Classifications

• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
  • G09G5/22—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators characterised by the display of characters or indicia using display control signals derived from coded signals representing the characters or indicia, e.g. with a character-code memory
  • G09G5/222—Control of the character-code memory

Definitions

• the present invention relates to a computer graphics system for representing graphical images on a terminal screen and in particular to a system for use on a non-graphics terminal.
• graphics and "graphical images” are used in this application to indicate images displayed on a screen, or part of a screen, which are not limited in the shapes or arrangement of lines in the image, these being selected freely by a user. While it is possible to display graphics on a terminal screen, current systems are expensive in terms of the amount of memory required and moreover require a specific graphics terminal having appropriate pre-programming. "Non-graphics” or “character” screens can only display characters from a predefined set, each character constituting a predefined pixel matrix on a screen. Hence, there are only a limited number of shapes which can be displayed to provide an image and it is not possible to display any freehand image created by the user. However, such terminals are cheaper than graphics terminals.
• the present invention arises from an attempt to provide a graphics representation capability for a non-graphics terminal.
• a method of displaying graphics on a computer terminal screen comprising: digitising an image to be displayed into a digital information array or predetermined dimensions; sub-dividing said information array into a plurality of identically sized pixel matrices, each corresponding in size to a standard character displayed on said screen; assigning a different predefined standard character code to each pixel matrix in the array; defining the screen display of the standard character code assigned to each pixel matrix according to the digitised image information in the respective pixel matrix in the array; displaying the defined characters on the screen in continuous arrangement corresponding to the arrangement of pixels in the array so as to display the image.
• the predefined character codes comprise the codes for ASCII standard characters, the redefinition of characters typically taking place at the terminal.
• the continuous arrangement is conveniently formed such there are no gaps between any pixels.
• the coding for the pixels may typically comprise a sub array of information comprising X and Y coordinates of the pixels and indication of the presence or absence of an image line. It is particularly preferred that the digitised information is analysed and points connected by a straight line are defined by the appropriate formula for X and Y coordinates, no information being stored about the points intermediate the end points of said straight line.
• the image to be displayed may typically be digitised using a pressure sensitive device, light or heat activated device or other devices such as X-ray devices, pencil cameras, sound devices etc.
• the first step in the process is the digitisation of the signature and this can be done using any conventional image digitiser.
• One particular preferred method of digitising the signature is using a digitising tablet such as a "sign On" (Alan Liebart Associates).
• the signature is written on a tablet which is sampled at 80 times a second and which captures and digitises the data into a window of 2550 by 1300 dots. This information can be transferred via an asynchronous RS232 line into the host computer.
• the terminal has commonly used character shapes e.g. A, B, % etc. stored permanently within in ROM made up of a combination of dots (often called 'pixels') in a matrix of 8 x 10 (8 horizontal by 10 verticle).
• character shapes e.g. A, B, % etc. stored permanently within in ROM made up of a combination of dots (often called 'pixels') in a matrix of 8 x 10 (8 horizontal by 10 verticle).
• 'pixels' dots
• 8 x 10 8 horizontal by 10 verticle
• the example below shows how an exclamation mark character can be re-defined to be an 'A' character. This information was obtained from a VT220 terminal handbook supplied by the manufacturer.
• a dot in a character matrix is shown as a '*' and a space is shown as '.'.
• Each column of the character definition is downloaded as 2 numbers (a and b).
• the value 'a' contains a binary representation of a0 - a5 (6 bits).
• the value 'b' contains the representation b0 - b3 (4 bits).
• a value of 64 is added to these binary values and one is subtracted from the final value.
• the binary representations are obtained by setting a binary bit if a dot (pixel) is present.
• the values are then ready for downloading.
• the escape sequence is structured in such a way that the final values are listed so that the eight 'a' values are output first (col. 8 first down to col. 1) and then the eight 'b' values are output (col. 8 first again down to col. 1).
• the signature plotting program takes the ASCII X, Y, Z coordinate data from the data file and converts them into integer values. In certain cases all the possible points between two sets of coordinates are calculated. The points are in the range 1 to 1300 in the Y direction and 1 to 2550 in the X direction. In order to display this information it is necessary to define a block of character shapes that, when printed out in the correct order, will represent the signature.
• the program currently uses a block of 48 characters (3 rows of 16) as its graphics window. This could be adjusted to user requirements although there is a limitation in the number of characters it is possible to define.
• Each character uses a matrix of 8 x 10 (10 rows, 8 cols.).
• a block of 16 x 3 characters gives a resolution of 30 dots (pixels) in the Y direction by 128 in the X.
• Each point is then scaled to this resolution, and the character that the particular dot will be contained in, is calculated.
• Once the actual character is known it is necessary to calculate the row and column with the character.
• In order to set a bit in a character cell it is necessary to check if the dot (pixel) is in the top six or bottom four rows of the cell as they are stored separately. This type of storage is used as different logical operations need to be performed on the pixel data depending on the row number within the cell.
• the signature can then be displayed.
• the characters are downloaded into the terminal by means of 'escape sequences' and the new character set becomes active.
• the block of characters are printed out on the screen in the correct order.
• Other 'escape sequences' to position the screen cursor are also used at this point.
• the signature will now be displayed on the screen.
• the character set is then set back to the original definitions so that normal characters will be available when the program terminates.
• the program operates in the following sequence:

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Computer Hardware Design (AREA)
• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• Controls And Circuits For Display Device (AREA)
• Digital Computer Display Output (AREA)

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• 1990
  • 1990-01-06 GB GB9000325A patent/GB2239771B/en not_active Expired - Fee Related
  • 1990-12-17 EP EP19900313774 patent/EP0437064A3/en not_active Withdrawn
  • 1990-12-27 JP JP2407841A patent/JPH0619453A/ja active Pending
• 1991
  • 1991-01-04 PT PT9643391A patent/PT96433A/pt not_active Application Discontinuation
  • 1991-01-04 AU AU68611/91A patent/AU6861191A/en not_active Abandoned

Non-Patent Citations (2)

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