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
  • G09G5/24—Generation of individual character patterns
  • G09G5/28—Generation of individual character patterns for enhancement of character form, e.g. smoothing
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
• • 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
  • G09G5/24—Generation of individual character patterns
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2300/00—Aspects of the constitution of display devices
  • G09G2300/04—Structural and physical details of display devices
  • G09G2300/0439—Pixel structures
  • G09G2300/0443—Pixel structures with several sub-pixels for the same colour in a pixel, not specifically used to display gradations
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2300/00—Aspects of the constitution of display devices
  • G09G2300/04—Structural and physical details of display devices
  • G09G2300/0439—Pixel structures
  • G09G2300/0452—Details of colour pixel setup, e.g. pixel composed of a red, a blue and two green components
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2340/00—Aspects of display data processing
  • G09G2340/04—Changes in size, position or resolution of an image
  • G09G2340/0407—Resolution change, inclusive of the use of different resolutions for different screen areas
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2340/00—Aspects of display data processing
  • G09G2340/04—Changes in size, position or resolution of an image
  • G09G2340/0457—Improvement of perceived resolution by subpixel rendering
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/2003—Display of colours

Definitions

• the present invention relates to methods and apparatus for displaying images, and more particularly, to display methods and apparatus which display an image by representing different portions of the image on each of multiple pixel sub- components, rather than on entire pixels.
• Color display devices have become the principal display devices of choice for most computer users.
• the display of color on a monitor is normally achieved by operating the display device to emit light, e.g., a combination of red, green, and blue light, which results in one or more colors being perceived by the human eye.
• CTR cathode ray tube
• the different colors of light are generated via the use of phosphor coatings which may be applied as dots in a sequence on the screen of the CRT.
• a different phosphor coating is normally used to generate each of the three colors, red, green, and blue resulting in repeating sequences of phosphor dots which, when excited by a beam of electrons will generate the colors red, green and blue.
• pixel is commonly used to refer to one spot in, e.g., a rectangular grid of thousands of such spots.
• the spots are individually used by a computer to form an image on the display device.
• the smallest possible pixel size will depend on the focus, alignment and bandwidth of the electron guns used to excite the phosphors.
• the intensity of the light emitted corresponding to the additive primary colors, red, green and blue, can be varied to get the appearance of almost any desired color pixel. Adding no color, i.e., emitting no light, produces a black pixel. Adding 100 percent of all three colors results in white.
• Fig. 1 illustrates a known portable computer 100, which comprises a housing 101, a disk drive 105, keyboard 104 and a flat panel display 102.
• Portable personal computers 100 tend to use liquid crystal displays (LCD) or other flat panel display devices 102, as opposed to CRT displays. This is because flat panel displays tend to be small and light weight as compared to CRT displays. In addition, flat panel displays tend to consume less power than comparably sized CRT displays making them better suited for battery powered applications than CRT displays. As the quality of flat panel color displays continues to increase and their cost decreases, flat panel displays are beginning to replace CRT displays in desktop applications. Accordingly, flat panel displays, and LCDs in particular, are becoming ever more common.
• LCD liquid crystal displays
• Color LCD displays are exemplary of display devices which utilize multiple distinctly addressable elements, referred to herein as pixel sub-elements or pixel subcomponents, to represent each pixel of an image being displayed.
• each pixel on a color LCD display is represented by a single pixel element which usually comprises three non-square elements, i.e., red, green and blue (RGB) pixel subcomponents.
• RGB red, green and blue
• LCD displays of the known type comprise a series of RGB pixel sub- components which are commonly arranged to form stripes along the display. The RGB stripes normally run the entire length of the display in one direction. The resulting RGB stripes are sometimes referred to as "RGB striping".
• RGB striping Common LCD monitors used for computer applications, which are wider than they are tall, tend to have RGB stripes running in the vertical direction.
• FIG. 2A illustrates a known LCD screen 200 comprising a plurality of rows (R1-R12) and columns (Cl-C 16) which may be used as the display 102. Each row/column intersection forms a square which represents one pixel element.
• Figure 2B illustrates the upper left hand portion of the known display 200 in greater detail. Note in Fig. 2B how each pixel element, e.g., the (Rl, C4) pixel element, comprises three distinct sub-element or sub-components, a red sub-component 206, a green sub-component 207 and a blue sub-component 208.
• each pixel element e.g., the (Rl, C4) pixel element
• Each known pixel subcomponent 206, 207, 208 is 1/3 or approximately 1/3 the width of a pixel while being equal, or approximately equal, in height to the height of a pixel. Thus, when combined, the three 1/3 width pixel sub-components 206, 207, 208 form a single pixel element.
• RGB pixel subcomponents 206, 207, 208 form what appear to be vertical color stripes down the display 200. Accordingly, the arrangement of 1/3 width color sub-components 206, 207, 208, in the known manner illustrated in Figs. 2A and 2B, is sometimes called "vertical striping".
• common column x row ratios include, e.g., 640x480, 800x600, and 1024x768.
• known display devices normally involve the display being arranged in landscape fashion, i.e., with the monitor being wider than it is high as illustrated in Fig. 2A, and with stripes running in the vertical direction.
• LCDs are manufactured with pixel sub-components arranged in several additional patterns including, e.g., zig-zags and a delta pattern common in camcorder view finders. While features of the present invention can be used with such pixel sub- component arrangements, since the RGB striping configuration is more common, the exemplary embodiments of the present invention will be explained in the context of using RGB striped displays.
• each set of pixel sub-components for a pixel element is treated as a single pixel unit. Accordingly, in known systems luminous intensity values for all the pixel sub-components of a pixel element are generated from the same portion of an image. Consider for example, the image represented by the grid 220 illustrated in Fig. 2C. In Fig.
• each square represents an area of an image which is to be represented by a single pixel element, e.g., a red, green and blue pixel sub-component of the corresponding square of the grid 230.
• a shaded circle is used to represent a single image sample from which luminous intensity values are generated.
• a single sample 222 of the image 220 is used in known systems to generate the luminous intensity values for each of the red, green, and blue pixel subcomponents 232, 233, 234.
• the RGB pixel sub-components are generally used as a group to generate a single colored pixel corresponding to a single sample of the image to be represented.
• each pixel sub-component group effectively adds together to create the effect of a single color whose hue, saturation, and intensity depend on the value of each of the three pixel sub-components.
• each pixel subcomponent has a potential intensity of between 0 and 255. If all three pixel subcomponents are given 255 intensity, the eye perceives the pixel as being white. However, if all three pixel sub-components are given a value turning off each of the three pixel sub-components, the eye perceives a black pixel.
• an image to be represented was a red cube with green and blue components equal to zero.
• the apparent position of the cube on the display will be shifted 1/3 of a pixel to the left of its actual position.
• a blue cube would appear to be displaced 1/3 of a pixel to the right.
• known imaging techniques used with LCD screens can result in undesirable image displacement errors.
• Text characters represent one type of image which is particularly difficult to accurately display given typical flat panel display resolutions of 72 or 96 dots (pixels) per inch (dpi). Such display resolutions are far lower than the 600 dpi supported by most printers and the even higher resolutions found in most commercially printed text such as books and magazines.
• the relatively coarse size of standard pixels tends to create aliasing effects which give displayed type characters jagged edges.
• the coarse size of pixels tends to result in the squaring off of serifs, the short lines or ornaments at the ends, e.g., bottom, of strokes which form a typeface character. This makes it difficult to accurately display many highly readable or ornamental typefaces which tend to use serifs extensively.
• stem weights can only be increased a pixel at a time. Thus, stem weights leap from one to two pixels wide.
• the present invention is directed to methods and apparatus for displaying an image by representing different portions of the image on each of multiple pixel subcomponents, rather than on entire pixels.
• the inventors of the present application recognize the well-known principle that human eyes are much more sensitive to edges of luminance, where light intensity changes, than to edges of chrominance, where color intensity changes. This is why it is very difficult to read red text on a green background, for example. They also recognize the well-known principle that the eye is not equally sensitive to the colors of red, green and blue. In fact, of 100 percent luminous intensity in a fully white pixel the red pixel sub-component contributes approximately 30% to the overall perceived luminance, green 60% and blue 10%.
• Various features of the present invention are directed to utilizing the individual pixel sub-components of a display as independent luminous intensity sources thereby increasing the effective resolution of a display by as much as a factor of 3 in the dimension perpendicular to the direction of the RGB striping. This allows for a significant improvement in visible resolution.
• the present invention can provide significant improvements in the quality of images, compared to known rendering techniques, even when taking into consideration the negative impact the techniques of the present invention may have on color quality.
• known monitors tend to use vertical striping. Because character stems occur in the vertical direction the ability to accurately control the thickness of vertical lines when rendering horizontally flowing text tends to be more important than the ability to control the thickness of horizontal lines.
• RGB striping resulting in improved resolution in the vertical direction as compared to conventional image rendering techniques.
• the present invention is directed to new and improved text, graphics and image rendering techniques which facilitate pixel sub-component use in accordance with the present invention.
• the display of images, including text involves steps that include scan conversion.
• Scan conversion is the process by which geometric representations of images are converted into bitmaps.
• Scan conversion operations of the present invention involve mapping different portions of an image into different pixel sub- components. This differs significantly from known scan conversion techniques where the same portion of an image is used to determine the luminous intensity values to be used with each of the three pixel sub-components which represent a pixel.
• Weighting may be applied during the scan conversion operation. When weighting is applied, different size regions of the image may be used to determine whether a particular pixel sub-component should be turned on or off. For example, weighting can be used during scan conversion so that 60% of the image area that is mapped into a pixel is used to determine the luminous intensity of the green pixel subcomponent, a separate 30% of the image area that is mapped into the same pixel is used to determine the luminous intensity of the red pixel sub-component, and a separate 10% of the image area that is mapped into the same pixel is used to determine the luminous intensity of the blue pixel sub-component.
• the scan conversion operations of the invention can be used with other operations, including image scaling, hinting, and color processing operations, that take into consideration pixel sub-component boundaries within an image and the separately controllable nature of pixel sub-components of flat panel display devices.
• Figure 1 is a diagram of a known portable computer.
• Figure 2A illustrates a known LCD screen.
• Figure 2B illustrates a portion of the known screen illustrated in Fig. 2A in greater detail than the Fig. 2 A illustration.
• Figure 2C illustrates an image sampling operation performed in known systems.
• Figure 3 illustrates known steps involved in preparing and storing character information for use in the subsequent generation and display of text.
• Figure 4 illustrates an electronic book with flat panel displays arranged in a portrait arrangement in accordance with one embodiment of the present invention.
• Figure 5 illustrates a computer system implemented in accordance with the present invention.
• Figure 6 illustrates image sampling performed in accordance with one exemplary embodiment of the present invention.
• Figure 7A illustrates a color flat panel display screen implemented in accordance with the present invention.
• Figure 7B illustrates a portion of the display screen of Fig. 7 A.
• Figure 7C illustrates a display screen implemented in accordance with another embodiment of the present invention.
• Figure 8 illustrates various elements, e.g., routines, included in the memory of the computer system of Fig. 5, used for rendering text images on the computer system's display.
• Figure 9 illustrates a method of rendering text for display in accordance with one embodiment of the present invention.
• FIGS. 10A and 10B illustrate scaling operations performed in accordance with various exemplary embodiments of the present invention.
• Figure 11 illustrates a weighted scan conversion operation performed in accordance with one embodiment of the present invention.
• Figure 12 illustrates a high resolution representation of a character to be displayed on a field of pixels.
• Figures 13 illustrates how the character of Fig. 12 would be illustrated using known techniques.
• Figures 14-17 illustrate different ways of illustrating the character shown in
• the present invention is directed to methods and apparatus for displaying images, e.g., text and/or graphics, on display devices by representing different portions of the image on each of multiple pixel sub-components, rather than on entire pixels.
• Various methods of the present invention are directed to using each pixel subcomponent as a separate independent luminous intensity source as opposed to treating the set of RGB pixel sub-components which comprise a pixel as a single luminous intensity unit. This allows for a display device with RGB horizontal or vertical striping to be treated as having an effective resolution in the dimension perpendicular to the direction of the striping that is up to 3 times greater than in the dimension of the striping.
• Various apparatus of the present invention are directed to display devices and control apparatus which take advantage of the ability to individually control pixel sub-components.
• Weighting may be applied during the scan conversion operation. When weighting is applied, different size regions of the scaled image may be used to determine whether a particular pixel sub-component should be turned on or off. Using weighting, at least one of the pixel sub-components of a pixel has two or more samples or segments of the image data mapped thereto.
• 60% of the image area that is mapped into a pixel is used to determine the luminous intensity of the green pixel sub-component
• a separate 30% of the image area that is mapped into the same pixel is used to determine the luminous intensity of the red pixel sub-component
• a separate 10% of the image area that is mapped into the same pixel is used to determine the luminous intensity of the blue pixel sub-component.
• FIG. 5 and the following discussion provide a brief, general description of an exemplary apparatus in which at least some aspects of the present invention may be implemented.
• Various methods of the present invention will be described in the general context of computer-executable instructions, e.g., program modules, being executed by a computer device such as a personal computer.
• Other aspects of the invention will be described in terms of physical hardware such as, e.g., display device components and display screens.
• Program modules may include routines, programs, objects, components, data structures, etc. that perform a task(s) or implement particular abstract data types.
• Program modules may include routines, programs, objects, components, data structures, etc. that perform a task(s) or implement particular abstract data types.
• aspects of the present invention may be practiced with other configurations, including hand-held devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, network computers, minicomputers, set top boxes, mainframe computers, displays used in, e.g., automotive, aeronautical, industrial applications, and the like.
• At least some aspects of the present invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices linked through a communications network.
• an exemplary apparatus 500 for implementing at least some aspects of the present invention includes a general purpose computing device.
• the personal computer 520 may include a processing unit 521, a system memory 522, and a system bus 523 that couples various system components including the system memory to the processing unit 521.
• the system bus 523 may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures.
• the system memory may include read only memory (ROM) 524 and/or random access memory (RAM) 525.
• a basic input/output system 526 (BIOS), including basic routines that help to transfer information between elements within the personal computer 520, such as during start-up, may be stored in ROM 524.
• the personal computer 520 may also include a hard disk drive 527 for reading from and writing to a hard disk, (not shown), a magnetic disk drive 528 for reading from or writing to a (e.g., removable) magnetic disk 529, and an optical disk drive 530 for reading from or writing to a removable (magneto) optical disk 531 such as a compact disk or other (magneto) optical media.
• the hard disk drive 527, magnetic disk drive 528, and (magneto) optical disk drive 530 may be coupled with the system bus 523 by a hard disk drive interface 532, a magnetic disk drive interface 533, and a (magneto) optical drive interface 534, respectively.
• the drives and their associated storage media provide nonvolatile storage of machine readable instructions, data structures, program modules and other data for the personal computer 520.
• a number of program modules may be stored on the hard disk 523, magnetic disk 529, (magneto) optical disk 531, ROM 524 or RAM 525, such as an operating system 535, one or more application programs 536, other program modules 537, and/or program data 538 for example.
• a user may enter commands and information into the personal computer 520 through input devices, such as a keyboard 540 and pointing device 542 for example.
• Other input devices such as a microphone, joystick, game pad, satellite dish, scanner, or the like may also be included.
• These and other input devices are often connected to the processing unit 521 through a serial port interface 546 coupled to the system bus.
• input devices may be connected by other interfaces, such as a parallel port, a game port or a universal serial bus (USB).
• a monitor 547 or other type of display device may also be connected to the system bus 523 via an interface, such as a video adapter 548 for example.
• the personal computer 520 may include other peripheral output devices (not shown), such as speakers and printers for example.
• the personal computer 520 may operate in a networked environment which defines logical connections to one or more remote computers, such as a remote computer 549.
• the remote computer 549 may be another personal computer, a server, a router, a network PC, a peer device or other common network node, and may include many or all of the elements described above relative to the personal computer 520.
• the logical connections depicted in Fig. 5 include a local area network (LAN) 551 and a wide area network (WAN) 552, an intranet and the Internet.
• LAN local area network
• WAN wide area network
• the personal computer 520 When used in a LAN, the personal computer 520 may be connected to the LAN 551 through a network interface adapter (or "NIC") 553.
• NIC network interface adapter
• the personal computer 520 When used in a WAN, such as the Internet, the personal computer 520 may include a modem 554 or other means for establishing communications over the wide area network 552.
• the modem 554, which may be internal or external, may be connected to the system bus 523 via the serial port interface 546.
• at least some of the program modules depicted relative to the personal computer 520 may be stored in the remote memory storage device.
• the network connections shown are exemplary and other means of establishing a communications link between the computers may be used.
• Fig. 7A illustrates a display device 600 implemented in accordance with an embodiment of the present invention.
• the display device 600 is suitable for use in, e.g., portable computers or other systems where flat panel displays are desired.
• the display device 600 may be implemented as an LCD display.
• the display and control logic of the known computer 100 are replaced by the display device 600 and display control logic, e.g., routines, of the present invention to provide a portable computer with horizontal RGB striping and pixel sub-components which are used to represent different portions of an image.
• the display device 600 includes 16 columns of pixel elements C1-C16 and 12 rows of pixel elements R1-R12 for a display having 16x12 pixels.
• the display 600 is arranged to be wider than it is tall as is the case with most computer monitors. While the display 600 is limited to 16x12 pixels for purposes of illustration in the patent, it is to be understood that monitors of the type illustrated in Fig. 7A can have any number of vertical and horizontal pixel elements allowing for displays having, e.g., 640x480, 800x600, 1024x768 and 1280x1024 ratios of horizontal to vertical pixel elements as well as ratios resulting in square displays.
• Each pixel element of the display 600 includes 3 sub-components, a red pixel sub-component 602, a green pixel sub-component 604, and a blue pixel subcomponent 606.
• each pixel sub-component 602, 604, 606 has a height that is equal to, or approximately equal to, 1/3 the height of a pixel and a width equal to, or approximately equal to, the width of the pixel.
• the RGB pixel sub-components are arranged to form horizontal stripes. This is in contrast to the vertical striping arrangement used in the previously discussed monitor 200.
• the monitor 600 may be used, e.g., in particular graphics applications where, because of the application, it is desirable to have a greater vertical, as opposed to horizontal resolution.
• Figure 7B illustrates the upper left hand portion of the display 600 in greater detail. In Fig. 7B, the horizontal RGB striping pattern is clearly visible with the letters R, G and B being used to indicated correspondingly colored pixel subcomponents.
• FIG. 7C illustrates another display device 700 implemented in accordance with the present invention.
• Fig. 7C illustrates the use of vertical RGB striping in a display device, e.g., an LCD display, having more vertical pixel elements than horizontal pixel elements. While a 12x16 display is illustrated, it is to be understood that the display 700 may be implemented with any number of columns/rows of pixels, including column/row ratios which result in square displays.
• each pixel element is comprised of 3 sub-pixel components, i.e., an R, G, and B pixel subcomponent.
• While the display 7A may be desirable for certain graphics applications, the accurate representation of character stems, the relatively long thin vertical portions of characters, is far more important than the representation of serifs in generating high quality characters.
• Vertical striping has the distinct advantage, when used according to the present invention, of allowing for stems which can be adjusted in width 1/3 of a pixel at a time.
• using a display device such as the device 200 or 700 with a vertical striping arrangement in conjunction with the display methods of the present invention can provide higher quality text than the known horizontal striping arrangement which limits stem width adjustments to one-pixel increments.
• Another advantage of vertical striping is that it allows for adjustments in character spacing in increments of less than a pixel size in width, e.g., 1/3 of a pixel size increments.
• Character spacing is a text characteristic which is important to legibility.
• using vertical striping can produce improved text spacing as well as finer stem weights.
• Figure 8 illustrates various elements, e.g., routines, included in the memory of the computer system of Fig. 5, used to render text images on the computer system's display in accordance with the present invention.
• the application routine 536 which may be, e.g., a word processor application, includes a text output sub-component 801.
• the text output subcomponent 801 is responsible for outputting text information, as represented by arrow 813, to the operating system 535 for rendering on the display device 547.
• the text information includes, e.g., information identifying the characters to be rendered, the font to be used during rendering, and the point size at which the characters are to be rendered.
• the operating system 535 includes various components responsible for controlling the display of text on the display device 547.
• the display information 815 includes, e.g., information on scaling to be applied during rendering and/or foreground/background color information.
• the display adapter receives bitmap images from the graphics display interface 802 and generates video signals which are supplied to video adapter 548 for optical presentation by the display 547.
• the arrow 816 represents passing of the bitmap images from the graphics display interface 802 to the display adapter 814.
• the graphics display interface 802 includes routines for processing graphics as well as text.
• Element 804 is a type rasterizer used to process text.
• the type rasterizer is responsible for processing the text information obtained from the application 536 and generating a bitmap representation therefrom.
• the type rasterizer 804 includes character data 806 and rendering and rasterization routines 807.
• the character data 806 may include, e.g., vector graphics, lines, points and curves, which provide a high resolution digital representation of one or more sets of characters.
• the rendering and rasterization routines 807 include a scan conversion subroutine 812 and can also include a scaling sub-routine 808, a hinting sub-routine 810, and a color compensation subroutine 813. While performing scan conversion operations to render text images is commonplace, the routines and sub-routines of the present invention differ from known routines in that they take into consideration, utilize, or treat a screen's RGB pixel sub-components as separate luminous intensity entities which can be used to represent different portions of an image to be rendered.
• the rendering and rasterizing routines that can be used according to the invention include a scaling routine and a scan conversion routine, which enable a display screen's RGB pixel sub-components to be used as separate luminous intensity entities which represent different portions of an image to be rendered.
• non-square scaling is performed as a function of the direction and/or number of pixel subcomponents included in each pixel element.
• high resolution character data e.g., the line and point representation of characters to be displayed as specified by text and font information
• scaling is performed in the vertical direction at a rate that is greater than that performed in the horizontal direction.
• screens with vertical striping e.g., screens illustrated in Figs. 2A and 7C
• scaling is performed in the horizontal direction at a rate that is greater than that performed in the vertical direction.
• Display information 815 is used to determine the scaling to be performed in a given embodiment.
• scaling is performed in the direction perpendicular to the striping at a rate which is unrelated to the number of pixel sub-components which form each pixel. For example, in one embodiment where RGB pixel sub-components are used to form each pixel, scaling is performed in the direction perpendicular to the striping at a rate 20 times the rate at which scaling is performed in the direction of the striping.
• the scaling of characters or images is, but need not be, performed in the direction perpendicular to the striping at a rate which allows further dividing the red, green and blue stripes in proportion to their luminous intensity contributions.
• Figs. 10A and 10B illustrate image data that has been scaled by a factor of three in the direction perpendicular to the striping and by a factor of one in the direction parallel to the striping.
• Fig. 11 illustrates image data that has been scaled in the direction perpendicular to the striping by a factor of ten. Accordingly, it can be readily understood that Fig. 11 represents one example of scaling and scan conversion whereby at least one of the pixel sub-components can have two or more samples mapped thereto.
• Figure 10A illustrates a scaling operation performed on a high resolution representation of the letter i 1002 in anticipation of the display of the letter on a monitor with horizontal striping such as the one illustrated in Fig. 7A.
• Figure 10B illustrates a scaling operation performed on a high resolution representation of the letter i 1002 in anticipation of the display of the letter on a monitor with vertical striping such as the one illustrated in Figs. 2A and 7C.
• scaling in the horizontal (X) direction is applied at a rate of x3 while scaling in the vertical (Y) direction is applied at a rate of xl.
• Scaling by other amounts is possible. For example, in cases where a weighted scan conversion operation is to be applied in determining luminous intensity values for pixel sub-components as part of a subsequent scan conversion operation, scaling is performed as a function of the RGB striping and weighting used. In one exemplary embodiment scaling in the direction perpendicular to the RGB striping is performed at a rate equal to the sum of the integer weights used during the scan conversion operation. In one particular embodiment, this results in scaling in the direction perpendicular to the striping at a rate of lOx while scaling is performed at a rate of lx in the direction parallel to the striping. Scaling at this rate generates scaled image data that can subsequently be used in a scan conversion operation, such as that illustrated by Fig.
• Scan conversion involves the conversion of the scaled geometry representing a character into a bitmap image.
• Conventional scan conversion operations treat pixels as individual units into which a corresponding portion of the scaled image can be mapped. Accordingly, in the case of conventional scan conversion operations, the same portion of an image is used to determine the luminous intensity values to be used with each of the RGB pixel sub-components of a pixel element into which a portion of the scaled image is mapped.
• Fig. 2C is exemplary of a known scan conversion process which involves sampling an image to be represented as a bitmap and generating luminous intensity values from the sampled values.
• the RGB pixel sub-components of a pixel are treated as independent luminous intensity elements.
• each pixel sub-component is treated as a separate luminous intensity component into which a separate portion of the scaled image can be mapped.
• the present invention allows different portions of a scaled image to be mapped into different pixel sub- components providing for a higher degree of resolution than is possible with the known scan conversion techniques. That is, in various embodiments, different portions of the scaled image are used to independently determine the luminous intensity values to be used with each pixel sub-component.
• Fig. 6 illustrates an exemplary scan conversion in which spatially displaced separate image samples 622, 623, 624 of the image represented by the grid 620 are used to generate the red, green and blue intensity values associated with corresponding portions 632, 633, 634 of the bitmap image 630 being generated.
• Sampling the image data and mapping separate image samples 622, 623 and 624 to the red, green, and blue pixel sub-components associated with portions 632, 633, and 634 as shown in Fig. 6 represent examples of acts that correspond to the step of mapping samples to individual pixel sub-components.
• image samples for red and blue are spatially displaced -1/3 and +1/3 of a pixel width in distance from the green sample, respectively.
• a first technique for determining if a pixel sub-component should be turned "on" during scaling is to determine if the center of the scaled image segment, represented by a portion of the scaling grid, being mapped into the pixel subcomponent is within the scaled representation of the image to be displayed. Another technique is to determine if 50% or more of the scaled image segment being mapped into the pixel sub-component is occupied by the image to be displayed. If it is, then the pixel sub-component is turned "on". For example, when the scaled image segment represented by grid segment 1202 is occupied at least 50% by the image 1004, then the corresponding pixel sub-component Cl, R5 is turned on. In the example of Fig.
• Fig. 11 represents one example of weighting being applied during the scan conversion operation. When weighting is applied, different size regions of the scaled image may be used to determine whether a particular pixel sub-component should be turned on or off or to a value in between (as in the case of gray scaling).
• Green contributes approximately 60%, red approximately 30% and blue approximately 10% to the perceived luminance of a white pixel which results from having the red, green and blue pixel sub-components set to their maximum luminous intensity output.
• weighting is used during scan conversion so that 60% of the scaled image area that is mapped into a pixel is used to determine the luminous intensity of the green pixel sub-component, a separate 30% of the scaled image area that is mapped into the same pixel is used to determine the luminous intensity of the red pixel sub-component, and a separate 10% of the scaled image area that is mapped into the same pixel is used to determine the luminous intensity of the blue pixel sub-component.
• the image is scaled in the direction perpendicular to the striping at a rate which is ten times the rate of scaling in the direction of the striping. This is done to facilitate a weighted scan conversion operation.
• the scaled image is then processed during scan conversion using a weighted scan conversion operation, e.g., of the type described above.
• Fig. 11 illustrates performing a weighted scan conversion operation on the first column 1400 of a scaled version of the image 1002 which has been scaled by a factor of 10 in the vertical direction and a factor of one in the horizontal direction.
• the portion of the image which corresponds to a single pixel comprises 10 segments.
• the first set of three segments or each pixel area of the scaled image are used to determine the luminous intensity value of a red pixel sub-component corresponding to a pixel in the bitmap image 1402.
• the next set of six segments of each pixel area of the scaled image 1400 are used to determine the luminous intensity value of a green pixel sub- component corresponding to the same pixel in the bitmap image 1402. This leaves the last segment of each pixel area of the scaled image 1400 for use in determining the luminous intensity value of the blue pixel sub-component.
• this process results in the blue pixel sub-component of column 1, row 4 and the red pixel sub-component of column 1, row 5 of the bitmap image 1402 being turned “on” with the remaining pixel sub-components of column 1 being turned “off 1 .
• the scan conversion process of the present invention has been described in terms of turning a pixel sub-component "on” or "off 1 .
• the scan conversion operation involves independently mapping portions of the scaled image into corresponding pixel sub-components to form a bitmap image.
• the intensity value assigned to a pixel sub-component is determined as a function of the portion of the scaled image area being mapped into the pixel sub- component that is occupied by the scaled image to be displayed.
• a pixel sub-component can be assigned an intensity value between 0 and 255, 0 being effectively off and 255 being full intensity
• a scaled image segment grid segment
• a pixel subcomponent being assigned an intensity value of 127 as a result of mapping the scaled image segment into a corresponding pixel sub-component.
• the neighboring pixel sub-component of the same pixel would then have its intensity value independently determined as a function of another portion, e.g., segment, of the scaled image.
• Exemplary Rendering Routines The scan conversion operations of the invention can be used with the rendering and rasterization routines 807 of Figure 9 to render text for display in accordance with one embodiment of the present invention.
• the routines 807 begin in step 902 wherein the routines are executed, e.g., under control of the operating system 535, in response to the receipt of text information from the application 536.
• input is received by text rendering and rasterization routines 807.
• the input includes text, font, and point size information 905 obtained from the application 536.
• the input includes scaling information and/or foreground/background color information and pixel size information 815 obtained, e.g., from monitor settings stored in memory by the operating system.
• the input also includes the data 806 which includes a high resolution representation, e.g., in the form of lines, points and/or curves, of the text characters to be displayed.
• a high resolution representation e.g., in the form of lines, points and/or curves
• operation proceeds to step 910 wherein the scaling subroutine 808 may be used to perform a scaling operation, such as those disclosed herein.
• step 912 in which hinting of the scaled image may be performed, e.g., by executing the hinting subroutine 810.
• the term grid-fitting is sometimes used to describe the hinting process.
• Hinting involves the alignment of a scaled character, e.g., the character 1004,
• the grid is determined as a function of the physical size of a display device's pixel elements.
• step 914 a scan conversion operation, such as those disclosed herein, is performed in accordance with the present invention, e.g., by executing the scan conversion sub-routine 812.
• Figures 12A, 12B, and 13 and the accompanying text of U.S. Patent Application Serial No. 09/168,012 further disclose general principles associated with the scan conversion operations of the invention.
• bitmap representation of the text to be displayed is generated in step 914 of Fig. 9 it may be output to the display adapter or processed further to perform color processing operations and/or color adjustments to enhance image quality. Details of exemplary color processing operations and color adjustments that can be used with the scan conversion operations of the invention are disclosed in U.S. Patent Application Serial No. 09/168,012.
• Figure 12 illustrates a high resolution representation of character n to be rendered superimposed on a grid representing an array of 12x12 pixels with horizontal striping.
• Figure 13 illustrates how the character n illustrated in Fig. 12 would be rendered using conventional display techniques and full size pixel elements each including three pixel sub-components. Note how the full pixel size limitation results in relatively abrupt transitions in shape at the ridge of the letter resulting in aliasing and a relatively flat top portion.
• Figure 14 illustrates how rendering of the letter n can be improved in accordance with the present invention by using a 2/3 pixel height base.
• the base is formed using 2 pixel sub-components as opposed to all three pixel sub-components in row 10, col. 1-4 and 8-10.
• Figure 15 illustrates how the ridge of the letter n can be reduced in thickness from one pixel in thickness to a 2/3 pixel thickness in accordance with the present invention.
• Figure 16 illustrates how the base of the letter n can be reduced, in accordance with the present invention, to a minimal thickness of 1/3 that of a pixel. It also illustrates how portions of the ridge of the letter n can reduced to a thickness of 1/3 that of a pixel.
• Figure 17 illustrates how the letter n can be illustrated, in accordance with the present invention, with a base and ridge having a thickness of 1/3 that of a pixel.
• Fig. 4 depicts a computerized electronic book device 400.
• the electronic book 400 comprises first and second display screens 402, 404 for displaying odd and even pages of a book, respectively.
• a display device of the type illustrated in Fig. 7C, for example, may be used as the displays 402, 404 of the electronic book 400 of Fig. 4.
• the electronic book 400 further comprises an input device, e.g., keypad or keyboard 408 and a data storage device, e.g., CD disk drive 407.
• a hinge 406 is provided so that the electronic book 400 can be folded protecting the displays 402, 404 when not in use.
• An internal battery may be used to power the electronic book 400.
• other portable computer embodiments of the present invention may be powered by batteries. While the present invention has been described largely in the context of rendering text, it is to be understood that the present invention can be applied to graphics as well to reduce aliasing and increase the effective resolution that can be achieved using striped displays such as conventional color LCD displays. In addition, it is to be understood that many of the techniques of the present invention can be used to process bitmapped images, e.g., scanned images, to prepare them for display.

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