Image sensor artifact elimination

• US 7,880,779 B2
• Filed: 09/28/2006
• Issued: 02/01/2011
• Est. Priority Date: 09/30/2005
• Status: Active Grant

• Current Assignee: STMicroelectronics Limited (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Limited (STMicroelectronics NV)
• Inventors: Storm, Graeme
• Primary Examiner(s): Ye; Lin
• Assistant Examiner(s): DIEP, TRUNG T
• Application Number:
  US11/536,166
• Publication Number:
  US 20070075883A1
• Time in Patent Office: 1,587 Days
• Field of Search: 348241-251, 348/376
• US Class Current: 348/241
• CPC Class Codes: H04N 25/627 Detection or reduction of inverted contrast or eclipsing effects

Abstract

The method and circuit corrects errors in an active pixel sensor which generates an output indicative of illumination intensity and which may experience an error in the output as a result of artifacts which produce an erroneous output. The approach includes determining the output from the pixel, comparing the output with a threshold value, and if the output is lower that the threshold value identifying the existence of an erroneous output and storing a value in a latching device in response thereto. A maximum value is generated in response to the latching device to replace the erroneous output, thereby correcting the error. The present invention switches the system from the analog to digital domain with respect to the issue of artifacts by using a latch to store a value which is then used to replace the actual output if the output is wrong.

Claims

1. A method of correcting errors in an active pixel sensor that generates an output indicative of illumination intensity, the method comprising:

determining the output from the active pixel sensor;

comparing the output with a threshold value;

if the output is lower than the threshold value identifying an erroneous output and storing a value in a latching device in response thereto;

generating a maximum value based upon the value stored in the latching device and correcting the erroneous output by replacing the erroneous output with the maximum value; and

controlling the latching device with a latch control signal so that a select signal output therefrom is used to determine whether an analog-to-digital converter (ADC) selectively outputs one of the maximum value and a converted output from the active pixel sensor.

2. The method of claim 1, wherein determining the output comprises sampling two pixel signals;

wherein comparing comprises comparing a first one of the pixels signals with the threshold value;

wherein the second of the pixel signals is output if the first signal is above the threshold, and the maximum value is output if the first signal is below the threshold.

3. The method of claim 1, further comprising outputting a pixel output through an analog to digital converter (ADC).

4. The method of claim 3, further comprising blocking the pixel output with the maximum value to cause the ADC to output the maximum value.

5. The method of claim 4, wherein generating the maximum value further comprises determining the maximum value from other active pixel sensors in an array of active pixel sensors which includes the active pixel sensor.

6. A method of correcting errors in an array of active pixel sensors for forming an image, wherein each pixel generates an output indicative of illumination intensity thereon which contributes to the image, the method comprising, for each active pixel sensor in the array:

determining the output from the active pixel sensor;

comparing the output with a threshold value;

if the output is lower than the threshold value identifying an erroneous output and storing a value in a latching device in response thereto; and

generating a maximum value based upon the value stored in the latching device and correcting the erroneous output by replacing the erroneous output with the maximum value; and

controlling the latching device with a latch control signal so that a select signal output therefrom is used to determine whether an analog-to-digital converter (ADC) selectively outputs one of the maximum value and a converted output from the active pixel sensor.

7. The method of claim 6, further comprising averaging the outputs of a number of active pixel sensors in the array to reduce resolution of the image.

8. The method of claim 7, wherein generating the maximum value comprises generating the maximum value for outputting based upon at least one of the latching devices and correcting the erroneous output.

9. The method of claim 7, further comprising selecting, as the output, the output from any active pixel sensor which does not include an erroneous output.

10. An active pixel sensor comprising:

a pixel section which is responsive to illumination thereon to produce an output;

a sampling section for sampling outputs from the pixel section to determine the output;

a correction section for identifying if the output is an erroneous output and replacing the erroneous output with a maximum output value;

the correction section including a comparator to compare the output with a threshold value and generate a value based thereon, and a latch to store the value if the output is below the threshold;

the maximum output value being based on the value stored in the latch; and

an analog-to-digital converter (ADC) configured to selectively output one of the maximum value and a converted output from the pixel section based upon a select signal output from the latch.

11. The active pixel sensor of claim 10, wherein the output comprises two pixel signals and the comparator compares a first one of the pixel signals with the threshold value and causes the second of the pixel signals to be output if the first pixel signal is above the threshold, and causes the maximum output value to be output if the first signal is below the threshold.

12. The active pixel sensor of claim 10 further comprising an analog to digital converter (ADC) to output a pixel output.

13. The active pixel sensor of claim 12, wherein the latch value causes the ADC to output the maximum output value.

14. The active pixel sensor of claim 10, wherein the maximum output value is based upon other pixels in an array of pixels which includes the active pixel sensor.

15. An imaging device comprising:

array of active pixel sensors for forming an image, wherein each active pixel sensor generates an output indicative of illumination intensity thereon which contributes to the image, each active pixel sensor including

a pixel section which is responsive to illumination thereon to produce an output,

a sampling section for sampling outputs from the pixel section to determine the output,

a correction section for identifying if the output is an erroneous output and replacing the erroneous output with a maximum output value,

the correction section including a comparator to compare the output with a threshold value and generate a value based thereon, and a latch to store the value if the output is below the threshold,

the maximum output value being based on the value stored in the latch; and

an analog-to-digital converter (ADC) configured to selectively output one of the maximum value and a converted output from the pixel section based upon a select signal output from the latch.

16. The imaging device according to claim 15, wherein the array of active pixel sensors includes an averaging circuit for averaging the outputs of a plurality of active pixel sensors in the array to reduce resolution of the image.

17. The imaging device according to claim 16, wherein the output of each active pixel sensor is compared to the threshold to determine if any active pixel sensor includes an erroneous output, and the maximum output value is based upon at least one of the latching devices.

18. The imaging device according to claim 16, wherein the output of each active pixel sensor is compared to the threshold to determine if any active pixel sensor includes an erroneous output;

and further comprising a logic circuit to generate an output based upon active pixel sensors which do not include an erroneous output.

19. The imaging device according to claim 15, wherein the imaging device defines a digital camera.

20. The imaging device according to claim 15, wherein the imaging device defines a mobile phone including a digital camera.