Method for dynamically viewing image elements stored in a random access memory array

What is claimed is:

1. A method of generating a graphics display having the illusion of smooth panning across an image represented by a plurality of discrete picture elements, said image being larger than that which can be displayed at one time on a video display device, comprising:

storing in the storage sites of a memory device a set of digital data corresponding to the discrete picture elements of said image, selected subsets of said digital data being readable from said memory to produce a corresponding raster signal displayable by said video display device;

specifying a first particular portion of said memory storage sites, said first particular portion containing a first subset of digital data corresponding to a first part of said image, said first part being displayable at one time on said video display device;

selecting a second particular portion of said memory storage sites, said second particular portion containing a second subset of digital data corresponding to a different, second part of said image, said second part also being displayable at one time on said video display device,

selecting a plurality of other portions of said memory storage sites, said other portions each containing a respective other subset of digital data corresponding to other parts of said image, said other parts being situated at contiguous spaced intervals in said image between said first part and said second part, each of said other parts also being displayable at one time on said video display device,

initially reading out in raster fashion the first subset of digital data contained in said first portion to develop a first raster signal;

sequentially reading out the other subsets of digital data in each of the other portions to develop a series of other raster signals;

then reading out in raster fashion the second subset of digital data contained in said second portion to develop a second raster signal; and

using said first raster signal, said other raster signals and said second raster signal in the order that they are developed to produce on said video display device a raster display of the data contained in the various selected portions such that the produced display creates the illusion of smooth panning across said image from said first part to said second part.

2. A method according to claim 1 wherein each of said steps of reading out is synchronized with a new frame of said video display device and wherein said first part, each other part and said second part of said image are sequentially spaced from each other by a very few discrete picture elements.

3. A method of generating a graphics display comprised of n rows and m columns of discrete picture elements, comprising:

storing a set of picture element data in a memory device having storage sites corresponding to an N.times.M array;

selecting a particular portion of the storage sites corresponding to an m/Z.times.n/Z array where n/Z is equal to or less than N and m/Z is equal to or less than M;

reading out in raster fashion the data contained in each row of said portion and supplying said data as a raster signal, the data in each storage site being supplied Z times, where Z is an integer, and the data read out of each row being repeated Z times before data from the next row is read out;

using said raster signal in a video display device to produce a "zoomed" display of the data contained in said portion, said display containing a Z.times.Z array of picture elements corresponding to each storage site in said portion of said N.times.M array, and

selectively inhibiting the supply of data from each storage site for one or more of the Z consecutive supply times, and inhibiting the corresponding ones of the repeat readouts of each row of data such that a zoomed display of a plurality of adjacent storage sites containing data will be displayed as an array of spaced apart dots rather than as a solid area.

4. A method of generating a graphics display having a background grid comprising:

storing a set of data in a memory device, said stored data respectively representing the displayable picture elements of an image;

sequentially reading out in raster fashion the data contained in said memory device to develop a raster data signal;

simultaneously generating a grid signal including a train of pulses which occur in a series of regularly timed intervals;

mixing said raster data signal and said grid signal to develop a composite raster display signal in which read out datum components of said raster data signal are combined with simultaneously occurring pulses of said grid signal, said composite raster display signal being utilizable by a raster-type video display device to produce a graphics display including the data read out of said memory device and a background grid including vertical and horizontal grid lines of data superimposed on the displayed picture element data.

5. A method of generating a graphics display as recited in claim 4 wherein certain ones of said pulses are modified so as to cause said grid to appear to contain major grid lines of data and minor grid lines of data.

6. In a computer graphics display apparatus for producing in raster fashion a display image having n rows and m columns of discrete image elements, a zoom system comprising:

a memory having storage sites each capable of storing data representing a discrete image element;

memory control means for storing in separate, non-intersecting subarrays of said memory, each subarray having at least n.times.m storage sites, data representing the same picture at different scales;

raster display generation means for reading out in raster fashion data from a block of n.times.m sites in a selected one of said subarrays and for generating therefrom a display image of at least a portion of the stored picture; and

zoom magnification control means, cooperating with said generation means, for selecting from which one of said subarrays said data is read out, selection of different subarrays thereby resulting in display images of the same picture at different effective "magnification" scales.

7. A zoom system according to claim 6 wherein said memory control means comprises:

means for entering data representing said picture into the subarray storing the maximum number of image elements per unit area of said picture, readout from this subarray producing a display image of greatest effective scale; and

means for entering subsets of the same picture-representing data into positionally corresponding storage sites in each of the other subarrays, so that readout from any other subarray will produce a display image of the same picture but at a different reduced scale.

8. A zoom system according to claim 7 wherein the entire picture is represented by the image elements stored in each subarray, but wherein for each dimensional unit of area of said picture, a different number of image elements are stored in each of said subarrays.

9. A zoom system according to claim 7 further comprising a display position control for selecting the portion of said picture that is to be produced as said display image, comprising:

selection means for selecting within a certain subarray the block of sites from which data is to be read out, said selection means thereby establishing the location in said picture of the center of the produced display image; and

centering means, cooperating with said zoom magnification control means, for causing said generation means to read out data from the block of sites having the same central location as the selected block read out from said certain subarray when any other subarray is selected for readout, so that the central position of the resultant display image will correspond to substantially the same location within said picture regardless of the effective "magnification" scale of the display.

10. In a graphic display system of the type in which a display is generated corresponding to the contents of a memory storing an image as a first set of data each representing an element of that stored image, the improvement for selectively supporting another image on the display without destruction of the initially stored image, said other image being represented by a second set of data each representing an element of that other image, comprising:

means for accessing from said memory the data for each element of said stored image for which a corresponding element of the other image is to be superimposed; and

logic means for logically exclusively ORing together the accessed data for each element of the stored image and the data for the corresponding element of the image to be superimposed, and for reentering the resultant logical data into the same memory locations, said display then being generated from the resultant contents of said memory.

11. The improvement according to claim 10 wherein to delete said superimposed other image from the display said accessing means accesses from said memory the data for each image element for which there exists a corresponding element of said other image to be deleted, and wherein said logic means logically exclusively ORs together the accessed data and the data for the corresponding element of said other image to be deleted, and reenters the resultant data into the same memory locations, whereby the resultant contents of said memory will be the initially stored image in unchanged form.

12. In a computer graphics display in which a display is generated from an image stored in a memory:

first means for storing a first set of data in said memory in alternate locations;

second means for storing a second set of data in locations intermediate said alternate locations, said second set of data representing a second image that is positionally overlapping the image represented by said first set of data; and

means for accessing said memory containing both first and second sets of said data and for generating a display therefrom, creating a display thereby including said first and second images in overlapping positions but with non-intersecting image elements.

13. A process for implementing smooth panning in a computer graphics display system of the type having a memory storing digital data corresponding to picture elements of an image that is larger than can be displayed at one time, and in which a subset of said stored digital data is read out from said memory and supplied to a video display device in raster fashion to produce on said device a display of the portion of said image represented by said data subset, each such data subset being specified by a corresponding origin address within said memory, comprising:

generating a pan clock signal that is synchronized with the frame rate of said video display device,

providing a first origin address specifying a first data subset representing that first position of said image at which panning is to begin,

selecting a second origin address specifying a second data subset representing the second portion of said image at which panning is to terminate,

establishing a group of intermediate origin addresses specifying data subsets representing closely, sequentially contiguous portions of said image intermediate said first and second portions, and

sequentially reading out said first, said group of intermediate and said second data subsets in raster fashion for supply to said video display device to produce corresponding sequential displays of the portions of said image represented thereby, each such sequential readout being synchronized with said pan clock signal, whereby the resultant display has the illusion of smooth panning in which each successive video frame synchronized display represents a portion of said image that is closely contiguous to the preceeding display.

14. A process according to claim 13 wherein each successive intermediate origin address differs from the preceding intermediate origin address by a very few picture element distances.

15. The process of claim 13 wherein said establishing is accomplished by:

setting a value corresponding to the desired spacing between said sequentially contiguous portions of said image,

comparing the portion of said image that is currently being displayed on said video display device with said second portion to determine if they are the same, and if not,

arithmetically combining said desired spacing value with the origin address of the data subset representing the currently displayed portion of said image to obtain a new origin address corresponding to the next sequential portion of said image.

16. A method for providing a "zoom" magnification effect in a computer graphics display system of the type wherein digital data representing each picture element of an image is stored in a memory and wherein a subset of said digital data is read out from said memory and supplied to a video display device in raster fashion to produce a display of a corresponding portion of said image, comprising:

supplying to said video device, during readout of the data for each raster scan line of said video display device, each datum a plurality of p times and supplying no datum for (Z-p) times, where Z is an integer equal to the desired "zoom" magnification scale,

repeating said readout of the data for each raster scan line a multiple of q raster scan line times and supplying no datum for (Z-q) raster scan line times before reading out the data for the next raster scan line,

whereby a "zoom" magnified display is produced in which each stored picture element datum in said subset is displayed on said video display device as a p.times.q array of contiguous picture elements that is spaced from the adjacent displayed array corresponding to a contiguous stored datum in said subset.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to computer-graphics apparatus and more particularly to a computer-graphics display system for displaying graphic information and enabling various operations to be performed upon the displayed information with minimal participation from the host computer once the raw data has been transferred from the host computer into the display system.

2. Description of the Prior Art

Among the various systems heretofore used to display computer-graphics information are the following:

Random stroke refresh display systems--In these types of devices an instruction list describing the graphics picture as lines and arcs, etc., is kept in a display memory and the entire list is read and transformed from list coordinates to screen coordinates by ultra high speed logic. Each line or arc is then "painted" on a display screen by deflecting an electron beam directly along the line coordinates and the entire list is typically periodically repainted at a rate of between 40 and 60 times a second. Selective erase or change of displayed information is accomplished by editing the picture list. These displays are often capable of zoom and pan operations accomplished by means of transformation hardware. The major limitations of this technique have been expense and allowable picture complexity, the latter referring to a practical limit as to how long a picture list can be before consequent flicker of the display makes it unusable by a human operator.

Direct view storage tube systems--In apparatus of this type an electron beam paints a picture directly on a bystable phosphor-coated screen, which then stores the image until a high voltage erase pulse floods the screen to return all the phosphors to the unwritten state. The picture can be of very high complexity, good quality curved lines can be generated and display flicker is not a problem. This technique has been preferred over the past few years for low cost graphics system. A disadvantage of such apparatus is that no pan or zoom of stored image can be accomplished and no selective erase of stored phosphors is permitted. Moreover, the phosphorous storage tubes have two further limitations in that they characteristically have low luminesence requiring subdued room lighting for best utilization, and the tubes normally age, especially around the center and edges of the display screen, and typically require replacement once or twice a year. Tube replacement is a high cost item which over a three-year period can cost as much as 80% to 200% of the initial purchase price of the display apparatus.

Plasma panel systems--A plasma panel is comprised of small neon gas discharge tubes arranged most popularly in a 512.times.512 matrix and provides a much brighter picture than the previously mentioned display tube. However, systems incorporating such panels cannot zoom or pan the stored image. With the exception that limited selective erase is permitted, the plasma panel display is similar to the storage tube display in that each neon tube "remembers" its on/off state and no complexity limit or flicker is apparent. Although the 512.times.512 raster causes some graininess in curved lines, the most serious drawback of this type of display for graphics uses is that no method of implementing a cursor (targeting symbol) on the panel is offered, whereas all other prior art devices provide such a feature.

Scan conversion memory systems--This technique uses an indirect view storage tube wherein a picture is drawn on a semiconducting surface with an electric charge. A reading beam is then swept over the charged surface in a raster pattern and the beam readout is output to a TV monitor. A major use of the scan conversion technique has been to convert European standard TV signals (over 600 lines) to American standard TV signals (525 lines). The display device operates much like a direct view storage tube and is capable of displaying a picture of high complexity. Good quality curved lines can be generated and various shades of grey can be displayed. At least two graphics devices of this type have been introduced since 1973 with both devices using interlaced video at 60 fields/30 frames per second. Zoom and pan are possible but of limited value since the effective resolution of the scan converter seems to be of about a 300 dot square, much too coarse to justify much zooming. By way of comparison, the direct view storage tube devices seem to have about two to four times the resolution of these types of devices. Limited selective erase is permitted on scan conversion displays and a video cursor may be mixed in with the video but with a 3%-5% estimated positional error since the cursor is not written on the storage surface and many variables such as beam focusing, intensity deflection, and pin cushion errors sum together to effect cursor misalignment. Under zoom, any cursor position error is even further exaggerated. Horizontal line flicker, an effect known as the "Kell factor" is also inherent in these types of displays.

Serial raster displays--These devices use a serial digital memory implemented from shift registers (using integrated circuit, CCD, magnetic bubbles or other techniques) or rotating serial memories, i.e., magnetic disks, or drums, or other rotating devices. The video control units utilized in such systems are relatively simple and no devices currently on the market include pan, zoom, or split-screen features. Although the displayed picture can be of very high complexity, the cost of such devices is slightly higher than the storage tube devices. The typical dot matrix for such systems is a single 256.times.256 raster with an alternate 512.times.512 raster as an extra cost option. In present systems, limited selective erase is offered with no XOR capability. Color display options are also offered but increase the price of the system by a factor of two or three. Good graphic cursors may be provided with essentially no location error between cursor and picture. The limitations of such devices are slow dot writing speeds, because of limited access to individual bits in the serial memory, and limited resolution causing very distinct graininess in curved lines. No such system offers split screen, zoom, pan, or XOR.

Random access raster displays--These types of systems are generally similar to the serial raster displays mentioned above but employ random access digital memories, (magnetic cores, integrated circuits, etc.) for the raster memory. Several devices of this type have recently been introduced, mainly due to the reduction in the cost of random access memories. Typical formats mentioned are 256.times.256 bits with 512.times.512 and color offered as optional extra cost features. The principal advantage of these devices over the serial type devices is faster dot write and erase time. Other performance characteristics are substantially identical to the serial raster displays and no system on the market offers split screen, zoom, pan or XOR.

U.S. patents relating to the above types of display systems include Strout, No. 3,396,377; Okuda et al, No. 3,836,902; and Schwartz et al, No. 3,906,480.

SUMMARY OF THE PRESENT INVENTION

Briefly, the preferred embodiment includes a 2048.times.2048 random access raster memory for storing data to be displayed, a raster memory control unit for writing data into the raster memory and causing such information to be displayed on a CRT display screen, a micro control unit for controlling the function and timing of the raster memory control unit and the video control unit, and a computer channel adapter for facilitating data exchange between the micro control unit and a host computer. A 416.times.312 raster is displayable on the CRT from the memory.

The displayed image can have extremely high complexity (much higher than any previously available device) with essentially no problem of display flicker. The brightness of the display far exceeds that of direct view storage tube apparatus and tube life is at least five times greater. Zoom and pan features allow the use of a very complex stored image in a flexible manner, and a split-screen technique enables an operator to work on a very complex picture at a detail level while still having an overview of the total picture (or any portion thereof) simultaneously presented before him. The split-screen feature also allows the simultaneous display of alphanumeric messages such as prompts, menus, or X-Y readouts to be added to the graphics display and a small area of the raster memory is usually reserved for this purpose. An XOR feature allows a selective erase superior to those of any prior art raster device especially if the XORed feature is to be moved or "dragged" into place in an existing drawing.

These and other objects, features and advantages of the present invention will no doubt become apparent to those of ordinary skill in the art after having read the following detailed disclosure of the preferred embodiment, which is illustrated in the several figures of the drawing.

IN THE DRAWING

FIG. 1 is a block diagram illustrating the principal components of a computer graphics display system in accordance with the present invention;

FIGS. 2a and 2b are diagrams illustrating organization of the raster memory shown in FIG. 1;

FIGS. 2c and 2d, respectively, illustrate prior art raster scan lines and background hashed scan lines in accordance with the present invention;

FIGS. 2e and 2f demonstrate the skip pattern memory feature of the present invention;

FIG. 3 is a block diagram illustrating the principal components of the computer channel adapted shown in FIG. 1;

FIG. 4 is a block diagram illustrating the principal components of the micro control unit shown in FIG. 1;

FIG. 5a is a block diagram illustrating the principal components of the raster memory control unit shown in FIG. 1;

FIG. 5b is a block diagram illustrating the principal components of the skip pattern control unit shown in FIG. 5a;

FIG. 6 is a block diagram illustrating the principal components of the video control unit shown in FIG. 1;

FIGS. 7a and 7b, and 8a and 8b, respectively, illustrate graphics changes without and with XORing in accordance with the present invention;

FIG. 9 illustrates XORing and even/odd skip features of the present invention;

FIGS. 10a and 10b illustrate possible relationships between raster memory data location and display permitted in accordance with the present invention;

FIG. 11 is a block diagram illustrating the principal components of a hardwired pan control circuit in accordance with the present invention; and

FIG. 12 is a block diagram generally illustrating alternative components for use in the video control unit to provide color video signals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1 of the drawing, there is shown a computer-graphics system including a programmed host computer 10 with its associated graphics input apparatus 12 and keyboard input 14, and a display system 16 in accordance with a preferred embodiment of the present invention. The host computer 10 and its associated input equipment may be any of a variety of well known devices capable of responding to input controls and developing corresponding signals for driving one or more visual display systems 16. In the illustrated preferred embodiment the visual display means is a conventional cathode ray tube (CRT) device 18 but could alternatively taken the form of any standard television monitor or display device capable of responding to the raster output developed by the system 16.

In addition to the CRT 18, the control system shown generally at 16 includes a computer channel adapter 20, a micro control unit (MCU) 22, a raster memory (RMEM) control unit 24, a video control unit (VCU) 26 and a raster memory (RMEM) 28. The function of the channel adapter 20 is generally to serve as an interface between the host computer 10 and the MCU 22 and its respective address and data buses 30 and 32. The information received from the host computer 10 is of a fixed format that is universally used for all graphics to be displayed. However, as is well understood to those skilled in the art, changes can be made to the format if required. It is immaterial what type of computer is used for the host computer since the channel adapter 20 is designed to make any adjustments that are necessary in the data to render it compatible with the display system 16.

MCU 22 takes information from the host computer 10 through channel adapter 20 and translates it into information that it can itself utilize and/or pass to the RMEM control unit 24 and the VCU 26. In addition, it generates and sends out function control information which will cause the RMEM control unit 24 to begin writing display information into the RMEM. It also sends out instructions to the VCU 26 to cause it to start reading information out of the RMEM 28 and to transmit such information to CRT 18 for display. VCU 26 also functions to send interrupt signals back to MCU 22 to indicate that it is at the end of a trace of the video scope and to request more information.

In the preferred embodiment RMEM 28 is a 2048.times.2048 random access memory (RAM) which is adapted to store bits of data corresponding on a 1-to-1 basis to the data contained on a graphic document such as, for example, might be drawn on the board 12. In other words, each storage situs in RMEM 28 could correspond to a unique location on the board 12. However, as will be pointed out below, in the preferred embodiment, part of the RMEM is reserved for nongraphics information such as alphanumerics and miscellaneous notes and instructions. In addition, transformations of stored data, i.e., shifts, zooms, rotations, etc., may be performed by the host computer 10. As illustrated in FIGS. 2a and 2b RMEM 28 is broken up into an array of 16 boards with each board consisting of a 512.times.512 memory unit. Actually, the memory units are comprised of random access memory chips which have been arranged on 16 boards to be addressed as a square matrix of sixteen 512.times.512 storage modules. This arrangement allows the memory to be considered somewhat of a map of the graphics information to be displayed.

The primary function of RMEM control unit 24 is to write graphics information into RMEM 28, and the primary function of video control unit 26 is to read out information stored in RMEM 28 and to cause it to be displayed in any of several modes by CRT 18. RMEM control unit 24 receives information from the MCU 22 in the form of a certain number of bytes of data which will tell it to perform certain operations. It then addresses RMEM 28 via X and Y addressing lines contained within the bus 34 and addresses a unique bit in the RMEM 28 and writes either a "1", an "0" or complements (XOR's) the data presently stored at the site via an exclusive OR function. The data transfer from RMEM control unit 24 to RMEM 28 is via the data bus 36. The particular block or blocks of RMEM 28 to be addressed are designated by board select data conveyed via bus 38.

Video control unit 26 reads out and displays in the selected form the information contained in RMEM 28. The data is received in parallel form and converted to serial form for input to CRT 18. Split and zoom control information is conveyed to VCU 26 from microcomputer unit 22 and in response thereto this unit selects and conveys the designated data in RMEM 28 to CRT 18 for display. As indicated previously, every bit in RMEM 28 normally represents one bit to be displayed on the screen, but alternatively, the display can be modified so that every bit stored in RMEM 28 represents some multiple of data positions on the CRT screen. This is effect provides for an expanded or zoomed view of the stored information. Video control unit 26 also generates grid and cursor signals and enables the cursor to be positioned on the screen in any of several splits displayed. VCU 26 conveys one write function to RMEM control unit 24 and that is an ERASE control.

CRT 18 is capable of operating in a raster scan, noninterlaced mode and can display approximately 9 levels of grey. However, the present invention only uses 6 levels of grey; the background is one level, the grid is two levels, the cursor is still another level, the data is a fifth level, and the split margins are a sixth level. These levels are of course effected by different analog voltages applied to CRT 18. The dot resolution of the display screen is 416 dots across a horizontal line and 312 lines in the vertical direction.

Among the novel features of the present invention to be discussed in detail below are its ability to display a selected portion of the data contained in RMEM 28 on either a 1-to-1 scale as compared to the original graphics information, or at any of several predetermined enlarged scales (although not yet included in the preferred embodiment, scale reductions could also be implemented); its ability to cause the display on CRT 18 to appear to pan across the data contained within RMEM 28; its capability of overlying graphics information with additional data without destroying the original information; its capability of splitting the screen to simultaneously display two or more different areas of RMEM 28; its ability to simultaneously display a background grid which corresponds scalewise to the displayed data; and its ability to make changes or additions to the displayed graphics data without requiring that the entire display be erased and rewritten each time a change is made.

The present display system is essentially an add-on device which can be adapted for use with any computer graphics system so as to take the data format used in the system and convert it into a particular form that can be displayed on a CRT screen rather than on the commonly used direct view storage tube. In addition, it includes expanded controls of information, whereby for example, the data can be split across the screen in the horizontal direction, vertically down screen, or in segments of the screen. The present invention makes it possible to easily modify data and to pan a displayed "window" across the overall graphic layout. It essentially makes it possible to move the equivalent of a window around a very large data base. An instruction to move the "window" to a new position advances the address registers in the video control unit and causes a new section of the memory to be read out and displayed on the screen. This can be accomplished in large steps or it can be done in very small steps to give the illusion of continuous movement over the data base, thus providing a panning motion.

Channel adapter 20 provides the interface to the host computer, and the buffer to the MCU 22, the RMEM control unit 24, and the video control unit 26. It provides a path for high speed data interchange between the host computer 10 and the MCU 22. Whereas the host computer 10 transmits information over the data channels in the form of a binary message, the MCU 22 is programmed to recognize the data and set up the CRT screen to display the selected splits, the proper zoom factor and the data in the selected area of RMEM 28. The data is then input to the RMEM 28 through RMEM control unit 24 and video control unit 26 is caused to constantly read RMEM 28 and display the select portions of the data on CRT 18.

Once the data is input to RMEM 28, MCU 22 has no further function to perform on the data, but any time that the video control unit 26 needs additional information, it will, during the CRT retrace period, interrupt MCU 22 and request the needed information. MCU 22 will then process the information and update VCU 26. During the time following the loading of VCU 26, MCU 22 can supply the control information to RMEM control 24. For example, if data is input to the system from the host computer 10 instructing it to go to some position X-Y and to draw a line of a certain character, this information will be digested by MCU 22 and corresponding instructions will be issued and input to the RMEM control unit 24. The RMEM control unit 24 will go BUSY and will perform its function and input data to RMEM 28