Preventing blur caused by motion of the subject in a digital image

• US 6,441,848 B1
• Filed: 05/19/2000
• Issued: 08/27/2002
• Est. Priority Date: 05/19/2000
• Status: Expired due to Fees

• Current Assignee: Damon L. Tull
• Original Assignee: Damon L. Tull
• Inventors: Tull, Damon L.
• Primary Examiner(s): Garber, Wendy R.
• Assistant Examiner(s): WILSON, JACQUELINE B
• Application Number:
  US09/574,533
• Time in Patent Office: 830 Days
• Field of Search: 348/222, 348/241, 348/297, 348/302, 348/308, 348/294, 348/208
• US Class Current: 348/208.99
• CPC Class Codes: H04N 23/68 for stable pick-up of the scene, e.g. compensating for camera body vibrations
• CPC Class Codes: H04N 23/6811 based on the image signal
• CPC Class Codes: H04N 23/683 performed by a processor, e.g. controlling the readout of an image memory
• CPC Class Codes: H04N 25/533 by using differing integration times for different sensor regions
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components

Abstract

A digital camera has a sensor array which removes subject motion blur by monitoring the rate at which charge is collected by the individual sensors within the array during scene imaging. If the rate at which photons are striking the sensor varies, then the brightness of the image which the sensor is viewing must be changing. When a circuit built in to the sensor array detects that the image brightness is changing, the amount of charge collected is preserved and the time at which brightness change wag detected is recorded. Each pixel corresponding to each sensor where exposure was stopped is adjusted to the proper exposure by linearly extrapolating the exposure the sensor did receive so that the pixel corresponding to the sensor has an intensity corresponding to the dynamic range of the entire image. The image sensing array will preferably be implemented as active-pixel sensor CMOS image sensors.

Claims

1. A digital camera incorporating circuitry for prevention of blur caused by motion of a photographic subject, comprising:

a multiplicity of photosensors arranged in an imaging array, each photosensor developing a first value proportional to the number of photons received by said sensor;

a photographic lens which projects an image onto the imaging array, wherein each photosensor in the imaging array is operatively connected to a circuit which is capable of calculating a second derivative with respect to time of the first value proportional to the number of photons received by said sensor; and

a programmable memory operatively connected to each circuit to store at least one time value for each photosensor corresponding to a length of exposure time for each photosensor, the length of exposure time for each photosensor connected to each circuit determined by the second derivative of the first value meeting a selected criteria which indicates movement was detected.

2. The digital camera of claim 1 wherein the first value is a voltage and each of the photosensors is a photodiode.

3. The digital camera of claim 1 further comprising a liquid crystal shutter in front of each of the multiplicity of photosensors.

4. The digital camera of claim 1 wherein the photosensors are based on CMOS technology.

5. The digital camera of claim 4 where in the photosensors are active-pixel sensors.

6. A method of preventing image blur caused by motion of photographic subjects, comprising the steps of:

forming an image on to an array of photosensors for a selected period of time;

for each sensor during said selected period of time, monitoring at least one value proportional to the rate at which photons are striking the sensor and calculating a second derivative of the at least one value;

for each sensor during said selected period of time, computing a second derivative of the at least one value, and comparing the second derivative with a criteria for determining motion; and

for each sensor during said selected period of time, upon the condition that motion is detected, because the second derivative meets the criteria for determining motion, recording a second value corresponding to the percentage of the selected period of time which has elapsed, and recording the at least one value.

7. The method of claim 6 wherein the step of recording the at least one value comprises closing a liquid crystal shutter so as to preserve the at least one value from change by the incidence of light on said sensor.

8. The method of claim 6 wherein the second value is a voltage which is linearly increasing during the exposure.

9. The method of claim 6 further comprising the step of forming a processed image, wherein each pixel making up the image corresponds to a sensor in the array, and the step of forming the processed image comprises:

where motion was not detected at a sensor, assigning a value to each pixel which is proportional to the light detected by each sensor; and

where motion was detected with respect to a particular sensor assigning a value equal to the recording of the at least one value divided by the percentage of the exposure which has elapsed.

10. A method of preventing image blur caused by motion of photographic subjects, comprising the steps of:

forming an image on to an array of photosensors for a selected period of time;

for each sensor during said selected period of time, monitoring a photon collection rate for the sensor;

for each sensor upon the condition that the photon collection rate varies more than a selected amount, recording a first value proportional to photons collected and recording a second value proportional to the percentage of the selected time which has elapsed; and

for each sensor wherein the photon collection rate does not vary more than a selected amount recording a third value proportional to the photons collected during the entire selected period of time.

11. The method of claim 10 further comprising the step of creating an image in a storage medium, composed of a multiplicity of pixels, each pixel having a one-to-one correspondence with a sensor in the sensor array, wherein when the sensor corresponding to a particular pixel has a first and second value recorded with respect thereto, assigning the particular pixel a value proportional to the first value divided by the second value, and when a particular pixel has a third value recorded with respect thereto assigning the particular pixel a value proportional to the third value.

12. The method of claim 11 wherein the step of recording the first value comprises closing a liquid crystal shutter so the photons collected by the photosensor form a record of the first value.

13. The method of claim 11 further comprising the step of, for each sensor which met the condition that the photon collection rate varies more than a selected amount, and for which the first value and the second value were recorded, recording a fourth value proportional to the photons collected during the entire selected period of time.

14. The method of claim 13 further comprising recording a multiplicity of sequential images to form a movie, storing the movie in a storage medium so that when viewed as a motion picture blur is not removed from individual images, but when viewed as a still, blur is removed from each frame.