JP2002207467A - Display adjusting device and display device provided therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display adjusting device and a display device provided therewith capable of automatically adjusting a display position in a basic input- output system screen displayed at the time of starting a computer. SOLUTION: Video signals IN are converted in the number of pixels by a 1st pixel number conversion circuit 2, and are outputted as liquid crystal panel digital data PD. Moreover, based on the resolution of the video signals IN discriminated by a frequency discrimination circuit 3 and the mean brightness level of the video signals IN detected by a mean brightness detection circuit 4, the video signals are discriminated by a CPU 6 whether or not they are for a BIOS screen. In the case of the BIOS screen, a start position of a text character is detected by a start position detection circuit 5, and a correction value for a display position is determined by the CPU 6. Based on the correction value, a synchronous signal SY is changed by a liquid crystal driving circuit 7 and outputted as a liquid crystal control pulse PP. Based on this, a video is displayed on a liquid crystal panel 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display adjusting device for adjusting a display state of an image on a display unit based on an image signal provided from a computer, and a display device including the same.

[0002]

2. Description of the Related Art In a conventional liquid crystal display device which samples and displays a video signal supplied from a personal computer, for example, as shown in a liquid crystal display TX-D5L31A-J of Matsushita Electric Industrial Co., Ltd.
Generally, resolution conversion is performed so that a video signal having a resolution different from that of the liquid crystal panel can be displayed.

At this time, even if the resolution is the same, the effective screen area of the video signal is different for each personal computer. As a result, the effective screen area of the video signal protrudes from the display area of the liquid crystal panel depending on the type of the video signal. As a result, a phenomenon occurs in which part of the video information is lost.

For this reason, the display position is adjusted so that the horizontal and vertical start positions of the video signal are detected and all video information is automatically contained in the display area of the liquid crystal panel. As a method of adjusting the display position, for example, as described in Japanese Patent Application Laid-Open No. 5-35240, a video display period (portion where a video is present) using a level of a video signal.
Was detected.

However, in the conventional display position adjustment method,
In order to detect the video display period, it is necessary that the level of the video signal in the frame portion of the effective screen area exceeds a certain threshold, but if such a video signal is always output from a personal computer, Not necessarily. For this reason,
In general, the user performs automatic adjustment by pressing a display adjustment button as necessary so that an image is displayed on the entire effective screen area.

[0006]

However, the basic input / output system (Basic Input / Output S) as shown in FIG.
ystem (BIOS) screen, usually, there are only text characters on a black background, the level of the video signal is low overall, and the display position cannot be automatically adjusted by the above method. . For this reason, some personal computers have a problem that text characters on the basic input / output system screen are missing in the liquid crystal display device.

An object of the present invention is to provide a display adjustment device capable of automatically adjusting a display position even on a basic input / output system screen displayed when a computer is started, and a display device having the same. is there.

[0008]

Means for Solving the Problems (1) First invention A display adjustment device according to a first invention adjusts a display state of an image on a display unit based on an image signal and a synchronization signal given from a computer. An adjusting device,
Resolution conversion means for converting the resolution of the video signal to a resolution suitable for the display unit and providing the video signal to the display unit, screen detection means for detecting a basic input / output system screen displayed when the computer is started, and screen detection means Starting position detecting means for detecting a starting position of a character signal in a video signal when a basic input / output system screen is detected by the basic input / output system screen, and a basic position detected by the screen detecting means based on the starting position detected by the starting position detecting means. Control means for controlling the synchronization signal so that the input system screen is displayed at a predetermined position on the display unit.

In the display adjusting device according to the first aspect of the invention, the resolution of the video signal is converted by the resolution conversion means into a resolution suitable for the display unit, and is provided to the display unit. The screen detection means detects a basic input / output system screen displayed when the computer is started. And
The start position detecting means detects the start position of the character signal in the video signal. Further, the control unit controls the synchronization signal so that the basic input / output system screen is displayed at a predetermined position on the display unit based on the character signal start position.

As described above, by detecting the start position of the character signal in the video signal, the display position can be automatically adjusted even when the video to be displayed is the basic input / output system screen.

(2) Second invention In a display adjustment device according to a second invention, in the configuration of the display adjustment device according to the first invention, the screen detecting means includes: a horizontal synchronization frequency and a vertical synchronization frequency of a synchronization signal; The basic input / output system screen is detected based on the average luminance in one frame of the video signal.

In this case, the basic input / output system screen is detected based on the horizontal synchronization frequency and the vertical synchronization frequency of the synchronization signal and the average luminance in one frame of the video signal. This makes it possible to accurately and easily detect the basic input / output system screen.

(3) Third invention A display adjustment device according to a third invention is the display adjustment device according to the first or second invention, wherein the resolution conversion means is a basic input / output system using a screen detection means. When a screen is detected, resolution conversion is performed using the first interpolation method, and when a screen other than the basic input / output system screen is detected, resolution conversion is performed using the second interpolation method.

In this case, when the basic input / output system screen is detected by the screen detection means and when a screen other than the basic input / output system screen is detected, a different interpolation method is used to obtain the basic input / output system screen. Can be more optimally displayed when the image is detected and when the basic input / output system screen is not detected.

(4) Fourth Invention A display adjustment device according to a fourth invention is the display adjustment device according to the third invention, wherein the first interpolation method is linear interpolation, and the second interpolation method is Is a polynomial interpolation.

In this case, the image of the basic input / output system screen can be displayed sharper by using linear interpolation when the basic input / output screen is detected, and a screen other than the basic input / output system screen can be detected. At times, by using the polynomial interpolation, it is possible to more smoothly display images on screens other than the basic input / output system screen.

(5) Fifth Invention The display adjustment device according to a fifth invention is the display adjustment device according to any one of the first to fourth inventions, wherein the basic input / output system screen is displayed by the screen detection means. The apparatus further includes a maximum luminance detecting means for detecting the maximum luminance of the video signal at the time of detection, and a level adjusting means for adjusting the level of the video signal based on the maximum luminance detected by the maximum luminance detecting means.

In this case, the maximum brightness of the video signal is detected by the maximum brightness detecting means when the basic input / output system screen is detected, and the level of the video signal is controlled by the control means based on the maximum brightness of the video signal by the level adjusting means. Adjusted.

Thus, the level of the video signal can be adjusted so that the video signal at the time of the basic input / output system screen can be digitized with the optimum dynamic range, and the basic input / output system screen can be displayed more sharply. it can.

(6) Sixth invention A display adjustment device according to a sixth invention is the display adjustment device according to the fifth invention, wherein the start position detection means has a character in the video signal adjusted by the level adjustment means. This is to detect the start position of the signal.

In this case, the start position of the character signal is detected by the start position detecting means based on the video signal adjusted by the level adjusting means.

Thus, even when the video signal has only a very low luminance, the start position can be easily detected, and the display position can be adjusted more optimally.

(7) Seventh invention A display adjustment device according to a seventh invention is the display adjustment device according to any one of the first to fourth inventions, wherein the basic input / output system screen is displayed by the screen detection means. Further comprising: a maximum luminance detecting means for detecting a maximum luminance of the video signal at the time of detection; and a binarizing means for binarizing the video signal based on the maximum luminance detected by the maximum luminance detecting means and giving it to the resolution converting means. It is.

In this case, the maximum luminance detecting means detects the maximum luminance of the video signal when the basic input / output system screen is detected, and the binarizing means binarizes the video signal based on the maximum luminance of the video signal. , Resolution conversion means.

As a result, the digitized video signal can be limited to binary, and the reliability of text characters on the basic input / output system screen can be improved.

(8) Eighth Invention The display adjustment device according to the eighth invention is the display adjustment device according to the seventh invention, wherein the start position detection means is binarized by the binarization means. The start position of the character signal is detected in the signal.

In this case, in the video signal binarized by the binarization means, the start position of the character signal is detected by the start position detection means, so that the video signal has very low luminance. However, the start position can be easily detected, and the display position can be adjusted more optimally.

(9) Ninth Invention A display adjustment device according to a ninth invention is a display device that displays an image based on a video signal and a synchronization signal given from a computer, and a display unit that displays the image. Resolution conversion means for converting the resolution of the video signal to a resolution suitable for the display unit and providing the video signal to the display unit, screen detection means for detecting a basic input / output system screen displayed when the computer is started, and screen detection Means for detecting a start position of a character signal in a video signal when a basic input / output system screen is detected by the means, and a start position detected by the screen detection means based on the start position detected by the start position detection means. Control means for controlling the synchronization signal so that the basic input system screen is displayed at a predetermined position on the display unit.

In the display device according to the ninth aspect, the basic input / output system screen displayed when the computer is started is detected by the screen detection means, and the basic input / output system screen is detected by the start position detection means. In this case, the start position of the character signal in the video signal is detected, and the control unit controls the synchronization signal so that the basic input / output system screen is displayed at a predetermined position on the display unit based on the start position of the character signal. The conversion unit converts the resolution of the video signal to a resolution suitable for the display unit, applies the video signal to the display unit, and displays the video on the display unit.

As described above, by detecting the start position of the character signal in the video signal, the display position can be automatically adjusted even when the video to be displayed is the basic input / output system screen. Images can be displayed.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) First Embodiment FIG. 1 is a block diagram showing a configuration of a liquid crystal display device having a display adjusting device according to a first embodiment of the present invention.

The liquid crystal display device shown in FIG. 1 has an A / D (analog / digital) converter 1, a first pixel number conversion circuit 2,
It comprises a frequency discriminating circuit 3, an average luminance detecting circuit 4, a start position detecting circuit 5, a CPU (Central Processing Unit) 6, a liquid crystal driving circuit 7, and a liquid crystal panel 8. In particular, A
/ D converter 1, first pixel number conversion circuit 2, frequency discrimination circuit 3, average luminance detection circuit 4, start position detection circuit 5,
The CPU (Central Processing Unit) 6 and the liquid crystal drive circuit 7 constitute a first display adjustment device 101, and the liquid crystal panel 8 constitutes a display unit.

A video signal IN containing video information and a synchronizing signal SY for synchronizing are input from a computer (not shown) to the liquid crystal display device of FIG. The video signal IN is
It consists of an R (red) signal, a G (green) signal and a B (blue) signal. The synchronization signal SY includes a horizontal synchronization signal H and a vertical synchronization signal V. The video signal IN output from the personal computer includes VGA (Video Graphics Arra
y), since there are various resolutions defined by standards such as SVGA (Super Video Graphics Array), in order to display various images on a fixed resolution display device such as the liquid crystal panel 8, the resolution of the video signal IN Needs to be converted to the resolution of the liquid crystal panel 8.

First, the A / D converter 1 digitizes an analog video signal IN. The digitized signal is subjected to pixel number conversion in the first pixel number conversion circuit 2 and output to the liquid crystal panel 8 as liquid crystal panel digital data PD. Thereby, an image can be displayed on the liquid crystal panel 8 with a resolution adapted to the liquid crystal panel 8.

The frequency determination circuit 3 determines the horizontal synchronization frequency and the vertical synchronization frequency of the video signal IN from the synchronization signal SY. The CPU 6 determines the resolution of the video signal IN based on each of the synchronization frequencies determined by the frequency determination circuit 3.

The average luminance detection circuit 4 detects the average luminance level of the video signal IN over one frame. On the basis of the average luminance level detected by the average luminance detection circuit 4 and the resolution of the video signal IN determined by the frequency determination circuit 3, the CPU 6 converts the image displayed on the liquid crystal panel 8 into a basic input / output system (Basic Input / Output). Output System; hereinafter, referred to as BIOS).

FIG. 7 is a diagram showing an example of a BIOS screen displayed when the personal computer is started. BIO
The S screen usually has a VGA resolution.

As shown in FIG. 7, on the BIOS screen, information is indicated by white text characters and the like on a black background, and the average luminance is considerably lower than that of a normal graphic screen. For this reason, when the video signal IN having a resolution of VGA and a low average luminance is detected for a few seconds after the power of the liquid crystal display device is turned on or the resolution is changed, Judge as the screen.

The start position detecting circuit 5 detects start positions of text characters in the horizontal and vertical directions. BIOS
On the screen, since the video information does not exist in the entire frame of the effective screen area, the video display period cannot be detected using the level of the video signal IN. Therefore, the display position is adjusted based on the start positions of the text characters in the horizontal and vertical directions.

The CPU 6 performs BIO based on the start position of the text character detected by the start position detection circuit 5.
A correction value for the display position of the S screen is obtained. LCD drive circuit 7
Changes the synchronization signal SY based on the display position correction value obtained by the CPU 6 and outputs a liquid crystal panel control pulse PP to the liquid crystal panel 8.

The liquid crystal panel control pulse PP includes a data enable signal representing an effective screen area, and the liquid crystal drive circuit 7 controls the phase of the data enable signal to thereby control the liquid crystal panel 8. Is changed.

As described above, by automatically adjusting the display position of an image based on the start position of a text character,
Even on the BIOS screen where the display position cannot be automatically adjusted conventionally, various video signals can be displayed without missing text characters.

In this embodiment, the first pixel number conversion circuit 2 corresponds to the resolution conversion means, and the frequency discrimination circuit 3
And the average luminance detection circuit 4 corresponds to the screen detection means, the start position detection circuit 5 corresponds to the start position detection means, and C
The PU 6 and the liquid crystal drive circuit 7 correspond to control means.

(2) Second Embodiment FIG. 2 is a block diagram showing a configuration of a liquid crystal display device having a display adjusting device according to a second embodiment of the present invention.

The liquid crystal display device shown in FIG. 2 includes a second display adjustment device 102 and a liquid crystal panel 8 as a display unit.

In the liquid crystal display device shown in FIG. 2, the second display adjusting device 102 is the same as that shown in FIG. 1 described in the first embodiment.
1 is different from the display adjustment device 101 in that a second pixel number conversion circuit 9 is used instead of the first pixel number conversion circuit 2 used in FIG. The point is that the number conversion circuit 9 is controlled.

In this embodiment, the second pixel number conversion circuit 9 corresponds to a resolution conversion circuit.

The second pixel number conversion circuit 9 is controlled by the CPU 6 and converts a video signal IN to a resolution optimum for the liquid crystal panel 8 when a BIOS screen is detected and a graphic for displaying a normal video. Different pixel number conversion is performed when a screen is detected.

FIG. 6 is a diagram showing different types of pixel number conversion by the pixel number conversion circuit 9 of FIG. In FIG.
(A) is a schematic diagram of linear interpolation, (b) is a schematic diagram of polynomial interpolation.

For example, the second pixel number conversion circuit 9 is
When the OS screen is detected, as shown in FIG. 6A, the data of the interpolation pixel I1 is calculated by linear interpolation using the data of the two original pixels D1 and D2. When a graphic screen is detected, the second pixel number conversion circuit 9 outputs the two original pixels D3 and D4 as shown in FIG.
Is used to calculate the data of the interpolated pixel I2 by the polynomial interpolation.

On a graphic screen, it is better to interpolate with as many orders as possible to restore a smooth image. For this reason, a smoother video can be displayed by using polynomial interpolation.

However, in the case of a video centered on text characters such as a BIOS screen, the use of polynomial interpolation makes the text characters look blurry. On the other hand, when the linear interpolation is used, the image is restored to a clear image, so that the text characters are displayed sharply. Therefore, a sharper image can be displayed on the BIOS screen by using linear interpolation.

As described above, the display position can be automatically adjusted on both the graphic screen and the BIOS screen centered on text characters, and both images can be displayed more optimally.

(3) Third Embodiment FIG. 3 is a block diagram showing a configuration of a liquid crystal display device provided with a display adjusting device according to a third embodiment of the present invention.

The liquid crystal display device shown in FIG. 3 includes a third display adjustment device 103 and a liquid crystal panel 8 as a display unit.

In the liquid crystal display device shown in FIG. 3, the third display adjusting device 103 is the same as that shown in FIG. 1 described in the first embodiment.
The difference from the display adjustment device 101 is that the maximum luminance detection circuit 11 is connected to the output side of the A / D converter 1, the amplifier 10 is connected to the preceding stage of the A / D converter 1, and the amplifier 10 is controlled by the CPU 6. It is controlled.

In this embodiment, the amplifier 10 corresponds to the level adjusting means, and the maximum luminance detecting circuit 11 corresponds to the maximum luminance detecting means.

The maximum luminance detecting circuit 11 detects the maximum value of the luminance of the video signal IN. Since there are white text characters on the BIOS screen, it is considered that the maximum values of the R signal, the G signal, and the B signal exist respectively. Therefore, the maximum luminance detection circuit 11 detects the maximum value of the luminance of the R signal, the G signal, and the B signal, and the maximum value of the number of bits of the A / D converter 1 is, for example, 255 if the number is 8 bits. Then, the gain of the amplifier 10 is controlled by the CPU 6 to adjust the level of the video signal obtained by the amplification.

As described above, the video signal I at the time of the BIOS screen is
The level of the video signal can be adjusted so that N can be digitized with an optimal dynamic range, and a sharper BIOS screen can be displayed.

Even when the video signal IN has a very low luminance due to deterioration or the like, the average luminance and the maximum luminance are detected first by the average luminance detection circuit 4 and the maximum luminance detection circuit 11, and the video signal IN After the IN is amplified by the amplifier 10, the start position can be detected by the start position detection circuit 5. By amplifying the video signal IN, the start position can be easily detected,
The display position can be automatically adjusted more optimally.

(4) Fourth Embodiment FIG. 4 is a block diagram showing a configuration of a liquid crystal display device provided with a display adjustment device according to a fourth embodiment of the present invention.

The liquid crystal display device shown in FIG. 4 includes a fourth display adjusting device 104 and a liquid crystal panel 8 as a display unit.

In the liquid crystal display device shown in FIG. 4, the fourth display adjusting device 104 is the same as that shown in FIG.
The difference from the display adjustment device 103 is that the binarization circuit 12 is connected to the stage preceding the first pixel number conversion circuit 2, and the binarization circuit 12 is controlled by the CPU 6. Further, the amplifier 10 of FIG. 3 is not provided.

In this embodiment, the binarizing circuit 12
Corresponds to a binarization unit. The binarization circuit 12 uses a CPU based on the maximum luminance detected by the maximum luminance detection circuit 11.
6, the video signal digitized by the A / D converter 1 is “0”, and the maximum value of the number of bits of the A / D converter 1 is, for example, only two values of “255” in the case of 8 bits. Convert to

In the third embodiment, even when the video signal IN is digitized by the amplifier 10 with the optimum dynamic range, the luminance level of the same text character may vary depending on the performance of the personal computer and the state of the transmission path. May be different.

For example, when the DC level fluctuates in the vertical direction or when the A / D converter 1 performs sampling at a frequency different from the dot clock frequency of the personal computer, the video signal IN is output in the vertical scanning direction. It becomes a sag waveform distorted. In such a case,
Even if an optimal interpolation method is selected as in the second embodiment, the character quality is not improved.

Therefore, by using the binarization circuit 12 in the fourth embodiment, the digitized video signal is limited to "0" and the maximum value, thereby improving the visibility of text characters. The display position can be improved, and the display position can be automatically adjusted.

(5) Fifth Embodiment FIG. 5 is a block diagram showing a configuration of a liquid crystal display device having a display adjusting device according to a fifth embodiment of the present invention.

The liquid crystal display device shown in FIG. 5 includes a fifth display adjusting device 105 and a liquid crystal panel 8 as a display unit.

In the liquid crystal display device shown in FIG. 5, the fifth display adjusting device 105 is the same as that shown in FIG.
The difference from the display adjustment device 104 is that the binarization circuit 12 is connected in common to the first pixel number conversion circuit 2, the average luminance detection circuit 4, the maximum luminance detection circuit 11, and the preceding stage of the start position detection circuit 5. It is a point.

The basic operation of the liquid crystal display device of the fifth embodiment is the same as that of the fourth embodiment. However, in the fifth embodiment, particularly, the video signal IN is deteriorated due to deterioration or the like. This is effective when the image has only a low luminance.

First, the CPU 6 stops the binarizing operation of the binarizing circuit 12. Accordingly, the video signal IN passes through the binarization circuit 12, and the average luminance and the maximum luminance are detected by the average luminance detection circuit 4 and the maximum luminance detection circuit 11, respectively. Thereafter, the CPU 6 operates the binarization circuit 12. As a result, the video signal IN is binarized in the binarization circuit 12, and thereafter, the start position detection circuit 5
At the start position of the text character. In this way, the start position of a text character can be detected more optimally.

By limiting the video signal IN to two values of "0" and the maximum value, the brightness level of the text characters can be increased uniformly, the visibility of the video can be improved, and the display position can be automatically adjusted. The video signal IN
It is possible to automatically adjust the display position optimally even when the state is bad.

[0074]

According to the present invention, when the basic input / output system screen displayed when the computer is started is detected, the display position is automatically adjusted based on the horizontal and vertical start positions of the text characters. By doing so, signals of various resolutions can be displayed without missing text characters.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a liquid crystal display device including a display adjustment device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a liquid crystal display device including a display adjustment device according to a second embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a liquid crystal display device including a display adjustment device according to a third embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of a liquid crystal display device including a display adjustment device according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram illustrating a configuration of a liquid crystal display device including a display adjustment device according to a fifth embodiment of the present invention.

FIG. 6 is a diagram showing different types of pixel number conversion by the second pixel number conversion circuit of FIG. 2;

FIG. 7 is a diagram showing an example of a basic input / output system screen displayed when the personal computer is started.

[Explanation of symbols]

 2 First pixel number conversion circuit 3 Frequency discrimination circuit 4 Average luminance detection circuit 5 Start position detection circuit 6 CPU 7 Liquid crystal drive circuit 8 Liquid crystal panel 9 Second pixel number conversion circuit 10 Amplifier 11 Maximum luminance detection circuit 12 Binarization circuit

Continued on the front page F term (reference) 5C006 AF14 AF47 BB11 BC03 BC11 BC16 BF02 FA05 5C021 PA72 RA07 SA06 XA35 XA61 YC01 ZA01 5C080 AA10 BB05 DD01 EE32 GG02 JJ01 JJ02 KK02 5C082 AA01 BA02 BA12 BC26 BB02 BB02 BB02 CB02 DA22 DA42 DA53 DA63 DA73 DA76 DA86 EA15 MM06 MM09

Claims (9)

[Claims] 1. A display adjustment device for adjusting a display state of an image on a display unit based on an image signal and a synchronization signal provided from a computer, wherein the resolution of the image signal is converted to a resolution suitable for the display unit. Resolution conversion means for applying the video signal to the display unit, a screen detection means for detecting a basic input / output system screen displayed when the computer is started, and the basic input / output system screen is detected by the screen detection means. A start position detecting means for detecting a start position of a character signal in the video signal; and a basic input system screen detected by the screen detecting means based on the start position detected by the start position detecting means. Control means for controlling the synchronization signal so as to be displayed at a predetermined position. Location. 2. The basic input / output system screen according to claim 2, wherein the screen detecting means detects the basic input / output system screen based on a horizontal synchronization frequency and a vertical synchronization frequency of the synchronization signal and an average luminance in one frame of the video signal. Item 1
The display adjustment device according to the above. 3. The resolution conversion means performs resolution conversion using a first interpolation method when detecting the basic input / output system screen by the screen detection means, and when detecting a screen other than the basic input / output system screen. The resolution conversion is performed by using a second interpolation method.
The display adjustment device according to the above. 4. The display adjustment device according to claim 3, wherein the first interpolation method is a linear interpolation, and the second interpolation method is a polynomial interpolation. 5. A maximum luminance detecting means for detecting a maximum luminance of said video signal when said basic input / output system screen is detected by said screen detecting means, and said video image based on a maximum luminance detected by said maximum luminance detecting means. The display adjustment device according to claim 1, further comprising a level adjustment unit that adjusts a signal level. 6. The display adjustment device according to claim 5, wherein the start position detection unit detects a start position of the character signal in the video signal adjusted by the level adjustment unit. 7. A maximum luminance detecting means for detecting a maximum luminance of said video signal when said basic input / output system screen is detected by said screen detecting means, and said video image based on a maximum luminance detected by said maximum luminance detecting means. 5. The display adjusting device according to claim 1, further comprising a binarizing unit that binarizes the signal and provides the binarized signal to the resolution converting unit. 8. The display adjusting device according to claim 7, wherein the start position detecting means detects a start position of the character signal in the video signal binarized by the binarizing means. 9. A display device for displaying an image based on a video signal and a synchronization signal given from a computer, comprising: a display unit for displaying an image; and a resolution of the video signal converted to a resolution suitable for the display unit. Resolution converting means for applying the video signal to the display unit, a screen detecting means for detecting a basic input / output system screen displayed when the computer is started, and the basic input / output system screen is detected by the screen detecting means. A start position detecting means for detecting a start position of a character signal in the video signal, and a basic input system screen detected by the screen detecting means based on the start position detected by the start position detecting means. Control means for controlling the synchronization signal so as to be displayed at a predetermined position of the display unit.