Signal restoration and gain control for image viewing devices

• US 4,216,503 A
• Filed: 03/26/1979
• Issued: 08/05/1980
• Est. Priority Date: 03/26/1979
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Wiggins, Douglas G.
• Primary Examiner(s): Martin, John C.
• Application Number:
  US06/023,570
• Time in Patent Office: 498 Days
• Field of Search: 358/212, 358/213, 358/168, 358/171, 358/174, 358/280, 358/282, 358/209, 358/293, 358/294, 250/578, 307/221 D
• US Class Current: 358/446
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/701 Line sensors

Abstract

A system for restoring image signal levels and setting signal gain for charge coupled imaging devices (CCDs). Following the last image signal or pixel in a line of image data, a predetermined sequence of dark level signals (D) and light level signals (L) are shifted out of the CCD. The dark level signals are the absence of all image information, while the light level signals represent signals introduced at the appropriate time early in the shifting cycle. At the CCD output, the dark and light level signals are isolated and processed by an MPU in accordance with pre-established functions to provide an offset potential and gain multiplicand. The offset potential and gain multiplicand determined are used to remove the offset and set signal gain for the next succeeding line of image signals. The process is repeated as each line of image signals are output from the CCD.

Claims

1. An image signal restoration and gain control for an image scanning device having an array of photosensitive elements for viewing an original image and generating image signals in response thereto, said image signals each being comprised of an offset potential and an image potential proportional to the intensity of the image portion viewed by said elements, and at least one output register for receiving said image signals, the improvement comprising:

(a) means for generating first and second nonimage signals in said register with each of a predetermined number of image signals;

(b) means for driving said rigister to serially output image signals and said first and second non-image signals from said register;

(c) means for separating said first and second non-image signals from image signals output from said register;

(d) processing means for determining from said first and second non-image signals an offset potential and a signal gain factor required to bring the image signals to a preset signal level;

(e) signal restoring means for removing said offset potential from succeeding image signals output by said scanning device to restore succeeding image signals to a substantially absolute level; and

(f) gain correcting means for adjusting the potential level of said succeeding image signals in accordance with said gain factor to provide image signals at a preset signal level.

2. The control according to claim 1 including

(a) analog-to-digital converter means for converting said first and second signals output by said scanning device to digital signals for input to said processing means;

and

(b) digital-to-analog converter means for converting the signal output of said processing means representing said potential and said signal gain factor to analog signals for use by said signal restoring means and said gain correcting means.

3. The control according to claim 1 including:

(a) buffer means for storing said first and second signals for use by said processing means in determining the potential derived from said scanning device and said signal gain factor;

(b) means for routing the signal output of said scanning device to said buffer means, and to said signal restoring means and said gain correcting means; and

(c) means for removing said first and second signals from the image signals routed to said signal restoring means and said gain correcting means whereby only image signals are input to said signal restoring means and said gain correcting means.

4. The control according to claim 1 in which said signal restoring means comprises subtractor means for subtracting said offset potential from said succeeding image signals.

5. The control according to claim 4 in which said gain connecting means comprises multiplier means for multiplying said succeeding image signals, said multiplier means being downstream of said subtractor means.

6. The method of restoring absolute image signal output levels to the image signals output by an image scanning device and setting signal gain to provide a uniform image signal output level, the scanning device having plural discrete photosensitive elements for generating image signals representative of the intensity of the image viewed by said elements, and at least one output register having a succession of storage gates temporarily holding image signals generated, the steps comprising:

(a) clocking said register to serially transfer image signals therein along said register from one storage gate to the next to said register output;

(b) as said register storage gates are emptied of image signals, providing predetermined black and light level signals in a preset number of empty register storage gates,

(c) continuing clocking of said register after the last image signal has been output from said register to output said dark and light level signals from said register; and

(d) restoring the absolute image signal levels to the image signals output from said register and setting signal gain to provide a uniform signal output level in response to said dark and light level signals.

7. The method of restoring absolute image signal output levels to the image signals output by an image scanning device and setting signal gain for an image viewing device with an array of image viewing elements, and at least one parallel in/serial out register coupled to said viewing elements in parallel for receiving image signals generated by said viewing elements and serially transferring said image signals along said register to an output of said register, the steps of:

(a) providing preset dark and light level signal to said shift register with a preset block of image signals from said viewing elements;

(b) clocking said shift register to transfer said block of image signals together with said preset dark and light level signals serially along said shift register to the shift register output;

(c) segregating said preset dark and light level signals from said block of image signals on output of said signals from said shift register;

(d) determining from said preset dark and light level output signals, the restoration potential required to restore image signals generated by said viewing elements to an absolute level and the gain factor required to produce an image signal output at a predetermined potential level;

(e) removing said restoration potential from the succeeding block of image signals generated by said viewing elements to thereby restore said succeeding block of image signals to said absolute level;

(f) multiplying image signals in said succeeding block of image signals by said gain factor to provide an image signal output at said predetermined potential level; and

(g) repeating steps a-f for each line of image signals.

8. The method according to claim 7 including the steps of:

(a) converting said preset dark and light image signals to binary level signals for use in determining said restoration potential and said gain factor; and

(b) converting the signals representing said restoration potential and said gain factor to analog signals for processing said succeeding block of image signals output by said viewing elements.

9. The method according to claim 7 including the steps of:

(a) separating the signal output of said register into a first signal stream comprising said preset dark and light level signals, and a second signal stream comprising said block of image signals only;

(b) buffering said first signal stream for use in determining said restoration potential and said gain factor; and

(c) processing said second signal stream with said restoration potential and said gain factor.