JPH0521239B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a character/figure luminance signal correction circuit, and is particularly applicable to a data display system that reproduces character/figure data (hereinafter referred to as data) using a color television set. It is suitable for this purpose.

[Background technology and its problems]

In recent years, with the spread of color television receivers, data transmission systems have been developed that use color television sets as display devices to reproduce news and various information. The first example is a captain system (Character System) that transmits data stored in a data center via a telephone line to a color television set installed on a subscriber's telephone terminal and reproduces color image information. And Pattern
Telephone Access Information Network
System). A second example is still image broadcasting, which utilizes television broadcasting and broadcasts data by inserting it into the blanking period of the television signal, and this data is received by a color television set and reproduced as color image information. .

By the way, when trying to display data about text and graphics on a television set, the text and graphics have a frequency of a luminance signal that corresponds to a narrow part such as a line or part of a character (hereinafter referred to as a "line part"). Since the frequency is close to the highest frequency of the television set, there is a risk that the signal processing system inside the television set will not be able to respond. For example, if there is a line with a minimum width of one dot on the screen, the luminance signal S1 obtained by scanning this line is as shown in Figure 1A.
The pulse has a time width of 175 ns, but when this luminance signal S1 is passed through the trap circuit 2 of the video receiving circuit 1 of the television set as shown in FIG. Inevitable.

Incidentally, the video reception circuit 1 amplifies the video detection signal S2 detected by the video detection circuit in the video amplification circuit 3, and then supplies it to the delay line 4 through the 3.58MHz trap circuit 2 to obtain the luminance signal Y. The video signal S3 is separated into the color demodulation circuit 5, and the carrier color signal S4 is sent to the output end of the band amplifier 6.
It is made to obtain. Here, the trap circuit 2 is provided to prevent the occurrence of a 3.58 MHz beat, and removes the 3.58 MHz signal component contained in the luminance signal Y.

However, this 3.58MHz trap circuit 2 is generally composed of an LC series resonant circuit 2A, and therefore its gain characteristics depend on the color subcarrier (f _s = 3.58MHz) and its surrounding frequencies, as shown in Figure 3A. components can be greatly attenuated. However, the group delay time of the series resonant circuit 2A becomes large near the frequency _fs of the color subcarrier, as shown in FIG. 3B.
Therefore, when a pulse with a relatively narrow time width arrives as shown in FIG. 1A, the output S5 of the trap circuit 2 has a ringing waveform portion P2 following the trailing edge of the pulse waveform portion P1 as shown in FIG. 1B. It becomes a waveform. Generally speaking, the impulse response in an ideal filter circuit is considered to have ringing waveform parts P12 and P13 at both the leading and trailing edges of the pulse waveform part P11, as shown in FIG. It is considered that the group delay time curve has a uniform group delay time curve in addition to having no curve or a curved curve.

Output waveform S6 (fourth waveform) of this ideal filter circuit
) is compared with the output waveform S4 of the trap circuit 2 (FIG. 1B), considering that in the case of the trap circuit 2, there is a ringing waveform portion P2 only at the trailing edge of the pulse waveform portion P1, this ringing waveform portion P2 is This is a cause of group delay distortion, and if the primary color signals R, G, and B sent to the color receiving tube are created based on the luminance signal Y having such a waveform, cross color will occur and the color at the trailing edge of the linear portion will change. It is unavoidable that the result will be smeared.

[Purpose of the invention]

The present invention is designed to eliminate such color bleeding phenomenon in consideration of the above points.

[Summary of the invention]

In order to achieve this purpose, the present invention includes:
By pre-processing the waveform of the brightness signal obtained by decoding data corresponding to the image to be displayed so as to approximate the output waveform of an ideal filter circuit and inputting it to the television set, the brightness signal of the television set is To prevent a luminance signal from being subjected to group delay distortion when passing through a system.

〔Example〕

Embodiments in which the present invention is applied to a captain system will be described in detail below with reference to the drawings. In this data transmission system, as shown in FIG. By switching, data transmitted from the data center 15 through the telephone exchange 12 and the telephone line 13 can be received and displayed by the information receiving device 16.

The information receiving device 16 transmits a command signal obtained by a signal processing circuit 19 based on the information selection input from the keyboard 18 to the telephone line 1 via a modem 17 connected to the line switch 14.
3, and is sent as an upstream data signal. At this time, the data returned from the data center 15 is again supplied to the modem 17 as a downlink data signal via the telephone line 13, demodulated, and sent to the signal processing circuit 19.
given to.

Here, the data is decoded in the image signal reproducing circuit 20 and converted into an image signal including color signals R, G, B, etc., and the color signals R, G, B and foreground signal _YD are provided to the luminance signal forming circuit 21. is,
After undergoing necessary correction, it is applied to a video signal forming circuit 22 together with other signals, and the video signal obtained at its output terminal is input to and displayed on a television set 23.

When the foreground signal _YD is at logic "1" level, it changes the brightness and color of the area where characters should be displayed (this is called the foreground) and the area where no characters are displayed other than this area (this is called the background). ) is used to make the brightness and color brighter (e.g. twice as bright) and have a different color, so that the character signal is generated during the time span of the foreground signal Y _D. being done.

As shown in FIG. 6, the luminance signal forming circuit 21 transfers the decoded color signals R, G, and B coming from the image signal reproducing circuit 20 via buffer circuits 31R, 31G, and 31B to a switching transistor 32.
Matrix circuit 33 received by R, 32G, 32B
has a matrix resistor 33 from its emitter.
The outputs derived through R, 33G, and 33B are combined at a common connection point 34 and output to an amplification transistor 35.
The luminance signal Y is outputted to the output terminal 36 via the luminance signal Y.

In this embodiment, transistors 32R, 32
A pull-up power supply resistor 39 connected to a transistor 38 that receives a foreground signal Y _D coming from the image signal reproducing circuit 20 via a buffer circuit 37 is connected to the base of G, 32B, and the foreground signal Y D is connected to the base of the foreground signal Y _D. By applying a pull-up voltage corresponding to a bright brightness level to the bases of transistors 32R, 32G, and 32B when the logic is "1", common connection point 34 and transistor 35 are
The voltage level of the luminance signal Y led out to the output terminal 36 through the gate is increased. On the other hand, when the foreground signal Y _D is logic "0", the transistor 3
By applying a pull-up voltage of a dark luminance level to the bases of 2R, 32G, and 32B, the voltage level of the luminance signal Y at the output terminal 36 is lowered. In this way, when the foreground signal Y _D is logic "1", by increasing the brightness signal Y, the brightness of the character part is made brighter than the background, thereby making the display of the character more noticeable.

The luminance signal Y is transmitted through transistors 41, 42,
The signal is supplied via a buffer amplifier circuit 46 consisting of 43, 44, and 45 to a brightness correction circuit 49 consisting of a delay circuit 47 and a bandpass filter circuit 48.

The bandpass filter circuit 48 is shown in FIGS. 7A and 7B.
As shown in the figure, it has gain and group delay time characteristics that are almost flat in the passband, and has a passband of ±500kHz centered around the color subcarrier frequency f _s (=3.58MHz). Therefore, when the bandpass filter 48 receives a pulse input as the luminance signal S1 as shown in FIG. 8A, a signal is generated at the output end over a period of time wider than the pulse width of the luminance signal S1, as shown in FIG. 8B.
A ringing waveform signal that includes a frequency component of 3.58MHz±500kHz, has an envelope with a maximum peak in the center, and the amplitude gradually decreases toward both ends, and the maximum peak value is relatively small. Output S12.

Further, the delay circuit 27 delays the pulse input as the luminance signal S1, and when a substantially central portion of the ringing waveform signal S12 is generated at the output end of the bandpass filter 28, a pulse output S13 as shown in FIG. 8C is output at the output end. Send out.

The output S13 of this delay circuit 47 is passed to the output S1 of the filter circuit 48 in a subtraction circuit 55 having a differential circuit configuration including transistors 52, 53, and 54.
2, and thus output to the output terminal 57 via the output transistor 56, as shown in FIG. The brightness signal S14 is the output of the brightness correction circuit 21
Sent as Y _L.

The corrected brightness signal Y _L created in the brightness correction circuit 21 in this way is the central pulse waveform portion P2.
1 and continuous ringing waveform portions P22 and P23 at its front and rear edges, and this configuration approximates the output waveform S6 of the ideal filter circuit described above with reference to FIG. However, this corrected luminance signal S14 is converted to RF in the video signal forming circuit 22.
It is applied to the antenna terminal of the television set 23 as a part of the high frequency composite video signal VID formed by modulation, and thereby the video receiving circuit 1 (second
When the video detection signal S2 is input to the video amplification circuit 3 shown in the figure, the trap circuit 2 traps the color subcarrier frequency f _s (=3.58MHz) and frequency components around it. However, trap circuit 2 at this time
The output S5 not only has a pulse waveform portion P1 and a trailing edge ringing waveform portion P2 that are almost the same as the waveforms described above with respect to FIG. 1B, but also has a pulse waveform portion P2.
An output substantially similar to the waveform of FIG. 8D having a similar ringing waveform portion at the leading edge of the waveform 1 is obtained.

However, the output waveform of this trap circuit 2 is
As mentioned above for the figure, the color subcarrier frequency f _s (=
The impulse response waveform is similar to the impulse response waveform of an ideal filter circuit that cuts sharply at 3.58 MHz), and therefore, it is as if trap circuit 2 were replaced with this ideal filter circuit. Similar output waveforms can be obtained. This means that there will be no color shift in the image on the picture tube of the television set.

In the above description, an embodiment has been described in which the present invention is applied to a captain system, but the present invention is not limited thereto, and can be widely applied to still image broadcasting and other applications where data is displayed using a color television set.

Further, in the above description, the composite video signal VID obtained based on the output of the character color signal correction circuit 11 is RF modulated and then applied to the antenna terminal of the television set.
Even if the signal is directly connected to the video detection output terminal of the television set without modulation, the same effect as described above can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, a trap circuit that is generally used in the brightness signal system of a television set can be used to generate a thin pulse corresponding to the linear part of a character figure (minimum 175 ns duration corresponding to one dot). Even if the brightness signal is passed through a filter circuit with a substantially uniform effective group delay time, it is possible to generate a luminance signal in a television set that is similar to that obtained through a filter circuit with a substantially uniform effective group delay time. Therefore, it is possible to prevent inconveniences such as color blurring at the position of the trailing edge of the linear portion on the display surface, and it is therefore possible to reproduce clear characters and figures.

[Brief explanation of drawings]

Fig. 1 is a signal waveform diagram to explain the problems of the trap circuit of a television set, Fig. 2 is a schematic block diagram showing the trap circuit, Fig. 3 is a curve diagram showing its characteristics, and Fig. 4 5 is a curve diagram showing the impulse response of an ideal filter circuit, FIG. 5 is a block diagram showing a data transmission system to which the character/figure luminance signal correction circuit according to the present invention is applied, and FIG. 6 is a connection diagram showing the luminance signal forming circuit. Figure 7 is a curve diagram showing the characteristics of the bandpass filter, Figure 8 is a curve diagram showing the characteristics of the bandpass filter.
This figure is a signal waveform diagram for explaining the operation of FIG. 6. 1... Video receiving circuit, 2... Trap circuit, 3
...Video amplifier circuit, 4...Delay line, 5...Color demodulation circuit, 6...Band amplifier, 11...Telephone, 12
...Telephone exchange, 14...Line switch, 15...
...Data center, 16...Information signal equipment, 17...
...Modulation/demodulation device, 18... Keyboard, 19... Signal processing circuit, 20... Image signal reproducing circuit, 21...
...Text color signal correction circuit, 22...Video signal forming circuit, 23...Color television set, 33...
... Matrix circuit, 46 ... Buffer amplifier circuit,
47...Delay circuit, 48...Band pass filter, 49...Brightness correction circuit, 55...Subtraction circuit.

Claims (1)

[Claims] 1. In a data display system that displays a color image by forming a video signal from an image signal reproduced from the data and supplying it to a television set having a trap circuit for a luminance signal, the trap circuit of the trap circuit is used in the pass band. a bandpass filter that receives a luminance signal obtained based on the image signal as an input pulse and sends out a ringing waveform signal, and a bandpass filter that receives the input pulse and corresponds to a position approximately at the center of the time width of the ringing waveform signal; and a subtraction circuit that subtracts the ringing waveform signal of the bandpass filter and the pulse waveform signal of the delay circuit from each other, and corrects the output of the subtraction circuit. A character/figure luminance signal correction circuit, characterized in that the above-mentioned video signal is formed by using the luminance signal as the luminance signal.