DE3240473A1 - Method for reproducing videotex pages on the monochrome screen of a grey-scale-capable television monitor - Google Patents

Abstract

To reproduce videotex pages on the monochrome screen of a grey-scale-capable television monitor, for example a data terminal, the signals of the videotex pages containing information items for a coloured reproduction of the text formed of characters and the graphic images on a screen which can be driven by a videotex decoder and the characters and graphic images being represented of individual picture elements arranged in the form of a matrix, adjacent picture elements are checked for the presence of a colour transition and in the case of such a one, the relevant picture elements in the line and/or column are imaged on the screen in a grey scale value which sufficiently differs from the grey scale value of the preceding or following picture elements in the row or column.

Description

Procedure for displaying on-screen text pages on the

monochrome screen of a gray-tone television monitor The invention relates to a method and a circuit arrangement for displaying screen text pages on the monochrome screen of a gray-tone television monitor, for example a data terminal, the signals of the teletext pages information for a color reproduction of the text made up of characters and the graphic Contains images on screens controllable by a video text decoder and the characters and the graphic images from individual, arranged in a matrix Pixels are represented.

The teletext or teletext service is a new form of communication in which the telephone network is used to transmit the image information that can be displayed on the screen of a normal color television set. Leave it not only texts made up of letters, numbers and symbols, but rather also display graphical representations. The user of such a service can now in a center, which provides the information, the desired information choose. The mapping is done page by page, i. H. over the telephone network the information to be displayed on a page is transmitted and in a so-called On-screen text decoder is stored and prepared accordingly for display. When a new page is called up, the information previously saved is overwritten. Further details about the teletext system can be found, for example, in the Pamphlet Telecommunications Journal (NTZ) ", Volume 34 (1981), Booklet 11, on pages 776 to 780.

The teletext system is tailored to a large group of users, hence the color television set found in most households as the playback device is used. Now becomes a gray-tone TV monitor with a monochrome Screen used to display the screen text pages, for example the gray tone capable. Screen of a data terminal, it is indeed an illustration of the screen text pages also easily possible by converting the color information into gray values However, there is a risk that the visibility of the representations will suffer, because under certain circumstances the gray values of the colors differ too little from one another. this is especially the case when instead of the previous eight colors, there is a multitude of colors of colors can be represented on the screen. For this, reference is made to the publication "telcom report" 4 (1981), No. 5, pages 378 to 383, referenced.

The object of the invention is now to provide a method and a Specify circuitry showing the display of screen text pages on a monochrome screen of a gray-tone television monitor enables whereby the legibility of the texts and the recognizability of the graphic representations is increased.

This object is achieved in that adjacent pixels the presence of a color transition can be checked and that in the event of a color transition the relevant pixels in the row and / or in the column in a gray tone value on the screen, which differs from the gray tone value of the previous one or the underlying pixels in the row or column sufficiently differentiates.

By evaluating the gray tone values for neighboring pixels different color values, the criterion for modification is created the gray tone values of the relevant image points is used. The gray tone value of this If necessary, image points are changed in such a way that they differ from the neighboring ones Image points stand out sufficiently / Since the inspection of all color transitions in both is carried out in the row and in the column, a is displayed Character or a graphic on the screen / with one of the gray-tone value of the same and / or the background distinguishing frame.

A further development of the invention consists in that in each case three one behind the other or. superimposed image points are checked between and that at a color transition / the the first and the second pixel, the gray tone value of the first and the second pixel and in the case of a color transition between the second and the third image point, the gray tone value of the second and the third pixel is changed.

In this way, an overarching representation is made Contouring achieved, because when there is a transition from one representation to one different representation (letters, characters or fine graphics, rough graphics) Parts of the border according to the invention are lost when using a special Control signal the method according to the invention only on certain types of display is restricted.

The invention is explained in more detail using an exemplary embodiment, which is shown in the drawing.

It shows: FIG. 1 the block diagram of the evaluation circuit for the signals of a chrominance, FIG. 2 shows the block diagram for carrying out the modification of the Gray tone values of the signals and Fig. 3 shows the representation of one of the individual Dots of characters formed on the screen, with a) unchanged and a contoured representation is shown under b).

The evaluation circuit V shown in Fig. 1 is for each of the three colors See (red, green, blue) each pre-digitized once (see Fig. 2). The / color value signal B; for example the color red is fed to the input of a shift register S1, the output of which is connected to the input of a second shift register S2. Its output is in turn connected to the input of a third shift register S3. All three shift registers have as many bit positions as there are pixels in one line. As the information from three interconnected Lines are each contained in the three shift registers are in each case at the Outputs of the shift registers S1 to S3 the pixels of a common column. The outputs of the first two shift registers S1 and S2 are provided with a comparator VG1 and the outputs of the last two shift registers S2 and S3 are with one Comparator VG2 connected.

Since the signals pending at the output of the shift register S2 for the representation on the screen is used, contains the shift register S1 the information of the previous line (n-1) and the shift register S3 the Information on the following line (n + 1). With the help of the comparator VG1 i.e. the color values of the same pixels of two superimposed lines, namely compared to the previous line and the line to be displayed, while-with With the aid of the comparator VG2, the same superimposed image points are to be displayed Line can be compared with the following line.

The signals of the line to be displayed are sent to a comparator VG3 fed, which this with the delayed by the delay circuit T2 Signal compares.

The latter signal is also used for the respective display on the Screen. It is also fed to a comparator G which interconnects it another delay circuit T3 compares delayed signal. So it takes place here the comparison of the color value signal of a pixel with that of a previous one Pixel (VG3) and the comparison of the color value signal of the pixel with that of a subsequent pixel (VG4) of a line instead.

The outputs of the comparators V1 and V2 are via an OR gate 02 combined and connected to a delay circuit T1. This delay circuit, which also has a delay time of the duration of one pixel, serves to compensate for the delay caused by the delay circuit T2 is, since, as is well known, the signal S to be displayed is present at the output thereof. At the exit of the delay circuit T1 and at the outputs of the comparators VG3 and VG4 an OR gate 01 is connected, at the output of which the control signal SV appears.

In summary, it can be stated that with a color transition of two adjacent pixels both in a column and in a row a control signal arises on the line SV. The total delay of the signal for the control of the pixel S is one line and one pixel.

As already mentioned, there is an individual evaluation circuit for each color V provided, these are correspondingly with the three colors red, green and blue VR, VG and VB in the block diagram in FIG. Everyone who has been digitized value circuits V is supplied with the relevant / color value signal BR, BG or BB. The SV outputs of the evaluation switch Services VR, VG and VB are over an OR gate, 03 combined and fed to an AND gateG. At the exits As is known, a control signal appears SV when a color transition occurs. Above the control line ST enables or disables the AND gate G.

The output of the AND gate is connected to the offset logic circuit OL connected and is used to activate the same.

This means that by a control signal from an evaluation circuit V the offset logic circuit OL is activated. This activation by a control signal from an evaluation circuit V can be prevented via the line ST will. In this way, the inventive manipulation of the gray-tone values can be carried out on certain types of representation, e.g. letters, characters, rough graphics, fine graphics, etc., broom drums.

Digitized at the outputs S of the evaluation circuits VR, VG and VB the / color value signal of the respective color appears.

These signals are fed to a converter U, which is digitized from the / the / color value signals R, G and B generates the luminance signal Y. This signal is fed to the offset logic circuit OL and unchanged on the line VS transmitted to the television monitor as long as there is no control signal from the AND gate the offset logic circuit OL arrives. At the same time the luminance signal is fed to a gray value comparator VGR. The task of this comparison device consists in the gray value corresponding to the luminance signal Y with the mean value to compare the gray scale. Each color value corresponds to a certain shade of gray, in which the representation of the color in question on the monochrome screen he follows.

The gray scale of the colors red, green, blue and the resulting ones Mixed colors are given in the table below. These gray values apply each with full intensity of the colors red, green and blue.

Example: b Standard color bar sequence Y White 1.00 Yellow (red and green) 0.89 Cyan (green and blue) 0.70 Green 0.59 Purple (red and blue) 0.41 Red 0.30 Blue 0.11 Black 0.00 The table shows the gray (Y) values in a rough gradation, since the specified gray values only apply with the full intensity of the basic colors. The different luminance values of the basic colors create a very finely graded structure of the gray values, the differences between which are no longer perceptible to the human eye.

The comparison device VGR determines the difference between the Gray value of the luminance signal Y and the mean value of the gray value scale as they are is given in the table. This difference value becomes the offset logic circuit transmitted.

The luminance signal Y changed in such a way that its gray value differs from that of the neighboring pixels more different. For example, if the gray value is below the mean value the gray scale, the relevant image point is shown lighter so that it stands out from the darker neighboring pixels. The opposite is the case Pixel shown darker if the neighboring pixels are lighter. As already described, the manipulation of the luminance signals of the pixels takes place only when a signal occurs at the output of AND gate G, d. H. when occurring of a color transition of neighboring pixels.

So far there has been talk of gray values, although the representation the information should be displayed on a monochrome screen. Under monochrome As is well known, screens fall all monochrome screens, i. H. also those which not a black / white representation, but a black / green or black / yellow representation enable. Gray-tone values are therefore to be understood as brightness values.

Based on Fig. 3, the mode of operation in the representation on the Screen explained. Under a is the representation on a color screen shown. A surface 2 is imaged in front of a background 1. It is assumed that that the background 1 is red and the area 2 is yellow.

The representation on a monochrome screen is shown under b. Area 2 is again located within the drawn out border. The red one The background is displayed with a gray value of 0.3. Due to the color transition between the red background and the yellow area is given the contour 3 by the offset logic circuit a value that stands out from the gray value of the color red, for example the Value 0.89. The color of the area 2 is in the area of the contour 4 in a gray value, for example of 0.11, while within the contour the yellow area 2 is marked with the corresponding value 0.89.

This example shows that the contour has a width of 2 pixels are each marked in two different shades of gray. Is in the offset logic circuit made a further delay by one pixel and the luminance signals of two successive pixels with one another compared, it is easily possible to obtain that from a width of two pixels formed contour in one, from the gray tones of the background 1 and the surface 2 strongly differentiating the same gray value.

In the illustration based on FIG. 3b, it is noticeable that the contour is present the corner points 5 is not available. This is a negligible one Blemish, which can be avoided by appropriate switching measures can, if the pixels of several columns and several rows in the monitoring of the color transitions can be included.

Claims (8)

Method for rendering on-screen text pages on the monochrome Screen of a gray-tone television monitor Patent claims: Method for reproduction of screen text pages on the monochrome screen of a gray-tone television monitor, for example a data terminal, with the signals of the teletext pages Information for a colored reproduction of the characters formed from characters and the graphic images can be controlled by a video text decoder Screens and the characters and graphic images from individual, pixels arranged in a matrix are represented, characterized in that that neighboring pixels are checked for the presence of a color transition and that in the event of a color transition, the relevant pixels in the line and / or in the column in a gray tone value on the screen, which from the gray tone value of the pixels in front or behind in the row or column is sufficiently different. 2. The method according to claim 1, characterized in that each three in a row or superimposed pixels are checked and that in the case of a color transition between the first and second image point, the gray tone value of the first and the second image point and with a color transition between the second and the third pixel the gray tone value of the second and third Image point is changed. 3. The method according to any one of claims 1 or 2, characterized in that that the change in the gray tone value depending on one of the type of Representation (characters, fine graphics, rough graphics, etc.) derived control signal he follows. 4. Circuit arrangement for performing the method according to a of Claims 1 to 3, characterized in that the signals are three connected in series Shift registers (S1 to S3) are fed, each shift register the signals for the pixels of a line contains that the outputs of the first two shift registers (S1, S2) with a first comparator (VG1) and the outputs of the last two Shift registers (S2, S3) are connected to a second comparator (VG2) and that the outputs of the two comparators (VG1, VG2) of an offset logic circuit (OL) are supplied via a delay circuit (T1). 5. Circuit arrangement according to one of claims 1 to 4, characterized in that that the output of the second shift register (S2) with a delay circuit (T2) and a third comparator (VG3) is connected that the output of the delay circuit (T2) also with the comparator (VG3), a fourth comparator (VG4) and one further delay circuit (T3) is connected, the output signal of the fourth Comparator (VG4) is supplied and 'that the outputs of the two comparators (VG3, VG4) are fed to the offset logic circuit (OL). 6. Circuit arrangement according to one of claims 4 or 5, characterized marked that the delay time of the delay circuits (T1 to T3) each is one pixel. 7. Circuit arrangement according to one of claims 1 to 6, characterized characterized in that for each of the three color value signals (red, green, blue) an individual Evaluation device (V) is provided that the outputs of the second shift register (S2) connected delay circuit (T2) with a device for generating of the luminance signal (Y) are connected and that in the absence of a color transition the luminance signals (Y) are fed to the television monitor unchanged. 8. Circuit arrangement according to one of claims 1 to 7, characterized in that that the luminance signal (Y), d. H. its gray value with the mean value of the gray value scale / Vuenglidcahsen difference signal the offset logic circuit (OL) is fed, which by the signals of the comparator (VG1 to VG4) activated due to the gray value signal, which generates a gray tone ensures a sufficient possibility of differentiation and that changed this Luminous signal is fed to the television monitor.