in the compressed state in the absence, the quality of the reproduced image is good. Further, since it is in the compressed state, it is possible to record an image for a relatively long time in the storage devices 154 and 204.
Since it is not necessary to provide an analog recording / reproducing device such as a VTR, the device can be downsized.

Furthermore, since the reproduction output is started from all the intra-frame coded images, an image which is disturbed at the beginning of reproduction is not displayed. Further, since the received data after the image which is all intra-frame coded is stored in the storage device, the storage capacity can be effectively utilized.

[0132]

As can be easily understood from the above description, according to the present invention, the presence / absence and the degree of γ correction on the image transmitting side can be controlled according to the image receiving side, so that the color reproducibility and the image quality can be improved. improves.

Further, according to the present invention, the image received when the user is absent can be recorded and reproduced appropriately. At this time, the reproduction output is started from all the intra-frame coded images, so that an image disturbed at the beginning of reproduction is not displayed. Since the received image information is recorded in a compressed state, the image quality of the reproduced image is good and it can be recorded in the storage device for a long time.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a procedure from call setting to disconnection.

FIG. 3 is a diagram showing an in-channel control procedure.

FIG. FIG. 221 is an explanatory diagram of a frame configuration of 221.

FIG. 5 is a bit configuration diagram of FAS.

FIG. 6 is a bit configuration diagram of BAS.

FIG. 7 is a detailed circuit block diagram of the process circuit 12b of FIG.

FIG. 8 is a characteristic diagram of γ correction.

FIG. 9 is a transmission format of γ correction control information.

FIG. 10 is an example of a γ correction circuit 52R, 52G, 52B.

FIG. 11 is a schematic block diagram of an embodiment of the present invention having an answering machine function.

FIG. 12 is a structural diagram of a BCH error correction frame.

FIG. 13 is a structural diagram of an image data multiplexing frame.

FIG. 14 is an explanatory diagram of image formats CIF and QCIF.

15 is a schematic block diagram of a characteristic part of FIG.

FIG. 16 is a schematic block diagram of a second embodiment having an answering machine function.

17 is a schematic block diagram of a characteristic part of FIG.

[Explanation of symbols]

10: Camera 12a: Image sensor 12b: Process circuit 14: Document camera 16: Image display device 18: Image input / output circuit 22: Image encoding circuit 24: Image decoding circuit 26: Handset 28: Microphone 30: Speaker 32: Audio Input / output interface 34: Speech coding circuit 36: Speech decoding circuit 38: Data terminal 40: Data interface 42: System control circuit 44: Operating device 46: Line interface 48:
Separation and multiplexing circuit 50R, 50G, 50B: White balance adjustment circuit 52R, 52G, 52B: γ correction circuit 54R, 54G, 54B: White clip circuit
56R, 56G, 56B: Low-pass filter (LP
F) 110: camera 114: document camera 116: image display device 118: image input / output circuit 12
2: image encoding circuit 124: image decoding circuit 126: handset 12
8: microphone 130: speaker 132: voice input / output interface 134: voice encoding circuit 136: voice decoding circuit 142: system control circuit 144: operating device 146: line interface 148: demultiplexing circuit 150: all INTRA detection circuit 152 :
Gate circuit 154: Storage device 160: BCH decoding circuit 162: Reception buffer 164: Switching circuit 1
64a, 164b: Switch 166: Image frame separation circuit 168: FH decoding circuit 170: GOBH decoding circuit 172: MBH decoding circuit 174: Variable length decoding circuit
176: Inverse quantization circuit 177: Quantization value setting circuit 178: Inverse DCT conversion circuit 180: Arithmetic circuit 180a, 180b: Switch 180c: Adder 1
82: Frame memory 184: Memory control circuit 18
6: Filter 188: Memory 190: Memory control circuit 202: All INTRA detection circuit 204: Storage device 206: FH decoding circuit 208: System control circuit
210: Memory 212: Memory Control Circuit

Claims (4)

[Claims] 1. An image receiving device of an image transmission system for compressing and transmitting image information by intra-screen coding and inter-screen coding, and a storage means for storing received image information in the absence state in a compressed state. Decoding means for decoding the compressed image information read from the storage means, and detection means for detecting an image in which one screen is entirely intra-coded from the compressed image information read from the storage means. An image receiving apparatus comprising: a control unit configured to control the reproduction output of the restored image signal output from the decoding unit according to the detection output of the detection unit. 2. An image receiving device of an image transmission system for compressing and transmitting image information by intra-picture coding and inter-picture coding, and a storage means for storing received image information in the absence of compression. Based on the received image information when the user is absent, a detection unit that detects an image in which one screen is entirely coded in the screen, and all the one screen is coded in the screen according to the detection output of the detection unit An image receiving apparatus comprising: a control unit that erases received image information prior to an image from the storage unit. 3. An image transmission system, characterized in that the correction value of the γ correction means on the image transmission side is adjustable and the γ correction means is controlled in accordance with the request from the image reception side. 4. A γ correction means for γ correcting an image, and the γ correction means.
It comprises a transmitting means for transmitting the output image of the correcting means, a control information receiving means for receiving the γ correction control information, and a control means for controlling the γ correcting means according to the γ correction control information received by the control information receiving means. An image transmission device characterized by the above.