Method and apparatus for enhancing the dynamic range of a CCD sensor

• US 6,188,433 B1
• Filed: 02/02/1999
• Issued: 02/13/2001
• Est. Priority Date: 02/02/1999
• Status: Expired due to Term

• Current Assignee: Ball Aerospace & Technologies Corporation (Ball Corporation)
• Original Assignee: Ball Aerospace & Technologies Corporation (Ball Corporation)
• Inventors: Orbock, Jeffrey D.
• Primary Examiner(s): Garber, Wendy
• Assistant Examiner(s): MOE, AUNG SOE
• Application Number:
  US09/241,981
• Time in Patent Office: 742 Days
• Field of Search: 348/297, 348/298, 348/362, 348/229, 348/221, 348/294, 348/255, 348/364, 348/365, 348/356, 348/308, 348/309, 348/363, 348/217, 348/299, 257/230, 257/229, 250/208.1
• US Class Current: 348/297
• CPC Class Codes: H04N 25/571 involving a non-linear response
• CPC Class Codes: H04N 25/59 by controlling the amount of charge storable in the pixel, e.g. modification of the charge conversion ratio of the floating node capacitance
• CPC Class Codes: H04N 25/71 Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors

Abstract

An imaging system having a CCD sensor varies the intensity of an input image presented to the sensor during an integration period of the sensor to enhance the intra-scene dynamic range of the imaging system. The sensor well depth of the CCD sensor is also varied during the integration period in a manner that complements the intensity variation to achieve the dynamic range improvement. In one approach, the intensity of the input image is progressively decreased during the integration period while the sensor well depth is correspondingly increased. In another approach, an intensifier unit is gated off during the integration period to provide the intensity variation. A closed loop control method is provided for controlling the image intensity and/or the well depth based upon the content of the present image.

Claims

1. An imaging system for responding to a range of image intensities, comprising:

an image input for receiving an image from an exterior environment;

an image sensor for sensing the image and for generating an electrical signal in response thereto, said image sensor including at least one charge well for collecting charge in response to the image during an integration period having a start and an end, said integration period being defined as including a first half and a second half with said first half beginning at said start of said integration period and said second half terminating at said end of said integration period, said at least one charge well having a variable well depth;

an intensity unit, located between said image input and said image sensor, for adjusting an image intensity of the image before the image reaches said image sensor; and

a control subsystem, coupled to said image sensor and said intensity unit, that increases a high end intensity of said range of intensities by decreasing overall said image intensity during said integration period while increasing overall said well depth of said at least one charge well during said integration period wherein, in the event that said image intensity, during at least said first half of said integration period is substantially the same, said control subsystem includes at least a first controller that controls said well depth of said at least one charge well such that said well depth increases at least during some portion of said second half of said integration period and, in the event that said image intensity, during greater than three-quarters of said integration period is substantially the same, said control subsystem includes at least a first controller that controls said well depth of said at least one charge well such that said well depth increases at least during said second half of said integration period, and in the event that said image intensity, during at least a majority of said integration period decreases in a step-wise manner, said control subsystem includes at least a first controller that controls said well depth of said at least one charge well such that said well depth increases during at least said second half of said integration period and in which, under control of said control subsystem, said image intensity has at least a first magnitude that occurs closer to said start than to said end of said integration period and during at least some of said second half of said integration period, said image intensity has at least one decreased magnitude that is less than said first magnitude and at the same time said image intensity has said at least one decreased magnitude, said well depth of said at least one charge well increases from at least a first depth to at least a second depth.

2. An imaging system, as claimed in claim 1, wherein:

during said second half of said integration period, said image intensity has a plurality of decreased magnitudes, with each of said plurality of decreased magnitudes being less than said first magnitude and, at the same time said image intensity has said plurality of decreased magnitudes, said well depth of said at least one charge well increases from said first depth to said second depth.

3. An imaging system, as claimed in claim 1, wherein:

said control subsystem determines a desired control procedure for one of said image intensity and said well depth of said at least one charge well and uses said desired control procedure in determining the other of said image intensity and said well depth of said at least one charge well.

4. An imaging system, as claimed in claim 1, wherein:

said first controller includes at least one of an intensifier for controllably increasing said image intensity and a variable attenuator for controllably decreasing said image intensity.

5. An imaging system, as claimed in claim 1, wherein:

said control subsystem includes a second controller that controls said image intensity.

6. An imaging system, as claimed in claim 1, wherein:

said control subsystem includes at least one of said first controller and a second controller that controls said image intensity, during at least said first half of said integration period, by one of the following;

maintaining said image intensity substantially the same and varying said image intensity in a step-wise manner from said start of said integration period.

7. An imaging system, as claimed in claim 1, wherein:

said image intensity remains greater than zero for substantially all of said integration period and then said image intensity is gated off.

8. An imaging system, as claimed in claim 1, wherein:

said control subsystem includes a parameter extraction unit for extracting at least one intensity parameter from another image being processed by said imaging system and also including a memory for storing predetermined information related to said at least one intensity parameter, wherein said control subsystem compares said at least one intensity parameter with said predetermined information to determine an output and uses said output to control said image intensity of the image.