Method for teletext character alignment and device for carrying out this method.

The present invention relates to a method for aligning the teletext characters on a television receiver screen. The invention also provides a device for implementing such a method.

Teletext system is described in French patent application 2 363 949. In this system, the display of characters on the screen of the television receiver is controlled by a character generator supplied with data by an image memory.

Characters are grouped in horizontal rows, each of which is formed by a number of TV scan lines, equal to 10 according to the specification ANTIOPE.

In regard to alphabetic characters, it is desirable to have the lowest possible with respect to the row. But as some characters have parts situated below the body of character, or legs, as y, p, q, j, g, respect for the alignment between the jambées letters and non letters jambées requires that the body character are shifted upwardly from the bottom of the row. In these conditions, with a row formed of 10 scan lines, taking into account the fact that the first line is not displayed, the remaining lines 9 are split into 5 lines for the character size, 2 lines jambs and 2 lines for the upper portions of letters such as 1, d and t.

ANTIOPE The system further provides the possibility of doubling the height of the characters by repeating the display element of a line on the next line. If the row - which then has a double number of lines - includes single character height (H) and double height characters (2H), applying the above principle will lead to an alignment defect pronounced since the letters 2H jambées present a jamb 4 lines high and result in a shift of 2 lines between 1H and 2H letters letters, enough to destroy the alignment to the viewer.

To solve this difficulty, the invention provides for analysis of the data of a row during the scanning of the first non-displayed line of said row and to adjust the alignment of the characters based on the data obtained.

More specifically, it is determined, during the scan of the first line of each row<ul><li>1) if the row is whether or not composed solely of 2H characters, and</li><li>2) if it contains at least one character 2H leg, and then sets the alignment as follows:<ul><li>a) If the row is only composed of 2H characters, the alignment is shifted by 2 lines up compared to that of 1 H characters;</li><li>b) if the row contains both 1 H and 2H characters characters, and contains no 2H character leg alignment is the same as in the case of 1 H characters;</li><li>c) if the row contains both 1 H and 2H characters characters, and has at least one 2H character leg alignment 2H characters is offset by one line upwardly relative to the alignment of 1H characters, the last line of characters 2H legs are not repeated.</li></ul></li></ul>

The method according to the invention, by taking into account parameters 1) and 2) above during the scanning of the first line, allow satisfactory alignment of the characters in all cases. In case c), the gap between the alignment of characters and that of 2H 1H characters is 1 line, and is not noticeable to the viewer.

The invention will be better understood from reading the description below, with reference to the accompanying drawings. In the drawings,<ul><li>- Figures for the lc give examples of the different alignment modes obtained according to the invention.</li><li>- Figure 2 is the diagram of a device for obtaining the alignment patterns illustrated in Figures la to lc.</li></ul>

Figures la to lc show a part of the teletext display screen, on which appears the word LYON. In ANTIOPE system, an array of characters usually occupies 10 scan lines, but here we consider only the case where the row has one or more double-height characters (2H) and has accordingly a doubled height, ie 20 lines scanning. The lines are numbered from 1 to 20 on each of the Figures to lc.

Alignment mode illustrated in the Figure is identical to that of the rows comprising only characters 1H, namely that the character size is arranged with a gap of two lines from the bottom of the row which corresponds to the height a H ​​character jamb. This alignment mode corresponds to the case where coexist in the same row of characters 1H (Y, Y, N) and 2H (L), and where no character has 2H jamb. As is evident, the 2H characters are obtained simply by repeating one-line display element on the next line.

The alignment mode of Figure lb is used when the row consists entirely of characters 2H. In this case, the row that comprises or not legs characters, the alignment is shifted by 2 lines with respect to the previous case. In other words, the character size is deviated from 4 lines of the bottom row, this space being occupied by the legs of which the height is 4 lines (2 x 2).

Finally, the alignment mode illustrated by Figure lc is applied in the case where a row contains both 1 H and 2H characters characters and where at least one of the 2H characters is leg. This alignment mode consists of shifting the body of the 2H characters of three lines with respect to the bottom row, suppressing the repetition of the second display element of the legs. thus observed in figure lc the horizontal leg of the leg of the Y is not doubled, contrary to what is observed in FIG lb.

Furthermore, 1H characters in the row have their normal disposition, that is to say that the body of 1H characters deviated from 2 lines at the bottom of the row. The resulting shift between 1H and 2H characters is not annoying for the viewer because it is limited to one line.

The selection of the alignment mode therefore requires knowledge of two elements characterizing the considered row. AL1 the first element is the coexistence of 1 H and 2H characters, and the second member AL2 presence 2H legs characters.

Knowledge of elements AL1 and AL2 is obtained by exploring the character data of the row during the scanning of the first line of the row, which is never used in the display to have a clear separation between the formed characters consecutive rows.

There is shown in Figure 2 a device for the consideration of AL1 and AL2 elements for the selection of the adjustment mode.

The device shown includes a PROM 1 which provides the character generator 2 a scanning sequence of four son AgCl AGC4 which controls the alignment mode characters.

The memory 1 receives four son ADL1 ADL4 in the address line of the row under consideration, between O and 9, which is provided by a line counter incremented by each top line synchronization.

The memory 1 receives a signal indicating that the 2H analyzed character is double height, a signal S /<o>I</o> indicating that it is in the upper half-row or in the lower half-row with a double row height.

The memory also receives signals AL1 and AL2 provided respectively by the rockers 3 and 4. The rockers 3 and 4 are JK flip-flops kind.

The J input of flip-flop 3 is at level "O".

Its K input receives the 2H signal indicating that the analyzed character is double height.

Its input P (preset) is connected to a NAND gate 5 which receives the output signal of an AND gate 6 to which are applied the line tops and TLG the LGNIO signal which appears during the scanning of each line of the lOth row.

Gate 5 also receives the signal S / I reversed, which is in state "1" when exploring the lower half-row with a double row height.

The signal applied to the input P therefore goes to state "0" to the arrival of the top line of the last line of the row above the row to explore. Consideration of the S / I signal avoids undesired change state of the latch 3 in the transition from the upper half-row to the lower half-row with a double row height.

A clock signal H is applied to the flip-flop 3 to each character time interval.

The output of the flip-flop 3 is set to "1" at the top line of the TLG LGN10 last line of the previous row, and it remains in this state if all the characters of the row are double height. But if even one character is simple height to the level of the 2H signal changes to "O". The Q output then goes to the "O".

The yoke 4 also has its P input connected to the output of the NAND gate 5.

J and M inputs are connected in the same way as the flip-flop 3.

The K input is connected to a NAND gate 7 receiving at one input the abovementioned 2H signal and having its other input connected to an AND gate 8 which receives a BITφ signal provided by the character generator indicating that the character is analyzed Jambé and a LGNφ signal that we explore the first line of the row.

The Q output of the latch 4 is set to state "0" by the signal from the gate 5. It goes to state "1" when exploring a 2H Jambé character during the era line of the row.

ALl when the signal is "1", the alignment mode is that of Figure lb.

When the ALL signal is "O" and that the signal AL2 is "O", the tracking mode is the one in FIG.

When at the signal AL1 is at "0" and the signal AL2 is "1", the alignment is that of Figure lc.