JPS6035871B2 - image display device - Google Patents

Description

[Detailed Description of the Invention] The present invention provides an image display device such as a television.
The present invention relates to an image display device that improves the quality of displayed images.

Generally, the resolution or sharpness of an image displayed on a display device is determined by both the resolution of the display device itself and the bandwidth of the input video signal.

Currently, the standard system for television signals is NT, for example.
A signal format such as the SC system is used, but the upper limit of the frequency of the video signal in this signal format is approximately the peak-M ratio in the case of the NTSC system. The horizontal resolution that can be achieved with this value is not sufficient for a large screen display device using a CRT of more than 20 inches, and a sharp image cannot be viewed. On the other hand, in recent CRm systems, the resolution of the CRT itself has improved, and it is now possible to display images with a wider frequency band than the video signal band limited by the above signal format, that is, images with higher resolution. It has performance. In this way, when the resolution expected from the resolution of the display device is higher than the resolution within the band of the input video signal, the present invention utilizes human visual characteristics to display the signal without changing the signal format. The present invention provides a method that can apparently improve the sharpness of an image.

The embodiment shown in the figures will be described below.

In Fig. 1, 1 is an input terminal for the video signal 11, 2 is a video intensifier, 3 is a synchronization circuit, 4 is a vertical deflection circuit, 5 is a horizontal deflection circuit, 6 is an auxiliary deflection circuit, 7 is a deflection yoke, and 1 Well, it's a CRT.

The synchronization circuit 3 generates vertical pulses to the vertical deflection circuit 4 and horizontal pulses to the horizontal deflection circuit 5, as in the case of a normal television, and also generates clock pulses 31 to the auxiliary deflection circuit 6. This clock pulse has a frequency s which is sufficiently larger than the highest frequency nam of the video signal, and is phase-locked to the horizontal scan. Generation of such clock pulses can be realized using conventional techniques. The auxiliary deflection circuit 6 receives the clock pulse 31 and generates a chain tooth-shaped auxiliary deflection current 61 whose period is equal to the period Ts of the clock pulse. This auxiliary deflection current is superimposed on the horizontal deflection current generated by the horizontal deflection circuit 5 and is applied to the deflection yoke 7. Meanwhile, the input video signal 11 is intensified by a video intensifier 2 and applied to the cathode or grid of the CRTIO to control the intensity of its electron beam. The operation of the CRTIO when configured in this way is as follows. 2 and 3 are diagrams for explaining the operation. First, in FIG. 2, A shows the waveform of the auxiliary deflection current, and B shows the waveform of the horizontal deflection current. If the oscillation K of this auxiliary deflection current is appropriately adjusted and superimposed on the horizontal deflection current, the deflection current flowing through the deflection yoke becomes as shown in C in the same figure, and as a result, the CRT
The IO electron beam is scanned in a stepwise manner in the horizontal direction. If the horizontal scanning time is TH and the period of the clock pulse is Ts, or N=TH/Ts, it is clear that one step of this stepped scanning is 1/N of the horizontal scanning. Let this scanning step (length) be S. When the electron beam is scanned in the horizontal direction as described above, C
The raster drawn on the RTIO screen is as shown in FIG.

In Fig. 3, the day is the scanning line pitch in the vertical direction (if the effective number of scanning lines is Nv, the day is 1/Nv of the vertical scanning)
, h is the middle of the scanning line, and a is the gap between the scanning lines. As mentioned above, recent CRTs have improved resolution, so h<
It is easy to set it to 1, and the gap a between the scanning lines is [black]
will be displayed. In the horizontal direction, scanning is performed in steps as described above, so the beam stopping time (second
A portion s where a spot is formed (portion s in the figure) and a portion b where a spot is formed (portion b in FIG. 2) where the beam is substantially displayed as black are formed because the beam moves at high speed (portion b in FIG. 2). In FIG. 3, the non-black portions are shown as rectangles to simplify the explanation, but in reality they have a shape close to that of the beam. Therefore, when the beam is circular, this non-black portion is circular and h≠s. As a result of such scanning, the input video signal is displayed on the screen of CRTI0 substantially as sampled in this non-black area as shown in FIG. The value of the video signal displayed at this sample point is the integral value of the video signal over the period Ts of the clock pulse. Hereinafter, this operation will be explained as dot sampling. For example, in the case of the NTSC system, this number of sample points is Nv±4
80, and if S≠day is selected in the horizontal direction, the aspect ratio is 4:3 and NH±640.

The frequency of the clock pulse for this S main H is s=1/
Ts is approximately 1 smz. Now, regarding various types of input images, there are two types: an image displayed by the display device shown in Fig. 1, that is, an image displayed by dot sampling as shown in Fig. 3, and an image displayed by a conventional display device, that is, a display device that does not perform dot sampling. As a result of conducting a comparative experiment based on subjective evaluation, it was found that in many cases, images subjected to dot sampling as shown in FIG. 3 are perceived as having higher sharpness.

Furthermore, when dot sampling is not performed, a scanning line structure is observed and scanning line interference occurs, but when sampling is performed, this scanning line interference disappears, and the image quality degradation due to dot interference caused by dot sampling is due to scanning line interference. The image quality degradation was found to be much smaller. That is, the display device shown in FIG.
It has been found that by performing dot sampling as shown in the figure, the apparent image quality can be improved. The reason for this is that the black part improves the contrast of the image, and also emphasizes the brightness change in the green part of the image, giving the impression that the sharpness has increased. {iii Sampling produces high frequency components that are not included in the input video signal, and when observed, the details of the original image are expressed and give a different impression.

{iii' Regarding scanning line interference, in contrast to the strong perceptual line structure caused by scanning lines in a normal table display device, when sampling is also performed in the horizontal direction as shown in Figure 3, the impression of this line structure becomes is alleviated.

etc. are possible.

As explained above, it is possible to achieve an effect equivalent to sampling the image on the screen in the horizontal direction by adding a sawtooth auxiliary deflection current to the horizontal scanning as shown in Figure 1. This makes it possible to display an image with improved apparent sharpness.

Moreover, scanning line interference can be reduced. This effect works effectively in the range where contrast remains between the black parts a, b and the non-black parts in FIG. Also the third
In the figure, the effect is greatest when S-main-H or s-d-h is used. Although FIGS. 1 and 2 illustrate the case where a chain-toothed current is used as the auxiliary deflection current, a similar effect can be obtained with either a triangular wave or a sine wave. In either case, the horizontal scanning is subjected to velocity modulation with a period Ts, creating a contrast between a fast moving part and a slow moving part, which produces the above-mentioned effect. In addition, if the phase of the auxiliary deflection current is shifted by 1/2 period for each scanning line, the sampling structure becomes as shown in Figure 4. In this way, dot interference due to sampling is virtually eliminated, and the sharpness is The improvement effect can be maintained.

Furthermore, if the separation ability of CRTIO is not very high and the scanning lines are only slightly separated, the sharpness can be improved by selecting the period of the auxiliary deflection current as the S main bait as shown in Figure 5. be able to. In this case, the sampling will be coarser, so some dot interference will occur, but
The method shown in FIG. 5 is also effective because the improvement in image quality due to the improvement in sharpness is greater than the reduction in image quality due to this interference.
Note that the frequency of the auxiliary deflection current at this time, that is, the sampling frequency in the horizontal direction, is about Hz,
As a result, an aliased spectrum of the video signal occurs, but by staggering the sample points as shown in FIG. 5, this aliased spectrum is canceled out between scanning lines, so it does not pose a problem in practice. Although the example shown in FIG. 1 was explained assuming the case of a black and white image, it is clear from the above explanation that the same effect can be seen even in the case of a color image. .

That is, since the three electron beams in the color ORm are commonly controlled by the deflection current, dot sampling for a color image can be realized by the auxiliary deflection current as shown in FIG. 1 without losing color information. In the embodiment shown in Fig. 1, the horizontal deflection current and the auxiliary deflection current are superimposed and then applied to the deflection yoke, but an auxiliary deflection coil is provided separately from the deflection yoke and the auxiliary deflection current is passed through it. It is clear that similar effects can be obtained by

As detailed above, by applying periodic intensity modulation with appropriate vibration to the horizontal deflection, it is possible to bring about the effect of dot sampling on the CRT display surface, resulting in less scanning line disturbance and This has the practical effect of being able to display an image with improved apparent sharpness.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2, Fig. 3,
FIGS. 4 and 5 are explanatory diagrams of the operation of the present invention. 1 is an input terminal, 11 is an input video signal, 2 is a video intensifier, 3 is a synchronization circuit, 4 is a vertical deflection circuit, 5 is a horizontal deflection circuit, 6 is a strong auxiliary deflection circuit, 7 is a deflection yoke, 10' or C
It is RT. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1 The horizontal deflection of the display CRT must have a cycle that is 1 to 2 times the scanning line pitch on the display screen, and that the phase is the same for each horizontal scan or shifts by 1/2 cycle for each scanning line. 1. An image display device, characterized in that the image is displayed on a display screen in a substantially dot-sampled manner by applying periodic scanning velocity modulation.