Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-11-01
2002-08-20
Allen, Stephone (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C378S146000, C345S506000
Reexamination Certificate
active
06437306
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of digital imaging. More specifically, the invention relates to a method for reducing motion artifacts in digital imaging.
BACKGROUND OF THE INVENTION
Cameras have historically recorded image data on film using digital control systems for focus, exposure, film advance and other functions. Recently, digital cameras have been developed which record digital imaging information on storage media such as flash memory cards.
In digital cameras, electronic image sensors are used to capture digital pixel data, where each image is comprised of a plurality of pixels and each pixel is represented by digital pixel information captured by one of the electronic image sensors. These electronic image sensors are typically arranged in a matrix of rows and columns, with each sensor capturing digital pixel information for one pixel in the matrix.
FIG. 1
a
illustrates a single typical electronic image sensor
100
. As shown, the electronic image sensor includes an NMOS transistor
110
having a drain coupled to a high voltage rail Vdd, a gate coupled to an ENABLE signal, and a source coupled to a node
125
. A storage capacitor
130
is also included in the electronic image sensor
100
, the capacitor
130
having a first terminal
132
coupled to a ground voltage Vss and a second terminal
134
coupled to the node
125
. When the ENABLE signal is active, the NMOS transistor
110
is turned on and the storage capacitor is charged by the high voltage rail Vdd. This occurs during a pre-charge phase. Finally, the electronic image sensor
100
includes a photo sensitive diode
135
having a cathode coupled to the node
125
and an anode coupled to the ground voltage Vss.
In operation, the storage capacitor
130
is precharged to a predetermined voltage level by the high voltage rail Vdd whenever the ENABLE signal is active. This is the pre-charge phase. Accordingly, an ENABLE signal is transmitted to all the electronic image sensors
100
in an image array, in order to precharge all the sensors before any digital pixel information is to be captured and stored. After all the sensors have been precharged and the pre-charge phase is complete, the ENABLE signal is disabled and the NMOS transistor
110
in each sensor is turned off. At this point, the capacitor
130
in each image sensor remains fully charged and the image array is ready to capture digital pixel information for an image.
Thereafter, when an image is to be captured, a shutter on the digital camera quickly opens and shuts, thereby allowing a small amount of light to reach the electronic image sensors
100
in the image array. As light hits the photo sensitive diode
135
, the predetermined voltage level which is stored on the storage capacitor
130
begins to drop as current is discharged through the photo sensitive diode
135
toward the ground voltage Vss. Assuming a constant intensity light source directed at the electronic image sensor
100
over a period of time T during which the shutter on the digital camera is open, the storage capacitor
130
will preferably discharge in a linear fashion during the time the shutter on the digital camera is open. Accordingly, if the voltage on the storage capacitor
130
is measured and recorded at several intervals over the time T, a straight line pattern should be observable. This is illustrated in
FIG. 1
b.
Typically, photo sensors used in digital image capturing technology have always been single read/erase—i.e. such cells can only be scanned with image data a single time and read once such that they must be automatically restored to their predetermined precharge voltage (typically 5 Volts) after the cell voltage is read before the next image can be captured. However, designers are now developing non-destructive photo sensing image capture cells in which multiple scans of an image may quickly captured before the cell needs to be restored to its precharged condition. This enables for the quick scanning of an image over a very short period of time while prolonging the life of the photo sensing image capture cells since they do need to be recharged after every read. Preferably, the scans are done at select intervals over a time period T
dis
, wherein the time period T
dis
is equal to the total amount of time it would take for the capacitor in a photo sensing image capture cell to completely discharge to reference or ground voltage Vss.
The voltages on these non-destructive photo sensing image capture cells are measured and recorded relative to the precharged voltage at several select intervals—e.g. the cell voltage may be measured at 1 ms, 2 ms, 4 ms and 8 ms. As explained earlier, assuming a constant intensity light source directed at the photo sensing image capture cell over the period of time T
dis
, during which the shutter on the digital camera is open, the capacitor in the cell will preferably discharge in a linear fashion. Accordingly, if the capacitor voltage is measured and recorded at several intervals over the time period T
dis
, a straight line pattern should be observable.
However, if there is a change in the light intensity applied to the sensors in the image array, which is typically caused by small movements in the image or the camera, then over time the scanned image will not be the same—i.e., the voltage on the capacitor will not discharge in a linear fashion. This phenomenon is known as motion artifact.
With these new digital cameras having multiple scan capability, the multiple scans of the same image are preferably performed at a preferred rate of XXXXXXX PREFERRED RATE HERE. The multiple scans are then combined in order to produce a single clear image. Unfortunately, there is no known way for compensating for motion artifact between the multiple scans. Accordingly, if the camera or image moves between subsequent scans, while the shutter on the digital camera is open, then the combined image will be unclear, foggy and blurred.
Accordingly, what is needed is a method for compensating for motion artifact which may occur between multiple images scans such that the scans may be combined in order to form one clear final image.
SUMMARY OF THE INVENTION
The invention is a process for reducing motion artifacts in digital images which are created from multiple scans using a digital camera. More specifically, the invention is a process for creating a single digital image from multiple scanned images which are scanned over a period time, and therein reducing the effects of motion artifact which may occur between each of the multiple scans by joining fractions of each scanned image using scaling and translation techniques.
In one embodiment of the invention, an image to be captured is scanned several times over a period of time T using a digital camera, with the integration times for each scan increasing by a scalable factor. In a preferred embodiment this scalable factor is a factor of two, such that the image may be scanned at 1 ms, 2 ms, 4 ms and 8 ms from an initial zero time starting point. Using a digital camera, digital pixel data from each of the scans is captured and read from an array of image capture cells. The digital pixel data scans are then combined using scaling and translation techniques designed to reduce the effects of motion artifacts between each of the subsequent scans.
Original scan data or digital pixel data from a plurality of scanned images are each translated into new scan data or new digital pixel data in order to compensate for any motion artifacts which may have occurred between each of the scanned images. In order to translate the original digital pixel data into new digital pixel data, each scanned image is broken down into a number of sections and the centroid or center of intensity for each section in the scanned image is calculated. Translation vectors are then calculated between each subsequently scanned image and a first or best scanned image, wherein the translation vectors account for differences in the position of the centroid or center of intensity between each of the corresponding sect
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