# Patent

## Title
Method and apparatus for three-dimensional parallax drawing

## Abstract

A three dimensional parallax drawing system for use in three dimensional graphics or virtual reality is disclosed. The parallax drawing system includes a three dimensional address generator which generates the original X-axis, Y-axis and Z-axis addresses of an image, and an address correction circuit for producing a corrected X-axis address in response to the original X-axis and Z-axis address outputs from the address generator. Also included is an address selection circuit for selecting either the original X-axis address supplied from the three dimensional address generator or the corrected X-axis address from the address correction circuit as a resultant X-axis address in response to a stereo graphic mode request signal. A frame buffer address generator is provided for converting the resultant X-axis address received from the address selection means and the Y-axis address received from the three dimensional address generator into the frame buffer linear address. The X-axis parallax of human eyes relative to all points of an object can be converted into the X-axis addresses. Thus, once the 3-D image of the object is projected by separating the left and right eyes' views and reflecting the corrected X-axis addresses, a more vivid image having a better perspective of distance can be seen though the LCD shutters.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of prior Application No. 09/583,495, filed on 30 May 2000, issued as U.S. Pat. No. 6,784,885, which was a continuation of prior Application No. 08/948,651, filed on 10 Oct. 1997, issued as U.S. Pat. No. 6,091,419, which claimed priority from Korean Patent Application No. 96-45143, filed on 10 Oct. 1996.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to three dimensional graphic accelerators, and more particularly to a three dimensional parallax drawing system for use with virtual reality systems.
2. Description of the Related Art
Most modem graphic boards have graphic accelerators which provide the ability to quickly move data to video memory from other places in the computer. Graphic accelerators have been improved for use in three-dimensional games or graphics as well as virtual reality. In order to implement the 3-D graphics, well known texture mapping, perspective projection, shading, fog and depth cueing techniques are widely used. Texture mapping allows the graphic accelerator to calculate the memory address of the desired 3-D image to read out the texture data stored in the video memory and again write into the frame buffer. These techniques provide two-dimensional images with a sense of perspective; however, the 3-D image produced by conventional graphic accelerators is somewhat different from what is seen by human eyes in the real world. The human eyes perceives how far away an object is by using parallax. FIG. 1 shows the binocular disparity relative to a hexahedral object. Assuming a view plane 10 in front of the human eyes, a left eye's view 20 and a right eye's view 30 are formed in the view plane 10 and reach the retinas of two eyes LE and RE. The left eye's view 20 is different in shape from the right eye's view 30 due to the distance between the two eyes. This binocular disparity results in a perception of how far or near the object is.
If the view plane 10 of FIG. 1 is replaced by the monitor screen, and the corresponding 3-D image produced by a conventional graphic accelerator is represented thereon, the image seen by the human eyes can be depicted as shown in FIG. 2. Once the image appears at the monitor, each eye focuses on the monitor screen and the composite images of views 20, 30 are simultaneously seen by the eyes. Thus, the images presented in the monitor screen cannot be seen with the parallax effect.
In order to separate the left eye's view 20 and the right eye's view 30 in the monitor screen and thus to give the parallax effect, LCD Shutter techniques have been widely used in combination with raster display systems. Such techniques are known in the art as “stereo graphics.” FIG. 3 illustrates the LCD Shutter technique. The stereo graphic system includes goggles placed nearby two eyes, and LCD shutters 60 and 70 are provided inside the goggles. In the interlaced monitor screen 40, the left eye's view 20 and the right eye's view 30 are separately presented according to even numbered scan lines 50 and odd numbered scan lines 55. The left shutter 60 and right shutter 70 are operated in synchronization with the even numbered scan plane and odd numbered scan plane, respectively, such that the left LCD shutter 60 is activated during the presentation of the left eye's view 20 while the right LCD shutter 70 is deactivated to shield the right eye's view 30 of the monitor screen.
However, the above LCD shutter system still has limitations in providing a realistic perspective of an object.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a three dimensional parallax drawing system in which a vivid perspective effect can be obtained.
In accordance with the present invention, there is provided a three dimensional parallax drawing system comprising: an address generator located at a graphic accelerator and generating the X-axis, Y-axis and Z-axis addresses of an image; an address correction means for producing a corrected X-axis address in response to the X-axis and Z-axis address outputs from the three dimensional address generator; an address selection means for selecting one of the original X-axis address supplied from the three dimensional address generator and the corrected X-axis address from the address correction circuit in response to a stereo graphic mode request signal; a frame buffer address generator for converting the X-axis address received from the address selection means and the Y-axis address received from the three dimensional address generator into the frame buffer linear address.
The address correction circuit comprises an operation unit for receiving the Z-axis address and calculating the corresponding corrected X-axis address, and an adder for producing a resultant X-axis address consisting of the original X-axis address and the corrected X-axis address. Also, the address selection means includes a multiplexer.
According to this invention, the X-axis parallax of human eyes relative to all points of an object can be converted into the X-axis addresses. Thus, once the 3-D image of the object is projected with separating the left and right eye's views and reflecting the corrected X-axis addresses, a more vivid image having better perspective can be seen through the LCD shutters.



BRIEF DESCRIPTION OF THE DRAWINGS
This invention may be understood and its object, features and advantages will become apparent to those skilled in the art by reference to the accompanying drawings in which:
FIG. 1 is a graphical representation for explaining parallax of human eyes relative to an object;
FIG. 2 is a diagram depicting the view plane of FIG. 1 on which two eyes' views are projected;
FIG. 3 is a graphical representation of a method that separates the left and right eyes' views of an object using a conventional LCD shutter system;
FIG. 4 is a block diagram depiction of a three dimensional parallax drawing system in accordance with the present invention;
FIG. 5 is a graphical representation for explaining a calculation method of a function F(z) for correcting the X-axis address of a monitor screen; and
FIG. 6 is a flow diagram showing a 3-D parallax drawing method in accordance with the present invention.



DETAILED DESCRIPTION
Referring to FIG. 4, there is shown a three dimensional graphic accelerator for use with a graphic board in accordance with the invention. The graphic accelerator includes a three dimensional address generator 80 and a frame buffer address generator 110. An address correction circuit 90 is coupled to X-axis and Z-axis address outputs of the three dimensional address generator 80. The address correction circuit 90 comprises an operation unit 92 and an adder 94. The output of the adder 94 and X-axis address output line are connected to inputs of an address selection part 100. The address selection part 100 includes a multiplexer. The control input of the multiplexer 100 is connected to a ‘stereo mode’ signal line. The multiplexer output and Y-axis address output of the three dimensional address generator 80 are connected to inputs of the frame buffer address generator 110. A frame buffer, not shown, is coupled to the output of the address generator 110 to supply frame buffer linear addresses for the raster display monitor.
In this arrangement, the three dimensional address generator 80 generates the original X-axis, Y-axis and Z-axis addresses of an image. The address correction circuit 90 receives the original X-axis address and Z-axis address outputs and produces the corrected X-axis address. The address selection part 100 outputs either the original X-axis address supplied from the three dimensional address generator 80 or the corrected X-axis address from the address correction circuit 90 in response to a control signal which requests the stereo graphic mode. The frame buffer address generator 110 converts the resultant X-axis address received from the address selection part 100 and the Y-axis address received from the three dimensional address generator 80 into the frame buffer linear address.
Correction of X-axis addresses is to provide parallax on scan lines of the monitor in the X-axis direction. The operation unit 92 of the address correction circuit 90 calculates the correction amount based on the Z-axis address supplied from the three dimensional address generator 80.
As shown in FIG. 5, if the monitor screen is replaced by the view plane 10, and an object to be seen by two eyes LE, RE is located at a point a distance Z behind the view plane 10, the correction amount relative to that point can be obtained by the rules of proportion in triangles as follows:




  
    
      
        
          
            
              F
              ⁡
              
                (
                z
                )
              
            
            2
          
          :
          
            EE
            2
          
        
        =
        
        ⁢
        
          Z
          :
          
            Z
            +
            EM
          
        
      
    
  
  
    
      
        
          
            EE
            ⁢
            
              
            
            ⁢
            Z
          
          2
        
        =
        
        ⁢
        
          
            
              F
              ⁡
              
                (
                z
                )
              
            
            ⁢
            
              
            
            ⁢
            
              (
              
                Z
                +
                EM
              
              )
            
          
          2
        
      
    
  
  
    
      
        
          F
          ⁡
          
            (
            z
            )
          
        
        =
        
        ⁢
        
          
            EE
            ⁢
            
              
            
            ⁢
            Z
          
          
            Z
            +
            EM
          
        
      
    
  




Where EE is the distance between two eyes, EM is the distance between the view plane 10 and the eyes, and F(z) represents the distance in the X-axis direction of view plane 10 between a line drawn from the left eye LE and the point and a line drawn from the right eye RE and the point.

In this equation, Z corresponds to the Z-axis address, and thus F(z) becomes the correction amount. This correction amount F(z) is added to the original X-axis address. The resultant X-axis address and the Y-axis address are supplied to the frame buffer address generator 110 upon receiving the stereo mode selection signal at the address selection part 100.
With this, the X-axis parallax of human eyes relative to all points of an object can be converted into the X-axis addresses. Thus, once the 3-D image of the object is projected with separation of the left and right eyes, views and reflecting the corrected X-axis addresses, a more vivid image having a better perspective can be seen though the LCD shutters.
The detailed 3-D parallax drawing method is shown in FIG. 6. There, when started, a determination is made as to whether the stereo mode control signal is received at step 10. If the control signal is received, a further determination is made as to whether the Y-axis vertical line is the one that is necessary to give a parallax on X-axis scan lines. The Y-axis vertical line can be odd vertical line or even vertical line. If it is determined that the Y-axis vertical line is odd, that is, the vertical line is necessary to give a parallax on X-axis scan lines, horizontal points of the X-axis can be determined by the following two expressions:

Horizontal point of even vertical line=mod(frame buffer address/horizontal resolution)

Horizontal point of odd vertical line=mod(frame buffer address/horizontal resolution)+F(z)

where the frame buffer address denotes the linear address that is converted from the two dimensional X-axis address and the Y-axis address, and is calculated from the following:

Frame buffer address=(Y-axis pixel numbers*horizontal resolution)+last scan line pixel numbers

where the horizontal resolution means the number of pixels in a scan line. Also, mod denotes an operator.

Thus, at the next step 30, the multiplexer 100 selects the output of the X-axis address in which the correction amount F(z) is added to the original X-axis address.
If it is found that the system does not require the stereo mode at step 10 or the Y-axis vertical line is not one that is necessary to give a parallax on X-axis scan lines at step 20, the multiplexer 100 outputs the original X-axis address as the X-axis address at step 40.
Then, in the frame buffer address generator 110, two dimensional X-axis and Y-axis addresses are generated at step 50 based on the resultant X-axis address received from the multiplexer 100 and the Y-axis address received from the three dimensional address generator 80. There, frame buffer linear address are generated.
As is apparent from the foregoing, the three dimensional parallax drawing system of the invention provides for vivid stereo graphics by correcting the X-axis address of the address generator and giving the parallax on the required X-axis scan lines in the address selection part of the 3-D graphic accelerator. Also, it is useful when the parallax drawing method is adopted for use with three dimensional virtual reality.
Having described and illustrated the principles of the invention in a preferred embodiment thereof, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications and variations coming within the spirit and scope of the following claims.

## Claims

1. A three dimensional parallax drawing system comprising:
an address generator for generating an original X-axis address, a Y-axis address, and a Z-axis address of an image;
an address correction unit for producing a corrected X-axis address in response to the original X-axis address and the Z-axis address from the address generator;
an address selection unit for selecting either the original X-axis address supplied from the address generator or the corrected X-axis address from the address correction means as a resultant X-axis address in response to a stereo graphic mode request signal; and
a frame buffer address generator for converting the resultant X-axis address received from the address selection means and the Y-axis address received from the address generator into a frame buffer linear address.

2. The system of claim 1, wherein the address correction unit comprises:
an operation unit for receiving the Z-axis address and calculating a correction amount; and
an adder for generating the corresponding corrected X-axis address responsive to the original X-axis address and the correction amount.

3. The system of claim 1, wherein the address selection unit includes a multiplexer.

4. A drawing method for a three dimensional parallax drawing system, the method comprising:
generating an original X-axis address, a Y-axis address, and a Z-axis address of an image with a 3-D address generator;
generating a corrected X-axis address in response to the original X-axis address and the Z-axis address;
selecting either the original X-axis address or the corrected X-axis address as a resultant X-axis address in response to a stereo graphic mode request signal; and
converting the resultant X-axis address and the Y-axis address into a frame buffer address.

5. A three dimensional parallax drawing system comprising:
an address correction circuit having a first input configured to receive an original X-axis address from an address generator, a second input configured to receive a Z-axis address from the address generator, and an output configured to provide a corrected X-axis address in response to the original X-axis address and the Z-axis address; and
an address selection circuit having a first input configured to receive the original X-axis address, a second input coupled to the output of the address correction circuit, a control input configured to receive a mode request signal, and an output configured to provide a resultant X-axis address to a frame buffer address generator in response to the original X-axis address, the corrected X-axis address, and the mode request signal.

6. The system of claim 5, wherein the address correction circuit comprises:
an operation unit having an input configured to receive the Z-axis address from the address generator and an output configured to provide a correction amount; and
an adder having a first input configured to receive the original X-axis address from the address generator, a second input configured to receive the correction amount, and an output configured to provide the corrected X-axis address responsive to the original X-axis address and the correction amount.

7. The system of claim 5, wherein the address selection circuit comprises a multiplexer configured to select either the original X-axis address or the corrected X-axis address as the resultant X-axis address responsive to the mode request signal.

8. A three dimensional parallax drawing method comprising:
calculating a correction amount responsive to a Z-axis address;
adding the correction amount to an original X-axis address, thereby generating a corrected X-axis address; and
selecting either the original X-axis address or the corrected X-axis address as a resultant X-axis address responsive to a stereo graphic mode request signal.

9. A three dimensional parallax drawing system comprising:
an address generator configured to generate an original X-axis address, a Y-axis address, and a Z-axis address of a plurality of points in a frame of an image; and
an address correction circuit coupled to the address generator, the address correction circuit configured to generate a correction amount for each of the plurality of points responsive to the Z-axis address for each point, wherein the correction amount for each of the plurality of points may be different, the address correction circuit also configured to generate a corrected X-axis address for each of the plurality of points responsive to the original X-axis address and the correction amount for each of the plurality of points.

10. The system of claim 9, wherein the address correction circuit generates the corrected X-axis address for each of the plurality of points by adding the correction amount to the original X-axis address for each of the plurality of points.

11. The system of claim 9, further comprising an address selection circuit coupled to the address generator and the address correction circuit for selecting either the original X-axis address or the corrected X-axis address as a resultant X-axis address in response to a stereo graphic mode request signal.

12. The system of claim 11, further comprising a frame buffer address generator coupled to the address generator and the address selection circuit for converting the resultant X-axis address Y-axis address into a frame buffer address.

13. A method of converting three dimensional image data into a two dimensional image having a first view for a first eye and a second view for a second eye, the method comprising:
generating an original X-axis address, a Y-axis address, and a Z-axis address of a three dimensional image;
generating a corrected X-axis address for the first view in response to the original X-axis address and the Z-axis address;
utilizing the corrected X-axis address and the Y-axis address for the first view; and
utilizing the original X-axis address and the Y-axis address for the second view.

14. The method of claim 13, wherein the first and second views are interlaced on a display.

15. The method of claim 14, further comprising utilizing shutters to present the first view to the first eye and the second view to the second eye.