Computer graphics processing and selective visual display system – Display peripheral interface input device – Cursor mark position control device
Reexamination Certificate
2001-07-30
2003-12-16
Wu, Xiao (Department: 2674)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Cursor mark position control device
C345S163000, C382S313000, C382S321000
Reexamination Certificate
active
06664948
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to tracking relative motion between a device and an adjacent surface using an optical detector circuit that responds to changes in images of the surface, and more specifically, to producing a signal indicative of the relative motion as a function of a cross correlation between a reference image and a comparison image, and an auto correlation of the reference image, where only pixel data for the reference image are retained in a memory.
BACKGROUND OF THE INVENTION
A “mechanical” mouse is the most common type of pointing device used for controlling a cursor and other graphic components on a computer display. Typically, to detect the motion of the mouse over a surface, a ball captured within a cavity on the bottom of the mouse contacts the surface and rotates as the mouse is moved over the surface by the user. The rotational movement of the ball in the cavity is transferred to two rollers that contact the ball. Shafts on which the rollers are mounted are coupled to rotary motion encoders. The rollers are orthogonally positioned relative to each other so that signals from the encoders correspond to orthogonal X axis and Y axis components of motion, where these two axes are determined relative to the mouse orientation. The &Dgr;X and &Dgr;Y components of motion derived from the encoder signals are input to a personal computer (PC) or other computing device through a serial port, a personal system/2 (PS/2) port, a bus mouse port, or a universal serial bus (USB) port and used to control a cursor or other graphical object on a display screen. A mouse also usually includes two or more switches that produce state signals when actuated by a user and may include a rotary wheel that is coupled to yet another rotational encoder and a state switch for controlling scrolling of the contents of a display window and/or other functions. A related type of pointing device called a “track ball” also employs a ball to actuate rotational encoders, but the ball is exposed on the upper surface of this pointing device so that it is movable by the user's fingers or hand, while the housing in which the ball is captive remains generally fixed in position.
The mechanical mouse described above can produce an erratic signal if the ball and rotational encoder rollers are not periodically cleaned to remove deposits that tend to buildup where the rollers contact the ball. Also, the ball may not roll properly over a slick surface, causing errors in tracking the motion of the mouse. More recently, an “optical” mouse has been developed that avoids most of the problems associated with the use of a rotatable ball in a mechanical mouse. In contrast to a mechanical mouse, an optical mouse does not include a rotatable ball in the mouse, but instead tracks the motion of the mouse by imaging the surface over which the mouse is being moved. An earlier version of an optical mouse sold by Mouse Systems, Inc. employed a special mouse pad having a reflective surface and included an orthogonal grid of closely spaced lines. Motion of this earlier type of optical mouse was detected by sensing the variations in the intensity of light reflected from the special surface, caused by the grid lines, and interpolating to resolve motion with a greater resolution than the grid spacing. In contrast, a more recently developed optical mouse sold by Microsoft Corporation is able to track movement of the device over most surfaces, thereby eliminating the need for any special surface or pad. Details of this type of optical mouse are disclosed in commonly assigned U.S. Pat. No. 6,172,354, which issued on Jan. 9, 2001. To detect motion, the optical mouse described in this patent employs a red light emitting diode (LED) source to illuminate the adjacent surface over which the mouse is being moved. A two-dimensional array of variable sensitivity photo detectors (i.e., an artificial retina) in the base of the optical mouse produces a pixel image of a portion of the surface in response to the red light reflected from the surface. The image signals from the photo detectors are periodically stored as pixel data in two different image buffers. These data are processed to determine a cross correlation from which a &Dgr;X component and &Dgr;Y component of the mouse movement can be determined as a function of the cross correlation results.
Two image buffers are used in the prior art optical mouse to determine the cross correlation, including one that stores an N×N pixel reference frame image, and another that stores an M×M comparison frame image of the portion of the surface over which the mouse is moved. Each pixel in a region of interest in the reference frame is read and compared with all pixels in the region of interest in the comparison frame to determine a cross correlation of the two image buffers. The result of this comparison is input to a correlation array. Each component of the correlation array includes the sum of the differences for a different offset between the comparison and reference frames. The differences are accumulated by processing the pixels stored in the comparison frame buffer against those stored in the reference frame buffer, which generally requires a total of M×M×N×N operations, as typically implemented in the prior art. As a result, the process to determine cross correlation in this prior art approach is both slow and computationally intensive. In addition, the process requires that two relatively expensive, moderately large memory arrays be provided to store the reference image frame and the comparison image frame data. All processing is done within circuitry included in the mouse, so that the signal sent to the computer for use in controlling a cursor of other portions of a display in response to the movement of the optical mouse is generally equivalent to that produced by a mechanical mouse. The movement signal is formatted to connect to a PS/2 port or a USB port. The maximum velocity of mouse movement that this prior art optical sensing system can accurately track is about 18 inches/sec.
Image recognition systems typically use cross correlation and auto correlation to determine the disposition of an object relative to a background. Such systems also normally use two memory arrays, one to store a reference image frame and another to store a comparison image frame, just as in the optical mouse currently sold by Microsoft Corporation. To reduce the cost of an optical mouse, it would be preferable to employ an application specific integrated circuit (ASIC) processing chip within the mouse that does not require two distinct memory arrays to store the reference and comparison frames used to determine cross correlation. It would be desirable to achieve better tracking performance by using such an optical mouse and desirable to determine the movement of the mouse using sub-pixel interpolation.
Accordingly, there is clearly motivation to develop a new approach for determining correlation that can achieve the desired more efficient tracking capability, with less demand for processing cycles, and at a lower cost than the current approach. This new approach should also achieve a lower cost by using only a single buffer memory rather than the two memory arrays normally required in calculating correlation.
SUMMARY OF THE INVENTION
In a pointing device that employs an optical imaging sensor for monitoring movement relative to a surface, successive image frames are compared to determine the direction and extent of the movement. The imaging sensor produces a signal corresponding to pixel image data for the adjacent surface. Image data for a reference frame are stored in a specialized memory buffer for use in determining a cross correlation with a comparison frame that is subsequently acquired by imaging the surface. Successive pixels of the comparison frame are processed to determine components of the cross correlation as the reference frame data are shifted through the buffer memory. Each component of the cross correlation represents the absolute va
Crane Randall T.
Hastings Brian L.
Anderson Ronald M.
Fatahi-yar M.
Microsoft Corporation
Wu Xiao
LandOfFree
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