Apparatus and method for correcting offset and gain drift present during communication of data

• US 5,519,441 A
• Filed: 07/01/1993
• Issued: 05/21/1996
• Est. Priority Date: 07/01/1993
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Rossi, Robert J., Hayes, Frederick O. III, Lovette, Whynn V., Gusmano, Donald J.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Shalwala, Bipin
• Application Number:
  US08/083,583
• Time in Patent Office: 1,055 Days
• Field of Search: 348/207, 348/209, 348/229, 348/255, 348/264, 348/266, 348/298, 348/294, 348/324, 348/257, 348/678, 348/691, 382/65, 382/67, 358/504, 358/516
• US Class Current: 348/207.99
• CPC Class Codes: H04N 1/401 Compensating positionally unequal response of the pick-up or reproducing head H04N1/403 takes precedence
• CPC Class Codes: H04N 1/4076 dependent on references outside the picture

Abstract

The present invention is directed to a system and method for compensating for offset and gain drift in a fast scan direction during an image forming process. To achieve compensation, the present invention samples a plurality of permanently darkened pixels upon powering up image sensors and circuitry therefor and during a sub-scanning process of an image and feeds this information into an offset value generating circuit. The offset generating circuit continually adjusts a pixel offset voltage according to a difference between sequential samples of the permanently darkened pixel, thereby compensating for fast scan offset drift. The present invention also samples a plurality of active pixels during a scanning of a calibration strip. From this scan, a gain corrective value is calculated. The present invention then samples active pixels during a scanning of a platen background. In response to this sampling, the gain corrective value is continually adjusted according to a difference between sequential samples of the platen background, thereby compensating for fast scan gain drift. The present invention can also compensate and balance transfer functions for a plurality of communication channels in a multi-channel system by using the same target values and same reference signals for each channel.

Claims

1. A method for correcting gain drift in a fast scan direction during an image forming process in an image apparatus having image sensors including a plurality of active pixels and permanently darkened pixels and control circuitry therefor, comprising the steps of:

(a) sampling the plurality of active pixels during a scanning of a calibration strip;

(b) calculating a gain corrective value from the samples collected during the scanning of the calibration strip;

(c) sampling the active pixels during scannings of a platen background;

(d) calculating a difference between sequential samples of the active pixels during the scannings of the platen background; and

(e) adjusting continually the gain corrective value according to the difference and applying the adjusted gain corrective value to image data signals produced by active pixels.

2. The method as claimed in claim 1, further comprising the steps of:

(f) sampling the plurality of permanently darkened pixels upon powering up the image sensors and control circuitry thereof and during a sub-scanning process of an image,

(g) calculating a difference between sequential samples of the permanently darkened pixels upon powering up the image sensors and control circuitry thereof and during the sub-scanning process of the image, and

(h) generating and applying a pixel offset voltage to image data signals produced by active pixels, the pixel offset voltage continually changing according to the difference between sequential samples of the permanently darkened pixel.

3. The method as claimed in claim 1, comprising the steps of:

(f) storing the gain corrective value;

(g) calculating an average gain value from the output sampled in said step (c);

(h) storing the average gain value as a reference value;

(i) sampling an output from each active pixel produced as a result of a scanning of a background between a complete scanning of an image;

(j) calculating an average gain value from the output sampled in said step (i); and

(k) determining a difference between the stored reference value and the average gain value calculated in said step (i);

said step (e) continually adjusting the gain corrective value according to the difference determined in said step (k).

4. The method as claimed in claim 3, further comprising the steps of:

(l) sampling an initial output from each of a plurality of permanently darkened pixels upon powering up image sensors and circuitry therefor;

(m) storing each sampled output as a reference value for the corresponding permanently darkened pixel;

(n) sampling, during a sub-scanning process of an image, an output from each permanently darkened pixel and each active pixel;

(o) determining a difference between the stored reference value and the output of each permanently darkened pixel sampled during the execution of said step (n), and

(p) adjusting an offset level to be applied to each signal output of the active pixels sampled during the execution of said step (n) according to the difference determined in said step (o).

5. The method as claimed in claim 4, wherein said step (m) stores the reference values in a memory.

6. The method as claimed in claim 4, wherein said step (m) stores the reference values as electrical charges in a capacitor bank.

7. A system for balancing an offset characteristic for a multi-channel system in an image apparatus having image sensors including a plurality of active pixels and permanently darkened pixels and control circuitry therefor, comprising:

first means for sampling an output of each channel;

channel offset means for generating and applying a separate channel offset voltage to each channel, said channel offset voltage continually changing according to sequential samples of each channel, thereby balancing an offset characteristic of the multi-channel system;

sampling means for sampling the plurality of permanently darkened pixels upon powering up the image sensors and the control circuitry therefor and during a fast scan of an image;

first difference means for calculating a difference between sequential samples of the permanently darkened pixels upon powering up the image sensors and control circuitry therefor and during the fast scan of the image;

pixel offset means for generating and applying a pixel offset voltage to image data signals produced by the plurality of active pixels according to the difference between sequential samples of the permanently darkened pixel;

said sampling means sampling a plurality of active pixels during a scanning of a calibration strip;

second means, operatively connected to said sampling means, for calculating a gain corrective value from the samples collected during the scanning of the calibration strip;

said sampling means sampling the active pixels during scannings of a platen background;

second difference means for calculating a difference between sequential samples of the active pixels during the scannings of the platen background;

pixel gain means for continually adjusting the gain corrective value according to the difference between sequential samples of the platen background.

8. A system for correcting gain drift in a fast scan direction during an image forming process using a platen background in an image apparatus having image sensors including a plurality of active pixels and permanently darkened pixels and control circuitry therefor, comprising:

sampling means for sampling the plurality of active pixels during a scanning of a calibration strip;

first means, operatively connected to said sampling means, for calculating a gain corrective value from the samples collected during the scanning of the calibration strip;

said sampling means sampling the active pixels during scannings of the platen background;

first difference means for calculating a difference between sequential samples of the active pixels during the scannings of the platen background;

pixel gain means for adjusting said gain corrective value according to the difference between sequential samples of the platen background and applying the adjusted gain corrective value to image data signals produced by active pixels.

9. The system as claimed in claim 8, further comprising:

second means for sampling the plurality of permanently darkened pixels upon powering up image sensors and circuitry therefor and during a fast scan of an image;

second difference means for calculating a difference between sequential samples of the permanently darkened pixels upon powering up the image sensors and control circuitry therefor and during the fast scan of the image; and

pixel offset means for generating and applying a pixel offset voltage to image data signals produced by the plurality of active pixels according to the difference between sequential samples of the permanently darkened pixel.

10. The system as claimed in claim 8, wherein:

said sampling means samples an output from each active pixel produced as a result of an initial scanning of a background;

said first means calculates an average gain value from the output sampled as a result of an initial scanning of the background;

said pixel gain means stores the average gain value as a reference value;

said sampling means samples an output from each active pixel produced as a result of a scanning of the background between complete scannings of an image;

said first means calculates an average gain value from the output sampled as a result of a scanning of the background between a complete scanning of an image; and

said pixel gain means determines a difference between the stored reference value and the average gain value calculated as a result of a scanning of the background between a complete scanning of an image and adjusts the gain corrective value according to the determined difference.

11. The system as claimed in claim 10, further comprising:

second means for sampling an initial output from each of the plurality of permanently darkened pixels upon powering up the image sensors and control circuitry therefor;

third means for storing each sampled output as a reference value for the corresponding permanently darkened pixel;

said sampling means and said second means sampling, during a fast scan of an image, an output from each of the plurality of permanently darkened pixels and each of the plurality of active pixels;

fourth means for determining a difference between the stored reference value and the output of each permanently darkened pixel sampled during a sub-scanning process of an image; and

fifth means for adjusting an offset level to be applied to each signal outputted from of the active pixels sampled during a sub-scanning process of an image according to the difference determined by said fourth means.

12. The system as claimed in claim 11, wherein said third means is a memory.

13. The system as claimed in claim 11, wherein said third means is a capacitor bank.

14. A system for balancing a gain characteristic for a multi-channel system in an image apparatus, comprising:

first means for sampling an output of each channel;

channel gain means for generating and applying a separate channel gain to each channel, said channel gain continually changing according to sequential samples of each channel, thereby balancing a gain characteristic of the multi-channel system;

sampling means for sampling a plurality of active pixels during a scanning of a calibration strip;

second means, operatively connected to said sampling means, for calculating a gain corrective value from the samples collected during the scanning of the calibration strip;

said sampling means sampling the active pixels during scannings of a platen background;

first difference means for calculating a difference between sequential samples of the active pixels during the scannings of the platen background; and

pixel gain means for continually adjusting the gain corrective value according to the difference between sequential samples of the platen background.

15. The system as claimed in claim 14, further comprising:

third means for sampling a plurality of permanently darkened pixels upon powering up image sensors and circuitry thereof and during a sub-scanning process of an image;

second difference means for calculating a difference between sequential samples of the permanently darkened pixels upon powering up the image sensors and control circuitry thereof and during the sub-scanning process of the image; and

pixel offset means for generating a pixel offset voltage, said pixel offset voltage continually changing according to the difference between sequential samples of the permanently darkened pixel, thereby compensating for fast scan offset drift.

16. The system as claimed in claim 15, further comprising:

fourth means for sampling an output of each channel; and

channel offset means for generating and applying a separate channel offset voltage to each channel, said channel offset voltage continually changing according to sequential samples of each channel, thereby balancing an offset characteristic of the multi-channel system.

17. A method for correcting a gain characteristic for a communication channel of a video system, comprising the steps of:

(a) injecting a channel white reference signal onto a channel;

(b) sampling an output of the channel downstream of a point where the channel white reference signal was injected in said step (a);

(c) calculating a gain value for the channel in accordance with the output sampled in said step (b);

(d) applying a gain to the channel according to the calculated gain value, thereby correcting a gain characteristic of the channel;

(e) sampling an initial output from a plurality of active pixels produced as a result of scanning a calibration strip;

(f) calculating a gain corrective value from the output sampled in said step (e);

(g) sampling an output from each active pixel produced as a result of scannings of a platen background between complete scannings;

(i) determining changes between sequential samples of the active pixels during the scannings of the platen background; and

(i) adjusting the pixel gain corrective value according to the changes in the sampled output of step (g).

18. The method as claimed in claim 17, wherein said steps (a)-(d) are repeated periodically so that the gain values can be adjusted for changes in the response characteristics of the channel due to changes in operating conditions.

19. The method as claimed in claim 17, wherein:

said step (a) injects a same channel white reference signal onto each channel of a plurality of channels;

said step (b) samples an output of each channel downstream of a point where the channel white reference signal was injected in said step (a);

said step (c) calculates a separate gain value for each channel in accordance with the output sampled therefrom in said step (b); and

said step (d) applies a separate gain to each channel according to the calculated gain value corresponding to that channel, thereby correcting a gain characteristic of the channel and balancing the gains of the plurality of channels.

20. The method as claimed in claim 17, further comprising the steps of:

(j) sampling an initial output from each of a plurality of permanently darkened pixels upon powering up image sensors and circuitry thereof;

(k) sampling, during a sub-scanning process of an image, an output from each permanently darkened pixel;

(l) calculating a difference between samples of the permanently darkened pixels upon powering up the image sensors and control circuitry thereof and during the sub-scanning process of the image; and

(m) generating a pixel offset voltage according to the difference between the output of each permanently darkened pixel sampled during the execution of said step (j) and the output of each permanently darkened pixel sampled during the execution of said step (k).

21. The method as claimed in claim 20, further comprising the steps of:

(n) injecting a channel black reference signal onto a channel;

(o) sampling an output of the channel downstream of a point where the channel black reference signal was injected in said step (n);

(p) calculating an offset value for the channel in accordance with the output sampled in said step (o); and

(q) applying an offset voltage to each channel according to the calculated offset value corresponding to that channel, thereby correcting an offset characteristic of the channel and balancing the offsets for the plurality of channels;

said steps (n)-(q) being performed before the execution of said steps (a)-(d).

22. The method as claimed in claim 21, wherein said steps (a)-(d) and (n)-(q) are repeated periodically so that the offset values and the gain values can be adjusted for changes in the response characteristics of the channel due to changes in operating conditions.

23. The method as claimed in claim 22, wherein:

said step (n) injects a same channel black reference signal onto each channel of a plurality of channels;

said step (o) samples an output from each channel downstream of a point where the channel black reference signal was injected in said step (n);

said step (p) calculates a separate offset value for each channel in accordance with the output sampled therefrom in said step (o);

said step (a) injects a same channel white reference signal onto each channel of a plurality of channels;

said step (b) samples an output of each channel downstream of a point where the channel white reference signal was injected in said step (a);

said step (c) calculates a separate gain value for each channel in accordance with the output sampled therefrom in said step (b);

said step (q) applies an offset voltage to each channel according to the calculated offset value corresponding to that channel, thereby correcting an offset characteristic of the channel and balancing the offsets for the plurality of channels; and

said step (d) applies a gain to each channel according to the calculated gain value corresponding to that channel, thereby correcting a gain characteristic of the channel and balancing the gains for the plurality of channels.

24. A method for correcting an offset characteristic for a communication channel of a video system, comprising the steps of:

(a) injecting a channel black reference signal onto a channel;

(b) sampling an output of the channel downstream of a point where the channel black reference signal was injected in said step (a);

(c) calculating an offset value for the channel in accordance with the output sampled in said step (b);

(d) applying an offset voltage to the channel according to the calculated offset value, thereby correcting an offset characteristic of the channel;

(i) sampling an initial output from each active pixel produced as a result of scanning a calibration strip;

(j) calculating a gain corrective value from the output sampled in said step (i);

(k) storing the gain corrective value;

(l) sampling an output from each active pixel produced as a result of an initial scanning of a background;

(m) calculating an average claim value from the output sampled in said step (k);

(n) storing the average gain value as a reference value;

(o) sampling an output from each active pixel produced as a result of a scanning of a background between complete scannings of an image;

(p) calculating an average gain value from the output sampled in said step (o);

(q) determining a difference between the stored reference value and the average gain value calculated in said step (p); and

(r) adjusting the gain corrective value according to the difference determined in said step (q).

25. The method as claimed in claim 24, wherein:

said step (a) injects a same channel black reference signal onto each channel of a plurality of channels;

said step (b) samples an output from each channel downstream of a point where the channel black reference signal was injected in said step(a);

said step (c) calculates a separate offset value for each channel in accordance with the output sampled therefrom in said step (b); and

said step (d) applies an offset voltage to each channel according to the calculated offset value corresponding to that channel, thereby correcting an offset characteristic of the channel and balancing the offsets for the plurality of channels.

26. The method as claimed in claim 25, further comprising the steps of:

(e) sampling an initial output from each of a plurality of permanently darkened pixels upon powering up image sensors and circuitry therefor;

(f) storing each sampled output as a reference value for the corresponding permanently darkened pixel;

(g) sampling, during a sub-scanning process of an image, an output from each permanently darkened pixel and each active pixel; and

(h) generating a pixel offset voltage according to a difference between the stored reference value and the output of each permanently darkened pixel sampled during the execution of said step (g).

27. The method as claimed in claim 24, further comprising the steps of:

(s) injecting a channel white reference signal onto a channel;

(t) sampling an output of the channel downstream of a point where the channel white reference signal was injected in said step (s);

(u) calculating a channel gain value for the channel in accordance with the output sampled in said step (t); and

(v) applying a gain to the channel according to the calculated channel gain value, thereby correcting a gain characteristic of the channel.

28. The method as claimed in claim 27, wherein:

said step (a) injects a same channel white reference signal onto each channel of a plurality of channels;

said step (b) samples an output of each channel downstream of a point where the channel white reference signal was injected in said step (a);

said step (c) calculates a separate channel gain value for each channel in accordance with the output sampled therefrom in said step (b); and

said step (d) applies a separate gain to each channel according to the calculated channel gain value corresponding to that channel, thereby balancing a gain characteristic of the plurality of channels.