FR2818858A1 - Teletext display system uses even and uneven fields for higher resolution - Google Patents

Abstract

A teletext character display system uses even and uneven pixel matrices scanned at double rate to create a higher resolution character by copying the selected font appropriately around the central position.

Description

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METHOD AND ASSOCIATED DEVICE FOR DISPLAYING CHARACTERS
ON A TELEVISION RECEIVER SCREEN
The invention relates to a method for displaying characters on a screen of a television receiver. The invention is more particularly interesting for displaying pages of a teletext service as defined in the ETS 300 706 standard created in the 1980s and updated in May 1997 (ETS "European Telecommunication Standard"). The invention is also interesting for displaying information for managing the operation of the television receiver for example.

 Teletext is an additional service for television channels intended to transmit written information in addition to video information. This written information is displayed on a TV screen in the form of teletext pages. Each page is transported in the form of a variable number of data packets transmitted in coded form in time intervals corresponding to the frame return between two video images; A teletext program, made up of a set of numbered pages, is broadcast continuously by a television channel, and this cyclically. Each teletext page contains, for display on the screen, a series of approximately 25 lines of 40 to 56 characters each, each character to be displayed being identified by an identifying code.

 The information for managing the operation of the television receiver is for example information for adjusting the sound level of the receiver, the contrast of the screen or simply the number of the television channel being received. Such information is presented on the screen in the form of one or more character strings which are superimposed on a video image. These informations

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 are provided for example by a circuit for managing the operation of the receiver and are intended to help the viewer to control the operation of his receiver.

 In the following, the expressions "teletext service", "teletext page", "teletext data", etc. will be used, for reasons of simplification, with reference either to a teletext program transmitted by a television channel or to information of the character string type relating to the operation of the receiver.

 In a television receiver, a known device 10 dedicated to the teletext service comprises, in accordance with FIG. 1, a reception and demodulation circuit 11, a decoder 12, a memory 13, a display memory 14, and a means of 'display 15.

 The reception and demodulation circuit 11 is connected to an antenna to receive the teletext data transmitted by a television channel and to provide a teletext page in return in the form of a series of lines of characters, each character being identified by an identifying code. .

 The decoder 12 is connected to the circuit 11 to receive the teletext page, and to the memory 13. The decoder 12 can also be connected to the operation management circuit (not shown) of the receiver to directly receive the data to be displayed.

 The memory 13 includes a table, also called font or typeface, associating, with each identifying code, a character matrix comprising 10 lines of 12 elements and defining a corresponding character. When it receives an identifier code, the decoder 12 will read the associated character matrix from the table and then store this matrix in the display memory 14.

 The display means 15 finally comes to read in

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 continues the content of the display memory 14 and copies its content to the screen 16 of the television receiver by a two-stage scanning mode known for video display. During a first step, the display means 15 copies the content of the display memory 14 onto the even lines of the screen, thus writing every other line, here we speak of displaying the even field. Then during a second step, the display means copies the content of the display memory on the odd lines of the screen, this is called display of the odd field.

 The font or font contained in the memory 13 associates, with each identifying code, a drawing of the associated character in the form of a matrix of 12 * 10 elements. Each element of the matrix can take two values, thus making it possible to carry out a drawing in two colors, an ink color and a background color, as will be seen better below.

The characters in the font are divided into different sets of characters, in particular: - a first set which groups the characters of the alphabet used to write the informative content of the pages (for example the Latin alphabet for European pages), and - a second set which groups together characters that are not part of an alphabet, such as geometric figures, drawings, etc.

correspondant à la lettre"0"est représentée sur la figure 2. Le code"0"indique que la couleur de fond doit être utilisée et le code"N"indique que la couleur

d'encre doit être utilisée pour l'affichage sur l'écran d'un élément correspondant de la matrice.
Ce mode d'affichage par caractère a été défini dans les années 1980 dans la norme ETS 300 706, à partir des As an example, a character matrix

corresponding to the letter "0" is shown in figure 2. The code "0" indicates that the background color should be used and the code "N" indicates that the color

ink must be used to display a corresponding element of the matrix on the screen.
This display mode by character was defined in the 1980s in standard ETS 300 706, from

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 technical characteristics of the materials of the moment. It makes it possible to display text in a simple way, by transmitting a limited number of numerical data.

 This display mode is however rather coarse because the definition of a character by a matrix of 12 * 10 elements is necessarily limited, as can be seen in Figure 2.

 This is all the more damaging since current equipment, in particular screens, makes it possible to display characters today with better resolution, which of course improves user comfort.

 An object of the invention is to remedy this lack, by producing a device and by implementing an associated method for displaying characters making it possible to increase the resolution of a character of the teletext page in order to increase the comfort of the user, without increasing the size of a character represented on the screen.

 For this, the invention relates to a character display method on a screen of a television receiver, a first scan and a second screen scan being carried out successively to display an even field and an odd field characteristic of a character to be displayed, the method being characterized in that the even field is different from the odd field.

 The use of different even and odd fields makes it possible, by doubling the number of elements defining the character to be displayed, to define more precisely and more precisely the shape and outline of this character. The visual aspect of the character is therefore improved.

 The character to display is defined by a character matrix. Even rank rows of the character matrix make up the even field and odd rank rows of the character matrix make up the field

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 odd.

 Preferably, a horizontal scanning frequency equal to twice a predefined frequency is used to carry out the first and the second scanning.

 According to one embodiment, a first font is used to store the character matrix comprising a number of lines and a number of columns equal to twice a number of lines and a number of predefined columns.

 The invention has the following characteristics compared to known devices: - the width of a character (and therefore of a line) represented on the screen is identical because the increase in scanning speed compensates for the increase in the number elements on a line of the character matrix.

 - the height of a character represented on the screen is identical because the same number of lines is displayed on the screen.

 - the size of the characters on the screen is therefore the same.

 - the drawing of the displayed character is finer, more precise.

 - the time required to display a character (or a page) is unchanged.

 According to another embodiment, a first font is used to store a first character matrix defining an alphabet type character and a second font is used to store a second character matrix defining a graphic type character, the first character matrix having a number of lines and a number of columns equal to twice a number of lines and a number of columns of the second character matrix.

 The method includes a storage step E1,

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in a display memory, of the character matrix defining the character to be displayed, the memorization step being carried out on reception of a code identifying the character to be displayed. According to the invention, the method also includes the following steps E21, E22:
E21: performing the first screen scan by copying even lines from the display memory onto corresponding even lines on the screen, then
E22: performing a second scan of the screen by copying odd lines from the display memory onto corresponding odd lines of the screen.

 The order of carrying out steps E21, E22 is indifferent.

If the first and second font are used, then the storage step E1 comprises the following sub-steps carried out on reception of the code identifying the character to be displayed:
E10: identification of the font in which the character matrix defining the character to be displayed is memorized, as a function of its identifying code, then: - carrying out of a step Ell if the identified font is the first font, or - carrying out a step E12 if the identified font and the second font, with: Ell: for all i between 1 and twice the predefined number of rows, for all j between 1 and twice the predefined number of columns, copy of the element eij of the character matrix at a corresponding place mij in the display memory, i being a line index and j being a column index of the character matrix defining the character to be displayed,
E12: for all i between 1 and the predefined number of lines and for all j between 1 and the

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nombre de colonnes prédéfini, copie de l'élément eij de la matrice du caractère à afficher à des emplacements m2i-1, 2j- ! < m21-1, 2j, m2i, 2j-1. m2i, 2j dans la mémoire d'affichage.

predefined number of columns, copy of the element eij of the matrix of the character to be displayed in locations m2i-1, 2d-! <m21-1, 2d, m2i, 2d-1. m2i, 2d in the display memory.

 The invention also relates to a character display device on a screen of a television receiver, the device comprising: - a data reception and demodulation circuit for supplying at least one code identifying a character to be displayed, and a display means for copying the content of a display memory on the screen.

 According to the invention, the device also comprises: - a first memory, for memorizing a first font comprising a set of identifier codes and a set of associated character matrices, at least one row of even rank of at least one character matrix being different from a line of odd rank preceding the at least one line of even rank, the number of lines and the number of columns of each matrix being equal to twice a number of line and a number of predefined columns, and - a decoder, for copying the matrix associated with the identifier code supplied by the reception and demodulation circuit, when it receives said identifier code.

 The device is improved by the addition of a second memory, for memorizing a second font comprising a set of identifying codes and a set of matrices of associated character, the number of rows and the number of columns of each matrix being equal to the number rows and the number of predefined columns.

 Finally, the invention also relates to a television receiver which comprises means for implementing the method described above.

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 The invention will be better understood and other characteristics and advantages will appear on reading the following description of an embodiment of the device and an example of implementation of the method of the invention. The description refers to the accompanying drawings in which: - Figure 1, already described, is a block diagram of a device dedicated to the teletext service, - Figure 2, already described, is a character matrix, according to the prior art , - Figure 3 is a character matrix, according to the method of the invention, and - Figure 4 is a diagram of an algorithm for implementing a teletext page display method according to the invention.

 In the simple embodiment of the invention described below, it is assumed that only the character "0" should be displayed on a television screen.

 A device according to the invention and dedicated to the teletext service is similar to that of FIG. 1 and it includes a circuit 11 for reception and demodulation, a decoder 12, a memory 13, a display memory 14 and a means of display 15.

 The reception and demodulation circuit 11 receives the teletext data transmitted by a television channel and provides a teletext page in return in the form of a series of lines of characters, each character being identified by a character code.

 The decoder 12 is connected to the circuit 11 to receive the teletext page, and to the memory 13. The decoder 12 can optionally be also connected to a circuit (not shown) for managing the operation of the receiver, if such a service exists.

 According to the invention, the memory 13 comprises a

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new table or font comprising a list of characters defined by an identifying code and an associated character matrix. The matrix includes 20 lines of 24 elements. Each character of the new font is thus defined by a matrix comprising twice as many rows and columns as that used in the prior art.

When it receives the identifier code of the letter 11011 (in the example), the decoder 12 will read in the memory 13 the associated character matrix then memorize the matrix read in the display memory 14.

 The display means 15 then read the content of the display memory 14 and copy it onto the screen, as will be seen more clearly below in the description of the process of the invention.

 Figure 3 shows an example of a matrix defining the letter "0" in the font according to the invention. As previously, the code "2" respectively "." Indicates that the background color, respectively the ink color, must be used for the display of the corresponding point of the matrix on the screen 16.

 Compared to the matrix in Figure 2, the matrix in Figure 3 has twice as many rows and columns. The matrix in FIG. 3 is also distinguished by the regions 32a, 32b, at the top of the letter "O", and by the regions 32c, 32d at the bottom of the letter "0" which have been modified to refine the plot of the letter.

 As it clearly appears in FIG. 3, by using a matrix comprising more rows and columns, it is in particular possible to define more precisely the outline of the letters, which allows, when the letter is displayed on the screen , to obtain a better finished design of the letter, less coarse than in the past and therefore more comfortable for the eye. We can thus represent for example letters such as "O", "Q"

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 or "C" with more curved lines, instead of the broken lines at right angles previously used.

The display method according to the invention essentially comprises the following two steps, carried out by the display means 15:
E21: horizontal screen sweep (even field display): copies even lines from display memory 14 to corresponding even lines on the screen.

 E22: 2nd horizontal scanning of the screen (display of the odd field): copies odd lines from the display memory 14 onto the corresponding odd lines of the screen.

 The order in which steps E21, E22 are carried out is immaterial, the main thing being that the two steps are carried out.

 Preferably, the scanning speed used is chosen to be equal to twice the scanning speed used in the prior devices.

 In this case, the invention has the following characteristics compared to known devices: - the width of a character (and therefore of a line) represented on the screen is identical because the increase in scanning speed compensates for the increase the number of elements on a line of the character matrix.

 - the height of a character represented on the screen is identical because the same number of lines is displayed on the screen.

 - the size of the characters on the screen is therefore the same.

 - the drawing of the displayed character is finer, more precise.

 - the time required to display a character (or a page) is unchanged.

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 A drawback of the method and the device of the invention is the need to use a memory 13 of size approximately four times larger than with the devices of the prior art, since the characters are defined according to the invention by matrices with four times as many elements.

 However, the matrices of certain characters of the font do not need to be modified because an increase in the size of these matrices does not make it possible to improve the display of the corresponding character on the screen. This is the case, for example, for certain punctuation characters. Furthermore, the matrices of certain other characters of the font must not be modified because these characters must be common to all the teletext devices, this is the case for example of the graphic characters of the second set of characters.

It is therefore not necessary to define these characters by matrices of size 24 * 20.

 The device of the invention can in this case be improved by modifying the content of the memory 13, by adding a memory 13 ′ and management means.

 The memory 13 is modified as follows.

It includes a first font, comprising a first list of characters each defined by an identifying code and a character matrix of size 24 * 20.

The first set of characters includes all the characters for which a definition in the form of a 24 * 20 matrix is advantageous from the point of view of the visual appearance on the screen. The characters in the first set of characters include, but are not limited to, the letters of the alphabet used.

 A memory 13 '(represented by dotted lines in FIG. 1) is added, which includes a second font comprising a second list of characters each defined by an identifier code and a matrix of

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 character size 12 * 10. The characters in the second set of characters include, but are not limited to, the graphic characters of the font originally used. Preferably, in order to further limit the memory space, all the characters are defined only once, in one or other of the fonts, but not both.

 Finally, management means are added to the decoder 12 to choose the first font or the second font based on an identifier code received.

si la deuxième fonte est choisie, alors réalisation d'une étape E12. The modifications made to the process of the invention as part of the improvement are as follows, in the simple example where a single identifier code is received. El, Ell, E12 steps are added:
El: choice of a font according to the identifier code received, then: if the first font is chosen, then carrying out of a step Ell, otherwise,

if the second font is chosen, then carrying out a step E12.

 Ell: for all i between 1 and 20, for all j between 1 and 24, copy of the element eij of the matrix of the character to be displayed (stored in memory 13) at a corresponding place mij in the memory of display 14, i being an index indicating a line and j being an index indicating a column of the matrix defining the character to be displayed.

 E12: for all i between 1 and 10 and for all i between 1 and 12, copy of the element eij in the locations m2i-l, 2d-l, m2i-l, 2J'm2i, 2d-l, m2i, 2d in the display memory.

 Step E21 is then carried out, after step Ell or step E12.

 Whatever step Ell or E12 is performed, the place used by the character in the memory

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 display 14 is the same and therefore the size of the character displayed on the screen is also the same.

This is particularly important if several characters are to be displayed successively.

 On the other hand, the space used to memorize the first font (memory 13) and the second font (memory 13 ') is lower than that used to memorize a single font according to the invention.

 Of course, the memory 13 and the memory 13 ′ can be replaced by a single memory comprising for example a first zone for memorizing the first font and a second zone for memorizing the second font.

 The operation of the method according to the invention has been explained above in simple examples where only one character is to be displayed. Of course, the invention is not limited to these cases.

 The method of the invention can also be used to display a set of characters or more generally a complete teletext page. In this case, if N characters are to be displayed simultaneously on the screen, the storage step El is repeated N times to copy into the display memory N character matrices each defining one of the N characters to be displayed, the N matrices being copied into successive areas of the display memory, in the order of reception of the codes identifying the N characters.

 The method of the invention can also be integrated into a more complex method of managing a teletext service, which can include, for example, steps of selecting pages to display, steps of memorizing certain pages of a program or any another step that is customary to carry out in a process for managing a teletext service.

 Finally, it should be noted that all the values

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 numbers given in the description above are given for information only, and can be modified accordingly, for example if a new standard is used for teletext services, if screens with line numbers and / or numbers different columns are used, etc.

 If, for example, a new standard suggests using a font comprising character matrices of size I * J, the invention can be applied simply by using a font comprising character matrices of size 2I * 2J.

Claims (11)

 1. A method of displaying characters on a screen (16) of a television receiver, a first scan and a second scan of the screen (16) being carried out successively to display an even field and an odd field characteristic of a character to be displayed, the method being characterized in that the even field is different from the odd field.  2. Method according to claim 1, characterized in that the character to be displayed is defined by a character matrix, lines of even rank of the character matrix constituting the even field and lines of odd rank of the character matrix constituting the odd field.  3. Method according to one of claims 1 or 2, characterized in that a scanning frequency equal to twice a predefined frequency is used to carry out the first and the second scanning.  4. Method according to one of claims 1 to 3, characterized in that a first font is used to memorize the character matrix comprising a number of lines and a number of columns equal to twice a number of lines and a number predefined columns.  5. Method according to one of claims 1 to 3, characterized in that a first font is used to store a first character matrix defining a character of the alphabet type and in that a second font is used to store a second character matrix defining a graphic type character, the first character matrix comprising a number of lines and a number of columns equal to two <Desc / Clms Page number 16>  times a number of lines and a number of columns of the second character matrix.  6. Method according to one of claims 2 to 5, the method comprising a storage step (El), in a display memory (15), of the character matrix defining the character to be displayed, the storage step (El) being carried out on receipt of a code identifying the character to be displayed, the method being characterized in that it also comprises the following steps E21, E22: E21: performing the first scan of the screen (16) by copying even lines of the display memory (14) onto corresponding even lines of the screen (16), then E22: performing a second scan of the screen (16) by copying odd lines from the display memory (14) onto corresponding odd lines of the screen (16), steps E21, E22 being carried out successively in a first order (E21, E22) or in a second order (E22, E21).  7. Method according to claim 6, characterized in that the memorization step (El) comprises the following sub-steps carried out on reception of the code identifying the character to be displayed: E10: identification of the font in which the character matrix defining the character to be displayed is memorized, according to its identifying code, then: - carrying out a step EU if the identified font is the first font, or - performing a step E12 if the identified font and the second font, with: Ell: for all i between 1 and twice the <Desc / Clms Page number 17> E12: for all i between 1 and the predefined number of lines and for all j between 1 and the predefined number of columns, copy of the element eij of the matrix of the character to be displayed at locations m2i-l, 2d- l, m2i-l, 2d, m2i, 2j-l, m2i, 2d in the display memory.  predefined number of lines, for all j between 1 and twice the predefined number of columns, copy of the element eij of the character matrix to a corresponding place mij in the display memory (14), i being an index of row and j being a column index of the character matrix defining the character to be displayed,  8. Method according to claim 7 characterized in that if N characters are to be displayed simultaneously on the screen, the memorization step (El) is repeated N times to copy into the display memory (14) N character matrices each defining one of the N characters to be displayed, the N matrices being copied into successive areas of the display memory (14), in a predefined order.  9. Character display device on a screen (16) of a television receiver, the device comprising: - a data reception and demodulation circuit (11) for supplying at least one code identifying a character to be displayed, display means (15) for copying the content of a display memory (14) onto the screen (16), the device being characterized in that it also comprises: a first memory (13), for memorize a first font comprising a set of identifying codes and a set of associated character matrices, at least one row of even rank of at least one <Desc / Clms Page number 18>  character matrix being different from an odd row preceding the at least one even row, the number of rows and the number of columns of each matrix being equal to twice a number of predefined rows and a number of columns, and a decoder (12), for copying the matrix associated with the identifier code supplied by the reception and demodulation circuit (11), when it receives said identifier code.  10. Device according to claim 9, characterized in that a second font is used, which comprises a set of identifying codes and a set of matrices of associated character, the number of rows and the number of columns of each matrix being equal to the number of lines and the number of predefined columns, the second font being stored either in the first memory (13) or in a second memory (13 ').  11. Television receiver characterized in that it comprises means for implementing the display method according to one of claims 1 to 8.