JPH05260337A - Moire improving circuit - Google Patents

Abstract

PURPOSE:To improve the horizontal moires in particular by attaining the improvement of moires with no deterioration of the image quality. CONSTITUTION:A moire correcting circuit 4 produces a sine wave having the frequency of an odd multiple of 1/2 fV (vertical scan frequency) synchronously with the fV received from a vertical deflecting circuit 2 and superimposes the sine wave on the horizontal synchronizing signal of a horizontal phase circuit contained in a horizontal deflection circuit 3. The horizontally deflected current flowing to a CRT is slightly modulated based on the sine wave. Thus the position of an image is varied on the CRT 1. As a result, the moire stripes caused in the horizontal direction can be visually erased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moire improving circuit in a color CRT display device, and more particularly to reducing moire caused by interference between the horizontal spacing of patterns displayed on a CRT and the spacing of holes in a shadow mask. The present invention relates to a moiré improving circuit that can be performed.

[0002]

2. Description of the Related Art Generally, a shadow mask type color CRT (cathode ray tube) used in a color CRT display device has an R-shaped surface as shown in FIG.
Three-color phosphors of (red), G (green), and B (blue) are coated, and three electron beams of R, G, and B emitted from three electron guns are deflected and scanned. A group of phosphor dots R, G, B (indicated by a broken line frame in the drawing) are simultaneously made to emit light through each of the plurality of holes formed in the shadow mask. As a result, scanning lines are sequentially formed on the phosphor screen of the CRT as shown in FIG. 8 (b). The spacing between these scan lines is approximately equal to the vertical screen amplitude divided by the number of display scan lines.

By the way, one of the factors that hinder the display resolution of a color CRT in a color CRT display device.
One of them is the moire phenomenon. This moire phenomenon is a fringe phenomenon due to interference between the scanning line beam trajectory in the color CRT screen and the hole arrangement of the shadow mask of the color CRT, and this phenomenon is emphasized by the flattening of the beam shape especially in the peripheral portion of the CRT screen. Tend to

As a method of improving the moire, the color CR is applied to the number of scanning lines (actually, the pitch between the scanning lines is related, so the screen size in the vertical direction is related).
It is necessary to select the shadow mask pitch of T to a pitch that minimizes moire, but in reality, due to non-uniformity of the deflection yoke magnetic field and minute variations in shadow mask attachment, the scanning line beam trajectory and shadow mask The hole arrangement is displaced at the peripheral portion of the screen to cause moire, which significantly impairs the display resolution.

Further, the moire caused by the interference between the intervals of the scanning lines in the vertical direction and the intervals of the holes of the shadow mask is improved by slightly varying the position of the electron beam in the direction of the vertical scanning. Is conventionally known.

However, when a vertical fine stripe pattern as shown in FIGS. 9A and 9B or a fine checkered video signal is displayed on a CRT, the horizontal interval of the pattern and the shadow mask The moire caused by the interference caused by the distance between the holes cannot be improved at all even if the electron beam is vertically changed.

Up until now, the only effect of this type of moire has been to deliberately defocus and defocus the focus adjustment to make the electron beam a little thicker. But,
Again, the moiré is slightly less noticeable, it does not disappear completely, and the problem caused by defocusing was more noticeable.

[0008]

As described above, there is no remedy for the moire caused by the pattern of the video signal, and the method by focus adjustment is blurred.

The present invention solves the above problems, and an object of the present invention is to provide a moire improving circuit capable of eliminating moire caused by a pattern of a video signal.

[0010]

A moire improving circuit of the present invention modulates a scanning line beam by a deflection coil arranged in a neck portion of a CRT and a current flowing through the deflection coil, and an image on the CRT is displayed. And a means for vibrating the display position in the same direction as the horizontal scanning direction or in an oblique direction.

[0011]

According to the present invention, the display position of the image on the CRT is oscillatingly changed in the same direction as the horizontal scanning direction or in the oblique direction, and the relative position between the position where the electron beam reaches and the hole of the shadow mask. Since the position changes, the appearance (pattern) of moire changes. When this change is integrated with the afterglow characteristic of the fluorescent substance and the afterglow characteristic of the human eye, the moire becomes invisible.

[0012]

EXAMPLES Examples will be described with reference to the drawings. FIG. 1 is a block diagram showing a moire improving circuit according to the first embodiment of the present invention.

FIG. 1 shows a deflection system of a CRT, CR
It is composed of T1, a vertical deflection circuit 2, a horizontal deflection circuit 3, and a moire correction circuit 4 existing between the two circuits. The vertical deflection circuit 2 is composed of a vertical oscillation circuit, a vertical drive circuit, and a vertical output circuit, and supplies a vertical deflection sawtooth wave current to the vertical deflection coil 11 of the CRT 1. Also,
The horizontal deflection circuit 3 includes a horizontal oscillation circuit and a horizontal phase circuit 31.
And a horizontal drive / output circuit 32. From the horizontal drive / output circuit 32 to the horizontal deflection coil 1 of the CRT 1.
The horizontal deflection sawtooth wave current is supplied to No. 2. The moire correction circuit 4 includes a 1/2 frequency divider circuit 41 and a PLL circuit 4
2, a VCO circuit 43, and a (1 / odd) frequency divider circuit 44. The 1/2 divider circuit 41 is the vertical deflection circuit 2
The signal of the vertical scanning frequency fV from is divided into 1/2 and output. PLL circuit 42 and VCO circuit 43 (1 / odd number)
The frequency dividing circuit 44 constitutes a PLL loop. (1 /
The (odd number) frequency dividing circuit 44 is a circuit that divides the oscillation frequency from the VCO circuit 43 into (1 / odd number). For example, 1/5
Divide to 25. The PLL circuit 42 is a 1/2 frequency divider circuit 41.
(1/2) fV from (1) and the frequency divided by the (1 / odd) frequency dividing circuit 44, and a low-pass filter for smoothing the phase comparison output. The smoothed phase comparison output is supplied as a control voltage to the VCO circuit 43 at the next stage. The VCO circuit 43 outputs a sine wave having a frequency that is an odd multiple of 1/2 of fV in synchronization with the vertical scanning frequency fV from the vertical deflection circuit 2 and supplies it to the horizontal phase circuit 31 in the horizontal deflection circuit 3. To be done. The horizontal phase circuit 31 superimposes the (1/2) fV sine wave on the signal of the horizontal scanning frequency. Based on this sine wave, the horizontal deflection current supplied from the horizontal drive / output circuit 32 to the horizontal deflection coil 12 is slightly modulated.

By doing so, the vertical lines of the image are bent as shown in FIG. 2, and further, the modulation is applied so that the modulation direction is reversed for each frame (for each field in the interlace specification). When the modulation frequency is selected to be an odd multiple of 1/2 of fV, the modulation direction is reversed for each frame, so the effect is most effective. Moreover, since the modulation frequency at a certain point on the screen is the beat frequency with fV, this beat frequency is maximized, and there is an advantage that the integration effect is maximized and moire is hard to see.

Further, when synchronized with the vertical scanning frequency fV, there is no problem that the stripes due to the moire left unerased are moved up and down on the screen to be detected, and the screen quality is improved. In addition, if the absolute value of the modulation frequency is several hundreds Hz or more, the improvement effect can be obtained.

With the above arrangement, there is a possibility that the vertical lines of the image may appear curved or the vertical lines may appear blurred, but 1/6
Since the bending direction is reversed every 0 seconds (when the vertical scanning frequency is 60 Hz), when integrated by the afterglow characteristic of the phosphor and the afterglow characteristic of the human eye, it looks like a straight line with no blur. It is not recognized, and I do not notice that I am changing the display position of the image.

Of course, if too much modulation is applied as shown in FIG. 3, vertical lines are blurred and the thickness is partially changed to change the horizontal resolution. However, in order to improve moire, one dot is used. Even if it is changed by about a minute, the blurring of the vertical line is not recognized.

Actually, a CRT having a dot pitch of 0.31 mm
Even in the result of experiment using, no defects such as blurring in the horizontal direction were detected, and the original display quality was not impaired.

However, since the modulation is sinusoidal, the moiré remains unchanged only at the point where the modulation is zero, and it looks like a striped pattern on the screen, but it is much more remarkable than when it is not improved. The screen quality is improved. The result confirmed by the experiment shows that the modulation is far better in quality and is sufficiently practical.

FIG. 4 is a block diagram showing a second embodiment of the present invention. In FIG. 4, the moiré correction circuit 4 is configured by a microcomputer 45 including a frequency detection circuit 46 and an arithmetic circuit 47, and a PLL loop including a PLL circuit 42 and a VCO circuit 43. Other configurations are the same as those in FIG. In this circuit, the vertical scanning frequency fV is detected by the frequency detection circuit 46, and based on this detection signal, the arithmetic circuit 47 creates a signal having a frequency that is an odd multiple of 1/2 of the vertical scanning frequency fV, and this is generated by the PLL circuit. In addition to the phase detector in 42, the VCO circuit 43 compares the phase with the oscillation frequency and feeds it back to the VCO circuit 43, so that the sine wave output from the VCO circuit 43 can be accurately output to the output frequency of the arithmetic circuit 47. I try to make them match (lock). With this configuration, the same function and effect as in FIG. 1 can be obtained.

In the embodiments shown in FIGS. 1 and 4, the part to be modulated by the moire correction signal is the horizontal phase circuit, but in the present invention, the part to be modulated is not limited to the horizontal phase circuit. .. For example, modulation may be added by superimposing a moire correction signal on the DC signal (screen position signal) of the horizontal centering circuit that adjusts the horizontal screen position.

FIG. 5 shows a third embodiment of the present invention. In addition to a deflection yoke composed of a vertical deflection coil 11 and a horizontal deflection coil 12, a moire correction deflection coil 13 is provided at the neck portion of the CRT 1. The electron beam may be changed by supplying the moire correction signal as described above from the modulation signal source 5 to the coil 13.

The above is a description of a method of applying a sinusoidal modulation to the scanning line beam in order to improve moire. However, the image position is changed frame by frame (or field by interlace specification). The same effect can be obtained by switching.

FIG. 6 is a block diagram showing a fourth embodiment of the present invention. In FIG. 6, the moire correction circuit 4 is
It is composed of a divide-by-2 circuit 41 and a switching transistor 48. Other configurations are the same as those in FIG. That is, the vertical scanning frequency fV from the vertical deflection circuit 2 is halved by the 1/2 frequency dividing circuit 41 so that a high level and a low level are alternately repeated for each frame (field for interlaced specifications). Is supplied to the base of the transistor 48 so that the transistor 48 is alternately turned on and off for each frame (or each field), and a DC signal for phase switching is applied to the emitter.
The horizontal scanning phase is switched by turning on / off the DC signal supplied from the collector to the horizontal oscillation circuit and the horizontal phase circuit 31 for each frame (or each field).

With this configuration, the position of the image can be switched for each frame (or each field) as shown in FIG. In FIG. 7, the position of the image can be alternately switched to the position of the thick solid line and the position of the broken line. Visually, the image can be seen at the position indicated by the thin solid line. As a result of the experiment, a change in moire is more easily detected than in the case of modulating in a sinusoidal shape, but the circuit configuration is as shown in FIG. 6, which is very simple. This is an extremely effective method because the change in image position is hardly noticeable when a CRT having a medium or long afterglow characteristic of the phosphor is used or when the vertical scanning frequency fV is high. Also in this embodiment, there is no problem that vertical lines appear to shake or appear blurry and thick.

In the embodiment described above, the scanning line beam is varied in the same direction as the horizontal scanning direction. However, in this method, the vertical spacing of the scanning lines and the shadow mask cause interference. It is not effective in reducing moire. However, the dedicated correction coil 1 shown in FIG.
It is possible to improve both moires at the same time by changing the scanning line beam in an oblique direction by a method such as using No. 3 or the like.

The present invention can be applied not only to a shadow mask type CRT but also to a chromatolone type CRT. Further, the present invention can be applied even to a multi-scan CRT display device.

[0028]

As described above, according to the present invention, the moire phenomenon can be improved without degrading the image quality. In particular, it is possible to improve the moire generated due to the pattern of the video signal and realize a very useful moire improving circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing a moire improving circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a display state of an image displayed on the CRT in FIG.

FIG. 3 is a CRT in FIG. 1 when overmodulation is applied.
The figure explaining the state of the image projected on the top.

FIG. 4 is a block diagram showing a moire improving circuit according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a moire improving circuit according to a third embodiment of the present invention.

FIG. 6 is a block diagram showing a moire improving circuit according to a fourth embodiment of the present invention.

FIG. 7 is a diagram illustrating a state of an image displayed on the CRT in FIG.

FIG. 8: Phosphor dots and CRT in color CRT
The figure explaining the scanning line projected on top.

FIG. 9 is a diagram illustrating a thin vertical stripe pattern and a fine checkerboard pattern displayed on the CRT screen.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... CRT (cathode ray tube) 2 ... Vertical deflection circuit 3 ... Horizontal deflection circuit 4 ... Moire correction circuit 11 ... Vertical deflection coil 12 ... Horizontal deflection coil 13 ... Moire correction coil (dedicated coil) 31 ... Horizontal oscillation circuit / horizontal phase Circuit 32 ... Horizontal drive / output circuit 41 ... 1/2 frequency divider circuit 42 ... PLL circuit 43 ... VCO circuit 44 ... (1 / odd number) frequency divider circuit 45 ... Microcomputer 46 ... Frequency detection circuit 47 ... Arithmetic circuit 48 ... Switch Transistor

Claims (1)

[Claims] 1. A deflection coil arranged at a neck portion of a CRT, and a scanning line beam is modulated by a current flowing through the deflection coil so that an image display position on the CRT is in the same direction as the horizontal scanning direction or A moire improving circuit, comprising: means for vibrating in an oblique direction.