Television receiver for teletext

Abstract: The present invention relates to a television receiver for teletext for receiving a composite video signal having text information multiplex on a television video signal, and more particularly to a television receiver for teletext capable of displaying the television video signal and teletext screen simultaneously on the picture screen by superimposing or dividing the screen, and according to this television receiver for teletext, which comprises preprocessing means for issuing various preprocessing correction signals on the basis of the teletext signal extracted by the teletext signal receiving means, the preprocessing correction signal issued by the preprocessing means. and the teletext signal received by the teletext signal receiving means are combined and displayed on the picture screen, and thereby the boundary of the television video signal and teletext signal is clearer, so that the text of thetelet ext signal is easier to read.

Description: BACKGROUND OF THE INVENTION The present invention relates to a television receiver for teletext for receiving a composite video signal having text information multiplexed on a television signal, and more particularly to a television receiver for teletext for displaying television video signal and teletext signal simultaneously on a picture screen by superimposing or dividing the screen. Further particularly, it relates to a television receiver for teletext for displaying a television video signal and teletext signal simultaneously on a screen of aspect ratio of 16:9 known as wide television. Fig. 1 shows a schematic constitution of a television receiver for teletext of a prior art. In the diagram, reference numeral 11 is an input signal of demodulated composite video signal, 12 is a television video signal processing circuit for receiving a composite video signal and converting into a television signal a (signal of three primaries R, G, B), 13 is a teletext signal receiving circuit for extracting a teletext signal superposed in a vertical blanking period of input composite video signal to convert into teletext video signal b (signal of three primaries R, G, B), and generating a composite control signal (YS signal ) c synchronized with the teletext video signal b, 14 is a synthesizing circuit for superimposing a teletext video signal b from the teletext signal receiving circuit 13 for the television video signal a from the television video signal processing circuit 12 on the basis of the composite control signal (YS signal) c from the teletext signal receiving circuit 13, and 15 is a display device such as CRT and LCD for displaying the composite video signal d. The operation is described below. Fig. 2 (a) shows a television video signal a in part of one horizontal line, and Fig. 2 (b) shows a teletext video signal b in part of one horizontal line. Fig. 2 (c) shows a composite control signal (YS signal) c generated completely at same timing (in same time width) synchronously with the teletext video signal b. The teletext video signal b, for example, at the timing of horizontal line 16 of letter " " in Fig. 3 (a), produces two waveforms as shown in Fig. 3 (b), and the composite control signal (YS signal) c is generated at the same timing as the teletext video signal b as shown in Fig. 3 (c). Fig. 2 (d) shows the composite video signal d having the television video signal a and teletext video signal b synthesized according to the composite control signal (YS signal) c. In the composite video signal d, the television video signal a is extracted at the timing of teletext video signal b. Fig. 4 shows the detail of the teletext signal receiving circuit 13 in the television receiver for teletext. In this diagram, reference numeral 31 is a teletext signal decoder for extracting and decoding the teletext signal superposed in the vertical blanking period from the input composite video signal, 61 is a memory for storing decoded teletext data, 62 is a memory control circuit for controlling writing and reading of the memory 61, 35 is a line memory for storing the teletext data for the portion of one horizontal line temporarily, 42 is a look-up table for converting the teletext data read out from the line memory 35 into color data of R, G, B, and 37 is a D/A converting circuit for converting the developed color data into analog video signal. Reference numeral 43 is an opaque color control signal generating circuit for receiving bit map data from the line memory 35, generating YM signal (opaque color control signal), and issuing into a video chroma signal processing circuit, and 44 is a changeover signal generating circuit of teletext signal/video chroma signal for receiving bit map data, generating YS signal (changeover signal of teletext signal/video chroma signal), and issuing into a switch. By changing over the switch by the YS signal, both video chroma signal and teletext signal are displayed simultaneously on the picture screen. In the case of superimposed broadcast of YM signal, the background of the script is opaque, and in the case of teletext, not superimposed broadcast, the text is displayed and accompanied by foreground color and background color. Furthermore, Fig. 5 shows a constitution of a television receiver for teletext for explaining the prior art especially from the aspect of synchronizing signal. In this diagram, reference numeral 501 is an antenna, and 502 is a receiving circuit for receiving television broadcast wave and extracting a composite video signal of base band. The composite video signal from the receiving circuit 502 is supplied simultaneously also to a video chroma signal processing circuit 503, a teletext signal receiving circuit 504, and a synchronism separating circuit 505. The video chroma signal processing circuit 503 is a circuit for demodulating the composite video signal, and extracting color signals of three primaries R, G, B, and the teletext signal receiving circuit 504 is a circuit for extracting the teletext signal superposed on the composite video signal, and converting into color signals of three primaries R, G, B. Reference numeral 506 is a double speed converting circuit for compressing the image of R, G, B signals from the video chroma signal processing circuit 503 by 1/2 in the horizontal direction, and 507 is a double speed converting circuit for compressing the image of R, G, B signals from the teletext signal receiving circuit 504 by 1/2 in the horizontal direction. These double speed converting circuits 506, 507 are individually composed of three A/D converters for converting R, G, B signals into digital data, three line memories for storing the converted data and reading out at double speed of writing speed, and three D/A converters for converting the read data into analog R, G, B signals. Reference numeral 510 is a changeover circuit having a switch 508 and a switch 509. The switch 508 is for changing over the signal from the double speed converting circuit 506 and the signal from the double speed converting circuit 507 at high speed in order to display the television video signal and teletext signal simultaneously, and the switch 509 is for selectively changing over the signal from the video chroma signal processing circuit 503, the signal from the teletext signal receiving circuit 504 and the signal from the switch 508. Reference numeral 511 is a picture tube drive circuit, and 512 is a picture tube. The switches 508, 509 in the changeover circuit 510 are designed to be changed over by a control signal from a controller 513. The horizontal synchronizing signal and vertical synchronizing signal separated in the synchronism separating circuit 505 are respectively supplied into a horizontal deflection circuit 514 and a vertical deflection circuit 515. The signal generated by the double speed converting circuits 506, 507 are compressed by 1/2 in the horizontal direction. On a wide screen of the picture tube 512, when displaying both television video signal and teletext signal simultaneously, generally, the aspect ratio is 4:3 in both signals (see Fig. 6). Accordingly, in both signals, the screen must be compressed also in the vertical direction, and a vertical amplitude changeover circuit 516 and a vertical screen position control circuit 517 are provided, and their outputs are supplied into the vertical deflection circuit 515. The vertical amplitude changeover circuit 516 and vertical screen position control circuit 517 are designed to be controlled by the controller 513. The vertical amplitude changeover circuit 516 reduces the amplitude of the sawtooth wave supplied to the vertical deflection circuit 515. The vertical screen position control circuit 517 adds a direct-current voltage to the sawtooth wave reduced in amplitude, and the timing of the sawtooth wave is adjusted in the vertical direction. As a result, as shown in Fig. 6, on the wide screen of the picture tube 512, a screen 512a of television video signal, and a screen 512b of teletext signal, both of aspect ratio 4:3, are displayed. At this time, the double speed converting circuits 506, 507 are changed over to high speed by the switch 508. Reference numeral 512c is a no-picture area without display. When the vertical positions of the both screens 512a, 512b are fixed, deterioration of phosphor in these portions is promoted, and the screen luminance is uneven in the case of full screen display. Accordingly, the vertical screen position control circuit 517 is operated and the vertical positions of the both screens 512a, 512b are changed appropriately as shown in Fig. 6 (a) to (c). Thus, in the prior art, if attempted to display the television video signal and teletext signal simultaneously on a same screen by overlapping, the composite control signal (YS signal) c is generated at the same timing and same time width as the teletext video signal b, and the television video signal a and teletext video signal b are synthesized by such composite control signal (YS signal) c, and therefore the boundary is not clear between each character of the teletext picture displayed in the display device 15 and the television picture in the immediate vicinity, and in particular when the luminance levels of the two are very close, it is hard to read the superimposed text. Yet, the text is always accompanied by foreground color and background color, and the foreground color and background color change variously, and hence the displayed text itself is hard to see. Further, on the wide screen with aspect ratio of 16:9, if attempted to display the television video signal and teletext signal simultaneously on the same screen by dividing the screen, the screen 512a of television video signal and screen 512b of teletext signal of aspect ratio 4:3 displayed by compressing in the horizontal direction and vertical direction are smaller than the full screen, and the no-picture area 512c is wide, and the full screen (wide screen) is not utilized effectively. EP-A-0553910 A1 discloses a television receiver for teletext having the features of the preamble of claim 1. Here a reduced contrast area is provided around the text display by arranging a switching signal, which causes either text or picture signals to be applied to the display, to switch between the picture signal and the blanking level at a fast rate so as to produce the effect of reduced luminance. Alternatively the pixels of the display could be switched to any background color or some pixels could be caused to appear black whilst others display picture information so as to retain certain picture information with reduced contrast. EP-A-0486129 discloses a switching signal output device for use with a display unit that is able to display characters or image signals. An attenuator attenuates the brightness of an image signal and a switch alternatively outputs the characters or an output from the attenuator. The attenuated image signal is mixed with a character signal when character pixels are to be displayed so that the character appears against a background image of lowered brightness. EP-A-0497235 discloses a teletext transmission receiver comprising means that allow for the simultaneous display of the television image and the teletext page, in which a part of a teletext page may be displayed on a part of a screen leaving the remainder free for the television image whereby the television and teletext signals are not mixed. SUMMARY OF THE INVENTION It is hence an object of the invention to display teletext signal more explicitly even when displaying the teletext signal on the picture screen together with television video signal, simultaneously by superimposing or by dividing the screen. The invention provides a television receiver for teletext as claimed in claim 1. Preferred features of the invention are described in claims 2 to 8. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing a constitution of a television receiver for teletext of prior art. Fig. 2 is a timing chart for explaining operation of the prior art. (a)Television video signal (b)Text multiplex video signal (c)YS signal (d)Composite video signal Fig. 3 is a timing chart showing generation of composite control signal of prior art. (a)Display image of letter " " (b)Text multiplex video signal (c)Composite control signal (YS signal) Fig. 4 is a block diagram showing an internal constitution of a color data conversion circuit in prior art. Fig. 5 is a block diagram showing a constitution of television receiver for teletext of prior art. Fig. 6 is a diagram showing state of divided display of two screens with aspect ratio of 4:3 on a wide screen of prior art. (a)Screen middle display (b)Screen top display (c)Screen bottom display Fig. 7 is a block diagram showing a constitution of television receiver for teletext for the purpose of explaining embodiments of the invention. Fig. 8 is a block diagram showing a constitution of television receiver for teletext according to a first embodiment of the invention. Fig.9 is a block diagram showing an internal constitution of teletext signal receiving circuit in the first embodiment of the invention. Fig. 10 is a flowchart of color data conversion process of the first embodiment. Fig. 11 (a) is a diagram showing display of television signal only, and (b) display of two screens in a vertical scroll display state of teletext signal in the first embodiment. Fig. 12 is a diagram for explaining the technique of reading out teletext data from VRAM for realizing display of teletext signal while scrolling vertically in the upward direction. Fig. 13 is a diagram for explaining the technique of reading out teletext data from VRAM for realizing display of teletext signal while scrolling vertically in the downward direction. Fig. 14 is a flowchart of color data conversion process of a second embodiment. Fig. 15 (a) is a diagram showing display of television signal only, and (b) display of two screens in a vertical scroll display state of teletext signal in the second embodiment. Fig. 16 is a flowchart of color data conversion process of a third embodiment. Fig. 17 is a flowchart of color data conversion process of a fourth embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, referred embodiments of the television receiver for teletext of the invention are described in detail below. Fig. 7 is a block diagram showing a constitution of a television receiver for teletext. A composite video signal multiplexing a teletext signal on a television video signal is received by receiving means 701 through an antenna, and is supplied into video signal receiving means 702 and teletext signal receiving means 703. In the video signal receiving means 702, general video signal processing is done such as demodulation and synchronism separation of television video signal, and its output is issued to synthesizing means 705, while related information, such as the boundary condition differing whether in the mode of displaying the multiplexed text signal and television video signal on a same screen by super-imposing, or in the mode of displaying by dividing the screen, is extracted and issued to preprocessing means 704. In the teletext signal receiving means 703, the multiplexed text information is decoded, and the video signal of the text information is issued to the synthesizing means 705, while the control signal contained in the teletext signal is issued to the preprocessing means 704. In the preprocessing means 704, in the case of superimposed mode, extracting the teletext data decoded by the teletext signal receiving means 703, and boundary conditions such as luminance difference and color difference from the surrounding background, it is preprocessed so that the boundary correction signal for clarifying the boundary may be issued. The output of the preprocessing means 704, television video signal demodulated by the video signal receiving means 702, and character information decoded by the teletext signal receiving means 703 are synthesized in the synthesizing means 705, and send out to display means 706. In the display means 706, according to the boundary correction signal from the preprocessing means, the boundary of the television video signal and teletext signal is more clarified, and the text of the teletext signal is displayed so as to be read easily. Moreover, in the case of the mode of displaying the teletext signal by dividing the screen, the preprocessing circuit corrects and outputs so that the video signal and teletext data may be synthesized without forming no-picture area in the picture screen, and the television video signal and text information are synthesized in the synthesizing means 705 so as to be distributed without producing no-picture area. By displaying this output by the display means 706, the screen can be divided to display the television video signal and teletext signal effectively. Fig. 8 is a block diagram showing a constitution of a television receiver for teletext according to a first embodiment. In Fig. 8, reference numeral 821 is an antenna, and 822 is a receiving circuit for receiving a television broadcast wave, and picking up a composite video signal of base band. The composite video signal from the receiving circuit 822 is simultaneously supplied to a video chroma signal processing circuit 823, a teletext signal receiving circuit 824, and a synchronism separating circuit 825. The video chroma signal processing circuit 823 is a circuit for demodulating the composite video signal, and picking up color signals of three primaries R, G, B, and the teletext signal receiving circuit 824 is a circuit for extracting the teletext signal superposed in the vertical blanking period of the composite video signal, and converting into color signals of three primaries R, G, B. Reference numeral 826 is a switch for changing over the signal from the video chroma signal processing circuit 823 and the signal from the teletext signal receiving circuit 824 at high speed, 827 is a picture tube drive circuit, and 828 is a picture tube with aspect ratio of 16:9. The horizontal synchronizing signal and vertical synchronizing signal separated in the synchronism separating circuit 825 are respectively supplied into a horizontal deflecting circuit 829 and a vertical deflecting circuit 830. From the teletext signal receiving circuit 824 to the switch 826, a YS signal (teletext signal/video chroma signal changeover signal, which is described later) for changing over video chroma signal and teletext signal is issued. From the teletext signal receiving circuit 824 to the video chroma signal processing circuit 823, a YM signal (opaque color control signal, which is described later) for making the background color opaque is issued. Fig. 9 is a block diagram showing an internal constitution of the teletext signal receiving circuit 824. In Fig.9, reference numeral 831 refers to a teletext signal decoder for extracting and decoding the teletext signal superposed in the vertical blanking period from the input composite video signal, 838 is a color data conversion processing unit for processing color data conversion of decoded text data, 832 is a memory for storing the teletext data processed by color data conversion, 833 is a VRAM (video RAM) for writing the data to be displayed which is built up inside the memory 832 in bit map format, 834 is a memory control circuit for controlling writing and reading of the memory 832 and VRAM 833, 835 is a line memory for storing temporarily the teletext data for the portion of one horizontal line, 842 is a lookup table for converting the teletext data being read out from the line memory 835 into color data of R, G, B, and 837 is a D/A conversion circuit for converting the color data of R, G, B of the lookup table into analog video signals. The memory control circuit 834 reads out the teletext data for specified lines (W lines) in every field from the VRAM 833 on the basis of the text display position signal, and transfers to the line memory 835, and by sequentially shifting the reading start line in each field when reading out, it is designed to scroll vertically the teletext signal in the lower side region of the wide screen with aspect ratio of 16:9 of the picture tube 812. The teletext signal receiving circuit 824 generates the YM signal for converting to opaque color and the YS signal for changing over the switch 826, aside from teletext signal analog signals of R. G, B. The operation is described below. The decoded video signal decoded in the receiving circuit 822 is put into the teletext signal decoder 831 of the teletext signal receiving circuit 824, and the teletext signal is extracted and decoded, and the decoded teletext data is converted into color data in the color data conversion processing circuit 838, and is accumulated in the memory 832, and the data to be displayed among the accumulated teletext data is written into the VRAM 833 in bit map format according to a write control signal from the memory control circuit 834. The operation of the color data conversion processing circuit 838 is described by referring to Fig. 10. From the decoded teletext data, it is judged if the data is the foreground color or background color, and in the case of foreground color, the decoded data is stored in the memory 832. In the case of background color, the decoded data is converted into opaque color (YM color), and stored in the memory 832. Herein, by the changeover action of the switch 826, as shown in Fig. 11 (a), it is allowed to obtain the state of displaying only the video chroma signal (TV) in the full screen 851 with aspect ratio of 16:9 on the wide screen of the picture tube 812 as shown in Fig. 11 (a), and the state of dividing the full screen 851 vertically into an upper screen portion 851a of a greater number of lines and a lower screen portion 851b with a smaller number of lines (W), as shown in Fig. 11 (b), to display the video chroma signal in the upper screen portion 851a, and display the teletext signal (text) in the lower screen portion 851b by scrolling vertically. The upward arrow indicates the state of vertical scrolling. To realize display of teletext signal while scrolling vertically, the technique for reading out the teletext data from the VRAM 833 is explained below by reference to Fig. 12. Fig. 12 refers to the case of vertical scroll in upward direction. The memory control circuit 834 reads out odd-number lines from the first line of the VRAM 833 for the portion of W lines in field 2n (supposing W=10, reading up to line 9), on the basis of the text display position signal. In time series, each line is read out and is sequentially written into the line memory 835. Consequently, in field 2n+1, from the second line, even-number lines are read out for the portion of W lines (up to line 10). As a result, the teletext signals for one frame area displayed in the lower screen portion 851b. In succession, in field 2(n+1), shifting the read start line by S lines (S=4 in the diagram), odd-number lines are read out from line 5 for the portion of W lines (up to line 13). Next, in field 2(n+1)+1, even-number lines are read out from line 6 for the portion of W lines (up to line 14). As a result, the teletext signals for the next one frame are displayed in the lower screen portion 851b. In this stage. from line I to line 4 of the VRAM 833 shifting by S lines, the data to be displayed in next cycle is extracted from the teletext data accumulated in the memory 832 and written in to update. Similarly, thereafter, the VRAM 833 is read out up to line 480, and as approaching line 480, the portion of W lines runs short, and in such a case, returning to line 1, the portion of W lines is read out. In this stage, the data is updated from line 1 to line (480-D) of the VRAM 833. The above operation is more specifically described below. In field 2n, lines 1, 3, 5, 7, 9 are read out; in field 2n+1, lines 2, 4, 6, 8, 10 are read out; in field 2(n+1), lines 5, 7, 9, 11, 13 are read out; and in field 2(n+1)+1, lines 6, 8, 10, 12, 14 are read out, and in this way the teletext signals are displayed in the lower screen portion 851b in upward vertical scroll. The vertical scroll may be also downward. This is explained by reference to Fig. 13. In field 2m, odd-number lines are read out from line 471 of the VRAM 833 for the portion of W lines (up to line 419, W=10). In field 2m+1, even-number lines are read out from line 472 for the portion of W lines (up to line 480). As a result, teletext signals for the portion of one frame are displayed in the lower screen portion 51b. Further ahead, in field 2n, for example, odd-number lines are read out from line 7 of the VRAM 833 for the portion of W lines (up to line 15). In field 2n+1, even-number lines are read out from line 8 for the portion of W lines (up to line 16). As a result. teletext signals for the portion of one frame are displayed in the lower screen portion 851b. In succession, in field 2(n+1), shifting the read start line by S lines (S=4 in the diagram), odd-number lines are read out from line 3 for the portion of W lines (up to line 11). Next, in field 2(n+1)+1, even-number lines are read out from line 4 for the portion of W lines (up to line 12). As a result, the teletext signals for the next one frame are displayed in the lower screen portion 851b. In this stage, from line 12 to line 16 of the VRAM 833 shifting by S lines, the data to be displayed in next cycle is extracted from the teletext data accumulated in the memory 832 and written in to update. Similarly, thereafter, the VRAM 833 is read out up to line 1, and as approaching line 1, the portion of W lines runs short, and in such a case, returning to line 480, the portion of W lines is read out. In this stage, the data is updated from line D to line 480 of the VRAM 833. The above operation is more specifically described below. In field 2m, lines 471, 473, 475, 477, 479 are read out; in field 2m+1, lines 472, 474, 476, 478, 480 are read out; and further ahead, in field 2n, for example, lines 7. 9, 11, 13, 15 are read out; in field 2n+1, lines 8, 10, 12, 14, 16 are read out; in field 2(n+1), lines 3. 5, 7, 9, 11 are read out; and in field 2(n+1)+1, lines 4, 6, 8, 10, 12 are read out, and in this way the teletext signals are displayed in the lower screen portion 851b in downward vertical scroll. Although omitted in the above explanation of operation, the bit map data being read from the VRAM 833 by vertical scroll as mentioned above is sequentially written into the line memory 835 by the portion of one line each, and is read out from the line memory 835 by the display clock corresponding to the display in the lower screen portion 851b, and the data of the foreground color generated in the foreground color/background color generating circuit 841 in the color data conversion circuit 836 is developed into color data of R, G, B in the lookup table 842, and converted into analog teletext signals (R, G, B signals) in the D/A converting circuit 837, and issued from the teletext signal receiving circuit 824. The data is further issued to the picture tube 812 from the picture tube drive circuit 811 through the switch 826, and is displayed in the vertical scroll state in the lower screen portion 851b. The bit map data being read out from the line memory 835 and the background color data generated in the foreground color/background color generating circuit 841 in the color data converting circuit 836 are fed into the opaque color control signal generating circuit 843 in the color data converting circuit 836 and the teletext signal/video chroma signal changeover signal generating circuit 844. The opaque color control signal generating circuit 843 generates an opaque color control signal corresponding to the background color, that is, a YM signal, and issues to the video chroma signal processing circuit 823. The video chroma signal processing circuit 823 converts the video chroma signal to the opaque color corresponding to the background color. The teletext signal/video chroma signal changeover signal generating circuit 844 generates a teletext signal/video chroma signal changeover circuit corresponding to the background color, that is, a YS signal, and issues to the switch 826. As a result, in the lower screen portion 851b of the picture tube 828, the background color of the teletext signal (foreground color) displayed in vertical scroll becomes an opaque color, and a video chroma signal lowered in luminance level is displayed in the background. The video chroma signal lowered in luminance is expressed in halftone in Fig. 11 (b). Meanwhile, as clear from Fig. 11 (b), the video chroma signal is displayed in the upper screen portion 851a of a larger area of the full screen 851 with aspect ratio of 16:9 known as wide screen, the teletext signal (foreground color) is displayed in the lower screen portion 851b of a smaller area in vertical scroll, and the video chroma signal is displayed in opaque color behind the background color of opaque color of the surrounding. As a result, both the video chroma signal and teletext signal in vertical scroll are both easy to see. No-picture area is not present at all, and therefore the video chroma signal can be displayed largely in an easy-to-view state in the upper screen portion 851a. Incidentally, the lower screen portion 851b is smaller in area, but it does not matter for the viewer because the teletext signal is scrolled vertically, and therefore the full screen (wide screen) is utilized effectively. In this embodiment, the opaque processing by YS signal is mentioned, but, needless to say, the same effects are obtained by the processing of merely decreasing the luminance. (Embodiment 2) A general constitution of the television receiver for teletext according to a second embodiment of the invention is similar to Fig. 8, and the internal structure of the teletext signal receiving circuit 824 is similar to Fig. 9,-and therefore their illustration and description are omitted. Fig. 14 is a flowchart of the color data conversion processing circuit 838a in the television receiver for teletext according to the second embodiment. This color data conversion processing circuit 838a is processed at the same position as in the color data conversion processing circuit 38 in Fig. 9. In Fig. 14, what differs from the first embodiment in Fig. 10 is that the teletext decoded data is converted into the fixed foreground color of determined type of color, in the case of foreground color, and stored in the memory 832. As the fixed foreground color, for example, white is available and white is preferable. For vertical scroll display, the method of reading out by W lines each in each field while shifting the read start line by the portion of S lines sequentially from the VRAM 833, and writing into the line memory 835 is same as in the first embodiment. The bit map data being read out from the VRAM 833 in vertical scroll as mentioned above is sequentially written into the line memory 835 by the portion of one line each, and is read out from the line memory 835 by the display clock corresponding to the display in the lower screen portion 851b, and converted into color data of R, G, B in the lookup table 842, and converted into analog R, G, B teletext signals in the D/A converting circuit 837, and issued from the teletext signal receiving circuit 824. The data is further issued to the picture tube 828 from the picture tube drive circuit 827 through the switch 826, and is displayed in the lower screen portion 851b as fixed foreground color (for example, white) in vertical scroll state. The bit map data being read out from the line memory 835 is fed into the opaque color control signal generating circuit 843 and teletext signal/video chroma signal changeover signal generating circuit 844. The opaque color control signal generating circuit 843 generates an opaque color control signal, that is, a YM signal, and issues to the video chroma signal processing circuit 823. The video chroma signal processing circuit 823, converts the video chroma signal into an opaque color corresponding to the YM signal. The teletext signal/video chroma signal changeover signal generating circuit 844 generates a teletext signal/video chroma signal changeover signal, that is, a YS signal, and issues to the switch 826. As a result, in the lower screen portion 851b of the picture tube 828, the background color of the teletext signal (fixed foreground color, for example, white) displayed in vertical scroll is changed to an opaque color, and the video chroma signal lowered in luminance level is displayed behind. The teletext signal of the fixed foreground color (for example, white) is displayed in a reversal state in Fig. 15 (b), and the video chroma signal lowered in luminance is expressed in halftone. The vertical scroll is indicated by an upward arrow. Since the teletext signal of vertical scroll is displayed in fixed foreground color (for example, white), the text display state is easier to read than in the first embodiment. (Embodiment 3) A general constitution of the television receiver for teletext according to a third embodiment of the invention is similar to Fig. 8, and the internal structure of the teletext signal receiving circuit 824 is similar to Fig. 9, and therefore their illustration and description are omitted. Fig. 16 is a flowchart of the color data conversion processing circuit 838b in the television receiver for teletext according to the third embodiment. This color data conversion processing circuit 838b is processed at the same position as in the color data conversion processing circuit 838 in Fig. 9. In Fig. 16, what differs from the first embodiment in Fig. 10 and the second embodiment in Fig. 14 is that the decoded data is judged to be whether character/external character or photographic on the basis of the data unit parameter value of the teletext decoded data, and the foreground color is the fixed foreground color and the background color is converted to YM color in the case of character/external character. In the case of photographic, the decoded data is issued directly, and stored in the memory 832. Incidentally, the fixed foreground color is, for example, white, and white is preferred. For vertical scroll display, the method of reading out by w lines each in each field while shifting the read start line by the portion of S lines sequentially from the VRAM 833, and writing into the line memory 835 is same as in the arrangement of Fig. 7. The bit map data being read out from the VRAM 833 in vertical scroll as mentioned above is sequentially written into the line memory 835 by the portion of one line each, and is read out from the line memory 835 by the display clock corresponding to the display in the lower screen portion 851 b, and converted into color data of R, G, B in the lookup table 842, and converted into analog R, G, B teletext signals in the D/A converting circuit 837, and, issued from the teletext signal receiving circuit 824. The data is further issued to the picture tube 828 from the picture tube drive circuit 827 through the switch 826, and is displayed in the lower screen portion 851b as fixed foreground color (for example, white) in vertical scroll state. The bit map data being read out from the line memory 835 is fed into the opaque color control signal generating circuit 843 and teletext signal/video chroma signal changeover signal generating circuit 844. The opaque color control signal generating circuit 843 generates an opaque color control signal, that is, a YM signal, and issues to the video chroma signal processing circuit 823. The video. chroma signal processing circuit 823 converts the video chroma signal into an opaque color corresponding to the YM signal. The teletext signal/video chroma signal changeover signal generating circuit 844 generates a teletext signal/video chroma signal changeover signal, that is, a YS signal, and issues to the switch 826. Since the teletext signal of vertical scroll is displayed in fixed foreground color (for example, white), the text display state is easier to read than in the second embodiment, and moreover the photographics are displayed without color data conversion, so that the graphics are sharper than in the second embodiment. (Embodiment 4) A general constitution of the television receiver for teletext according to a fourth embodiment of the invention is, similar to Fig. 8, and the internal structure of the teletext signal receiving circuit 824 is similar to Fig. 9, and therefore their illustration and description are omitted. Fig. 17 is a flowchart of the color data conversion processing circuit 838c in the television receiver for teletext according to the fourth embodiment. The color data conversion processing circuit 838c is processed at the same position as in the color data conversion processing circuit 838 in Fig. 9. In Fig. 17, what differs from the first embodiment in Fig. 10, second embodiment in Fig. 14, and third embodiment in Fig. 16 is that the decoded data is judged to be character/external character or photographic depending on the data unit parameter value of the teletext decoded data, and in the case of character/external character, the foreground color is the fixed foreground color and the background color is converted to YM color. In the case of photographics, the foreground color and background color are discriminated, and in the case of the foreground color, its decoded value is issued, and in the case of the background color, the background color is converted to YM color if the decoded value is a transparent color, or the decoded value is issued if not transparent color and is stored in the memory 832. The fixed foreground color is, for example, white, and white is preferred. For vertical scroll display, the method of reading out by w lines each in each field while shifting the read start line by the portion of S lines sequentially from the VRAM 833, and writing into the line memory 835 is same as in the first embodiment. The bit map data being read out from the VRAM 833 in vertical scroll as mentioned above is sequentially written into the line memory 835 by the portion of one line each, and is read out from the line memory 835 by the display clock corresponding to the display in the lower screen portion 851b, and converted into color data of R, G, B in the lookup table 842, and converted into analog R, G, B teletext signals in the D/A converting circuit 837, and issued from the teletext signal receiving circuit 824. The data is further issued to the picture tube 828 from the picture tube drive circuit 827 through the switch 826, and is displayed in the lower screen portion 851b as fixed foreground color (for example, white) in vertical scroll state. The bit map data being read out from the line memory 835 is fed into the opaque color control signal generating circuit 843 and teletext signal/video chroma signal changeover signal generating circuit 844. The opaque color control signal generating circuit 843 generates an opaque color control signal, that is, a YM signal, and issues to the video chroma signal processing circuit 823. The video chroma signal processing circuit 823 converts the video chroma signal into an opaque color corresponding to the YM signal. The teletext signal/video chroma signal changeover signal generating circuit 844 generates a teletext signal/video chroma signal changeover signal, that is, a YS signal, and issues to the switch 826. Since the teletext signal of vertical scroll is displayed in fixed foreground color (for example, white), the text display state is easier to read than in the first embodiment, and moreover since the foreground color of the photographics is directly displayed, the graphics are sharper than in the second embodiment. Still more, by showing the transparent color of the photographics in the YM color, the viewer is easier to see than in the third embodiment. In this way, according to the embodiments of the invention, when displaying teletext signal simultaneously with the television video signal on the picture screen by superimposing or dividing the screen, various preprocessing is done for explicit display of teletext signal, and the object is achieved by adding a correction signal for clarifying the boundary. As evident from the foregoing embodiments, according to the television receiver for teletext of the invention, in the display region of teletext signal of the picture screen, the background color around the foreground color of the text is half in luminance (opaque color), and a video chroma signal of opaque color is displayed behind, so that the text is easy to see. When the foreground color is fixed in color variety to display fixed foreground color, especially white, the text is easier to see. When scrolling the text vertically, the vertical width of the display region of the teletext signal may be small, and the text of vertical scroll is easy to see. In the foregoing embodiments, the display position of the teletext signal displayed in vertical scroll state is at the lower side of the screen, but, to the contrary, it may be designed to display at the upper side. Moreover, according to the television receiver for teletext of the invention, since a dark trimming is formed around the displayed superimposed text, the text may be displayed in an easy-to-read state if the text and television picture are close at the same luminance level. In particular, when the dark trimming is formed at the right and left side of the text, the text may be displayed in a clearer state. Still more, according to the television receiver for teletext of the invention, since the teletext signal is displayed in a narrow strip at the lower side or upper side of the screen, so that the television video signal may be displayed in a wide, easy-to-see state, and the teletext signal is displayed without forming no-picture area, so that the full screen can be utilized effectively and although the display area of teletext signal is small, it is scrolled vertically, and hence there is no problem for viewing the teletext signals. It is particularly useful in the picture tube of which aspect ratio is 16:9. The teletext display technique of the invention is applied not only to teletext, but also to other information processing applications by superimposing information of other network on the television screen such as the Internet.

Claims: A television receiver for teletext comprising: a video chroma signal processing circuit (823) for demodulating a received composite video signal, a teletext signal receiving circuit (824) for extracting a teletext signal superposed in the composite video signal comprising a teletext decoder (831) for decoding a teletext signal, and a switch (826) for displaying the video chroma signal from the video chroma signal processing circuit and the teletext signal from the teletext signal receiving circuit simultaneously on a picture screen, characterised in that the teletext signal receiving circuit further comprises: color data conversion processing means (838) for generating a foreground color and a background color from the decoded teletext data, and converting the foreground color and background color data into color data, the color data converted from the background color having lowered luminance, a memory (832) for storing the converted color data in a bit map format, a line memory (835) for storing temporarily the color data which is read out for displaying, a lookup table (842) for converting bit map color data to RGB color data, a D/A converter circuit (837) for converting RGB converted data into analog RGB signal, a background color lowered in luminance (YM color) control signal generating means (843) for generating a YM color control signal (YM signal) based on the background color data read out from the line memory (835), and feeding the YM signal into the video chroma signal processing circuit to allow the video chroma signal lowered in luminance, teletext signal/video chroma signal changeover signal generating means (844) for generating teletext signal/video chroma signal changeover signal (YS signal) based on the background color data read out from the line memory (842), and feeding the YS signal into the switch (826) to switch the decoded teletext and the YM color for displaying, and the video chroma signal lowered in luminance is displayed around the text foreground color in the display region of teletext signal on the picture screen. A television receiver for teletext of claim 1, wherein the color data conversion processing means (838) converts the foreground color to color data having a fixed type of color. A television receiver for teletext of claim 1, wherein the color data conversion processing means (838) judges whether the decoded teletext data consist of character/external character or photographics said means (838) converts the foreground color of the character/external character to color data having a fixed color, and said means (838) converts photographics to color data which is identical to the ones of the decoded teletext data. A television receiver for teletext of claim 1, wherein the color data conversion processing means (838) judges if the data is a character/external character or photographics from the decoded teletext data, (i) in the case of the character/external character, said means (838) converts the foreground color to color data having a fixed color and, (ii) in the case of photographics, when the background color is transparent color, said means (838) converts the background color to color data of the video chroma signal lowered in luminance, and otherwise, said means (838) converts the photographics to color data which is identical to the ones of the decoded teletext data. A television receiver for teletext of claim 2, 3 or 4, wherein the fixed foreground color is white. A television receiver for teletext of any one of claims 1 to 5, wherein the teletext signal receiving circuit (824) is composed to convert the teletext signal to be displayed in vertical scroll state at the lower side or upper side of the picture screen. A television receiver for teletext of any preceding claim wherein the picture tube is composed in an aspect ratio of 16:9.

Inventors: KAWANE TIMOE, MONTA HIROKI, KAWANE, TIMOE, MONTA, HIROKI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1996
Main classification: H04N7
IPC codes: H04N7, H04N5