JPH11338450A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of memory used and to restrain degradation of image quality by varying the clock frequency according to the display size of a subdisplay, lowering the clock frequency in the case of a small display size, and roughly fetching data. SOLUTION: A sampling means 11 samples a picture signal of a subdisplay by a sampling clock from a sampling clock generating means 17 to be output to a memory means 12. An image converting means 13 displays image data of the memory means 12 through a picture switch SW14 by an image display means 15. A size recognizing means 16 obtains a horizontal size ratio of both from the connecting time of the picture switch SW to the master display side and the subdisplay side during one horizontal period, and according to the ratio, the sampling clock means 17 outputs sampling clock frequency to the sampling means 11 and the image converting means 13. By a low-frequency sampling clock, a picture signal for a subdisplay is sampled to reduce the data quantity and restrain degradation of an image.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-scan display capable of displaying video signals of various video output devices such as a TV tuner, various personal computers, and EWS, and more particularly to a multi-scan display which is displayed in a limited area on a screen. And memory means for holding the images.

2. Description of the Related Art Conventionally, in an image display device with a so-called picture-in-picture function for displaying a plurality of screens on one screen, a sampled data is stored in a memory as it is and output as needed to display a sub-screen. Was.

However, with the recent increase in resolution, the amount of data corresponding to one screen increases, and the amount of memory required to hold the data also increases, so that the amount of image data to be sampled is efficiently reduced. However, it is necessary to take measures to prevent an increase in memory usage. SUMMARY OF THE INVENTION An object of the present invention is to provide an image display device which prevents an increase in the amount of data to be held as described above and reduces the amount of memory used.

According to the present invention, a clock frequency for sampling a video signal for a sub-screen is varied in accordance with the display size of the sub-screen, and when the display size is small, the clock frequency is changed. It is characterized in that the amount of memory for holding image data can be reduced by taking in low and coarse data.

FIG. 1 shows an embodiment of a display device according to the present invention. Numeral 11 denotes a means for sampling a video signal, which samples the video signal of the small picture based on the sampling clock output from the sampling clock generating means 17 and outputs the sampled signal to the memory means 12. 13 is an image conversion means, a memory means
The image data read from 12 is output to the image display means 15 through the video switching SW 14 and displayed. Size recognition means 16
Monitors the control signal output by the CPU 18 to switch the video switching SW 14 between the main screen side and the sub screen side, and connects the time when the video switching SW is connected to the main screen side during one horizontal cycle and the sub screen side. The horizontal size ratio between the parent screen and the child screen is obtained from the calculated time, and is output to the sampling clock generation means 17. If the horizontal size of the child screen is, for example, 50%, 30%, or 10% of the parent screen, the sampling clock generation means 17 sets the frequency of the base sampling clock to 50%.
The frequency is divided into%, 30% and 10% and output to the sampling means 11 and the image conversion means 13. By sampling the video signal for the small screen with the frequency-divided sampling clock of the low frequency, the data amount held in the memory means 12 is reduced, and the image data amount held according to the screen size of the small screen is reduced. Because of the reduction, deterioration of image quality can be suppressed.

As described above, according to the present invention, the amount of memory used can be reduced, and the deterioration of image quality can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a display device of the present invention.

[Explanation of symbols]

11 ... sampling means, 12 ... memory means, 13 ...
Image conversion means, 14: Video signal switching SW, 15: Image display means, 16: Size recognition means, 17: Sampling clock generation means, 18: CPU.

Claims (2)

[Claims] An image display device having a so-called picture-in-picture function for inputting a plurality of video signals and displaying a parent-child screen, means for sampling a video signal, memory means for holding the sampled video signal, Image conversion means for returning the output of the memory means to a video signal; and a signal changeover switch for switching between a video signal for the main screen and a video signal for the child screen output from the image decompression means and outputting the video signal to the display means. An image display device, characterized in that: 2. An image display apparatus having a so-called picture-in-picture function for inputting a plurality of video signals and displaying a parent-child screen, a size recognizing means for recognizing a horizontal size of the child screen display, An image display device comprising: a calculating means for calculating a horizontal size ratio; and a sampling clock generating means for changing a clock frequency for sampling a small-screen video signal based on the horizontal size ratio.