Offset, gain and bad pixel correction in electronic scanning arrays

• US 4,920,428 A
• Filed: 07/08/1988
• Issued: 04/24/1990
• Est. Priority Date: 07/08/1988
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Lin, Ying-wei, Calarco, Anthony F.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Svihla, Randall S.
• Application Number:
  US07/216,475
• Time in Patent Office: 655 Days
• Field of Search: 358/163, 358/443, 358/448, 358/461, 358/471, 358/474, 358/482, 358/494, 358/213.15, 358/213.16, 358/213.17, 358/213.18
• US Class Current: 358/461
• 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 1/409 Edge or detail enhancement; Noise or error suppression
• CPC Class Codes: H04N 25/673 by using reference sources
• CPC Class Codes: H04N 25/68 applied to defects
• CPC Class Codes: H04N 25/701 Line sensors

Abstract

Method and apparatus to increase the range of correction of photosite offset and gain response. Each photosite is provided with a correction value for offset and gain response based on measured light intensity value, which is stored in memory. Each photosite correction value is also provided with an attribute value which indicates whether the correction values are to be used as stored, whether a shift of the values is appropriate, in accordance with a stored shift value, or whether the photosite is noncorrectable, and accordingly requires the implementation of a bad pixel routine. Depending on the attribute value, logic is enabled to vary the correction values in accordance with a stored routine for shifting the stored correction value, or implementing a bad pixel routine. If the attribute requires a shifted value, the correction value is shifted a number of places in accordance with a shift stored in the decoder, before it is applied. If the attribute indicates that the photosite response is not correctable, a bad pixel correction routine is enabled, to produce substitute data.

Claims

1. An image scanning device having a scanning array with a plurality of photosites detecting light from an image, each photosite producing a response indicative of light intensity, and including means for correction of responsivity of the photosites, comprising:

a memory storing correction values for photosites along the array;

correction means for applying said correction values to the responses from the photosites;

said correction values each including a correction portion and an attribute value;

means to apply said correction portions to the photosite responses;

a decoder for detecting said attribute values;

shift means for shifting said correction portions prior to application to the photosite responses by a selected number of places, said shift means responsive to detection by said decoder of attribute values indicating that shifting should occur.

2. The device as defined in claim 1 wherein each said attribute value has one of a limited number of different values, each different value indicating a different shift to be applied to said shift means.

3. The device as defined in claim 1 and including means for substituting an approximated response for the actual response from a particular photosite.

4. The device as defined in claim 3 wherein said means for substituting an approximated response for the actual response from a particular photosite is responsive to detection by said decoder of attribute values indicating that said substitution should occur.

5. An image scanning device having a scanning array with a plurality of photosites detecting light from an image, each photosite producing a response indicative of light intensity, and including means for correction of responsivity of the photosites, comprising:

a memory storing correction values for photosites along the array;

said correction values each including an offset correction, a gain correction and an attribute value;

offset correcting means for correcting the offsets of the photosite responses in accordance with the stored offset corrections;

gain correcting means for correcting the gains of the photosite responses in accordance with the stored gain corrections;

a decoder for detecting the attribute values;

shift means for shifting said offset corrections and said gain corrections prior to the application thereof to said photosite responses, by a selected number of places, said shift means responsive to detection by the decoder of attribute values indicating that shifting should occur.

6. The device as defined in claim 5 wherein each said attribute value indicates one of a plurality of shift functions, each shift function stored in a memory for use by said shift means.

7. The device as defined in claim 6 wherein each said correction value is a multi bit binary value, including a first number of bits for the gain correction, a second number of bits for the offset correction and a third number of bits for the attribute value.

8. The device as defined in claim 7 wherein said third number of bits for the attribute value is equal to two bits, providing a total of four choices for the attribute value.

9. The device as defined in claim 5 and including means for substituting an approximated response for the actual response from a particular photosite.

10. The device as defined in claim 9 wherein said means for substituting an approximated response for the actual response from a particular photosite is responsive to detection by said decoder of attribute values indicating that said substitution should occur.

11. The device as defined in claim 10 wherein each said correction value is a multi bit binary value, including a first number of bits for the gain correction, a second number of bits for the offset correction and a third number of bits for the attribute value.

12. The device as defined in claim 11 wherein said third number of bits for the attribute value is equal to two bits, providing a total of four choices for the attribute value.

13. The device as defined in claim 12 wherein for the possible choices for the attribute value, a first value indicates that the gain and offset correction should be shifted by 0 places, second and third values indicate that said gain and offset correction should be shifted selected numbers of places respectively, and a fourth value indicates that an approximated photosite response should be substituted for the actual photosite response.

14. A method of correcting the responsivity of photosites in an image scanning device having a scanning array with a plurality of photosites detecting light from an image, each photosite producing a response indicative of light intensity, said method comprising the steps:

storing correction values for correction of the responses of photosites along the array in a memory;

providing each said correction value with an attribute value;

for each photosite response to be corrected, sensing said attribute value;

applying a predetermined shift function to said correction value responsive to said attribute value to derive a new correction value; and

applying said new correction value to said photosite response to be corrected.

15. The method as defined in claim 14 wherein said attribute value is selected from a limited number of values, indicating a choice of predetermined shift functions to be applied.

16. The device as defined in claim 14 and including the step of substituting an approximated response for the actual response from the photosite response to be corrected, responsive to sensing an attribute value indicating that said substitution should occur.

17. A method of correcting the responsivity of photosites in an image scanning device having a scanning array with a plurality of photosites detecting light from an image, each photosite producing a response indicative of light intensity, said method comprising the steps:

storing correction values for correction of offset and gain of photosite responses along the array in a memory;

providing each said correction value with an attribute value, said attribute value having one of a limited number of different values, each different value indicating that a different particular function is to be performed;

for each photosite response to be corrected, automatically selecting one of the different functions in response to detection of the attribute value, at least one of said different functions applying a shift function to said offset and gain correction values to derive new correction values; and

applying said new offset and gain correction values value to said photosite response to be corrected.

18. The method as defined in claim 17 wherein at least one of said different functions represented by said attribute value indicates that substitution of an approximated response for the actual response from a particular photosite, should be performed;

and

substituting an approximated response for the actual response from the photosite response to be corrected.

19. A method of correcting the responsivity of photosites in an image scanning device having a scanning array with a plurality of photosites detecting light from an image, each photosite producing a response indicative of light intensity, said method comprising the steps:

storing binary values for correction of offset and gain of photosite responses along the array in a

20. A method of correcting the responsivity of photosites in an image scanning device having a scanning array with a plurality of photosites detecting light from an image, each photosite producing a response indicative of light intensity, said method comprising:

for each photosite response correctable to a normalized value, storing a correction value in a correction memory to be applied to the photosite response for correction thereof;

said correction value including an attribute value, indicating that a shift function should be applied to said correction value prior to application thereof to the photosite response;

for each photosite response not correctable to a normalized value, storing a distinctive value in said correction memory indicating that an approximated photosite response should be substituted for the actual photosite response;

detecting each said attribute value and enabling a shift function to be applied to the associated correction value in response to the attribute value detected to derive a new correction value;

detecting each said distinctive value and enabling a photosite response approximation function to produce an approximated photosite response;

applying each new correction value to the associated photosite response to correct said photosite response to a normalized value;

substituting each approximated photosite response for the associated actual photosite response not correctable to a normalized value.

21. A method of correcting the responsivity of photosites in an image scanning device having a scanning array with a plurality of photosites detecting light from an image, each photosite producing a response indicative of light intensity, said method comprising:

for each photosite response correctable to a normalized value, storing a correction value in a correction memory to be applied to the photosite response for correction thereof;

for each photosite response not correctable to a normalized value, storing a distinctive value in said correction memory indicating that an approximated photosite response should be substituted for the actual photosite response;

detecting each said distinctive value and enabling a photosite response approximation function to produce an approximated photosite response;

applying each correction value to the associated photosite response to correct said photosite response to a normalized value;

substituting each approximated photosite response for the associated actual photosite response not correctable to a normalized value.