Extending sensor dynamic range by use of a photochromic filter

This application claims priority from U.S. Provisional Application Ser. No. 61/674,427, filed Jul. 23, 2012; the disclosure of which is incorporated herein by reference.

1. Field of Invention

The current invention relates generally to apparatus, systems and methods related to optics. More particularly, the apparatus, systems and methods relate to optics used in cameras. Specifically, the apparatus, systems and methods provide for a photochromic filter which reacts to Ultra-Violet (UV) light, reduces the transmission through the camera optics in bright sunlight; thereby extending the exposure range of the camera without the need for a mechanical iris.

2. Description of Related Art

Traditionally, a camera that uses a complementary metal-oxide-semiconductor (CMOS) image sensor that needs to operate over a wide range of light (bright sunlight to ¼ moon illumination) is not capable of providing a full dynamic range of coverage. Cameras in this situation normally would employ variable iris diaphragms to allow widely for varying light conditions. This mechanical solution creates extreme size, weight, and power constraints. For applications such as the Nano Unmanned Aerial Systems (Nano-UAS) and Micro-Unmanned Aerial Systems (MUAS), the size, weight, and power of a mechanical iris is prohibitive. What is needed is a better optics for use in cameras.

The preferred embodiment of the invention includes a camera that can capture images from variety of brightness ranges. The camera has an optical lens and a photochromic filter. The photochromic filter is placed in front of the lens. The photochromic filter extends an exposure range of the camera without the need for a mechanical iris.

Another configuration is a method of processing an image in a camera. The method begins by passing light through a photochromic filter to product filtered light. Next, the filtered light is passed through optics to produce focused light. An image from the focused light is captured at a sensor. Either a digital or an analog image may be captured.

One or more preferred embodiments that illustrate the best mode(s) are set forth in the drawings and in the following description. The appended claims particularly and distinctly point out and set forth the invention.

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate various example methods, and other example embodiments of various aspects of the invention. It will be appreciated that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the figures represent one example of the boundaries. One of ordinary skill in the art will appreciate that in some examples one element may be designed as multiple elements or that multiple elements may be designed as one element. In some examples, an element shown as an internal component of another element may be implemented as an external component and vice versa. Furthermore, elements may not be drawn to scale.

FIG. 1 illustrates the preferred embodiment of a camera with a photochromic filter.

FIG. 2 is a response curve for a typical photochtromic material such as Corning's Photogray Thin&Dark™ (transmission vs. wavelength).

FIG. 3 is a response curve for Corning's Photogray Thin&Dark™ as a function of temperature.

FIG. 4 illustrates an embodiment of a method for processing an image in a camera.

Similar numbers refer to similar parts throughout the drawings.

FIG. 1 illustrates a sample embodiment of a camera 1 that includes a photochromic filter 3 , optics 5 (e.g., one or more lenses) and image processing logic 7 . “Logic”, as used herein, includes but is not limited to hardware, firmware, software and/or combinations of each to perform a function(s) or an action(s), and/or to cause a function or action from another logic, method, and/or system. For example, based on a desired application or needs, logic may include a software controlled microprocessor, discrete logic like an application specific integrated circuit (ASIC), a programmed logic device, a memory device containing instructions, or the like. Logic may include one or more gates, combinations of gates, or other circuit components. Logic may also be fully embodied as software. Where multiple logics are described, it may be possible to incorporate the multiple logics into one physical logic. Similarly, where a single logic is described, it may be possible to distribute that single logic between multiple physical logics.

The photochromic filter 3 of FIG. 1 may be a separate component from the optics 5 (or a lens) of the camera. In other configurations, the photochromic filter may be deposited directly onto the optics 5 of the camera 1 . The image processing logic 7 processes images collected by the filter 3 and optics 5 . The photochromic filter 3 has a property of transmitting less light through the photochromic filter as the amount of light impinging on the photochromic filter increases. The process logic 7 can include a complementary metal-oxide-semiconductor (CMOS) image sensor or the like and capture images at this sensor. In the preferred embodiment, the images are digitized into digital images, however, in other embodiments they can be analog images. In some configurations, the image processing logic 7 can store the digitized images in a memory 9 in the camera 1 .

A photochromic filter 3 is especially useful in systems such as Nano-UAS and other applications demanding small size, lower power, and low weight. The filter 3 provides for the operation of the camera 1 over a very wide dynamic range from % moonlight to bright, sunlight conditions. Photo-chromic filters exhibit the property of changing transmission based on the amount of UV light that impinges on the filter. In applications such as Nano-UAS, it is desirable to achieve great attenuation of light during the day, and as little attenuation as possible in dusk/dark conditions. As mentioned previously, the selected photo-chromic filter 3 can achieve up to 8× attenuation to the sensor in bright sunlight, while less than 10% attenuation at night. The use of a photochromic filter in this application satisfies a unique set of circumstances and does so without consuming any power or adding any significant weight or volume to the camera 1 .

The Fairchild Imaging (FI) CIS1023 camera was developed for BAE Systems. The CIS1023 camera has excellent performance in very low light and also operates over a wide dynamic range of >10 7 LUX using various electronic settings. Specifically, imaging from ¼ moon (0.01 LUX) to bright sunlight (>100,000 LUX) without the need for a mechanical iris system. This is desirable because, as stated previously, the iris system increases the size and weight of the system. While favorable results were achieved for low light conditions, the camera was unable to operate fully (unsaturated) in bright sunlight. However, photo-chromic materials are easily available as they are used in the eye glass industry. The addition of a photo-chromic material can provide up to 8× attenuation at 68° F. One material that achieved good results is produced by Corning Inc. and is called Photogray Thin&Dark™ the response curve of which (transmission vs. wavelength) is illustrated in FIG. 2 . Additionally, FIG. 3 illustrates the performance of Photogray Thin&Dark™ as a function of ambient temperature. As one can see, the transmission increases as a function of temperature.

Example methods may be better appreciated with reference to flow diagrams. While for purposes of simplicity of explanation, the illustrated methodologies are shown and described as a series of blocks, it is to be appreciated that the methodologies are not limited by the order of the blocks, as some blocks can occur in different orders and/or concurrently with other blocks from that shown and described. Moreover, less than all the illustrated blocks may be required to implement an example methodology. Blocks may be combined or separated into multiple components. Furthermore, additional and/or alternative methodologies can employ additional, not illustrated blocks.

FIG. 4 illustrates a method 400 of method processing an image in a camera. The method 400 begins by passing light through a photochromic filter, at 402 , to product filtered light. Next, the filtered light is passed through optics, at 404 , to produce focused light. In other embodiments, the light may pass through photochromic material on a lens of the optics so that the filtering and the passing through optics occur simultaneously. An image from the focused light is captured, at 406 . Either a digital or an analog image may be captured by a sensor.

In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. Therefore, the invention is not limited to the specific details, the representative embodiments, and illustrative examples shown and described. Thus, this application is intended to embrace alterations, modifications, and variations that fall within the scope of the appended claims.

Moreover, the description and illustration of the invention is an example and the invention is not limited to the exact details shown or described. References to “the preferred embodiment”, “an embodiment”, “one example”, “an example”, and so on, indicate that the embodiment(s) or example(s) so described may include a particular feature, structure, characteristic, property, element, or limitation, but that not every embodiment or example necessarily includes that particular feature, structure, characteristic, property, element or limitation. Furthermore, repeated use of the phrase “in the preferred embodiment” does not necessarily refer to the same embodiment, though it may.