JPH01874A - Text blur prevention circuit in video circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a character blur prevention circuit in a video circuit such as a still image reproduction device.

BACKGROUND OF THE INVENTION In recent years, still image playback devices have been commercially available that magnetically record photographic images taken with a camera on a still image floppy disk and play the recorded images on a regular television. Here, the video signal is recorded on a plurality of tracks on the disk in a relationship of one track-one screen, that is, one revolution-one field. Then, such a video signal is read from the disk by a head, demodulated, and output.

By the way, in the normal television standard system, a 1/2 interlaced scanning (so-called interlaced scanning) system is adopted. For example, in the NTSC system like Japan, the number of horizontal scanning lines in one field is 262.5H, and the number of striped scanning lines for one screen in two fields, that is, one frame, is 52.
It is set to be 5H. When a still image disc or the like on which one field (ie, 262.degree. 5H horizontal scanning line) of video signals is recorded on one track is played back by such a television, the recording seam becomes a problem. In other words, the video signal on the same track (always the same video signal for each field) is read while the still image disc is continuously rotated, but at the recording joint (i.e., end point = start point) This means that each field is shifted by .5H1, that is, 172 minutes of the horizontal synchronization period. Therefore, if the image is reproduced as is on a normal television receiver, the screen will be distorted, making it impossible to display a normal still image.

Therefore, by alternately passing the 1-field repeated playback signal from the recording joint on the track through 0 and 5H delay circuits that correspond to 1/2 horizontal horizontal period for each field, and by synthesizing these signals, continuous horizontal synchronization can be achieved. It is necessary to create a playback signal.

For this reason, a block configuration as shown in FIG. 3 is generally adopted. First, after a video playback signal on a certain track read by the playback head 1 is amplified by the head amplifier 2, one side becomes a non-delayed through signal, and the other side becomes a through signal.
0 through 0.5H delay circuit 3 for /2 horizontal period,
The signal is input to the demodulation circuit (FM) 4 as a 5H delay signal. Here, in the demodulation circuit, these through signals and 0.
5H delay signal and switching pulse signal 5WP (
Y) (Y means a luminance signal) is alternately switched for each field. The demodulated signal is then separated by a synchronization signal separation circuit 5 as a composite synchronization signal (C-5ync), which is then separated by a synchronization signal generation circuit 6.
A synchronizing signal is generated through the video signal, and the signal demodulated by the demodulation circuit 4 is synthesized by the waveform synthesis circuit 7 and output as a frame signal (video signal) to the receiver. Here, the switching pulse signal 5WP(Y) is the fourth
As shown in the figure, a through signal and a 0°5H delay signal are selected by switching between H level and L level for each field, and a through period and a 0°5H delay period are generated. The switching pulse signal swp(y) has a vertical through period (H level) during the 0°5H delay period, and is in a through signal selection state only during the vertical synchronization period.

In the timing chart shown in FIG. 4, the video signal is placed between the horizontal synchronizing signals in the IH row. Also, near vertical synchronization, there are multiple equivalent pulses arranged in 0.5H,
Six of these equivalent pulses, ie, 3H, are used as the vertical synchronization signal (2). Before and after such a vertical synchronizing signal (2), there are also six equivalent pulses, that is, 3H's worth of 0.5H array (2) detection portions. Switching pulse signal 5WP
(Y) has a vertical through period of about 18 equivalent pulses within the 0.5H delay period,
Among them, the actual vertical synchronization signal (2) is detected and output as is as a through signal.

This is the basic method for preventing image blur for each field.

By the way, when playing such a still image, the characters of the track number in which the still image is recorded may be displayed on the screen together with the still image.

Such character information such as a track number is not recorded on the disc, but is processed by a circuit as shown in FIG. 5, for example. First, the microcomputer 8 writes data for determining the character display position to the character generation IC 9, and when the character generation IC 9 reaches the display position, the character data is outputted and displayed. At this time, the track number is displayed, for example, at the upper right position of the screen, but in any case, it is preferable to specify the position where the character is displayed and always display it at the same position. Therefore, the character generator IC 9 receives the vertical synchronizing signal V-5ynC through the integrating circuit 10 based on the composite synchronizing signal C-8ynC, and passes the horizontal synchronizing signal H-5ynC through a signal obtained by inverting the composite synchronizing signal C-5ync by the transistor 11. receive. Then, as shown in FIG. 6, the number of horizontal synchronizing signals H-5 sync is counted from the time (rising edge) when the vertical synchronizing signal SYNC is detected through the integrating circuit 1o.
The track number characters are displayed at predetermined positions determined by the program, that is, at n H positions.

Problem to be Solved by the Invention However, at the rising edge of the switching pulse signal Swp(y) at 3 H from the falling edge of the pulse generator PG, which occurs once per rotation of the floppy disk, the broken line in FIG. Whisker-like switching noise as shown by pulse A may appear on the composite synchronization signal C-3sync.

Here, in order to determine the character display position of the track number, the horizontal synchronizing signal H-3 sync is counted sequentially from the rising edge of the vertical synchronizing signal SYNC, but this noise pulse A is also counted as 18 minutes. As a result, the nXH count value is about IH earlier than the through period, resulting in a display position of 18 minutes. I like this
Since the character display shifted by H is repeated alternately, the track number display becomes a state where the characters flicker vertically and are blurred.

Means for Solving the Problems] A differentiation circuit for differentiating the switching control signal and a noise canceling circuit for grounding the output section of the composite synchronization signal when there is an output from the differentiation circuit are connected to the output section of the composite synchronization signal.

A differentiating circuit that differentiates the switching control signal to the output line of the composite synchronizing signal that includes the noise pulse generated at the rising edge of the switching synchronizing signal, and a noise canceling circuit that grounds the output section of the composite synchronizing signal when there is an output of this differentiating circuit. Because the circuit is connected, the output of the composite sync signal is grounded for a certain period of time at the rise of the switching control signal, so the noise pulses contained in the composite sync signal are effectively canceled, and the track Numbers, letters, etc. are always output to the same horizontal synchronizing signal portion, and no vertical blurring or the like occurs.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 and 2. Components that are the same as those shown in FIGS. 3 to 6 are indicated using the same reference numerals. First, a noise canceling circuit 12 is connected to the output part of the integrating circuit 10, that is, the output part of the composite synchronization signal C-8ync, and the switching pulse signal 5WP(Y) is connected to the noise canceling circuit 12.
A differentiating circuit 13 is connected to the differential circuit 13, which differentiates the signal and generates a pulse having the width of the noise A described above. Further, a transistor 11 is connected to the noise canceling circuit 12 .

In such a configuration, the composite synchronization signal C-8
When a noise pulse A exists in ync, the output from the differentiating circuit 13 generated at the rising edge of the switching pulse signal swp(y) turns on the transistor of the noise canceling circuit 12, and the output part of the composite synchronization signal C-5ync turns on. ground.

As a result, the noise pulse A included in the composite synchronization signal C-5ync is erased, and the output from the transistor 11 becomes the composite synchronization signal C-3ync in FIG.
As seen in c, the noise pulse A is no longer present. Therefore, when counting the horizontal synchronizing signal H-5ync sequentially from the rising edge of the vertical synchronizing signal -sync to determine the character display position of the track number, there is no risk of miscounting and the character display does not flicker.

Effects of the Invention As described above, the present invention connects to the output section of the composite synchronization signal a differentiation circuit that differentiates the switching control signal and a noise cancellation circuit that grounds the output section of the composite synchronization signal when there is an output from the differentiation circuit. Therefore, the output part of the composite sync signal can be grounded for a certain period of time with the rising edge of the switching control signal, thereby effectively canceling the noise pulses contained in the composite sync signal, thereby causing the track number to change. Characters, etc. are always output to the same horizontal synchronizing signal portion, and no vertical blurring or the like occurs.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a timing chart showing its operation, Fig. 3 is a circuit diagram showing general video signal processing, and Fig. 4 is a timing chart showing its operation. 5 is a circuit diagram showing a conventional example, and FIG. 6 is a timing chart showing its operation. 9...Character generation IC112...Noise cancellation circuit, 1
3...Differential circuit, 5WP(Y)...Switching pulse signal (switching control signal), C-3ync...Composite synchronization signal

Claims (1)

[Claims] A composite synchronization signal in which a horizontal synchronization signal and a vertical synchronization signal are mixed is used, and a through period in which the video signal is output as a through signal, and the through signal is set to 0.5.
Output as a 0.5H delayed signal 0
．． Vertical synchronization is achieved by using a switching control signal that has a vertical through period that switches the 5H delay period for each field, and outputs the vertical synchronization signal in a through signal state without delay during vertical synchronization during the 0.5H delay period. Output of a composite synchronization signal in a character blur prevention circuit in a video circuit equipped with a character generation IC that counts the number of pulses of a horizontal synchronization signal in the composite synchronization signal based on signal detection to determine an output position of a displayed character. A character blur prevention circuit for a video circuit, characterized in that a differentiating circuit for differentiating a switching control signal and a noise canceling circuit for grounding the output part of the composite synchronization signal when there is an output from the differentiating circuit are connected to the part.