EP0439714A2 - Méthode anti-aliasing pour un dispositif d'affichage graphique - Google Patents

Méthode anti-aliasing pour un dispositif d'affichage graphique Download PDF

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Publication number
EP0439714A2
EP0439714A2 EP90122594A EP90122594A EP0439714A2 EP 0439714 A2 EP0439714 A2 EP 0439714A2 EP 90122594 A EP90122594 A EP 90122594A EP 90122594 A EP90122594 A EP 90122594A EP 0439714 A2 EP0439714 A2 EP 0439714A2
Authority
EP
European Patent Office
Prior art keywords
pixels
triangular
region
triangular regions
color
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.)
Granted
Application number
EP90122594A
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German (de)
English (en)
Other versions
EP0439714B1 (fr
EP0439714A3 (en
Inventor
Willie Williamson, Jr.
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International Business Machines Corp
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International Business Machines Corp
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Publication of EP0439714A2 publication Critical patent/EP0439714A2/fr
Publication of EP0439714A3 publication Critical patent/EP0439714A3/en
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Publication of EP0439714B1 publication Critical patent/EP0439714B1/fr
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    • 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
    • G09G5/20—Function-generator circuits, e.g. circle generators line or curve smoothing circuits
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G1/00—Control arrangements or circuits, of interest only in connection with cathode-ray tube indicators; General aspects or details, e.g. selection emphasis on particular characters, dashed line or dotted line generation; Preprocessing of data
    • G09G1/28—Control arrangements or circuits, of interest only in connection with cathode-ray tube indicators; General aspects or details, e.g. selection emphasis on particular characters, dashed line or dotted line generation; Preprocessing of data using colour tubes
    • 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
    • G09G5/36—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators characterised by the display of a graphic pattern, e.g. using an all-points-addressable [APA] memory
    • G09G5/39—Control of the bit-mapped memory
    • G09G5/391—Resolution modifying circuits, e.g. variable screen formats

Definitions

  • the present invention relates generally to the display of raster images, and more specifically to an anti-aliasing algorithm for use with such displays.
  • Raster images are typically displayed using a raster image.
  • the raster image is a rectangular array of rectangular picture elements known as pixels.
  • Raster images can be displayed on CRT monitors in monochrome or various colors. Raster images are also used to display text and graphics on printers, plotters, and other display devices.
  • Aliasing is the jagged, stair-step appearance when lines and edges are displayed which are neither vertical nor horizontal. This problem is more noticeable when a small number of large pixels are used for a given area. Increasing the resolution of the display device, thereby increasing the number of pixels per unit area, improves the appearance of the raster image.
  • One of the more successful anti-aliasing algorithms involves edge blur. Along the edge of the diagonal or curved line, where stair-steps occur, there is ordinarily a sharp transition between the pixels that are drawn in the different colors of the two regions. The staircase appearance occurs because pixels of one color lay immediately adjacent to those of another color, making the jagged transition between them noticeable.
  • edge blur algorithm With an edge blur algorithm, however, it is possible to average the color values of the two regions along the edge and then display missing pixels in the staircase using this in-between color. The result is a blurring or softening of the edge, smoothing over the transition between the colors of the different regions.
  • One disadvantage of this approach is that the display device must be able to display colors which are intermediate between the colors of the two different regions.
  • the larger display or printout usually has more pixels for displaying the image than the original image.
  • a simple method to enlarge the original raster image is to simply enlarge the original pixels, mapping them to the pixels of the enlarged image. If, for example, the zoom factor is 8, each pixel of the original image becomes an 8x8 square of pixels in the resulting image. If the pixels are simply enlarged in this manner, each of the 64 pixels in a square corresponding to an original pixel is simply given the same color value as the original pixel. This gives the same appearance as simply using very large pixels in the resulting image, and the stair-step phenomena is generally more noticeable than in the original image. Use of intermediate colors for these large pixels does not completely solve the problem.
  • a method for determining the values of pixels in a resulting image having a greater number of pixels than an original image describes a technique for calculating the values of the new pixels in the resulting image.
  • a rectangular region centered on a junction of four pixels in the original image is used as the basis for calculation. This rectangular region contains one-fourth of the adjacent original pixels, and is divided into 8 triangular regions. All of the pixels of the resulting image within a triangular region are given the same color, and the color assigned to the pixels in each such triangular region is a function of the colors of the four adjacent pixels in the original image.
  • Figure 1 shows a portion of a raster image 10 formed from a plurality of pixels.
  • the pixels of Figure 1 are divided into four rows R1, R2, R3 and R4, and four columns C1, C2, C3 and C4. Pixels can be referred to by their coordinates, so that pixel 12 is identified by the location (R2, C4) and pixel 14 is identified by the location (R4, C2).
  • FIG 2 shows the four adjacent pixels in the upper left hand corner of Figure 1. Shading of the pixels is omitted in Figure 2 for clarity.
  • a method for calculating the pixel colors in the resulting image utilizes rectangular region 16. Rectangular region 16 has the same shape as each of the pixels, which is square as shown in Figures 1 and 2. Rectangular region 16 is centered on the intersection point 18 of the four pixels. In Figure 2, the four pixels illustrated are shown as being slightly spaced apart both for clarity and because adjacent pixels are actually separated by a small space in some types of displays. Rectangular region 16 is considered to include the nearest one-fourth of each adjacent pixel.
  • Figure 3 illustrates logical regions 1-8 into which rectangular region 16 is divided. Regions 1 and 5 correspond to the lower right hand corner of pixel (R1, C1) of Figure 2. Regions 2 and 6 correspond to the lower left hand corner of pixel (R1, C2). The remaining regions likewise correspond to the remaining pixels adjacent to intersection point 18. The numbered regions will be used in connection with the detailed description of the preferred method for assigning pixel colors as described in connection with Figure 4.
  • Figure 4 is a flowchart of the calculations necessary to assign colors to all of the pixels within one rectangular region 16. In order to determine the colors of all of the pixels in the resulting array, the calculation outlined in Figure 4 is performed for a rectangular region 16 for the intersection point 18 between every set of four adjacent pixels in the array. The calculation of Figure 4 is therefore performed a number of times equal to (N-1)*(M-1) for an N X M array of pixels.
  • the first step 30 is to assign colors to the pixels located in regions 1, 2, 3, 4.
  • the pixels in these regions are assigned the same color as the color of the original pixel of which each region is a part. Therefore, for example, considering rectangular region 16 of Figure 2, regions 1, 3, and 4 are assigned the shaded color, while region 2 is assigned the unshaded color.
  • the next step is to perform the conjunctive logical comparisons of step 32. If the color of region 1 is equal to the color of region 2, region 3, and region 4, the YES branch is taken. When this condition occurs, all four of the original pixels have the same color, and the entire area of rectangular region 16 is assigned this color. Therefore, regions 5, 6, 7, and 8 are assigned the same color as region 1 is step 34.
  • step 36 the test shown in step 36 is performed. This is a comparison to see whether the color of region 1 is the same as the color of 4, and the color or region 2 is the same as that of region 3. If this is the case, the four original pixels formed a checkerboard pattern using two colors, and no changes will be made within the area encompassed by rectangular region 16. Thus, if the result of test 36 is true, control skips ahead to step 38 which assigns interior triangular regions 5, 6, 7, and 8 to have the same color as their adjacent exterior triangular regions 1, 2, 3, 4. After step 38, processing is complete.
  • step 40 the color of region 1 is compared to the color of region 4. If they are the same color, control passes to step 42. If this point is reached in the flowchart, it is known that the upper left and lower right pixels have the same color, while the lower left and upper right pixels are of differing colors. This means that a line is formed by the upper left and lower right pixels, and all of the interior regions 5, 6, 7, 8 are given the same color as region 1.
  • step 42 the test of step 42 is performed. This test is analogous to that performed in step 40, except that a check is made to see whether the same colors are found in regions 2 and 3. If so, control passes to step 46. If this point in the flowchart is reached, it is known that regions 2 and 3 have the same color, while regions 1 and 4 have dissimilar colors. Therefore, all of the interior triangular regions 5, 6, 7, 8 are assigned the same color as region 2.
  • step 38 assigns each of the interior triangular regions the same color as their adjacent exterior triangular region. If step 38 is reached, it is known that one of three situations has occurred with respect to the four adjacent pixels. If control passes from step 44 to step 38, either each of the adjacent pixels is a different color from all of the others, or any adjacent pixels of the same color are vertically or horizontally adjacent. If control has reached step 38 from step 36, the two color checkerboard pattern described above occurs. In either event, the four corners of the rectangular region 16 are given the same value as the original pixels from which they are derived.
  • Figure 5 illustrates the effect of the method of Figure 4 on a portion of the raster image of Figure 1.
  • the four original pixels (R2, C2), (R2, C3), (R3, C2), and (R3, C3) are shown.
  • the zoom, or magnification, factor is 8, meaning that each original pixel is translated to an 8x8 region of pixels in the resulting image. If the pixels of Figure 1 were translated unchanged into Figure 5, a large stair-step would be evident.
  • Applying the method of Figure 4 to the various intersection points of Figure 1 gives the result of Figure 5, wherein the upper right hand corners of the (R2, C2) and (R3, C3) regions are set to the non-shaded color, and the lower left triangular region of (R2, C3) is shaded.
  • the method described above can be used when a raster image is converted to be shown on a CRT display having a greater number of pixels than that of the original display. It is also suitable for use when a raster image is to be greatly enlarged so that it can be printed on a printer or plotter. This allows, for example, an image suitable for viewing on a CRT display to be enlarged and printed on a large chart suitable for showing to an auditorium.
  • the detailed embodiment described above can be generalized to include more than eight triangular regions if desired. For example, if diagonal lines are drawn between the corners of rectangular region 16 in Figure 3, 16 triangular regions would result. These can be assigned colors as a function of the four adjacent pixels. It is also possible to center such a 16-piece region on a pixel instead of an intersection, and color the triangular regions as a function of the eight surrounding pixels. Dividing the rectangular region 16 into a large number of triangular regions is not preferred because it is computationally expensive. Also, the information content of the original pixels is much lower than that of the resulting image, and performing complex interpolations usually does not improve the resulting image to a degree which justifies the extra computation. It is usually more fruitful to simply recreate the original image at a higher resolution if possible.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Image Processing (AREA)
  • Editing Of Facsimile Originals (AREA)
EP19900122594 1990-01-05 1990-11-27 Méthode anti-aliasing pour un dispositif d'affichage graphique Expired - Lifetime EP0439714B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US46134290A 1990-01-05 1990-01-05
US461342 1990-01-05

Publications (3)

Publication Number Publication Date
EP0439714A2 true EP0439714A2 (fr) 1991-08-07
EP0439714A3 EP0439714A3 (en) 1992-04-01
EP0439714B1 EP0439714B1 (fr) 1995-05-24

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EP19900122594 Expired - Lifetime EP0439714B1 (fr) 1990-01-05 1990-11-27 Méthode anti-aliasing pour un dispositif d'affichage graphique

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EP (1) EP0439714B1 (fr)
JP (1) JPH03252778A (fr)
DE (1) DE69019723T2 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1100068A2 (fr) * 1999-11-11 2001-05-16 Grundig AG Dispositif pour améliorer l'affichage sur un dispositif de visualisation
WO2001080496A1 (fr) * 2000-04-13 2001-10-25 Nokia Corporation Procede permettant le mosaiquage en triangles d'une zone de reseau local radio, et dispositif portable correspondant

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1982003290A1 (fr) * 1981-03-20 1982-09-30 Brockhurst David Mark Decodeur pour informations numeriques dans un signal de television
GB2120899A (en) * 1982-05-24 1983-12-07 Dainippon Screen Mfg A method of and apparatus for forming magnified reproduction image
JPS62229428A (ja) * 1986-03-31 1987-10-08 Toshiba Corp ハ−ドコピ−制御装置
EP0336776A2 (fr) * 1988-04-07 1989-10-11 Fujitsu Limited Agrandissement d'image

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5966261A (ja) * 1982-10-08 1984-04-14 Hitachi Ltd ２値画像の密度変換装置
JPS61264482A (ja) * 1985-05-18 1986-11-22 Nippon Telegr & Teleph Corp <Ntt> 画面変換処理方式

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1982003290A1 (fr) * 1981-03-20 1982-09-30 Brockhurst David Mark Decodeur pour informations numeriques dans un signal de television
GB2120899A (en) * 1982-05-24 1983-12-07 Dainippon Screen Mfg A method of and apparatus for forming magnified reproduction image
JPS62229428A (ja) * 1986-03-31 1987-10-08 Toshiba Corp ハ−ドコピ−制御装置
EP0336776A2 (fr) * 1988-04-07 1989-10-11 Fujitsu Limited Agrandissement d'image

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, vol. 12, no. 97, (P-682), 8th October 1987; & JP-A-62 229 428 (TOSHIBA CORP.) *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1100068A2 (fr) * 1999-11-11 2001-05-16 Grundig AG Dispositif pour améliorer l'affichage sur un dispositif de visualisation
EP1100068A3 (fr) * 1999-11-11 2003-01-08 Grundig AG Dispositif pour améliorer l'affichage sur un dispositif de visualisation
WO2001080496A1 (fr) * 2000-04-13 2001-10-25 Nokia Corporation Procede permettant le mosaiquage en triangles d'une zone de reseau local radio, et dispositif portable correspondant

Also Published As

Publication number Publication date
DE69019723D1 (de) 1995-06-29
EP0439714B1 (fr) 1995-05-24
EP0439714A3 (en) 1992-04-01
JPH03252778A (ja) 1991-11-12
DE69019723T2 (de) 1996-01-25

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