EP0479587A2 - Méthode d'affichage de caractères - Google Patents

Méthode d'affichage de caractères Download PDF

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Publication number
EP0479587A2
EP0479587A2 EP91309062A EP91309062A EP0479587A2 EP 0479587 A2 EP0479587 A2 EP 0479587A2 EP 91309062 A EP91309062 A EP 91309062A EP 91309062 A EP91309062 A EP 91309062A EP 0479587 A2 EP0479587 A2 EP 0479587A2
Authority
EP
European Patent Office
Prior art keywords
colour
colours
character
grey
colour table
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP91309062A
Other languages
German (de)
English (en)
Other versions
EP0479587A3 (en
Inventor
Denis Hennessey
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
nHance Dev Corp
nHance Development Corp
Original Assignee
nHance Dev Corp
nHance Development Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by nHance Dev Corp, nHance Development Corp filed Critical nHance Dev Corp
Publication of EP0479587A2 publication Critical patent/EP0479587A2/fr
Publication of EP0479587A3 publication Critical patent/EP0479587A3/en
Withdrawn legal-status Critical Current

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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
    • G09G5/02—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators characterised by the way in which colour is displayed
    • G09G5/06—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators characterised by the way in which colour is displayed using colour palettes, e.g. look-up tables

Definitions

  • the present invention relates to display of characters.
  • the term "character” is intended to cover any type of display including text, drawings, or graphics.
  • the invention relates to a method of operating a computer system for displaying characters on a video screen comprinsing the steps of writing to a screen memory an index for a pre-defined colour table for display of each pixel of a character and retrieving each index from the screen memory and inputting it to the colour table to obtain colour separated signals.
  • aliasing When a character is displayed on a lower resolution screen having typically 60 to 90 pixels per inch, the sampling rate is often too low to accurately represent the original image. This effect is known as "aliasing".
  • One approach to improved character definition involves giving the impression that a high resolution screen is being used in such situations by displaying boundary pixels of the characters at varying degrees of intensity between full on and full off to give the impression of a smooth contour. This is known as “grey scaling” or "anti-aliasing". In this method, pixels at the boundaries of characters are each assigned a grey scale value. Displaying of a character involves subtracting the background colour component from a characters colour component to provide a difference value, which value is combined with the grey scale value. Because this must be carried out for each pixel, it will be appreciated that a large amount of processing power is required.
  • Another approach is to use a video unit having a high-definition screen with a large number of pixels per unit area, and a special control circuit. Disadvantages of this approach are that such units add considerably to the expense of computer hardware and are thus not available to most user of personal computers.
  • the invention is characterised in that the colour table includes a plurality of grey scaled colours representing display of a character colour against a different background colour for a plurality of grey scale values.
  • a computer system which is constructed to display characters at diferent colours may display anti-aliased characters without extra processing, thus avoiding the need for extra processing hardware or a high definition screen.
  • inverse grey scaled colours of the colour table have inverse indices. This allows colour inversion in a very simple manner.
  • two adjacent bits of the grey scaled colour indices are the same, thus reducing processing time.
  • the indices are four bits long, defining sixteen different colours, eight of which are grey scaled colours including and between the extremes of a character colour and a background colour.
  • the invention provides a computer system for displaying characters on a video screen, the system cmprising:-
  • the system 1 comprises a computer processor 2 which is connected to a screen memory 3.
  • the screen memory 3 is four bits deep having four planes A, B, C and D as illustrated.
  • the screen memory 3 has one location for each pixel of a display device or screen.
  • the screen memory 3 is connected to a colour table 4 storing a digital colour representation for each of the sixteen combinations of the four-bit bus from the screen memory 3.
  • Each colour is digitally repesented by three eight-bit codes representing red, green, and blue components (R,G,B,).
  • the colour table 4 includes sixteen colour values having indices ranging between 0000 and 1111.
  • the colour table is similar in struture to a conventional "VGA" colour table which stores representations of sixteen different colours, including dark green, mustard, dark blue, dark red, green, yellow, blue, magenta, cyan or turquoise.
  • the colour having index 0000 is black and the colour having index 1111 is white.
  • the colour table 4 of the invention has similar indices for black and white, and additionally includes representations of grey scaled colours having indices 0001, 0010, 0011 at one end of the colour table and indices 1100, 1101 and 1110 at other end of the table.
  • the grey scaled colours have similar intensities (derived from the associated grey scale value) for the components of red, green and blue, and each grey scaled colour.
  • grey scale values For grey scaling, only one character colour is chosen, namely black, and there is only one background colour, namely white.
  • various intensities represented by grey scale values for this combination have the colour which is conventionally known as grey.
  • This combination has been chosen because it is the most common for both display and printing, however, it is envisaged that any other character and background colours may be chosen.
  • the important point is that only one combination of character and background colours has a set of grey scale values and these are entered in the colour table at the expense of other colours such as mustard and purple, which colours are rarely required for displaying and printing text.
  • the computer system 1 Before characters are to be displayed, the computer system 1 has stored therein fonts for characters, the fonts comprising screen memory indices for each pixel of the characters.
  • the indices have been pre-defined with reference to the stored colour table.
  • the processor 2 When the processor 2 is writing indices to the screen memory 3, it is more efficient to write or draw one row to each of the planes A, B, C and D at a time.
  • the processor 2 identifies a character to be drawn and in step 11 it writes one row of plane A.
  • the date written to plane A is made up of the least significant bits of the colour table indices for each pixel of the row.
  • step 12 a row made up of the second least significant bits for these pixels is drawn to plane B. If the processor 2 has identified the character to be drawn as being a text character, the colours of the colour table 4 between dark blue and turquoise are not used the third and fourth most significant bits have the same value. Thus, step 13 involves writing simultaneously to planes C and D the same bit value. This bit value is 0 for the lower-intensity colours and always 1 for the higher-intensity grey colours. It will also be noticed that to invert a colour it is only necessary to invert the index. Once written to the screen memory 3, the indices are retrieved and used to generate the RGB signals for display.
  • the invention applies the use of existing colour table techniques to the drawing of anti-aliased characters.
  • Advantage is taken of the fact that it is generally only necessary to have anti-aliasing for one combination of character and background colours, grey scaled colours for this combination are obtained at the expense of colours such as mustard which are rarely used.
  • what has been achieved is the apparent quality of a laser printer having 300 pixels per inch on a screen having say 68 pixels per inch. This has been achieved without the need for additional processing powerora high-resolution screen and associated control circuit.
  • the great benefit of the invention is it's simplicity.
  • the only disadvantage is the non-availability of colours which are rarely required.
  • the process of writing to the screen memory is speeded up by 25%. Further, invention of the colours is easily obtained by simple inversion of the indices.

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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)
EP19910309062 1990-10-03 1991-10-03 A method of displaying characters Withdrawn EP0479587A3 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IE354290 1990-10-03
IE354290 1990-10-03

Publications (2)

Publication Number Publication Date
EP0479587A2 true EP0479587A2 (fr) 1992-04-08
EP0479587A3 EP0479587A3 (en) 1992-05-27

Family

ID=11038818

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19910309062 Withdrawn EP0479587A3 (en) 1990-10-03 1991-10-03 A method of displaying characters

Country Status (1)

Country Link
EP (1) EP0479587A3 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101894543A (zh) * 2010-06-12 2010-11-24 广东欧珀电子工业有限公司 一种用于电纸书阅读器的矢量字体显示方法

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0065424A1 (fr) * 1981-05-19 1982-11-24 Western Electric Company, Incorporated Mémoire, indépendant de terminal, contenant l'information couleur d'un système d'affichage d'image numérique

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0065424A1 (fr) * 1981-05-19 1982-11-24 Western Electric Company, Incorporated Mémoire, indépendant de terminal, contenant l'information couleur d'un système d'affichage d'image numérique

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101894543A (zh) * 2010-06-12 2010-11-24 广东欧珀电子工业有限公司 一种用于电纸书阅读器的矢量字体显示方法

Also Published As

Publication number Publication date
EP0479587A3 (en) 1992-05-27

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