System and methods for dynamic range extension using variable length integration time sampling

• US 20050145780A1
• Filed: 02/17/2005
• Published: 07/07/2005
• Est. Priority Date: 10/15/2002
• Status: Active Grant

• Current Assignee: Dmitry M. Sagatelyan, Tor Slettnes
• Original Assignee: Dmitry M. Sagatelyan, Tor Slettnes
• Inventors: Sagatelyan, Dmitry M., Slettnes, Tor
• Granted Patent: US 7,067,791 B2
• Time in Patent Office: Days
• US Class Current: 250/214.A
• CPC Class Codes: G01J 1/42 using electric radiation detectors optical or mechanical part G01J1/04; by comparison with a reference light or electric value G01J1/10
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/645 Specially adapted constructive features of fluorimeters
• CPC Class Codes: G01N 2201/1241 Multirange
• CPC Class Codes: H03F 3/08 controlled by light
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/73 by influencing the exposure time
• CPC Class Codes: H04N 23/741 by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors
• CPC Class Codes: H04N 23/76 by influencing the image signals
• CPC Class Codes: H04N 25/589 with different integration times, e.g. short and long exposures

Abstract

A photo-detector generated signal is measured as a sample set comprising a long signal and a short signal. The short signal is scaled to the value of the long signal if the long signal exceeds a dynamic range associated with the photo detector. In one embodiment, the short signal is obtained during a short time interval that is at the approximate middle of a long time interval such that the short and long intervals share a common median time value. Given such symmetry, an approximately linear signal yields a proportionality parameter between the long and short signals thereby allowing the short signal to be scaled. The proportionality parameter facilitates determination of an integration independent component of the photo detector signal that should be removed from the measured long and short signals before scaling. A plurality of sample sets can also be processed such that each sample set overlaps with its neighboring sample set, thereby increasing the effective number of sample sets.

Claims

1. A method of sampling a photo-detector signal, the method comprising:

performing a series of integrations of the photo-detector signal wherein the series comprises alternating long and short integration intervals; and

forming a plurality of overlapping sample sets wherein each sample set comprises integrations performed during at least one long interval to yield a first signal value and at least one short interval to yield a second signal value and wherein each sample set overlaps with its neighboring sample set by at least one of the long or short intervals.

2. The method of claim 1, wherein the sample set comprises integrations performed during a sequence of long-short-long time intervals so as to overlap with its neighboring sample set by at least one of the long intervals thereby increasing the number of sample sets obtained from the series of integrations.

3. The method of claim 2, wherein the sample set further comprises idle intervals so as to yield a sequence of long-idle-short-idle-long intervals.

4. The method of claim 1, wherein the first signal value comprises a sum of integrations of the photo-detector signal performed during the long-short-long intervals, and wherein the second signal value comprises the integration of the photo-detector signal performed during the short interval such that the first and second signal values share a common median time value.

5. The method of claim 1, wherein for an approximately linear photo-detector signal, the common median time value of the first and second signal values allow the second signal to be scaled to the first signal value when the first signal value exceeds a specified dynamic range.

6. The method of claim 1, wherein the first signal value comprises a sum of integrations of the photo-detector signal performed during the two long intervals while excluding the short interval, and wherein the second signal value comprises the integration of the photo-detector signal performed during the short interval such that the first and second signal values share a common median time value.

7. The method of claim 1, wherein the first signal'"'"'s signal to noise ratio is improved by excluding a noise associated with the photo-detector during the short component wherein the noise includes a shot noise and a read noise.

8. The method of claim 1, wherein the photo-detector signal comprises a CCD, a photomultiplier, or a semiconductor based device.