Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2000-09-28
2003-02-11
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140AG, 30, 30
Reexamination Certificate
active
06518558
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an optical sensor consisting of an arrangement of pixel units, each comprising an optoelectronic converter for converting the incident radiation into a photoelectric current that depends on intensity and wavelength, an integrator means for deriving a measured value corresponding to the photoelectric current detected, and a controllable storage means for storing the measured value, and a readout control device for readout of the stored measured values relative to one pixel unit, wherein the image striking the sensor can be composed of the measured values based on pixel units.
BACKGROUND OF THE INVENTION
The function of optical sensors is to pick up an image scene and convert it to electric signals so that multiple image segments are generated, differing in weighting of the various spectral components emitted by the scene. For the visible spectral range, the break-down into the blue, green and red spectral ranges has proven especially advantageous, because this spectral weighting permits a colored reproduction of image scenes adapted to the human eye.
Known image sensors with color resolution (A. J. P. Theuwissen, Solid-State Imaging with Charge-Coupled Devices, Kluwer Academic Publishers, Dordrecht, chapter 6.2, p. 2, pp. 165 ff., 1995) are characterized in that more than one signal must be detected for each pixel. As a rule, a three-way division is performed according to the three color components red, green and blue. Only these color signals, taken together, yield the complete color information of a pixel which can be reproduced from the three linearly independent individual signals within the context of a signal transmission link.
Technically, there are multiple possibilities of implementing the aforementioned color resolution. The methods of generating the spectrally weighted image segments can be subdivided roughly into two types. The first,type of such color imaging methods (A. J. P. Theuwissen, Solid-State Imaging with Charge-Coupled Devices, Kluwer Academic Publishers, Dordrecht, chapter 6.2.4, pp. 171 ff., 1995) uses multiple image sensors whose spectral sensitivities differ by the introduction of color filters into the respective beam paths of the individual sensors. This method has the disadvantage that the individual beam paths must be adjusted so that they lead to completely identical images of the scene on the image sensors, because otherwise the reconstructed component color images cannot be combined so that they coincide, which leads to color shifts.
The second type of color imaging method (A. J. P. Theuwissen, Solid-State Imaging with Charge-Coupled Devices, Kluwer Academic Publishers, Dordrecht, chapter 6.2.2, pp. 168 ff., 1995) uses special color image sensors where adjacent pixels for different spectral ranges are made sensitive by applying multiple color filters in a mosaic. Although the component color images of these sensors are thus automatically congruent to one another in this way, the effective resolution with this method drops by a factor of three to four, because three or four adjacent sensor pixels are needed to extract the complete color information of a pixel.
Furthermore, it is also possible to combine the types described previously (A. J. P. Theuwissen, Solid-State Imaging with Charge-Coupled Devices, Kluwer Academic Publishers, Dordrecht, chapter 6.2.4, pp. 171 ff., 1995), where one spectral range, for example, the green component, is recorded by one sensor, while the other spectral ranges, namely the red and blue components in this example, are recorded by a mosaic two-color sensor. This compromise has the disadvantages of both of the basic.types, although to a diminished extent.
An alternative to this is formed by sequential recording of three image segments, representing the red, green and blue components, respectively, of the light assigned to the pixel. The complete image must be read out immediately after exposure of an image segment. Meanwhile, the three component color images are separated from one another in time by the unavoidable readout operations. The duration of the readout operations depends on the number of pixels and consequently on the lateral resolution of the image sensor, so that following an increase in resolution and number of pixels, an increase in readout time can also be expected in this regard. The readout cycles inserted between exposures of component color images consequently make it impossible to record scenes in which there is movement, because then the three image segments no longer coincide. Moreover, this mode of operation of a color sensor does not allow a color image to be recorded within the flash time available for an exposure with a flash apparatus.
The object of the invention is to create an optical sensor which permits operation within a short exposure time.
SUMMARY OF THE INVENTION
The problem is solved according to this invention by the fact that the optoelectronic converter can be controlled selectively with regard to its spectral sensitivity and that each pixel unit comprises an integrator means and at least two storage means arranged in parallel, such that at least two measured values assigned to different spectral ranges of the incident radiation can be detected and stored during the measurement period and then read out together to form the relevant color information for the pixel element.
According to this invention, each of the pixels of a color sensor is equipped with multiple storage cells which permit temporary storage of the color components. In this way, multiple image segments corresponding to the individual color components can be recorded in succession without having to read out the information of the complete image sensor after exposure of an image segment. The time-consuming readout operations can now be shifted to the end of the entire exposure cycle, consisting of multiple successive individual exposures.
The solution achieved according to this invention thus creates an integrating imaging optical color-sensitive image sensor, where each pixel can record the complete color information according to the light striking it and can make it available in electronic form in each subsequent image cycle. The sensor is characterized by two essential properties: each pixel of the sensor structure, which is organized in a matrix, has a plurality of information storage devices to permit temporary storage of the different color information. In addition, the sensor contains controllable detector elements whose spectral sensitivity can be varied. An image sensor according to this invention thus makes it possible to record all the color information of an image scene by immediate successive exposure of the individual color components without requiring a readout operation between the individual exposures. In this way, short exposure times can be implemented with undiminished resolution at the same time. In particular, the present sensor structure is suitable for recording color images within a single exposure cycle of a short-term lighting system (flash apparatus), for example.
A complete image cycle using a color image sensor according to this invention consists of the following steps, for example:
1. Exposure of the first individual image (e.g., red).
2. Storage of the first individual image.
3. Exposure of the second individual image (e.g., green).
4. Storage of the second individual image.
5. Exposure of the third individual image (e.g., blue).
6. Storage of the third individual image.
7. Readout of the first individual image.
8. Readout of the second individual image.
9. Readout of the third individual image.
Essentially any sequence is possible for recording and storage of the measured values belonging to the individual images and their readout. The individual images may also be exposed and stored simultaneously.
The important advantage of a color sensor that operates according to this mode of operation in comparison with a mode of operation wherein the individual exposures are each interrupted by readout of the individual images is the short total
Böhm Markus
Lulé Tarek
Rieve Peter
LandOfFree
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