Image transmission system - Patent Review 4953196

What is claimed is:

1. A video phone comprising:

input means for sequentially entering image data;

digitizing means for digitizing said input image data into digital image data;

memory means for sequentially storing said digital image data;

image signal producing means for producing an output image signal based on said digital image data sequentially read out from said memory means;

display means for sequentially displaying an image described by said output image signal;

compression and expansion means for compressing said digital image data read out from said memory means into compressed image data in an image transmitting mode and for expanding compressed image data into digital image data in an image receiving mode;

telephone means having telephone functions for transmitting and receiving a call;

line control means coupled to a public analog telephone line for selectively coupling one of said compression and expansion means and said telephone means to said public analog telephone line, said line control means including modem means for modulating said compressed image data from said compression and expansion means into a voice frequency signal in the image transmitting mode and for demodulating a voice frequency signal received through said public analog telephone line into compressed image data in the image receiving mode; and

control means for controlling at least said memory means and said compression and expansion means,

said control means having means for freezing the image displayed on said display means at an arbitrary time by stopping the sequential storage of said digital image data into said memory means so that said compressed image data related to a frozen image is read out from said memory means and supplied simultaneously to said image signal producing means and said compression and expansion means in the image transmitting mode,

said control means controlling said memory means and said compression and expansion means in the image receiving mode so that said compressed image data related to said voice frequency signal received through said public analog telephone line is first stored in said memory means and read out therefrom to be expanded in said compression and expansion means into digital image data which is then stored in said memory means, said digital image data being read out from said memory means to be supplied to said image signal producing means.

2. A video phone comprising:

input means for sequentially entering image data;

digitizing means for digitizing said input image data into digital image data, said digitizing means comprising means for producing three kinds of digital primary color signals as said digital image data;

memory means for sequentially storing said digital image data;

image signal producing means for producing an output image signal based on said digital image data sequentially read out from said memory means;

display means for sequentially displaying an image described by said output image signal;

compression and expansion means for compressing said digital image data read out from said memory means into compressed image data in an image transmitting mode and for expanding compressed image data into digital image data in an image receiving mode, said compression and expansion means comprising a compression part and an expansion part;

telephone means having telephone functions for transmitting and receiving a call;

line control means coupled to a public analog telephone line for selectively coupling one of said compression and expansion means and said telephone means to said public analog telephone line, said line control means including modem means for modulating said compressed image data from said compression and expansion means into a voice frequency signal in the image transmitting mode and for demodulating a voice frequency signal received through said public analog telephone line into compressed image data in the image receiving mode; and

control means for controlling at least said memory means and said compression and expansion means,

said control means having means for freezing the image displayed on said display means at an arbitrary time by stopping the sequential storage of said digital image data into said memory means so that said compressed image data related to a frozen image is read out from said memory means and supplied simultaneously to said image signal producing means and said compression and expansion means in the image transmitting mode,

said control means controlling said compression and expansion means and said memory means in the image receiving mode so that said compressed image data related to said voice frequency signal received through said public analog telephone line is expanded into digital image data in said compression and expansion means and stored in said memory means and read out therefrom to be supplied to said image signal producing means,

said compression part comprising first converting means for converting said digital primary color signals into a digital luminance signal and two kinds of digital color difference signals, a first modulator for modulating the digital luminance signal into a modulated digital luminance signal, and a second modulator for independently modulating the two kinds of digital color difference signals into two kinds of modulated digital color difference signals, said second modulator modulating at least one of the two kinds of digital color difference signals according to a second modulation system which is different from a first modulation system which is used by said first modulator,

said expansion part comprising a first demodulator for demodulating said modulated digital luminance signal into said digital luminance signal, a second demodulator for demodulating said two kinds of modulated digital color difference signals into said two kinds of digital color difference signals, and second converting means for converting said digital luminance signal and said two kinds of digital color difference signals into three kinds of reproduced digital primary color signals.

3. A video phone as claimed in claim 1 in which said control means controls said first and second converting means in a simulation mode to simulate on said display means a display of said input image data as viewed on a receiving end of said public analog telephone line, said control means controlling said first converting means to store said digital luminance signal and said two kinds of digital color difference signals in said memory means and controlling said second converting means to read out said digital luminance signal and said two kinds of digital color difference signals and to store said reproduced digital primary color signals in said memory means, said reproduced digital primary color signals being read out from said memory means and supplied to said image signal producing means in said simulation mode.

4. A video phone as claimed in claim 1 which further comprises first means for controlling one of a write-in sequence and a read-out sequence of said memory means, and second means for selecting one of a normal mode and a mirror mode and controlling said first means responsive to a selection so as to display a selected one of a normal image and a mirror image of said input image data.

5. A video phone as claimed in claim 1 in which said control means controls said compression and expansion means in a simulation mode to simulate on said display means a display of said input image data as viewed on a receiving end of said public analog telephone line, said control means controlling said compression and expansion means to store said reproduced digital primary color signals in said memory means, said reproduced digital primary color signals being read out from said memory means and supplied to said image signal producing means in said simulation mode.

6. A video phone as claimed in claim 1 in which said compression and expansion means further comprises thin-out means in said compression part and interpolator means in said expansion part, said thin-out means thinning out said two kinds of digital color difference signals before modulation by said modulator means, said interpolator means interpolating said two kinds of demodulated digital color difference signals before conversion in said second converting means.

7. A video phone as claimed in claim 1 in which said input means comprises a video camera for picking up an image.

8. A video phone as claimed in claim 1 in which said input means outputs said input image data in conformance with a standardized color television system, and said image signal producing means produces said image signal in conformance with a standardized color television system.

9. A video phone as claimed in claim 1 in which said display means comprises a liquid crystal display panel.

10. A video phone as claimed in claim 1 in which said control means comprises a keyboard for entering data and instructions.

11. A video phone as claimed in claim 1 which further comprises enabling and disabling means for enabling and disabling a monitoring of an image displayed on said display means.

12. A video phone as claimed in claim 11 in which said enabling and disabling means comprises a slidable cover, said slidable cover having first and second positions respectively for exposing and covering said display means so as to enable and disable monitoring of the image displayed on said display means.

13. A video phone comprising:

input means for sequentially entering image data;

digitizing means for digitizing said input image data into digital image data;

memory means for sequentially storing said digital image data;

image signal producing means for producing an output image signal based on said digital image data sequentially read out from said memory means;

display means for sequentially displaying an image described by said output image signal;

compression and expansion means for compressing said digital image data read out from said memory means into compressed image data in an image transmitting mode and for expanding compressed image data into digital image data in an image receiving mode;

telephone means having telephone functions for transmitting and receiving a call;

line control means coupled to a public analog telephone line for selectively coupling one of said compression and expansion means and said telephone means to said public analog telephone line, said line control means including modem means for modulating said compressed image data from said compression and expansion means into a voice frequency signal in the image transmitting mode and for demodulating a voice frequency signal received through said public analog telephone line into compressed image data in the image receiving mode;

control means for controlling at least said memory means and said compression and expansion means; and

enabling and disabling means for enabling and disabling a monitoring of an image displayed on said display means,

said control means having means for freezing the image displayed on said display means at an arbitrary time by stopping the sequential storage of said digital image data into said memory means so that said compressed image data related to a frozen image is read out from said memory means and supplied simultaneously to said image signal producing means and said compression and expansion means in the image transmitting mode,

said control means controlling said compression and expansion means and said memory means in the image receiving mode so that said compressed image data related to said voice frequency signal received through said public analog telephone line is expanded into digital image data in said compression and expansion means and stored in said memory means and read out therefrom to be supplied to said image signal producing means,

said enabling and disabling means comprising means for electrically enabling and disabling the display of the image on said display by controlling said line control means.

14. A video phone as claimed in claim 13 which further comprises means for manually operating said enabling and disabling means.

15. A video phone as claimed in claim 14 in which said means for manually operating said enabling and disabling means disables the display of the image on said display means when manipulated.

16. A video phone as claimed in claim 14 in which said means for manually operating said enabling and disabling means enables the display of the image on said display means when manipulated.

17. A video phone as claimed in claim 13 which further comprises register means for registering predetermined codes, and means for automatically enabling the display of the image on said display means when one of said codes is received prior to a reception of said voice frequency signal through said public analog telephone line and automatically disabling the display of the image on said display means when none of said codes is received prior to the reception of said voice frequency signal through said public analog telephone line.

18. A video phone as claimed in claim 17 in which said codes are telephone numbers of callers from which said video phone is permitted to receive an image data to be displayed on said display means.

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BACKGROUND OF THE INVENTION

The present invention generally relates to image transmission systems, and more particularly to an image transmission system suitable for use in a video phone, a facsimile machine and the like.

Various video phone systems have been proposed in the past. The video phone was developed mainly in the United States around 1950 to 1970 and experimental results on various systems were announced, but none were reduced to practice. The fundamental problems of the proposed video phone were that the system required a wide band video line exclusively for image transmission. However, the need for setting up the wide band video line exclusively for the video phone made it impractical costwise.

Coming into the 1980's, it has now become possible to reduce into practice a digital data line capable of data transmission at a transmission rate in the order of 56 bps to 64 bps. And, new image transmission systems have been proposed by combining such a digital data line with advanced digital image data compression techniques. But still, such new image transmission systems have not been reduced to practice since the digital data line above described has yet to come into wide use.

There are also image transmission systems which transmit a still picture on a public analog telephone line by using the digital image data compression technique. However, these systems take a long time to transmit the still picture. For example, it takes several tens of seconds to several minutes to transmit one still picture. Accordingly, these systems are not of much use in a personal video phone from the practical point of view.

There is a personal video phone employing a system which transmits one still picture within a few seconds by sacrificing the picture size and picture quality, that is, greatly reducing the quantity of transmitting image data. But this system is restricted to the transmission of a black-and-white picture.

In order to transmit image data related to a color picture, the quantity of the transmitting image data becomes extremely large and it inevitably takes a long time to transmit the image data. As a result, it is extremely difficult to realize an inexpensive personal video phone which can transmit the image data related to the color picture quickly without greatly deteriorating the picture quality.

When transmitting a still picture or a picture having negligibly small movements therein from a video phone, a facsimile machine and the like, a differential pulse code modulation (hereinafter simply referred to as a DPCM) or a delta modulation is usually used for efficiency. The still picture may be a page of a book, a scenery, a portrait and the like.

The DPCM is a predictive coding as is well known, and uses a correlation between picture element data or line data. In other words, the DPCM predicts by use of this correlation a value of a present picture element data from a value of a picture element data which is already encoded, and encodes a difference between the predicted value with an actual value. A difference signal is pulse code modulated into three to four bits.

On the other hand, the delta modulation approximates a signal waveform by a staircase wave having an amplitude which varies by .+-..DELTA., and obtains one step of the staircase wave as a binary code. Hence, the delta modulation essentially quantizes the difference signal in the DPCM into one bit. According to the delta modulation, the quantization step size (width) is constant with respect to a change in the data.

When the DPCM is used for an image data compression system to separate color image data related to a relatively small picture into a luminance signal and color difference signals, independently encode the luminance signal and the color difference signals and transmit the encoded data on the public line, the picture quality of the transmitted image data is satisfactory but the data compression rate is insufficient. As a result, the data transmission cannot be completed within a short time.

The data compression rate is sufficient when the delta modulation is used for the image data compression system, but noise becomes conspicuous with respect to the luminance signal, and it is impossible to obtain a satisfactory picture quality from the transmitted image data.

On the other hand, a delta modulation with adaptive control (hereinafter simply referred to as adaptive delta modulation) can also be used for transmitting a still picture. The adaptive delta modulation uses the fact that the difference between mutually adjacent samples becomes small as the sampling frequency becomes high, and encodes the difference signal into one bit by carrying out the sampling at a high frequency. When encoding the difference signal into one bit, the quantization step size is determined from past transmission pulse train. In other words, when pulses of the same polarity are repeated, the quantization step size is increased so as to follow a large difference between the mutually adjacent samples. On the other hand, the quantization step size is decreased to suppress the quantization noise when pulses of different polarities occur. Hence, according to the adaptive delta modulation, the quantization step size varies with a predetermined rate with respect to a change in the data.

However, because 50% or more picture element data out of the total picture element data constituting a still picture usually have no change in the tone. For this reason, the tone of a reproduced picture becomes unstable when the delta modulation or the adaptive delta modulation is used. To the human eye, it is a large tone change in the still picture that has a large effect visually.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to provide a novel and useful image transmission system in which the problems described heretofore are eliminated.

Another and more specific object of the present invention is to provide a video phone comprising input means for sequentially entering image data, digitizing means for digitizing the input image data into digital image data, memory means for sequentially storing the digital image data, image signal producing means for producing an output image signal based on the digital image data sequentially read out from the memory means, display means for sequentially displaying an image described by the output image signal, compression and expansion means for compressing the digital image data read out from the memory means into compressed image data, telephone means having telephone functions for transmitting and receiving a call, line control means coupled to a public analog telephone line for selectively coupling one of the compression and expansion means and the telephone means to the public analog telephone line, where the line control means includes modem means for modulating the compressed image data from the compression and expansion means into a voice frequency signal and for demodulating a voice frequency signal received through the public analog telephone line into compressed image data, and control means for controlling at least the memory means and the compression and expansion means. The control means has means for freezing the image displayed on the display means at an arbitrary time by stopping the sequential storage of the digital image data into the memory means so that the compressed image data related to a frozen image is read out from the memory means and supplied simultaneously to the image signal producing means and the compression and expansion means in an image transmitting mode. In addition, the control means controls the memory means in an image receiving mode so that the compressed image data related to the voice frequency signal received through the public analog telephone line is stored in the memory means and read out therefrom to be supplied to the image signal producing means. According to the video phone of the present invention, it is possible to transmit and receive an image having a satisfactory picture quality on the public analog telephone line within a short time by use of an inexpensive circuit.

Still another object of the present invention is to provide a video phone which is further provided with means for enabling and disabling a monitoring of the image displayed on the display means. According to the video phone of the present invention, it is possible to freely refuse to see an image which is received on the public analog telephone line.

A further object of the present invention is to provide a video phone in which the compression and expansion means during a compression modulates a luminance signal according to a first modulation system and modulates at least one of two kinds of color difference signals according to a second modulation system which is different from the first modulation system, where the luminance signal and the two kinds of color difference signals are obtained by converting the input image data. The two kinds of color difference signals may be thinned out before the modulation thereof. According to the video phone of the present invention, it is possible to transmit a color still picture at a low transmission bit rate.

Another object of the present invention is to provide a video phone which has a simulation mode for simulating on the display means a display of the input image data as viewed on a receiving end of the public analog telephone line. According to the video phone of the present invention, the user can check how the receiving end will actually view the transmitted image.

Still another object of the present invention is to provide a video phone which is further provided with means for selectively displaying one of a normal image and a mirror image of the input image data. According to the video phone of the present invention, it is easy for the user to check the image which is transmitted, especially when sending a portrait of himself, because people are used to attending to their personal appearance by looking at a mirror image on a mirror.

A further object of the present invention is to provide an image transmission system for transmitting an input color image data in a compressed and encoded form comprising first converting means for converting the input color image data into a luminance signal and two kinds of color difference signals, first modulator means for modulating the luminance signal into a modulated luminance signal, and second modulator means for independently modulating the two kinds of color difference signals into two kinds of modulated color difference signals. The second modulator means modulates at least one of the two kinds of color difference signals according to a second modulation system different from a first modulation system used by the first modulator means. The modulated luminance signal and the two kinds of modulated color difference signals are transmitted as the input color image data in the compressed and encoded form. According to the image transmission system of the present invention, it is possible to transmit a color still picture at a low transmission bit rate and within a short period of time.

Another object of the present invention is to provide an image transmission system in which the second modulator means uses an advanced adaptive delta modulation as the second modulation system, where the advanced adaptive delta modulation has three modes of describing whether a first of two successive samples is greater than, equal to or smaller than a second of the two successive samples of one of the two kinds of color difference signals. According to the image transmission system of the present invention, it is possible to transmit a color still picture having a satisfactory picture quality, even when the two kinds of color difference signals are thinned out before the modulation thereof.

Still another object of the present invention is to provide an image transmission system for transmitting an input image data in a compressed form comprising density buffer means for outputting a buffer value, adder means, subtracting means for subtracting the output buffer value of the density buffer means from an input density value of the input image data to output a resulting difference value DF, first threshold output means for outputting a threshold value T, comparator means for comparing the difference value DF and the threshold value T and for producing an output signal of a first logic level when the difference value DF is greater than the threshold value T, an output signal of a second logic level when the difference value DF is smaller than -T which is complementary to the threshold value T, and an output signal of a logic level different from a logic level of an immediately preceding output signal when the difference value DF is less than or equal to the threshold value T and is greater than or equal to -T, second threshold output means for outputting a threshold value Ta, first counter means for counting a number of first logic levels of the output signal of the comparator means, and second counter means for counting a number of second logic levels of the output signal of the comparator means. The first and second counter means output counted values thereof which determine the threshold value T to be read out from the first threshold output means and the threshold value Ta to be read out from the second threshold output means. The first counter means is reset to zero when the second counter means receives the output signal of the comparator means having the second logic level, and the second counter means is reset to zero when the first counter means receives the output signal of the comparator having the first logic level. The second threshold output means outputs the threshold value Ta to the adder means to be added to the output buffer value of the density buffer means. The threshold value Ta read out from the second threshold output means is equal to zero when the counted value of one of the first and second counter means is zero and the counted value of the other of the first and second counter means is one. The output signal of the comparator means is outputted as the input image data in the compressed form. According to the image transmission system of the present invention, it is possible to transmit image data at a low transmission bit rate and still ensure reproduction of a picture having a satisfactory picture quality.

Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system block diagram generally showing a first embodiment of the image transmission system according to the present invention applied to a video phone;

FIG. 2 is a system block diagram showing the first embodiment in more detail;

FIG. 3 is a system block diagram showing an embodiment of a compression and expansion circuit of the first embodiment;

FIG. 4 is a diagram for explaining the operation of the compression and expansion circuit;

FIG. 5 is a system block diagram showing an embodiment of a modem line control circuit of the first embodiment;

FIG. 6 shows an embodiment of a transmission data format used in the first embodiment;

FIG. 7 is a flow chart for explaining the operation of a system controller of the first embodiment when making a manual calling;

FIG. 8 is a flow chart for explaining the operation of the system controller of the first embodiment when making an automatic calling;

FIG. 9 shows an example of a display on an LCD panel for explaining the automatic calling in the first embodiment;

FIG. 10 shows an embodiment of a transmission data format for the case where the mode information and the character information are transmitted;

FIG. 11 is a flow chart for explaining the image transmission procedure of the first embodiment;

FIGS. 12A and 12B are flow charts for explaining the image reception procedure of the first embodiment;

FIGS. 13A and 13B are perspective views respectively showing an embodiment of the external appearance of the video phone;

FIG. 14 is a system block diagram showing a second embodiment of the image transmission system applied to the video phone;

FIG. 15 is a system block diagram showing a third embodiment of the image transmission system applied to the video phone;

FIG. 16 is a flow chart for explaining a modification of the image transmission procedure applicable to the embodiments;

FIGS. 17A and 17B are system block diagrams respectively showing embodiments of an advanced adaptive delta modulator and a demodulator of the compression and expansion circuit; and

FIG. 18 shows the input density value and the demodulated density value which is obtained by demodulating the advanced adaptive delta modulated density data with respect to the input data number.

DETAILED DESCRIPTION

First, a description will be given on a first embodiment of the image transmission system according to the present invention applied to a video phone. FIG. 1 generally shows a block system of the video phone applied with the first embodiment. The video phone comprises an input device 1, a digitizing circuit 2, a memory 3, an image signal producing circuit 4, a display device 5, a compression and expansion circuit 6, a transmitting and receiving circuit 7, a telephone part 8, a line control circuit 9, and a control device 10.

The telephone part 8 has the functions of an ordinary telephone, and this telephone part 8 and the transmitting and receiving circuit 7 can be selectively coupled to a public analog telephone line PL through the line control circuit 9. The user can make and receive a telephone call with the telephone part 8.

When transmitting a color still picture, the color still picture is sequentially entered from the input device 1 and is converted into a digital image signal in the digitizing circuit 2. The digital image signal is sequentially stored in the memory 3. The digital image signal is sequentially read out from the memory 3 under the control of the control device 10 and is converted into a color image signal in the image signal producing circuit 4, and the display device 5 sequentially displays a color still picture reproduced from the color image signal. When the user decides on the color still picture to be transmitted, the digital image signal read out from the memory 3 is also supplied to the compression and expansion circuit 6 wherein the digital image signal is compressed under the control of the control device 10. A compressed digital image signal is supplied to the transmitting and receiving circuit 7 and is transmitted on the public analog telephone line PL through the line control circuit 9.

On the other hand, when receiving a color still picture, the compressed digital image signal is received by the transmitting and receiving circuit 7 through the public analog telephone line PL and the line control circuit 9. The compression and expansion circuit 6 expands the compressed digital image signal back into the original digital image signal which is then stored in the memory 3 under the control of the control device 10. The digital image signal read out from the memory 3 is converted into the color image signal in the image signal producing circuit 4, and the display device 5 displays the color still picture reproduced from the color image signal.

FIG. 2 shows a more detailed block system of the first embodiment. The video phone comprises a color charge coupled device (CCD) video camera 11, a video signal input circuit 12, a video memory 13, a video signal output circuit 14, a color liquid crystal display (LCD) panel 15, a system bus 16, a video compression and expansion circuit 17, a modem line control circuit 18, a voice processing circuit 19, a handset 20, a keyboard 21, and a system controller 22.

The video camera 11, the video signal input circuit 12, the video memory 13, the video signal output circuit 14 and the LCD panel 15 respectively correspond to the input device 1, the digitizing circuit 2, the memory 3, the image signal producing circuit 4 and the display device 5 shown in FIG. 1. The video compression and expansion circuit 17 and the modem line control circuit 18 respectively correspond to the compression and expansion circuit 6 and the line control circuit 9. The voice processing circuit 19, the handset 20 and the keyboard 21 correspond to the telephone part 8. In addition, the system controller 22 correspond to the control device 10.

The video camera 11 uses CCD as the image pickup device and is most suited for a portable video phone in that the video camera 11 is compact and light and has a low power consumption and a high sensitivity. The video signal input circuit 12 receives an output composite color video signal of the video camera 11. This composite color video signal is an NTSC system color video signal, for example. Accordingly, it is possible to supply to the video signal input circuit 12 an output composite color video signal of a general television apparatus or a video tape recorder, and transmit the image described by such a composite color video signal. The video signal input circuit 12 separates synchronizing signals and a video signal from the incoming composite color video signal, and produces analog RGB signals (primary color signals of red (R), green (G) and blue (B)) by subjecting the separated video signal to a chroma processing. The analog RGB signals are sampled and then subjected to an analog-to-digital conversion so as to obtain digital RGB signals. The digital RGB signals are written into the video memory 13 responsive to the synchronizing signals separated in the video signal input circuit 12.

In the present embodiment, the image to be transmitted is a portrait and the like, and the accuracy required of the image is not extremely high. For example, it is sufficient that the digital RGB signals describe the image in 96.times.96 picture elements and each of the RGB signals describe the gradation in four bits (that is, sixteen gradation levels).

The digital RGB signals stored in the video memory 13 are read out by the video signal output circuit 14 and are subjected to a digital-to-analog conversion so as to obtain analog RGB signals. The analog RGB signals are then processed into a video signal by an encoding process, and the video signal is formed into a composite color video signal by being added with synchronizing signals produced within the video signal output circuit 14. The output composite color video signal of the video signal output circuit 14 is an NTSC system color video signal, for example. Thus, the output composite color video signal of the video signal output circuit 14 may be supplied to the general video tape recorder, a video printer and the like for recording or displaying the color still picture. The video printer is sometimes also referred to as a hard copy device since it makes a hard copy of the color still picture.

In the present embodiment, the output composite color video signal of the video signal output circuit 14 is supplied to the LCD panel 15 for displaying the color still picture. The LCD panel 15 is built into the video phone. The LCD panel 15 is thin and light and has a low power consumption, making it most suited for use in the person