JPH0139268B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image display device such as a television, which 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 band of the input video signal. Currently, as a standard method for television signals, for example,
A signal format such as the NTSC system is used, but the upper limit of the frequency of the video signal in this signal format is about 4MHz in the case of the NTSC system. The horizontal resolution that can be achieved with this value is not sufficient for large-screen CRT display devices over 20 inches, and sharp images cannot be viewed. On the other hand, recent
In CRTs, the resolution of the CRT itself has improved, and it has the ability to display images with a wider frequency band than the video signal band limited by standard signal formats, that is, images with higher resolution. .

In this way, when the resolution expected from the resolution of the display device is higher than the resolution determined from the band of the input video signal, the present invention is capable of adjusting human visual characteristics by sampling the input video signal and adding it to the display device. An object of the present invention is to provide a method that can apparently improve the sharpness of a displayed image while keeping the signal format unchanged.

The content of the invention will be explained below with reference to the drawings.

FIG. 1 is a diagram for explaining the present invention, and in the figure, 1
2 is an input video signal, and 2 is a first video amplifier having a bandpass characteristic commensurate with the band of the input signal. Reference numeral 3 denotes a sampling pulse generation circuit which generates a sampling pulse 31 having a frequency s sufficiently larger than the highest frequency m of the input video signal 1 and whose phase is locked to horizontal scanning. A sampler 4 samples the input video signal using the sampling pulse. 5 is the second
The video amplifier has a bandpass characteristic suitable for the band of the CRT 10, which will be described next, and applies the sampled video signal to the cathode or grid of the CRT 10 to control the intensity of the electron beam. 1
0 is a CRT whose resolution is sufficiently larger than the resolution determined from the band of the input video signal. In FIG. 1, the vertical and horizontal deflection circuits are omitted because they may be standard ones.

With this configuration, the image displayed on the screen of the CRT 10 will be as shown in FIG.
In FIG. 2, H is the scanning line pitch in the vertical direction (where Nv is the effective number of scanning lines, H is 1/Nv of the vertical scanning width), h is the scanning line width, and a is the gap between the scanning lines. As mentioned above, since the resolution of recent CRTs has improved, it is easy to set h<H, and the gap a between the scanning lines is displayed as [black].
In the horizontal direction, the video signal display section S and the [black] display section b are alternately arranged and displayed by turning the sampling pulse on and off. The horizontal pitch S is the period of the sampling pulse
Determined by Ts. When the resolution of the CRT 10 is high as described above, as a result of sampling, images are displayed in a dot-like arrangement on the screen of the CRT 10, as shown in FIG. For example _, in the case of NTSC with Nv≈480, the number of sample points (image sections) N _H is 640, assuming that S≈H in the horizontal direction is selected and the aspect ratio is 4:3. The frequency s of the sampling pulse for this S≈H is about 12 MHz.

Now, regarding various input images, there are two types: an image displayed by the display device shown in FIG. 1, that is, an image displayed as a dot sample, that is, an image arranged in a dot shape as shown in FIG. As a result of conducting a comparative experiment based on subjective evaluation with a displayed image by , it was found that in many cases, the dot-sampled image as shown in FIG. 2 is perceived as having higher sharpness. Furthermore, if dot sampling is not performed, a scan line structure is observed and scan line disturbance occurs, but when dot sampling is performed, this scan line disturbance is eliminated. It was also found that the image quality deterioration due to dot interference caused by dot sampling is much smaller than the image quality deterioration due to scanning line interference. That is, it has been found that by performing dot sampling as shown in FIG. 2 using the display device of FIG. 1, the apparent image quality can be improved. The reasons for this are: (i) The black display area improves the contrast of the image and emphasizes the brightness changes at the edges of the image, giving the impression that the sharpness has increased.

(ii) Sampling produces high frequency components not included in the input video signal, which when observed give the impression that the details of the original image have been expressed.

(iii) Regarding scanning line interference, while in a normal display device the line structure due to scanning lines is strongly perceived, when sampling is also performed in the horizontal direction as in the second example, the impression of this line structure is eased. etc. are possible.

As explained above, if the image is sampled in the horizontal direction as shown in FIG. 1, it is possible to display an image with improved apparent sharpness and to reduce scanning line interference. This effect works effectively in the range where contrast remains between the black display areas a and b and the non-black display area (video signal display area) in FIG. Further, in FIG. 2, the effect is greatest when S≒H or S≒h.

Furthermore, if the phase of the sampling pulse is shifted by 1/2 period for each scanning line, the sampling structure becomes as shown in Figure 3, but in this way, the dot interference due to sampling is virtually eliminated, and the sharpness is reduced. The improvement effect can be maintained.

Furthermore, if the resolution of the CRT10 is not very high and the scanning lines can be separated,
The sharpness can be improved by selecting the period of the sampling pulse to be S'≈2H and s≈b as shown in FIG. In this case, since the sampling interval becomes coarse, some dot interference occurs, but the image quality improvement effect due to the sharpness improvement is greater than the decrease in image quality due to this interference. Note that the sampling frequency at this time is approximately
6MHz, and as a result, a folded spectrum of the video signal occurs, but by staggering the sample points as shown in Figure 4, this folded spectrum is canceled out between the scanning lines, so there is no real problem.

Although FIG. 1 illustrates the case of a monochrome image, the same effect can be obtained even in the case of a color image. The case of a color image will be explained with reference to FIG.

In FIG. 5, 6 is a color demodulation circuit which demodulates and decodes the input video signal to generate the three primary color signals 61.
Generates R, 61G, and 61B. These three primary color signals are sampled by samplers 4R, 4G, and 4B, respectively, and are sent to respective color signal amplifiers 50R and 50.
G, 350B to the corresponding cathode of the CRT 10. Color signal amplifier 50R, 50G,
50B is designed to have wideband bandpass characteristics commensurate with the resolution of the CRT10. In this way, each of the three primary color signals is sampled with a common sampling pulse 31, so as shown in FIGS.
Each sampling point in the diagram contains original color information, so that the desired dot sampling operation for a color image can be achieved.

FIG. 6 shows an embodiment of the present invention. This is a method in which sampling is performed only for the luminance signal. In the figure, 6A is a color demodulation circuit, which in this case has a luminance signal 62Y and a color difference signal 62Y.
It is configured to generate R, 62G, and 62B. During this output, only the luminance signal 62Y is sampled by the sampler 4. The sampled luminance signal 41Y is applied to the color signal amplifiers 5R, 5G, 5B, where the color difference signals 62R, 62G, 62
B is added to generate color signals 51R, 51G, and 51B. In this way, the color signals 51R, 51
G and 51B are both sampled luminance signals 4
When 1Y is [black], it becomes [black], and as a result, a display equivalent to that shown in FIG. 5 is obtained on the screen of the CRT 10. This configuration has the practical advantage that only one sampler is required.

As detailed above, according to the present invention, the luminance signal is sampled at an appropriate sampling frequency and the color difference signal is added to obtain the color signal. A dot-sampled color image can be displayed in conjunction with directional sampling, and a great practical effect can be obtained in that a color image with less scanning line interference and apparently improved sharpness can be displayed.

[Brief explanation of drawings]

Figure 1 is a diagram explaining the present invention, Figure 2, Figure 3.
FIG. 4 is an explanatory diagram of its operation, FIG. 5 is an explanatory diagram of the present invention, and FIG. 6 is a diagram showing an embodiment of the present invention. In the figure, 1 is an input video signal, 2 is a first video amplifier, 3 is a sampling pulse generation circuit, and 4
is the sampler, 5 is the second video intensifier, and 10 is the sampler.
CRT, 4R, 4G, 4B are samplers, 50R,
50G and 50B are color signal amplifiers, 6 is a color demodulation circuit, 5R, 5G, and 5B are color signal amplifiers, and 6A is a color demodulation circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In an image display device that receives a video signal and displays a color image on a display screen of a display device having a resolution higher than the resolution of the video signal, a color demodulation circuit that receives the video signal and generates a luminance signal and a color difference signal; , a sampling pulse generation circuit that generates a sampling pulse whose pulse width is one to two times the scanning line pitch on the display screen and whose phase is aligned for each horizontal scan or shifted by 1/2 period for each scanning line; A sampler that samples the luminance signal based on the sampling pulse; and a color signal amplifier that receives the sampled luminance signal and the color difference signal and generates a color signal; What is claimed is: 1. An image display device characterized in that the non-display areas and the non-display areas are alternately arranged and displayed in a dot shape.