Television – Camera – system and detail – Optics
Reexamination Certificate
1999-08-30
2004-11-09
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Optics
C348S255000, C348S256000, C348S364000, C348S703000
Reexamination Certificate
active
06816200
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to color digital cameras, and more particularly to the processing of pixel information generated by the sensor of a color digital camera.
Digital color cameras are used with computer or other digital processing systems. Such cameras include a sensor, optics, preprocessing electronics, and a cable or other communication link to transfer data to the digital processing system. Digital cameras are made by Connectix, Intel, and others.
In a conventional digital camera, the sensor is often a charge coupled device (CCD) that produces electrical image signals corresponding to an object producing or reflecting light onto the sensor. The electrical image signals are then processed and recorded on a storage medium such as a memory card or other computer readable medium.
A problem encountered with digital cameras is that the sensor can become saturated when the light intensity exceeds the intensity saturation limit of the sensor. When the light level is above the saturation level of the sensor, all further video information, other than the saturation information, is lost. In the past, this problem has been addressed by attempting to manipulate the amount of light striking the sensor or adjusting the sensor itself.
Some of the prior art has attempted to utilize a light intensity measuring circuit which processes data from the sensor and controls movement of an iris. The iris closes to restrict the amount of incident light striking the sensor and opens to allow more incident light to strike the sensor. However, the movement of the iris is slow compared to other means of intensity adjustment. Furthermore, due to its mechanical nature, the iris often closes more than necessary or doesn't close enough, at which point it must be repositioned. The result is slow correction time and fluctuations in brightness, ending in degradation of picture quality. The latter is especially if utilized with video cameras, where the fluctuating brightness is captured. Furthermore, a solitary bright light can cause the iris to close so much that gradation of the dark regions becomes compressed and deteriorated. The same occurs when direct strong light is incident, such as in the case of strong rear lighting.
In a system in which an electric charge corresponding to an amount of light received is accumulated on a photodiode and passed to an n-layer substrate of the sensor, other prior art has sought to draw away excess voltage that flows from the photodiode of the sensor when an excessive amount of light is received. For example, a p-layer is positioned between the photodiode and substrate of the sensor and grounded. This applies a reverse bias voltage to the substrate and p-layer so that a depletion layer is formed between the photodiode and the substrate. Surplus electric charges that overflow from the photodiode, due to an excessive amount of received light, are absorbed in the depletion layer. The voltage of the substrate is then adjusted to accommodate bright and dark scenes. A great disadvantage is that signals from the photodiodes are disrupted in that they must now pass through a layer specifically designed to absorb such signals. Another disadvantage of this is that the voltage of the substrate must be preset based on estimated light conditions, especially disadvantageous for capturing moving video. Another disadvantage is that the voltage of the entire substrate must be changed, not just for the portion receiving the excessively intense light. This results in poor picture quality in that bright areas of light are compensated for but dim spots are not.
Another problem encountered with digital cameras is that picture quality drops as the light intensity falls below a certain level. Furthermore, even images in a dark portion of a scene can be hard to observe if a direct strong light is incident in the scene. The prior art has attempted to correct such problems by monitoring signals from the sensor that have been separated into red, green and blue component signals and have also been gamma corrected. Then, a dark area proportion in a whole picked up image is detected. Next, a portion of the processed original signal is modified to stretch the dark signal region to improve the gradation of the dark area. The processed original signal and the modified signal are combined to output a resultant gradation improved signal. The disadvantage of this prior art method is that separation and gamma correction of the original signal are performed before the dark area is detected. This reduces the accuracy of the detection of the dark area. Further, the dark area is estimated from the processed original signal as a whole, not on a pixel by pixel basis, further reducing the accuracy of the detection of the dark area and making correction of the dark area more difficult.
SUMMARY OF THE INVENTION
In the present invention, an electrical signal from a light sensor is monitored to detect an intensity saturation condition of at least one pixel of the light sensor. The intensity saturation condition of the pixel is at saturation upon receiving light with an intensity above a predetermined level and below saturation upon receiving light with an intensity below a predetermined level. The electrical signal is converted to a digital signal. A reserved bit combination is imposed on the digital signal indicating the intensity saturation condition of the pixel. A control signal is transmitted in response to the bit combination of the digital signal to compensate for the intensity saturation condition of the pixel. An analog to digital converter can be utilized to convert the electrical signal to the digital signal. The analog to digital converter may be programmable to receive electrical signals of different intensities from the light sensor.
Monitoring the electrical signal may include determining whether a voltage of an electrical signal from the light sensor is above a predetermined level. Further, the control signal may reset the predetermined level of voltage. The analog to digital converter may form part of an analog to digital circuit that also includes an AND gate and an OR gate.
The electrical signal from the light sensor may include a series of signals scanned from preselected pixels from an array of pixels of the sensor, or may include a series of signals scanned pixel by pixel from the array of pixels of the sensor.
In one aspect of the invention, an integrated circuit may perform the aforementioned actions. The integrated circuit may form part of a camera module. Optionally, the camera module may further include the light sensor, a lens assembly aligned with the light sensor, and a printed circuit board supporting the integrated circuit.
In another embodiment of the present invention, pixel data from an output of a light sensor is monitored to determine a number of pixels at saturation. The number of pixels at saturation are compared to a predetermined threshold number. The light sensor is reprogrammed to adapt to more brightness if the number of pixels at saturation is above the threshold number. The light sensor may also be programmed to adapt to less brightness if the number of pixels at saturation is below the threshold number.
A saturation detector may be coupled to the light sensor for detecting an intensity saturation condition of the light sensor. The saturation detector can be reprogrammed to adapt to more brightness if the number of pixels at saturation is above the threshold number. The monitoring of the pixel data may be performed without disturbing data flow. Optionally, reprogramming of the saturation detector can be performed in predetermined increments.
In yet another embodiment of the present invention, pixel data from an output of a light sensor is monitored to determine a number of pixels near saturation. The number of pixels near saturation are compared to a predetermined threshold number. The light sensor is reprogrammed to adapt to less brightness if the number of pixels near saturation is below the threshold number.
A saturation detecto
Garber Wendy R.
Hannett James M.
Neostar, Inc.
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