JPH0355831B2 - - Google Patents

Description

[Detailed description of the invention]

<Technical Field of the Invention> The present invention relates to improvement of an image display device in which unit pixels are arranged in a matrix, and more specifically, the present invention relates to an improvement in an image display device in which unit pixels are arranged in a matrix. An image display device that eliminates the blurring of characters on an image or the distortion of character shapes caused by any signal when inserting and displaying characters given to an image display device using the TUX method, making it possible to display clear characters. It is related to. <Technical Background of the Invention and its Problems> Currently, various image monitor devices, including video camera viewfinders, display text at the same time as the image, thereby providing various information such as out-of-focus and underexposure. A device that communicates the information to the user has been developed and put into practical use. These devices generally combine or superimpose a character signal at an arbitrary position on the video signal, resulting in black and white
When displaying on a CRT, it is possible to display characters with clarity determined by the transmission characteristics of the character signal generator and signal transmission system and the characteristics of the display device itself. However, when the above character signals are displayed on a dot matrix image display device, if the pixel pitch of the image display device and the dot pitch of the character signal do not match, the character image may be blurred or the character shape may be blurred. There was a problem where distortion occurred. In other words, in a display device that is not provided with a signal storage capacitor for storing pixel drive signals for each pixel, the display shading of each pixel (determined by luminance for light-emitting devices, reflectance, transmittance, etc. for non-light-emitting devices) ) is the average value of the period during which the corresponding pixel is selected. Therefore, if the pixel pitch and the signal pitch match, the density of the text will be at the desired value, as shown in section a in Figure 4, and there will be no problem. Since the signal pitches do not match, for example, if there is a difference of θ, the density of the corresponding pixel will be different from the signal value of the background of the character by θ.
The display quality is shifted from a predetermined value by a value determined by the above, and the quality of the display is degraded as blurring and distortion of characters occur. An example of displaying white characters on an image with a black background is shown in section b of FIG. In this interval b, the image displayed on the display device is such that the signal level of the corresponding pixel is lower than the white level (W) by the value x = θ/τ ₀ X ₀ , which is proportional to the phase shift θ, and the black level (B). It is displayed as an image when shifted to . In addition, in display devices in which each pixel is provided with a signal storage capacitor that stores a pixel drive signal, the display density of each pixel is determined by whether the signal storage capacitor of the pixel is charged or discharged during the period in which the pixel is selected. is,
The density corresponds to the signal level such as the signal storage capacity at the time when the selection of the corresponding pixel is completed. Therefore, the time constant of signal storage capacitance, etc. is low, that is, the signal voltage of the same element can follow the video signal applied from the outside sufficiently quickly, and the signal level of the same element can be reduced within the period when the pixel is selected. If it is charged or discharged to the same level as the externally applied video signal, a desired density display can be obtained without any problem. but,
If the time constant of the signal storage capacity is large, that is, it takes time for the signal voltage of the same element to charge or discharge to the same level as the externally applied video signal voltage, the image may not reach the desired level. It will be displayed. An example of this case is shown in FIG. In FIG. 5, the time constant for charging or discharging the signal storage capacitor is τ, and as shown in section c in FIG. If there is sufficient time for discharge, that is, τ ₀ -θ>τ, the displayed image will be the desired image and there will be no problem. On the other hand, if the phase difference θ between the pixel pitch and the character signal is large and the signal level of the signal storage capacitor is not sufficiently charged or discharged, as shown in section d in FIG. As shown in d, a predetermined level (white level W in the figure) is shifted to black level B (

[Formula]) will be displayed as an image. <Objects and Structure of the Invention> The present invention provides an image display device that prevents blurred display of characters due to a phase shift between a character signal and a pixel that are synthesized (including superimposed) on the above-described image signal. In order to achieve this object, the present invention provides a dot matrix display device in which unit pixels are arranged in a matrix, and a composite display signal in which a character signal is synthesized with a video signal is supplied to the dot matrix display device. In an image display device that displays a character signal synthesized with a video signal, the character signal or the composite display signal is sampled and held in synchronization with the scanning timing of the unit pixel. The present invention is characterized in that a sample and hold circuit is provided for outputting the character signal, and the dot timing of the character signal matches the scanning timing of the dot matrix type display device. <Embodiments of the Invention> The present invention is characterized in that the phase of a character signal applied to an image display device is forced to match the pixel pitch, and as shown in the following embodiments, sample and hold By providing a circuit between the character signal or composite signal generator and the display device, the character signal or composite signal is maintained for the display period of a unit pixel. Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a dot matrix type display device, which selectively displays one pixel in one cycle from the rising edge of the pulse signal _φH to the next rising edge. 2 is an image synthesis device that synthesizes (including superimposition) the input video signal and character signal and provides it to the display device 1; 3 is a sample hold provided between the character signal input terminal and the image synthesis device 2; This circuit holds the video signal at the rising edge of the signal φ _H for one cycle of φ _H , that is, for one pixel scan period, using a sample hold signal to be described later. 4 is a sample/hold signal generation circuit, which generates the sample/hold signal.
The hold signal generating circuit 4 is configured to receive the signal φ _H , create a sample hold signal indicating the rising edge of the signal _H , and supply it to the sample hold circuit 3. Further, the signals φ _V and _V supplied to the display device 1 are pulse signals for scanning the display device 1 in the vertical direction. FIG. 2a is a block diagram showing a specific example of the configuration of the sample-and-hold signal generating circuit 4, which includes a delay circuit 11, an inverter 12, and an AND gate 1.
3, and by inputting the signal φ _H to the terminal a, a sample and hold signal is output from the terminal b. FIG. 2b is a block diagram showing a specific example of the configuration of the sample-and-hold circuit 3 shown in FIG. A sample and hold signal is input to terminal b, and an input character signal is input to terminal b, and a sample and hold output of the character signal is derived from terminal c. FIG. 3 is a signal waveform diagram for explaining a display example of the device according to the embodiment of the present invention shown in FIG. 1, and the operation waveform shown in FIG. This will be explained with figures. The sample-and-hold signal generating circuit 4 to which the signal φ _H is input generates a sample-and-hold signal and supplies it to the terminal a of the sample-and-hold circuit 3. The sample hold circuit 3 to which the sample bold signal is input holds the video signal of the rising portion of the pulse signal φ _H input to the terminal b by the sample hold signal for one period of the signal φ _H , that is, for one pixel scanning period. Then, a character signal synchronized with the pixel pitch is generated, outputted from terminal c, and supplied to the image synthesizing device 2. As a result, a character signal synchronized with the pixel pitch is supplied to the display device 1, and a clear character display without blur or distortion of character shape is achieved. As described above, according to the embodiment of the present invention described above, when a video signal and a character signal for representing characters are combined (including superimposition) and provided to a dot matrix display device, the character A sample-and-hold circuit is installed between the character signal and the display device to match the scanning timing determined by the dot timing of the signal and the number of pixels of the display device, so that blurring of the characters or character shape on the image due to signal deviation is prevented. This eliminates distortion and allows clear characters to be displayed. In the above embodiment, an example in which a sample and hold circuit is provided between a character signal and a display device has been described, but the present invention is not limited to this. Needless to say, it may also be provided as follows. <Effects of the Invention> As described above, according to the present invention, even when a character signal synthesized with a video signal (including superimposition) is given to an image display device in which unit pixels are arranged in a matrix, By adding circuit means, it is possible to eliminate blurring of characters on images or distortion of character shapes, and display clear characters.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2a is a block diagram showing an example of the configuration of a sample-and-hold signal generation circuit, and FIG. 2b is a block diagram showing an example of the configuration of the sample-and-hold circuit. , FIG. 3 is a signal waveform diagram for explaining the operation of the device according to the embodiment of the present invention, FIG. 4 is a diagram for explaining the display operation of a conventional display device without a video signal storage element, and FIG. 1 is a diagram for explaining a display operation in a display device having a conventional video signal storage element. 1...Dot matrix display device, 2...
...Image synthesis device, 3...Sample hold circuit,
4...Sample and hold signal generation circuit.

Claims (1)

[Scope of Claims] 1. A dot matrix display device in which unit pixels are arranged in a matrix, and an image synthesis device that supplies a composite display signal obtained by combining a video signal with a character signal to the dot matrix display device. However, in an image display device that displays a character signal synthesized with a video signal, in synchronization with the scanning timing of the unit pixel,
A sample-and-hold circuit is provided that samples the character signal or composite display signal, holds it, and outputs it, and the sample-and-hold circuit matches the dot timing of the character signal with the scanning timing of the dot matrix display device. An image display device characterized by: