Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1998-07-21
2003-12-16
Le, Vu (Department: 2612)
Television
Camera, system and detail
Solid-state image sensor
C348S362000, C348S301000, C348S308000
Reexamination Certificate
active
06665010
ABSTRACT:
BACKGROUND
The invention relates to controlling integration times of pixel sensors.
Referring to
FIG. 1
, a typical digital camera
12
uses an imager
18
to electrically capture an optical image
11
. To accomplish this, the imager
18
typically includes an array
13
(see
FIG. 2
) of photon sensing, pixel sensors
20
. During an integration time, or interval, each pixel sensor
20
typically measures the intensity of a portion, or pixel, of a representation of the image
11
that is focused (by optics of the camera
12
) onto the array
13
. To accomplish this, the pixel sensor
20
accumulates light energy that is received from the associated pixel and at the expiration of the integration interval, indicates (via an analog voltage, for example) the accumulated energy which also, in turn, indicates an intensity of light of the pixel.
The camera
12
typically processes the indications from the pixel sensors
20
to form a frame of digital data (which digitally represents the captured image) and transfers the frame (via a serial bus
15
, for example) to a computer
14
for processing. For video, the camera
12
may successfully capture several optical images and furnish several frames of data, each of which indicates one of the captured images. The computer
14
may then use the frames to recreate the captured video on a display
9
.
Referring to
FIG. 2
, the sensors
20
may be arranged in rows and columns. This arrangement allows column
22
and row
24
decoders to selectively retrieve the indications from the sensors
20
after the integration interval. The decoders
22
and
24
route the selected indications to signal conditioning circuitry
26
which might include, for example, analog-to-digital converters (ADCs) and circuitry to compensate for noise that is introduced by the sensors
20
. The signal conditioning circuitry
26
may furnish the resultant data signals to an output interface
28
which includes circuitry for interfacing the imager
18
to other circuitry of the camera
12
. A control unit
30
may coordinate the above-described activities of the imager
18
.
The duration of the integration interval determines how long the pixel sensors
20
sense, or are exposed to, the optical image
11
. In this manner, if the duration of the integration interval is too short, the pixel sensors
20
may be underexposed, and if the duration is too long, the pixel sensors
20
may be overexposed.
The camera
12
typically controls the duration of the integration interval based on the camera's measurement of the brightness of the optical image
11
. In this manner, for bright lighting conditions, the camera
12
uses a shorter duration (to prevent overexposure of the pixel sensors
20
) than for low lighting conditions (to prevent underexposure of the pixel sensors
20
). The camera
12
may measure the brightness of the image based on a histogram of sampled intensities.
The histogram represents a distribution of intensity levels of the pixel image over an available dynamic range (a range spanning from an intensity level of 0 to an intensity level of 255, for example). If the intensity levels are distributed over a large portion of the available dynamic range, then the image appears more vivid than if the intensity levels are distributed over a smaller portion of the available dynamic range. For example, a histogram
40
(see
FIG. 3
) for an image having an unacceptably low contrast exhibits a higher concentration of the lower intensities than a histogram
41
(see
FIG. 4
) for an image that has an acceptable contrast and thus, a larger dynamic range.
For purposes of determining the proper duration for the integration interval, the camera
12
may enter a calibration, or premetering, mode during which the camera
12
uses an iterative process to determine the duration. The camera
12
typically chooses a predetermined duration of the integration interval to sample intensities of the image
11
by using a small group of the pixel sensors
20
. In this manner, the camera
12
may statistically evaluate a histogram of these intensities and based on this evaluation, upwardly or downwardly adjust the predetermined duration before sampling intensities again. The camera
12
continues the iterations until the camera
12
determines the duration of the integration interval is appropriate. However, this iterative process may consume a significant amount of time which may adversely affect the click-to-capture performance time of the camera. Furthermore, this delay may prevent the camera
12
from responding to changing lighting conditions in a timely fashion.
As described above, the camera
12
may set the duration of the integration interval based on the intensities indicated by a small group of the pixel sensors
20
. However, the intensities sensed by this small group may not accurately represent the range of intensities of the optical image
11
. For example, the small group may sense bright pixels of an otherwise dark image, and as a result, the camera
12
may use an integration interval that is too short to adequately capture the image.
Thus, there is a continuing need for a digital imaging system that addresses the to problems stated above.
SUMMARY
In one embodiment, an imager includes groups of pixel sensing units and a control circuit. Each group of the pixel sensing units integrates photons from a different associated portion of an optical image over an integration interval for the group. The control circuit independently regulates the integration intervals for the groups.
In another embodiment, a method includes integrating photons from an optical image to capture a pixel image. An energy that is indicated by the integration is determined. The times for the energy to reach different predetermined threshold levels are measured, and a duration of the integration is regulated based on the measured times.
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Bell Cynthia S.
Morris Tonia G.
Le Vu
Trop Pruner & Hu P.C.
Ye Lin
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