Method and apparatus for synchronizing the polarization control signal of an AC-polarized arc-discharge lamp with the exposure timing signals of a CCD line sensor

• US 5,495,361 A
• Filed: 05/08/1995
• Issued: 02/27/1996
• Est. Priority Date: 05/08/1995
• Status: Expired due to Term

• Current Assignee: Binding Solutions LLC (Intellectual Ventures LLC)
• Original Assignee: Bayer Intellectual Property GmbH (Bayer AG)
• Inventors: Cresens, Marc L.
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US08/437,459
• Time in Patent Office: 295 Days
• Field of Search: 355/69, 355/67, 355/228, 355/229, 355/233, 358/505, 358/510, 358/509, 358/516, 359/246
• US Class Current: 359/246
• CPC Class Codes: H04N 1/193 using electrically scanned linear arrays , e.g. linear CCD arrays
• CPC Class Codes: H04N 1/40056 Circuits for driving or energising particular reading heads or original illumination means H04N1/401, H04N1/407 take precedence

Abstract

A method and apparatus for synchronizing the line time and color channel exposure timing signals of a CCD line sensor with the polarization control signal of an AC-polarized arc-discharge lamp in a scanning system. The scanning system comprises a scanner illumination system, including an AC-polarized arc-discharge lamp, for illuminating a document to be scanned, and a scanner imaging system for scanning the illuminated document in a line-wise manner. The scanning system of the present invention is designed to minimize brightness fluctuations on the document being scanned, improving the quality of the scanned image.

Claims

1. In a scanning system including an array of light sensitive sensors and a polarized arc-discharge lamp arrangement for illuminating said array of light sensitive sensors during a plurality of successive scan lines, a method for synchronizing a periodic polarization control signal of said polarized arc-discharge lamp arrangement with an exposure time of said array of light sensitive sensors, comprising the steps of:

synchronizing a polarity change of the periodic polarization control signal of said polarized arc-discharge lamp arrangement with a start time of each scan line, said polarity change occurring a predetermined time after the start time of each scan line;

exposing said array of light sensitive sensors for a predetermined length of time during each scan line; and

initiating said exposure step a predetermined time after the start time of each scan line.

2. The method according to claim 1, wherein said plurality of successive scan lines occur at a frequency f_CCD-LINE and said periodic polarization control signal has a polarization frequency f_pol, and wherein, during said synchronization step, said polarization frequency f_pol and said scan line frequency f_CCD-LINE are constrained such that:

space="preserve" listing-type="equation">f.sub.pol =i·

f.sub.CCD-LINE

space="preserve" listing-type="equation">i≧

1,2,3 . . . .

3.

3. The method according to claim 2, wherein, during said synchronization step, said periodic polarization control signal changes polarity at a predetermined time τ

del_pol after the start time of each scan line, each scan line occurring for a time τ

_CCD-LINE, and wherein τ

del_pol and τ

_CCD-LINE are constrained such that;

space="preserve" listing-type="equation">τ

del.sub.pol /τ

.sub.CCD-LINE =CONSTANT.

4. The method according to claim 2, wherein, during said exposing step, said array of light sensitive sensors is exposed for a predetermined length of time τ

_exp, and wherein during said initiating step the exposure of said array of light sensitive sensors is initiated at a predetermined time τ

_del after the start time of each scan line, each scan line occurring for a time τ

_CCD-LINE, τ

_exp and τ

_del being constrained such that;

space="preserve" listing-type="equation">τ

del/τ

.sub.CCD-LINE =CONSTANT

space="preserve" listing-type="equation">τ

exp/τ

.sub.CCD-LINE =CONSTANT

space="preserve" listing-type="equation">0≦

τ

del+τ

exp≦

τ

.sub.CCD-LINE.

5. The method according to claim 4, wherein said array of light sensitive sensors is an x-polychrome CCD line sensor having an x-number of color channels (x≧

1), and wherein;

space="preserve" listing-type="equation">τ

del.sub.j /τ

.sub.CCD-LINE =CONSTANT

space="preserve" listing-type="equation">τ

exp.sub.j /τ

.sub.CCD-LINE =CONSTANT

space="preserve" listing-type="equation">0≦

τ

del.sub.j +τ

exp.sub.j ≦

τ

.sub.CCD-LINE

space="preserve" listing-type="equation">1≦

j≦

x.

6.

8. The method according to claim 1, wherein said polarized arc-discharge lamp arrangement includes a metal halide arc-discharge lamp.

9. The method according to claim 1, wherein said polarized arc-discharge lamp arrangement includes a medium source rare-earth arc-discharge lamp.

6. A method for scanning an image comprising the steps of:

illuminating said image with a polarized arc-discharge lamp;

driving said polarized arc-discharge lamp with a periodic polarization control signal;

scanning successive lines of said illuminated image with a light sensitive sensor arrangement to provide ..t. digital representation of a series of scan lines each scan line occurring for a first predetermined time T₁ ; and

synchronizing a polarity change of said periodic polarization control signal with a start time of each scan line, said polarity change occurring a predetermined time T₂ after the start of each scan line, wherein T₂ /T₁ remains constant.

7. The method according to claim 6 further including steps of:

exposing said light sensitive sensor arrangement to each successive line of said illuminated image, said light sensitive sensor being exposed to each line of said illuminated image for a predetermined time T₃, wherein T3/T1 remains constant; and

initiating said exposure step a predetermined time T₄ after the start time of each scan line, wherein T4/T1 remains constant.

10. The method according to claim 6, wherein said polarized arc-discharge lamp is a metal halide arc-discharge lamp.

11. The method according to claim 6, wherein said polarized arc-discharge lamp is a medium source rare-earth arc-discharge lamp.