PATENT DOCUMENT

Publication Number: US-8405727-B2
Application Number: US-23889808-A
Country: US
Kind Code: B2

Title: Apparatus and method for calibrating image capture devices

Abstract:
An apparatus and method are disclosed for calibrating image capture devices, such as the type used in electronic devices. In some embodiments, the electronic device may include at least one array of pixels and a memory coupled to the at least one array of pixels. The electronic device may further include a central processing unit (CPU) coupled to the memory and at least one color filter optically coupled to the at least one array of pixels. The memory may further include one or more storage locations that include a response of the at least one color filter to one or more predetermined wavelengths from a target test source, as well as, one or more storage locations that include a response of one or more baseline color filters.

Claims:
What is claimed is: 
     
       1. An electronic image capture device, comprising:
 an array of pixels configured for receiving wavelengths of light; 
 a filter coupled to the array of pixels and configured for filtering the wavelengths of light; 
 a processor coupled to the array and configured for:
 selecting a correction value based on data received from the array and a baseline value, the baseline value being a ratiometric comparison of intensities of the wavelengths of light passing through a baseline filter; and 
 applying the correction value to an image captured by the device. 
 
 
     
     
       2. The electronic device of  claim 1 , wherein the baseline value is a ratiometric comparison of an intensity of a first one of the wavelengths of light to an intensity of a second one of the wavelengths of light. 
     
     
       3. The electronic device of  claim 1 , wherein the correction value comprises at least one correction constant. 
     
     
       4. The electronic device of  claim 1 , wherein one of the wavelengths includes a wavelength in the infrared spectrum. 
     
     
       5. The electronic device of  claim 1 , wherein:
 the filter comprises an infrared blocking filter; and 
 one of the wavelengths includes a wavelength near the cut-off wavelength of the infrared blocking filter. 
 
     
     
       6. The electronic device of  claim 1 , wherein the baseline value is updated when a firmware executed by the processor is updated. 
     
     
       7. The electronic device of  claim 1 , wherein a response of the filter is calculated based on ratios of the wavelengths measured from a plurality of wavelength emanating regions. 
     
     
       8. The electronic device of  claim 1 , wherein the response of the filter is stored in one or more memory locations after the electronic device has been manufactured. 
     
     
       9. The electronic device of  claim 1 , wherein the data received from the array is measured in response to the wavelengths. 
     
     
       10. A method for calibrating an electronic image capture device, comprising:
 storing, in a memory within the electronic device, a first color response of a baseline filter; 
 storing, in the memory within the electronic device, a second color response of a filter located within the electronic device to a light source having predetermined wavelengths; 
 comparing a first ratiometric value based on intensities of the first color response of the baseline filter with a second ratiometric value based on intensities of the second color response of the filter located within the electronic device,
 wherein the first ratiometric value is determined based on a comparison of intensities of the predetermined wavelengths of light passing through the baseline filter; and 
 
 based on the comparison, adjusting the second color response of the filter located within the electronic device. 
 
     
     
       11. The method of  claim 10 , further comprising exposing the electronic device to a target test structure after the electronic device has been manufactured. 
     
     
       12. The method of  claim 11 , wherein the target test structure comprises calibration patterns that include a plurality of wavelength emanating regions. 
     
     
       13. The method of  claim 12 , further comprising measuring the intensity ratios of the filter located within the electronic device from at least two of the plurality of wavelength emanating regions. 
     
     
       14. The method of  claim 13 , wherein measuring the ratios of color responses is executed in a processor within the electronic device. 
     
     
       15. The method of  claim 14 , further comprising updating the first color response of the baseline filter when a firmware executed by the processor is updated. 
     
     
       16. The method of  claim 10 , wherein at least one of the predetermined wavelengths of light is in the infrared range. 
     
     
       17. The method of  claim 10 , further comprising determining the first color response of the baseline filter based on the light source having predetermined wavelengths. 
     
     
       18. A system for calibrating an image capture device comprising:
 at least one color filter that is operative to react to a combination of a calibration pattern and a light source that is optically coupled to the at least one color filter; 
 a memory coupled to the at least one color filter, the memory comprising one or more storage locations; and 
 a processor accessing the memory; 
 wherein the calibration pattern comprises two or more regions that emanate a plurality of predetermined wavelengths; 
 wherein the two or more regions that emanate a plurality of predetermined wavelengths are oriented in substantially close physical proximity within the calibration pattern; and 
 wherein a comparison between outputs of at least two of the two or more regions that emanate predetermined wavelengths is stored in one or more storage locations of the memory. 
 
     
     
       19. The system of  claim 18 , wherein a response of one or more baseline color filters to the one or more regions that each emanates a predetermined wavelength is stored in the one or more storage locations of the memory. 
     
     
       20. The system of  claim 19 , wherein the comparisons between the outputs of at least two of the two or more regions that emanate predetermined wavelengths are ratiometric comparisons.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit to U.S. Provisional Patent Application No. 61/049,716, filed on May 1, 2008 and entitled “Apparatus and Method for Calibrating Image Capture Devices,” the disclosure of which is hereby incorporated herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates generally to image capture devices, and more particularly to an apparatus and method for calibrating image capture devices. 
     2. Background 
     Electronic devices are ubiquitous in society and can be found in everything from wristwatches to cellular telephones. With the proliferation of integrated circuitry, these electronic devices are becoming more and more sophisticated. Many of these electronic devices—especially consumer electronic devices—include the ability to take pictures using an image capture device embedded within the electronic device. The actual image capture devices employed in these electronic devices are often solid-state. Examples of image capture devices are charge coupled devices (CCDs) and complementary metal oxide semiconductor (CMOS) sensors devices. These solid-state type image capture devices are often cost effective (which may be especially important when being implemented in consumer electronics) because they are manufactured using semiconductor fabrication principles. 
     One disadvantage in utilizing solid state image capture devices, however, is that the color balance may vary between image capture devices due to manufacturing variations among the image capture devices. In other words, despite two electronic devices (such as two CCD cameras) being the same make and model, they may have different color balances so that pictures taken of the same object by each device may depict color variations when compared to one another. Color imbalances of this type may be particularly acute for the red content of the image, due to variations in the red and infrared (IR) content of the illumination source, and the effect of the IR blocking filter. 
     Accordingly, there is a need for calibrating the color response of image capture devices. 
     SUMMARY 
     An apparatus and method are disclosed for calibrating image capture devices, such as the type used in electronic devices. The electronic device may calibrate the response of its pixel and/or pixel processing path to certain wavelengths of light (e.g., the IR wavelength) based upon comparisons between the response of its color filter to the response of a baseline color filter. In some embodiments, the calibration of the electronic device may occur after the electronic device has been manufactured, which allows the electronic device to be calibrated without disassembling the electronic device. 
     In certain embodiments, the electronic device may include at least one array of pixels and a memory electronically coupled to the at least one array of pixels. The electronic device may further include a central processing unit (CPU) coupled to the memory and at least one color filter optically coupled to at least one array of pixels. The memory may store a response of at least one color filter to one or more predetermined wavelengths from a target test source, as well as, further storing a response of one or more baseline color filters to one or more predetermined wavelengths from a target test source. 
     Another embodiment takes the form of a method for calibrating an image capture device of an electronic device. The method may include the acts of storing, the color response of one or more baseline filters to a source of light having one or more predetermined wavelengths, storing the color response of one or more filters located within the electronic device to the source of light having one or more predetermined wavelengths, comparing the color response of the one or more baseline filters with the color response of the one or more filters located within the electronic device, and adjusting the response of one or more filters located within the electronic device to correspond to the response of the one or more baseline filters. 
     Yet another embodiment takes the form of a system for calibrating an image capture device configured to react to a light source of a predetermined wavelength, a calibration pattern optically coupled to the light source, at least one color filter optically coupled to the calibration pattern, a memory coupled to the at least one color filter, the memory comprising one or more storage locations, and a central processing unit (CPU) coupled to the memory. The calibration pattern further comprises one or more regions that emanate a predetermined wavelength, where the one or more regions that emanate a predetermined wavelength may be oriented in substantially close physical proximity within the calibration pattern, and where comparisons between at least two of the one or more regions that emanate a predetermined wavelength may be stored in one or more storage locations of the memory. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an electronic device with an exemplary image capture device. 
         FIG. 2A  illustrates an exemplary system that may used to test and calibrate the color response of an image capture device. 
         FIG. 2B  illustrates an exemplary calibration pattern. 
         FIG. 2C  represents an alternative calibration pattern. 
         FIG. 2D  depicts yet another alternative calibration pattern. 
         FIG. 3A  illustrates an exemplary response of the color filter from the image capture device (dashed line) superimposed on spectral responses of an exemplary calibration pattern. 
         FIG. 3B  represents a color filter characteristic based upon empirical measurements of a baseline color filter. 
         FIG. 4  illustrates an exemplary flowchart to calibrate one or more image capture devices. 
     
    
    
     The use of the same reference numerals in different drawings indicates similar or identical items. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following discussion describes various embodiments that may improve camera calibration and, thus, potentially camera performance. Although one or more of these embodiments may be described in detail, the embodiments disclosed should not be interpreted or otherwise used as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application. Accordingly, the discussion of any embodiment is meant only to be exemplary and is not intended to intimate that the scope of the disclosure, including the claims, is limited to these embodiments. 
     One embodiment takes the form of an electronic device that may adjust the response of its pixel and/or pixel processing path to certain wavelengths of light (such as the IR wavelength) based upon comparisons between the response of its color filter and stored data, which in some embodiments, corresponds to the response of a baseline color filter. In some embodiments, adjustment of the response of the electronic device&#39;s pixel and/or pixel processing path may occur after the electronic device has been manufactured, which allows the electronic device to be calibrated without disassembly. As one example, the response of a pixel processing path may be changed based on one or more measured properties of an optical component or components of the electronic device, such as an infrared filter. That is, a correction value may be determined by comparing the response of the IR filter against an ideal IR filter. This correction value may then be used to change the response of the pixel processing path to account for differences between the device&#39;s IR filter and the ideal IR filter, as described in more detail below. 
       FIG. 1  depicts an exemplary electronic device  100 . In this embodiment, the electronic device  100  may be any of many different types of consumer electronic devices, such as computers, cellular telephones, televisions, wristwatches, and/or standalone camera units to name but a few. 
     An image capture device  105  may be incorporated within the electronic device  100  and may allow the electronic device  100  to have camera-type functionality (e.g., permitting the device to take photographs). The actual image capture device  105  implemented in the electronic device  100  may take various forms and may include one or more arrays of pixels  106 , where each pixel has a certain photoelectric response when exposed to an object  102 . In some embodiments, the image capture device  105  includes CCDs and/or CMOS image sensors fabricated according to semiconductor manufacturing principles. 
     Each of the pixels in the array  106  may be pan-chromatic. That is, in the absence of any color filter, each pixel may respond to all wavelengths of visible light (although not necessarily equally to all such wavelengths). As a result the image capture device  105  may further include one or more filters  110 A-B. The filters  110 A-B may include an IR filter  110 A as well as a color filter  110 B, where light is filtered by the IR filter  110 A prior to being filtered by the color filter  110 B. In embodiments where the image capture device is fabricated according to semiconductor manufacturing principles, the filters  110 A-B may be integrated within the image capture device  105  at the time the image capture device  105  is manufactured. Furthermore, in some embodiments, the color filter  110 B may be an array of red, green, and blue filters arranged in a Bayer-type array pattern—i.e., with twice as many green items in the array as the red and blue so as to mimic the human eye&#39;s greater ability to resolve green light. Essentially, the color filter  110 B restricts the band of wavelengths of light that may impact the pixel, which in turn makes each such pixel function as if it were sensitive only to that particular set of wavelengths. 
     During operation, the electronic device  100  may focus on the object  102  through an optional lens  115 . The combination of the filters  110 A-B and the array  106  may render a “raw” image, where the incoming light to each pixel in the array  106  has been filtered to produce less than all of the colors that make up an image. For example, in some embodiments, each pixel in the array  106  may detect/output one color chosen from the group of red, green, and blue ( the “RGB” color grouping). Since these raw images may contain less than all of the colors required to render the full color image, one or more de-mosaicing algorithms may be implemented. A de-mosaicing algorithm is a digital image process used to interpolate a complete image from the partial raw image received from the color-filtered image sensor. Thus, even though each pixel may render only a single primary color, such as red, green, or blue, the de-mosaicing algorithm may estimate, for each pixel, the color level of all color components rather than a single color component. 
     In other embodiments, alternative arrangements for the filters  110 A-B and/or the arrays  106  may be implemented. For example, the filter  110  may be a Cyan-Yellow-Green-Magenta filter or a Red-Green-Blue-Emerald filter, each of which may require similar de-mosaicing. In still other embodiments, the arrangements for the filters  110 A-B and/or the arrays  106  may not require de-mosaicing. For example, some embodiments may include a Foveon X3 sensor or the like, which layers red, green, and blue sensors vertically rather than using a mosaic. Other embodiments may utilize three separate CCDs, one for each color, with each one having a separate color filter. 
     If de-mosaicing or other algorithms are executed by an embodiment, they may be stored in a memory  120  and executed by a central processing unit (CPU), graphics processor or other suitable processor  125 . (The term “CPU” is intended to encompass all suitable processors.) In some embodiments, the memory  120  and/or CPU  125  may be implemented with the image capture device  105 . For example, if the image capture device  105  is fabricated using semiconductor manufacturing, then the memory  120  and/or CPU  125  may be implemented as part of the same integrated circuit. As will be described in detail below, one or more color-balancing algorithms also may be stored in the memory  120 . 
     Implementing the filters  110 A-B as part of the same circuitry as the array  106  and the other components within the image capture device  105 , in general, may make the electronic device  100  cheaper to build, which may be a design consideration in consumer electronic devices. While some embodiments utilize these more cost effective color filter construction, the ability to filter each of the different colors may vary between electronic devices. Thus, in the embodiments where the filters  110 A-B are configured to provide RGB filtering, one or more of the red, green, or blue colors may not be as intense, post-filtering in the raw image. As a result, even though two electronic devices (for example, cellular telephones or web cameras) may be the same make and model, they may produce different images, color-wise, of the same object. For example, in many commercial electronic devices, the amount of light passing through the red filter elements will depend on the response of the IR filter  110 A, which typically blocks light above 650 nanometers while passing light below 650 nanometers. The manufacturing tolerance on the IR filter  110 A is typically +/−10 nm, which may allow appreciable variation in light transmission through the red filter elements, given the typical pass band of the red filters. 
     For the ease of discussion the remainder of this disclosure will focus on the response of the filters  110 A-B with regard to variatons in the IR filter  110 A. However, it should be noted that this disclosure applies equally to the response of the filters  110 A-B to any wavelength of light. 
       FIG. 2A  illustrates an exemplary system  200  that may used to test and calibrate the color response of the image capture device  105  and/or the IR filter  110 A to wavelengths of IR light. In some embodiments, the system  200  may be capable of testing and calibrating the electronic device  100 , for example, in a manufacturing environment as part of the final electronic testing of the electronic device  100  prior to sale. This may allow the IR filter  110 A (which may be integrated within the image capture device  105  in some embodiments) to be tested and calibrated without disassembling the electronic device  100 . In other embodiments, the system  200  may be used after the electronic device  100  has been sold, (for example, at a repair shop), to re-test and/or re-calibrate if the electronic device  100  is suspected of malfunctioning. 
     Referring to the system  200 , each of the electronic devices  100  may be exposed to a target test structure  205 . The target test structure  205  may include a light source  210  of a controlled wavelength. For example, a low temperature incandescent bulb may be used in some embodiments. Also, or alternatively, the target test structure  205  may include a predetermined calibration pattern  215  with one or more openings  220  that allow light from the light source  210  to emanate toward the image capture device  105  as shown. In some embodiments, the light may shine through the one or more openings  220 , while in other embodiments, the light may reflect off the one or more openings  220 . 
     Each of the openings  220  may be configured to emanate a desired wavelength of light. During operation of the system  200 , the electronic devices  100  may be exposed to the light emanating from the calibration pattern  215  such that the color response of the image capture device  105  and/or filters  110 A-B to IR wavelength of light may be characterized as explained below. This characterization data may be stored in the memory  120 . Software or firmware executing on the CPU  125  may then utilize this characterization data to correct for the color filter&#39;s response to IR light as described below. 
     The calibration pattern  215  may be implemented in a variety of ways. In some embodiments, a GRETAG MACBETH® color chart may be used. Other embodiments include the exemplary calibration pattern  250  shown in  FIG. 2B . 
     Referring to  FIG. 2B , the calibration pattern  250  may include one or more reference points  255 . While the color of the reference points may vary in different implementations, in the exemplary calibration pattern  250  shown in  FIG. 2B , the one or more reference points  255  are black and white in color. The white and black reference points  255  may be used by the image capture device  105  as the upper and lower limits respectively of possible colors visible to the electronic device  100 . The calibration pattern  250  also may include a large grey or neutral region  263  that facilitates the auto-expose and auto-white balance features of the image capture device  105  during calibration. 
     Furthermore, the calibration pattern  250  may include one or more colored zones  270 ,  275 , and  280 . These color zones  270 ,  275 , and  280  may be configured to emanate predetermined wavelengths of light in order to test the response of the image capture device  105 . A first color zone  270  may be configured to emit a wavelength from approximately 620 nanometers to 640 nanometers. A second color zone  275  may be configured to emit a wavelength from approximately 640 nanometers to 660. Likewise, a third color zone  280  may be configured to emit a wavelength from approximately 660 nanometers to 680 nanometers. As one example, an ideal transmission characteristic for the IR filter  110 A in response to exposure to the calibration pattern  250  may include 100% transmission for 400-640 nanometers, 50% transmission at 650 nanometers, and 0% transmission from 660 nanometers to infinity. 
     In the embodiment shown in  FIG. 2B  three such color zones are shown. However, any number of color zones in various orientations are possible. For example,  FIGS. 2C and 2D  illustrate alternative calibration patterns  285  and  290  having different orientations for the of the color zones. 
     The transmittance of the IR filter  110 A to each of the color zones  270 ,  275 , and  280  is represented in  FIG. 3A . Referring to  FIG. 3A , the normalized intensity transmittance for each of the color zones  270 ,  275 , and  280  is represented as the abscissa axis. The ordinate axis represents the wavelength λ of the light associated with each of the color zones  270 ,  275 , and  280 . As can be appreciated by inspection of  FIG. 3A , the light emanating from each of the color zones  270 ,  275 , and  280  may be centered about the exemplary wavelengths (640, 650, and 660 nanometers respectively). The actual transmittance transfer function  305  of the color filter  110 , which may represent the wavelengths actually “seen” by the image capture device  100 , is also shown. 
     In the present example, the manufacturing tolerance of the IR cut-off wavelength for the IR filter  110 A may be 650±10 nanometers as indicated by the double-sided arrows around the 650 nanometer wavelength in  FIG. 3A . This variance in manufacturing tolerance may cause the response of the filters  110 A-B to vary between electronic devices  100 . In other words, the amount of red “seen” emanating from the color zone  275  (which emits light from 640 to 660 nanometers) by the image capture device  100  may depend on the properties of the IR filter  110 A. 
     In some embodiments, the variance between different IR filters  110 A within the electronic devices  100  may be categorized into different “bins” within the total variance. Each bin may represent a range of wavelengths that receive similar adjustment (as is described below). The approximately 20 nanometers of variance around the desired 650 nanometer cut-off wavelength shown in  FIG. 3A  may be categorized among an equal number of bins. For example, a first bin may be associated with the wavelengths in the 640 to 644 nanometer range, a second bin may be associated with the wavelengths in the 644 to 648 nanometer range, and so on until the 20 nanometer wavelength variance is divided among multiple bins each spanning 4 nanometers. As each IR filter  110 A is tested within the system  200 , the result may fall somewhere in the 20 nanometer variance. For example, if the IR filter  110 A shown in  FIG. 2  has a cut-off wavelength of 642 nanometers then it will be associated with the first bin having a range of 640-644 nanometers. 
     With the IR filters  110 A binned in this manner, one or more algorithms may be implemented to adjust the color response characteristics to match a baseline IR filter, where IR filter  110 A falling within the same bin may be adjusted similarly. As one example, the embodiment may calculate, via the CPU  125 , differences between the response characteristics of the electronic device&#39;s filter  110 A and an ideal IR filter to the calibration pattern. Such differences may be stored in the memory  120  as a correction constant or set of constants and used by the CPU  120  to adjust image/color data received from the array  106 . 
       FIG. 3B  depicts an exemplary baseline IR filter&#39;s characteristic  310 . In some embodiments, the exemplary baseline IR filter&#39;s characteristic may be based on selecting an IR filter  110 A from among a plurality of IR filters to be used in manufacturing the electronic devices  100 . A manufacturer of the electronic device  100  may purchase a group image capture devices  105  and/or IR filters  110 A from a certain vendor. Samples from within this group of IR filters  110 A may be tested, either in response to the calibration pattern  250  or in an alternative systems. From these samples, a baseline filter may be selected that has a cut-off wavelength closest to the desired behavior. For example, the IR filter  110 A from the sample that has a wavelength closest to 650 nanometers may be selected as the baseline filter. 
     As shown in  FIG. 3B , the IR filter&#39;s characteristic  310  may almost completely transmit light below about 640 nanometers and begin to taper off above that point by emitting about half as much light at 650 nanometers, and then transmitting almost no light at or above 660 nanometers. In some embodiments, the data associated with the baseline filter&#39;s response may be stored in the memory  120  at the time the electronic device  100  is manufactured. 
     By comparing the IR filter&#39;s characteristic  310  with the characteristics of the IR filter  110 A associated with the established bins, adjustment factors for the IR filter  110 A may be determined. For example, in some embodiments one or more look-up tables may be constructed so that for a particular bin pixel intensity measurements in the raw image may be scaled by values in the look-up tables. Thus, if the IR filter  110 A has a cutoff wavelength of 642 nanometers and therefore falls within a first bin (because they have a wavelength range of 640-644 nanometers), then the measured pixel intensities in the raw image coming may be scaled up according to the values in the look-up table by the CPU  125 . Utilizing a look-up table in this manner may reduce the calculation requirements of the CPU  125 . In other embodiments, instead of using look-up tables the amount of adjustment for each of the pixel intensities may be calculated according to mathematical algorithms. 
     In some embodiments, the ratios of the response of the IR filter  110 A to each of the color zones  270 ,  275 , and/or  280  may be made. By using ratios of the response to each of the color zones  270 ,  275 , and/or  280 , variations (e.g., due to light source aging, temperature variations, etc.) may be compensated for. For example, as the light source  210  ages the intensity of the light emanating from any one of the color zones  270 ,  275 , and/or  280  may fade. Despite any one of the color zones  270 ,  275 , and/or  280  fading as the light source  210  ages, if the ratio of the response to the color zones  270 ,  275 , and/or  280  is used instead of just one of the values, then aging or other variations may cancel each other out. Mathematically, this concept may be expressed as: 
             Intensity   =         ↓   Green       ↓   Red       .           
Thus, the intensity of the red primary color alone over time may be decreasing if monitored alone as a representation of image intensity, but the ratio of the green primary color to the red primary color would track this out if it were used as a measure of image intensity.
 
     In some embodiments, the empirical calibration data and/or response of the IR filter  110 A to the target test structure  205  may be tracked by the manufacturer of the electronic device  100 . The manufacturer may keep track of which bin the IR filter  110 A falls in for each electronic device manufactured. In this manner, the manufacturer may later decide to update the look-up tables or mathematical algorithms used to calculate color adjustment values by updating the values stored in the memory  120 . For example, this may occur during a firmware update. 
     This information may assist the manufacturer in the event that a malfunction is discovered with the electronic devices  100  that may be associated with a batch of filters  110 A-B, such as filters from a particular manufacturer. 
       FIG. 4  is an exemplary flowchart of a method that may be implemented by the electronic device  100 , or associated with software and/or hardware, to calibrate the image capture device  105 . In operation  405 , data associated with the baseline IR filter to the target test structure  205 , may be stored in the memory  120 . Note that multiple sets of calibration data, each associated with different baseline filter responses (for example, mimicking filters associated with different colors) may be stored in the memory  120 . 
     The electronic device  100  is exposed to the target test structure  205  in operation  410 . In some embodiments, the electronic device  100  is exposed to the same target structure that the high quality IR filter was exposed to. 
     During the exposure of operation  410 , a ratiometric comparison of wavelengths of light emanating from the one or more openings  220  may be made by the CPU  125 . As described above, this ratiometric comparison may allow variations—e.g., due to aging of the target test structure  205 —to be negated or minimized. The results from the exposure that occurred in operation  410  may be stored in the memory in operation  412 . 
     In operation  415 , the stored ratiometric comparison may be compared to data from the baseline filter to determine the spectral properties of the IR filter  110 A. With the comparison between the IR properties of the IR filter  110 A and the spectral properties of the baseline filter made, one or more correction methods may be implemented as shown in operation  420 . The one or more correction methods may be executed by the CPU  125 , for example, by executing firmware or software stored in the memory  120  when the electronic device  100  was built. 
     The actual adjustments made by the exemplary methods in operation  420  may vary based upon the function being performed by the image capture device  105 . For example white balancing the raw image may include calculating the maximum and minimum operating ranges based upon the black and white reference points  255 . If 8-bit color is used, the black point may be associated with a binary value of 0 while the white point may be associated with a binary value of 255. Accordingly, measuring the intensity of each of the red, green, and blue channels, may yield the following relationships: 
               Gain   red     =         255   200     ⁢           ⁢     Gain   green       =         255   255     ⁢           ⁢     Gain   blue       =       255   128     .               
These may be used as the expected gains and coded into the firmware for color balancing operations. The cut-off wavelength of the IR filter  110 A may vary, for example the IR filter  110 A may have a higher cutoff wavelength as depicted by the right hand side of the double sided arrow in  FIG. 3A . In the event that the IR filter  110 A has a higher IR cutoff wavelength, then the expected intensity value of the red channel may be higher than expected and skew the color balancing operations. Accordingly, the Gain red  may be adjusted based upon the color filter&#39;s measured response to the target test structure  205 , such as when the image capture device  105  is performing a white balance.
 
     In some embodiments, the methods used to correct the color filter  110  may be modified by connecting the image capture device  100  to a data feed from the manufacturer. For example, if the electronic device  100  is a multifunctional cellular telephone (such as the iPhone manufactured by Apple Inc. of Cupertino, Calif.), then connecting the cellular telephone to the manufacturer&#39;s web site through the Internet (e.g., wired or wireless) may periodically update the data and/or methods used to correct the color filter  110  that are stored in the firmware. 
     Although the present invention has been described with reference to certain embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Metadata:
Filing Date: 20080926
Publication Date: 20130326
Grant Date: 20130326
Priority Date: 20080501
Inventors: GERE DAVID S.
CHEN TING
BRONSTEIN CHAD ANDREW
Assignee: APPLE INC
CPC Classifications: [{"code": "H04N25/134", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N23/843", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/136", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/136", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N23/843", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/134", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N17/002", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04N17/002", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 41256842