Smart progressive-scan charge-coupled device camera

• US 6,549,239 B1
• Filed: 11/06/1998
• Issued: 04/15/2003
• Est. Priority Date: 05/06/1996
• Status: Expired due to Term

• Current Assignee: Cimatrix, Microscan Systems Inc (Omron Corporation)
• Original Assignee: Cimatrix
• Inventors: Tao, Fan-Ching
• Primary Examiner(s): Garber, Wendy R.
• Assistant Examiner(s): Ye, Lin
• Application Number:
  US09/180,565
• Time in Patent Office: 1,621 Days
• Field of Search: 348/370, 348/371, 348/296, 348/297, 348/376, 382/274
• US Class Current: 348/371
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 23/72 Combination of two or more compensation controls
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means

Abstract

A progressive-scan charge-coupled device (PSCCD) camera (2) may capture an entire frame of an image of an optically readable code. The camera generates a histogram or probability distribution function (PDF) of the images and uses the histogram or PDF to automatically adjust the contrast of the image. The camera also generates a cumulative distribution function (CDF) which is used to automatically adjust the illumination intensity including the brightness of the image and the duration over which the image is obtained. The captured analog video image is converted to a digital video image which may be output over the camera'"'"'s bidirectional bus interface (14) to a component outside of the camera. Updated programs, parameters and other information may be sent in the opposite direction over the bus interface to the camera. The camera may be mounted at a fixed station or may be incorporated into a portable unit, and may be hand-held and/or battery operated.

Claims

1. A system for video imaging of an object having an illumination source with an adjustable intensity, comprising:

a progressive-scan charge-coupled device (PSCCD) sensor having an exposure time, an exposure time signal input, an optical input and an analog electrical signal output corresponding to an optical image at said optical input;

a lens assembly positioned relative to said PSCCD sensor to image said object on said optical input;

an

A/D converter for converting the analog electrical signal into a digital data set corresponding to a video image of the object, said A/D converter comprising a high reference input and a low reference input which are adjustable to adjust the contrast, and further comprising a first D/A converter connected from said processing means to said high reference input of said A/D converter to adjust the high reference level and a second D/A converter connected from said processing means to said low reference input of said A/D converter to adjust the low reference level;

a timing circuit having a time control signal output coupled to the PSCCD sensor exposure time input to control an exposure time during which the PSCCD sensor senses said optical input, said exposure time signal corresponding to an effective shutter speed for the video system; and

a processing means operatively connected to said illumination source, having an adjustable brightness and duration, and said timing circuit for automatically adjusting the intensity of the illumination source, including the brightness and duration thereof, and for controlling the timing circuit to adjust the effective shutter speed in response to changing lighting conditions, including processing means for selecting a digital video data set, processing means for determining a histogram and a cumulative distribution function of brightness levels of a selected digital video data set, and means for determining a change in lighting conditions.

2. A method of capturing a video image, of an object having an optically readable code having two predominant brightness levels, a light level and a dark level, comprising the steps of:

illuminating the object with an illumination source which is adjustable in intensity brightness, including brightness or duration;

obtaining an optical image of the illuminated object;

providing a sensor having an exposure time to sense an image and an analog output;

controlling the exposure time during which the sensor senses the optical image, thereby. producing an effective shutterspeed;

converting the optical image using said sensor into an analog electrical signal providing an A/D converter having a high reference and a low reference for converting the analog electrical signal into the digital video data set corresponding to a video image of the object;

determining a histogram and a cumulative distribution function of brightness levels of the digital video image signal; and

automatically adjusting the contrast of the image, in response to a determined changed lighting condition, by

identifying a first peak for said light level and a second peak for said dark level from said histogram;

determining a desired contrast;

determining the distance between the first and second peaks on the histogram to determine an actual contrast and determining whether an adjustment to the actual contrast is required to achieve the desired contrast; and

,

if necessary, adjusting the contrast by changing at least one of the high and low references of the A/D converter to achieve the desired contrast.