Method and apparatus for processing optical tracking signals

• US 4,539,590 A
• Filed: 03/08/1983
• Issued: 09/03/1985
• Est. Priority Date: 03/08/1983
• Status: Expired due to Fees

• Current Assignee: Epsilon Systems Incorporated
• Original Assignee: Epsilon Systems Incorporated
• Inventors: Gage, Richard J.
• Primary Examiner(s): Britton, Howard W.
• Application Number:
  US06/473,225
• Time in Patent Office: 910 Days
• Field of Search: 358/125, 358/126, 358/107, 358/282
• US Class Current: 348/172
• CPC Class Codes: G01S 3/7864 T.V. type tracking systems

Abstract

In an optical tracking system utilizing a TV camera, a method and apparatus for effectively removing the background of the scene and passing only target information to the tracking system. The analog video signal from the camera is converted to a 6-bit byte digital bit stream and top and bottom scanning lines representative of the background are stored. Scanning lines containing target data are compared to the stored lines and are converted to a serial digital bit stream having a ZERO base line representative of the background and variable width ONEs representative of the target. The centroid of the target is calculated and utilized to generate a tracking error between the centroid and the camera boresight.

Claims

1. In an optical tracking system having a television camera, having an analog video signal output, said camera disposed on a stabilized platform, and a tracking system for maintaining a target against a background centered on the boresight of the camera, the method of eliminating the background from the tracking system and providing a single level signal representative of the target comprising the steps of:

converting the analog video signal output to an n-bit per byte digital bit stream wherein each byte defines the gray level of a pixel;

storing a first sequence of n-bit bytes representative of the pixels of a first single television scanning line near the top of the television frame;

storing a second sequence of n-bit bytes representative of the pixels of a second single television scanning line near the bottom of the television frame;

comparing the sequence of n-bit bytes representative of the pixels of each horizontal scan occurring between said first scanning line and said second scanning line with said stored first sequence and with said stored second sequence, such comparison producing a serial digital two-level bit stream having a ZERO base line replacing said background and a plurality of variable width ONEs representative of a target being tracked by the optical tracking system; and

calculating an error signal between the target center and the boresight of the television camera for controlling of the tracking system.

2. The method defined in claim 1 in which said step of calculating an error signal includes the steps of:

storing successive television frames formed by said serial digital two-level bit stream; and

calculating the centroid of the target in said successive frames for measuring said error signal between said centroid and said boresight.

3. The method as defined in claim 2 which further comprises the steps of:

calculating the velocity of the target being tracked;

recirculating a stored television frame a number of times proportional to the calculated target velocity before storing a succeeding frame.

4. In an optical tracking system having a television camera disposed on a stabilized platform, and a tracking system for maintaining a target against a background centered on the boresight of said camera, apparatus for removing said background and for producing a target pattern for controlling said tracking system comprising:

analog-to-digital converter for converting an analog video signal from said television camera to an n-bit byte digital bit stream wherein each byte is representative of one of 2ⁿ gray levels;

system timing means synchronized with said television camera;

memory means timed by said system timing means for storing a first sequence of bytes representative of the pixels of a first horizontal scanning line near the top of the television frame, and for storing a second sequence of bytes representative of the pixels of a second horizontal scanning line near the bottom of said television frame;

first comparator means connected to said memory means for performing a first comparison of the sequence of bytes representative of the pixels of each active horizontal scan line occurring between said first stored horizontal line and said second stored horizontal line with the corresponding pixels of said stored first horizontal line and with the corresponding pixels of said second horizontal line on a pixel by pixel basis to thereby produce an output only when pixels being compared differ; and

decoder means connected to said comparator means to receive a first output from said comparisons with said first stored horizontal line and a second output from said comparisons with second stored horizontal line, said decoder thereby producing a video output having a base line of one logic level when said active horizontal line pixel is representative of the background and a variable width pulse of a second logic level when said horizontal line pixel is representative of a target.