GB2255429A

GB2255429A - A bar pattern coding method for reducing memory capacity

Info

Publication number: GB2255429A
Application number: GB9126877A
Authority: GB
Inventors: Kang Bong-Soon
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1991-04-29
Filing date: 1991-12-18
Publication date: 1992-11-04
Also published as: DE4142781A1; GB9126877D0; JPH0511739A

Description

22--,54---'9 A BAR PATTERN CODING METHOD FOR REDUCING MEMORY CAPACITY The

present invention relates to a method of coding characters for storage in memory. For example, the method relates to a bar pattern coding method for writing character information or data into a read only memory (ROM) mounted in an on-screen display integrated circuit (IC) used in an image processing system such as a video tape recorder (VTR), television (TV) or the like. The bar pattern coding method for coding character data to be displayed on a TV screen may be used to enable storage of the data in the ROM even though this is of small capacity.

In the description and claims, an on-screen display is simply referred to as an IOSDI. In general, an OSD circuit used in an image processing system such as a video tape recorder or video cassette recorder (VTR), TV or the like, comprises a synchronising/separating circuit for receiving composite image signals and generating a synchronous signal, and a circuit for receiving data supplied from a microcomputer synchronously with the synchronous signal and generating characters related to the received data and a background scene. The characters are conventionally generated in dependence upon a frequency of 7MHz produced by an oscillator, whilst the background is generated by using a frequency of 14.32MHz (NTSC mode) or 17.73MHz (PAL mode) produced by a crystal- oscillator, and then the position and width of the characters on the TV screen is determined. Thus, when image signals are input to the VTR or TV, the OSD receives an output signal from the microcomputer and displays the characters to be displayed onto the input image signals. Alternatively, when image signals are not input, the OSD displays the characters onto the background.

Figure 1 shows a block diagram of a conventional OSD circuit which generates the characters to be displayed on the screen. In this circuit, if a signal is transferred or transmitted from a remote controller 10, a microcomputer 30 receives and analyses the signal so as to produce address signals related to the characters to be displayed on the screen. The addresses are transmitted to a random access memory (RAM) 40. This RAM 40 stores the address of the characters to be displayed on the screen for one-field period and, at the same time, supplies the addresses to a

ROM 50 in which has been previously stored binary data of the characters to be used.

Accordingly, the ROM 50 generates character-pattern signals on the basis of the address supplied from the RAM 40 and transmits the characters-pattern signals to a switch circuit 60. This switch circuit 60 mixes the pattern signals with a directly input image signal 20, and the mixed signal is transferred to a screen 70, such as, a cathode-ray tube (CRT), which displays the mixed signal as a visual image for viewers.

Now, a method of coding the character data to be used by the OSD into the ROM will be described. Conventionally, each character is displayed in a matrix pattern.of 18 rows x 12 columns in consideration of a chip size of the OSD IC circuit and the shape of the character. Figure 2A shows a black and white image of the character "A", whilst Figure 2B shows this black and white image coded in binary code, that is, in "1's" and MIC. Figure 2C illustrates a method of coding the ROM 50 in the OSD IC circuit. In the method shown in Figure 2C each respective column-vector is transposed and combined in serial with the coded image signal. Therefore, in the coding of the character 'W' into the ROM, it requires 216 bits (= 18 x 12) for the transposed data Cl', C21,..., C12', and 27,648 bits (128 x. 216) in total capacity of the ROM are required for coding 128.characters. In Figures 2A to 2C, references Cl, C2, C12 denote the column vectors and Cl', C21,..., C121 denote the transposed data, respectively.

With the conventional OSD circuit, the coding has been performed by a socalled one by one (hereinafter referred to "1:1") ROM coding method, and the size of the ROM is equal to that of the matrix. As a result, if the ROM is mounted in an IC circuit there is the problem that the chip 10 size may have to be increased to accommodate the ROM.

It is an object of the invention to avoid the aforementioned problems.

According to a first aspect of the present invention there is provided a method of coding characters for storage in memory where each character can be represented as an image on a matrix of rows and columns, the method comprising the steps of determining a bar pattern in the form of a binary coded representation of each row or column of the image, storing each distinct bar pattern in memory at an associated address, and representing the image of the character by the addresses of the bar patterns for each column or row.

This method provides a ROM coding method capable of storing a lot of data into a certain capacity of a ROM for storing characters, numbers, symbols and the like, or enables storage of the same amount of data as that of the conventional method, with the use of relatively small capacity of the ROM.

The present invention also provides a ROM coding arrangement comprising a microcomputer for generating and controlling addresses of characters to be displayed, a RAM for storing the address of characters to be displayed for a one-field period, a first ROM storing bar pattern addresses of respective characters, a second ROM for storing bar pattern data of characters to be displayed, and switching means for mixing the character data supplied from the 5 second ROM with directly input image signals.

The invention also extends to a method of displaying characters on an on screen display, wherein the characters to be displayed are stored in code in memory associated - with processing means for controlling the application of selected characters to the screen, the method comprising the steps of analysing the character set to be stored in memory to determine for a number of coding schemes the memory capacity required for its storage, and selecting the coding scheme requiring the least capacity, and coding the character set in accordance with the selected coding scheme, and storing the coded character set in memory.

According to a further aspect of the invention there is provided an apparatus for storing a character set for application to an on screen display, said apparatus comprising a first memory in which a plurality of bar patterns are stored, each bar pattern representing in binary form a row or column of an image of a character, and a second memory in which each character of the character set is stored as a series of addresses of the bar patterns, and processing means to enable the retrieval of each character from said first and second memories.

The invention also extends to a method of coding a ROM for storing binary data of characters to be displayed on a screen, said method comprising: a first step of determining bar patterns having a certain size of the binary data to be coded into said ROM as basic unit; a second step of obtaining kinds of different bar patterns in the whole of the binary data to be used; a third step of producing 1 address of said bar patterns obtained at said second step; a fourth step of forming said ROM to be stored with the address given at said third step; and a fifth step of forming said ROM to be stored with the binary data of the 5 respective bar patterns.

Embodiments of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a circuit diagram, partially in block, of a conventional on-screen display IC, Figure 2A is a view illustrating a black and white image of a character "A", Figure 2B shows a binary-coded pattern of the character "A" of Figure 2A, Figure 2C is a view explaining a method of coding a ROM mounted in a conventional OSD IC, Figure 3 shows a block circuit diagram of an on-screen display IC of the present invention, Figure 4 is a flow chart illustrating a character coding method of an embodiment of the present invention, Figure 5A is a view illustrating address and bar patterns of a character "A" coded according to a method of the present invention, Figure 5B is a view illustrating a method of coding a ROM with the bar pattern address shown in Figure 5A, Figure 6 is a graph illustrating the capacity of a ROM to store data in accordance with a method of the present invention, Figure 7 shows a character set including English characters for use in a VTR, Figure 8 shows a Korean (Han-gul) character set for use in the present invention, and Figure 9 shows a Japanese character set for use in a VTR.

Figure 3 shows a block diagram of an OSD IC of the present invention which comprises a microcomputer 30 for generating and controlling the addresses of characters to be displayed, a RAM 40 for storing the addresses of the characters to be displayed for a one-field period, a first ROM 80 for storing bar pattern coded addresses of the respective characters, and a second ROM 90 for storing bar pattern data. A switching circuit 60 is provided for mixing the character signal supplied from the second ROM 90 directly with an input image signal 20.

A method of coding to be used with the apparatus illustrated in Figure 3 will now be explained with reference to Figures 4 to 9. In this respect, and as shown in Figure 4, the size of a bar pattern of binary data which is to be coded into the ROM as a basic unit is determined at a function block 100. At a next step 110 a choice is made of different bar patterns in the whole of binary data used. Then, at a step 120 the bar patterns are addressed.

After, the kinds of the differential bar patterns have been obtained at the step 110, the capacity of ROM needed to the bar pattern coding method is calculated and compared with the capacity according to the conventional.1:1 ROM coding method, at a step 130. If, as a result, the capacity of the 1:1 coding method is smaller than that of the bar pattern coding method, it is determined whether or not the basic unit of the bar pattern must be re- selected, at a step 140. If the reselection of the basic unit is needed, the procedure is returned to the step 100. On the contrary, if no reselection is needed, the ROM is formed for storing the binary data by using the conventional 1:1 coding method, at a step 150.

Meanwhile, at the step 130, if the capacity of ROM according to the 1:1 coding method is larger than that of E z the bar pattern coding method, it is determined that the capacity of ROM is satisfied, at a step 170. As a result, if the capacity is unsatisfied, the procedure proceeds to the step 140. Alternatively, at the step 170 if the capacity has been satisfactorily reduced in size, the ROM is formed at step 180, for storing the bar pattern address of the binary data, and the ROM is formed for storing the bar patterns of the binary data calculated as described above, at a step 190 by using the bar pattern coding method - according to the present invention.

Next, a process of reducing the capacity of ROM by using the bar pattern coding method will be described in comparison with the conventional coding method. As described above, in the conventional coding method, a black and white image of a character is converted into binary codes and then column vectors are transposed into binary codes using the 1:1 ROM coding method and those codes are then stored in the ROM. As a result, the capacity of ROM required is not reduced, and the ROM capacity has to be determined in dependence upon the number and the matrix size of the characters to be stored. More particularly, if the number of characters is X and the matrix size of the characters is ZXY, the capacity S, of the ROM ca.n be expressed by:

S, = X- Z- Y.....

................... (1) Where, X denotes the number of characters, Y denotes the number of column directional patterns, and Z denotes the number of row directional patterns.

With a character coding method of the invention, the black and white image of a character, for example, as "A" shown in Figure 2A, is indicated by binary codes as shown in Figure 2B. From Figure 2B it can be seen that the bar pattern of the column vector Cl is the same as the bar pattern of the column vector C12, and that the column vectors C2, C3 and C6 are the same as the column vectors C11, C10 and C7 respectively. Thus, the character A can be represented by the six different bar patterns as shown in Figure 5A. Each of these bar patterns is provided with a respective 3 bit address, for example, 000 to 101, as shown. Thus, when the address of the character "A" is input from the RAM 40, the first ROM 80 in which addresses - of the bar patterns of respective transposed column vectors are stored serves to enable the second ROM 90 having the bar pattern data produced from the whole characters to be used.

Therefore, if the character "A" is expressed by the ROM coding method using the bar patterns, 144 bits (= 6 x 18 + 3 x 12) are needed in the capacity of the ROM. This is as compared to 216 bits using the conventional coding method. Thus, utilisation of the bar coding method enables, in this instance, the capacity of the ROM for storing character data to be reduced.

Consider that the number of the bar patterns obtained from a character by the bar pattern coding method is P, and an address of N bits is needed to indicate the bar patterns, and thus represent the character. The address can be given as:

N = log2P (when P is a power of base 2) N = 11092P + 11 (else)...

Where, "[]" denotes an integral, disregarding values down a decimal.

Accordingly, the capacity S2 of ROM required in the bar pattern coding method can be expressed as:

t -g- S,, = XYN + P Z XY10g2P + PZ (when P is a power of base 2) = XY11092P + 11 + PZ (else)........ (3) Therefore, the capacity required can be reduced only if the following equations 4 and 5 are formed in the bar pattern method, as shown from equations 1 and 3.

- S1 > S, (4) XY(Z-10g2p)-PZ > 0, when P is a power of base 2 MZ-11092P + 11 - PZ > 0, else (5) Table 1 shows data obtained by comparing the ROM capacity of a bar pattern coding method with that of the conventional coding method, giving the number of characters, the character matrix size (18 x 12 in this case) and the bar pattern number. This data is illustrated in Figure 6 in which references "a" and 'W' denote the maximum and minimum capacity of ROM when an address of 7 bits is used for indicating the pattern, "b" and "B" denote the maximum and minimum capacity of ROM when an address is formed of 8 bits, "c" and "C" denote the maximuT and minimum capacity of ROM when an address is formed of 9 bits, and "d" and "D" denote the maximum and minimum capacity of ROM when the address is formed of 10 bits. 1IE" denotes the capacity of ROM required using the conventional coding method.

Table 1 character capacity n the capacity in the bar-pat ' tern coding method number lconventional 1:1, x'un-t/b-.tlj 1 lcod'ng method pattern address E A/a Bib Cic Did %.unjt/b4,t'i bit number: 7 8 9 10 1 64 1 13,82L 6,546 8,466 11,538 16,914 7,680 /10,752 /16,128 /21,504 128 27,648 11,922 14,610 18,450 24,594 /13,056 /16,896 /23,040 /33,792 1 256 55,296 22,674 26,898 32,2'14 5 4 6 39 /23,808 /29,184 /36,86,4 A '951 2 49.1 2 As can be seen from Table 1, when 64 characters are to be coded and stored in ROM, at least 13,824 bits (= 64 x 18 x 12) are required with the conventional coding method.

However, by using the bar pattern coding method, when the address of the bar pattern produced is 7 bits, 65 to 128 kinds of different bar patterns are obtained. When, for example, 65 kinds of bar patterns are present, the coding can be achieved by using 6,456 bits (= 64 x 12 x 7 + 65 x 18) in ROM capacity. Where 128 kinds of bar patterns are present, 7,680 bits (= 64 x 12 x 7 + 128 x 18) are required. As a result, the capacity of the ROM required by the bar pattern coding method is reduced.

Meanwhile, when the kinds of bar pattern are entirely different, and if 64 characters are used, a total of 768 kinds (= 64 x 12) of bar pattern will exist and 10 bit addresses are needed. In this case, if the bar pattern coding method is adopted to store the binary data in ROM, a ROM capacity of 21,504 (= 64 x 12 x 10 + 768 x 13) will be required, which is significantly more than that of the conventional coding method. Thus, if the bar patterns are 5 entirely different, the 1:1 coding method can be adopted. The capacity of ROM required in the case of 128 and 256 characters is also indicated in Table 1.

As will be apparent from the above description, with the bar pattern coding method there is an advantage if the capacity of ROM is determined on the basis of the different kinds of bar pattern used, dissimilarly to the conventional 1:1 coding method in which the capacity is determined according to the number of characters to be used and the matrix size. As a result, if many symmetrical character patterns are used to the bar pattern coding method, the capacity of ROM can be reduced considerably.

Figure 7 shows a set of 128 English characters used in a VTR, the characters including 10 Arabic numerals, 55 English characters, 8 Chinese characters, 53 symbols and 2 spaces.

In a Korean character only OSD, it is knowp that 56 Korean characters are needed. Figure 8 shows the set of 56 Korean characters indicated in a matrix size of 18 x 12 of the same size as the English character matrix.

Figure 9 shows a set of 128 characters used in a Japanese character VTR OSD, the characters including 10 Arabic numerals, 48 Japanese characters, 9 English characters, 33 Chinese characters, 21 symbols and 2 spaces.

With the conventional coding method, at least 27,648 bits in the capacity of the ROM are used in order to store the set of 128 English OSD characters. However, if this character set is coded according to the bar pattern method, 249 kinds of bar patterns are derived from the 128 characters and a bar pattern address of 8 bits will be required to address the bar patterns. Therefore, 16,770 128 x 12 x 8 + 249 x 18) bits in ROM total capacity will be required for indicating 128 English OSD characters. This allows the capacity of the ROM to be reduced by 39% as compared to the conventional coding method.

Moreover, 211 kinds of bar patterns are obtained from the 56 Korean characters shown in Figure 8. When these bar patterns are coded by using the bar pattern coding method, the capacity of the ROM is reduced from 12, 096 bits to 9,174 bits, thereby allowing the capacity to be reduced by 24%. In Figure 9, 498 kinds of bar patterns are produced from 128 Japanese OSD characters. When the bar patterns are coded by using the bar pattern coding method, the capacity of the ROM is reduced from 27,648 bits to 22,788 bits, thereby allowing the capacity to be reduced by 18%.

Further, when 128 English OSD characters and 56 Korean characters, that is, a total of 184 characters, are coded by the conventional coding method, at least 39,774 bits in ROM capacity are needed. But, if these characters are bar pattern coded, there will be 435 kinds of bar pattern, and the character set will require only 27,702 bits in the ROM. As a result, the bar pattern coding method enables the coding of 184 characters, including 56 Korean characters to use the same capacity as that required for coding 128 English OSD characters by the conventional coding method.

The resultant data thus obtained are shown in Table 2. As can be seen from Table 2, the bar pattern coding method is generally more effective than the conventional coding method and shows a very high degree of efficiency when characters having symmetrical bar patterns are to be coded.

Table 2 characters 1:1 codling method kind of bar-pattern capacity bar Patterns codling reduciing method rate (un4,t/bi,tl, (un-ts/k4tnds) (un-.t/b-$t) xlun-,t:%.' 128 English 27,648 249 16,7170 39.3 characters 56 Korean 12,096 211 9,174 24.2 characters 128 Japanese 27,64.8 498 22,788 17.6 characters 128 Englsh characters + 56 Korean 39,774 435 '27,702 30.3 characters As has been made clear above, using the bar pattern coding method enables a lot more data to be stored in the same capacity of ROM, and thus the method can be used as a capacity reducing method. This capacity reduction and the coding of the character data can be achieved without it being necessary to change the environment of the conventional OSD system. Furthermore, the bar pattern method can be applied to the OSD of the present VTR and other systems for storing character data in ROM, such as data banks for storing, telephone numbers.

Although, a preferred embodiment has been shown and described, it should be understood that changes and modifications may be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method of coding characters for storage in memory where each character can be represented as an image on a matrix of rows and columns, the method comprising the steps of determining a bar pattern in the form of a binary coded representation of each row or column of the image, storing each distinct bar pattern in memory at an associated address, and representing the image of the character by the addresses of the bar patterns for each column or row.

2. A method of displaying characters on an on screen display, wherein the characters to be displayed are stored in code in memory associated with processing means for controlling the application of selected characters to the screen, the method comprising the steps of analysing the character set to be stored in memory to determine for a number of coding schemes the memory capacity required for its storage, and selecting the coding scheme requiring the least capacity, and coding the character set in accordance with the selected coding scheme, and storing the coded character set in memory.

3. Apparatus for storing a character set for application to an on screen display, said apparatus comprising a first memory in which a plurality of bar patterns are stored, each bar pattern representing in binary form a row or column of an image of a character, and a second memory in which each character of the character set is stored as a series of addresses of the bar patterns, and processing means to enable the retrieval of each character from said first and second memories.

4. A method of coding a ROM for storing binary data of characters to be displayed on a screen, said method comprising:

a first step of determining bar patterns having a certain size of the binary data to be coded into said ROM as basic unit; a second step of obtaining kinds of different bar patterns in the whole of the binary data to be used; a third step of producing address of said bar patterns obtained at said second step; a fourth step of forming said ROM to be stored with the address given at said third step; and a fifth step of forming said ROM to be stored with the binary data of the respective bar patterns.

5. The method according to Claim 4, wherein said first step includes a step of analysing said characters indicated by a certain matrix pattern into bar-shaped patterns of binary data having a row and column direction of periodicity and a step of determining a basic unit of the analysed bar patterns.

6. The method according to Claim 4 or Claim 5, wherein said second step includes a step of comparing whether or not the respective bar pattern produced at said first step is coincide with a predetermined bar pattern to obtain a kind of the differential bar patterns.

7. The method according to any preceding claim, wherein addresses corresponding to the number of column directional patterns in the address produced at the third step are stored in said first ROM.

8. The method according to any preceding claim, wherein data corresponding to the addresses specified by said first ROM are previously stored in said second ROM.

9. The method according to any preceding claim, wherein said second ROM is enabled by said first ROM.

10. A method of coding characters for storage in memory substantially as hereinbefore described with reference to the accompanying drawings.

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11. A method of displaying characters on an on screen display, substantially as hereinbefore described with reference to the accompanying drawings.

12. Apparatus for storing a character set for application - to an on screen display, substantially as hereinbefore described with reference to the accompanying drawings.

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