Abstract:
A system and method for use in testing and calibrating both electronic and traditional photographic devices. An illuminator with solid-state emitters and having independent control of both output spectral characteristics and power level enable the system and method to accurately test and calibrate the desired equipment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to U.S. application Ser. No. 10/108,975, filed Mar. 28, 2002, by Richard M. Vogel, et al., and entitled, “ILLUMINATOR AND METHOD OF MAKING SAME,” which is herein incorporated by reference. 
     FIELD OF THE INVENTION 
     This invention relates generally to the field of test and measurement systems. More particularly, the invention concerns a system and method suitable for use in testing and calibrating electronic imaging and traditional photographic equipment. 
     BACKGROUND OF THE INVENTION 
     Test and measurement systems for use in testing and calibration of electronic imaging and traditional photographic equipment often include some form of illumination system having a set of characteristics suitable for the type of tests and calibrations to be performed. Other accessories such as electromagnetic shutters, color-conversion filters, neutral-density filters and the like are typically included in such test fixtures to tailor the response of the illumination source to suit the requirements of a particular test. 
     Recent developments have made possible the replacement of the traditional types of light sources, along with their requisite accessories, with a solid-state light source having independently programmable output spectra and power level. U.S. application Ser. No. 10/108,975, by Richard M. Vogel, et al., entitled “ILLUMINATOR AND METHOD OF MAKING SAME” (incorporated herein by reference), describes such a solid-state illuminator. All of the features, benefits, advantages and claims of this co-pending application are incorporated herein by reference. 
     Therefore, a need persists for a system and method for calibrating an imaging device that exhibits independent control over both the output spectral characteristics and power level. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the invention to provide a system and method for calibrating an image capture device that exhibits independent control over both spectral characteristics and power level. 
     The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a method of calibrating an image capture device includes the step of providing an image capture device and an illuminator. The illuminator has an integrating chamber with energy inlet ports and energy outlet ports and a plurality of emitter means arranged for directing energy along a predetermined optical path through the energy inlet ports into the integrating chamber and through the energy outlet ports of the integrating chamber. The image capture device is positioned proximate to the energy output ports of the integrating chamber. Means is provided for transferring emitted energy from the integrating chamber of the illuminator to the image capture device. Also, a master control means is used for controllably coordinating the illuminator and image capture device during calibration. Prior to the calibration operation, the controller is directed to set the image capture device into an imagewise exposing state for the purpose of forming an image. Also, the illuminator is instructed to sequentially present to the image capture device a plurality of stimulus. The stimulus have both a programmable spectral and exposure characteristics according to a test-specific predetermined algorithm. The controller is then directed to store the image resulting from previous steps. Once the images are formed, the controller is directed to operate on the formed images according to the test-specific predetermined algorithm so as to generate a data set characteristic of the test-specific predetermined algorithm. The data set from the test specific predetermined algorithm is then compared with a predetermined set of product specification limits characteristic of the image capture device. Finally, the calibration parameters are stored in a media associated with the image capture device for subsequent processing of newly formed images. 
     In another aspect of the invention, a system for calibrating an image capture device includes an illuminator having an integrating chamber with energy inlet ports and energy outlet ports. A plurality of emitter means are arranged in the illuminator for directing energy along a predetermined optical path through the energy inlet ports onto the integrating chamber and through the energy outlet ports of the integrating chamber. Means are provided for transferring emitted energy from the integrating chamber of the illuminator to the image capture device. A master control means provides coordination between the illuminator and image capture device during calibration. The master controller sets the image capture device into an imagewise exposing state for the purpose of forming an image. Finally, means are provided for operably interfacing the image capture device to the master control means. 
     Therefore, advantages of the present invention include an ability to test and calibrate both electronic and traditional imaging systems. Another advantage is that the system and method of the invention can test and calibrate while maintaining independent control over the spectral characteristics and power level of the illuminator assembly. Yet another advantage is that the system and method are easy to use and produce far greater accurate calibrations compared to existing systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features, and advantages of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical features that are common to the figures, and wherein: 
         FIG. 1  is a block diagram of a first preferred embodiment of a test and calibration system for testing and calibration of an image capture device having an aperture; 
         FIG. 2  is block diagram of a second preferred embodiment of a test and calibration system for testing and calibration of an image capture device having a condenser lens; and, 
         FIG. 3  is a block diagram of the calibration process. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings, and in particular to  FIGS. 1 and 2 , the system  1  of the invention is illustrated. According to  FIG. 1 , a preferred embodiment of the system  1  for testing and calibrating an image capture device  13  has an illuminator  10  positioned proximate to image capture device  13 . Illuminator  10  has a plurality of LED emitters (not shown) arranged in the inlet port  5  of an integrating chamber  4 . The LED emitters emit radiant energy into the chamber and out an exit port of the chamber in the manner described in details in U.S. patent application Ser. No. (D82167). Means, preferably an aperture  11 , transfers radiant output energy from the LED emitter through the illuminator  10  and a light-tight chamber  12 . The radiant output energy is then allowed to pass from the light-tight chamber  12  onto the image capture device  13 . Each of the illuminator  10 , light tight chamber  12 , and image capture device  13  is conveniently supported for operations by test fixture support electronics  14 . 
     Referring again to  FIG. 1 , a test system controller  15  provides a suitable interface means  16  for controlling the LED illuminator  10  and test fixture support electronics  14 . According to  FIG. 1 , frame grabber  17  for inputting images from the image capture device  13  to the test system controller  15  is also provided. Moreover, an aperture  11  is located proximate to the exit port of the LED illuminator  10 . Preferably, aperture  11  has a diameter ‘D’ and is located a distance ‘F’ from the image capture device  13 . The aforementioned system parameters may be adjusted to provide the desired f-number of the illuminating cone on the image capture device  13  to be tested according to the formula:
 
 f -number= F/D, 
     wherein f is the f-stop;   wherein F is the distance from the aperture to the image capture device; and,   wherein D is the diameter of the aperture.   

     Referring to  FIG. 1 , LED Illuminator  10  receives control information from the test system controller  15  via a bi-directional control interface  18  supported by an interface means  16  which is part of the test system controller  15 . The interface means  16  may be a parallel or serial interface port that is built-in to the test system controller  15  or may be an accessory which is mounted internally or externally to the test system controller  15 . The command set for the LED Illuminator  10  comprises selection of the operating mode (continuous, repetitive, single-shot, gated) and specification of the output level and spectral shape. The LED Illuminator  10  further receives synchronization signals from the test fixture support electronics  14  via a bi-directional synchronization interface  19 . The synchronization signals includes signals both for triggering the LED Illuminator  10  in single-shot or gated modes and inhibiting periodic calibration during repetitive or continuous modes. Moreover, the synchronization signals includes signals for initiating calibration during singleshot or gated modes and a BUSY signal to instruct the test fixture support electronics  14  that the LED Illuminator  10  is currently processing a synchronization request. 
     Still referring to  FIG. 1 , light-tight chamber  12  ensures that no stray light enters the optical path between the LED Illuminator  10 , aperture  11  and image capture device  13  while a test or calibration is in progress. 
     As depicted in  FIG. 1 , test fixture support electronics  14  provides for any miscellaneous support functions as may be necessary and comprises the functions of operating the test fixture mechanism and image capture device  13  and coordinating such operation with the test system controller  15  and LED Illuminator  10 . The test fixture support electronics  14  receives control information from the test system controller  15  via a bi-directional control interface  20  supported by an interface means  16  which is part of the test system controller  15 . The interface means  16  may be a parallel or serial interface port that is built-in to the test system controller  15  or may be an accessory which is mounted internally or externally to the test system controller  15 . According to  FIG. 1 , test system controller  15  includes a frame grabber  17  that receives images from the image capture device  13  by way of test fixture support electronics  14 . A video interface  21  coordinates the communications between test fixture support electronics  14  and frame grabber  17 . 
     Turning now to  FIG. 2 , a second embodiment of a test and calibration system  2  for testing and calibration of an image capture device is illustrated. According to  FIG. 2 , system  2  has practically all of the elements previously described except for the aperture  11  (shown in  FIG. 1 ). In this embodiment, aperture  11  is replaced with a condenser lens  22  as the means of conveying the radiant output energy from the LED illuminator  10  to the image capture device  13  to be tested. 
     Referring now to  FIGS. 1 and 3 , prior to the start of testing, software within the test system controller  15  determines the control parameters necessary for the LED illuminator  10  to produce each of the plurality of spectral power distributions (SPDs) required by the predetermined test algorithm  24 . These commands may then be sent to the LED illuminator as each SPD is required or queued in the LED illuminator  10  and executed sequentially as each SPD is required. Once the test begins  26 , the test algorithm directs the test system controller  15  to set the image capture device  13  into an imagewise exposing state for the purpose of forming an image  28 . Next, the test system controller  15  instructs the LED illuminator  10  to present a stimulus having the desired spectral and exposure characteristics according to a test-specific algorithm  30 . Following completion of the exposure, the test algorithm instructs the test system controller  15  to read out  32  the resulting image from the image capture device  13  and store it for later analysis. This process is repeated until all of the SPDs have been presented to the image capture device  13  and the resulting images read out and stored for analysis. Following read out of the last image  34 , the test algorithm instructs the test system controller  15  to extract test and calibration parameters  36  from the plurality of stored images. These test parameters are then compared  38  to a set of predetermined specification limits to determine whether the image capture device is performing acceptably or not  40 . If the image capture device does not perform within specified limits it is rejected  42 . However, the calibration parameters are saved in a storage media (refer to feature  23  in  FIGS. 1 and 2 ) for later use  44 . The storage media  23  may, for example, be a non-volatile portion of the image capture device  13  itself or a non-volatile memory device located on the circuit module containing the image capture device  13  or elsewhere within the product containing the image capture device  13 . The storage media  23  may also be located external to the image capture device  13  in, for example, the test system controller  15 . 
     The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. 
     PARTS LIST 
     
         
           1  system 
           2  second system 
           3  exit port 
           4  integrating chamber 
           5  inlet port 
           10  LED illuminator 
           11  aperture 
           12  light-tight chamber 
           13  image capture device 
           14  test fixture support electronics 
           15  test system controller 
           16  controller interface means 
           17  frame grabber 
           18  LED illuminator bi-directional control interface 
           19  LED illuminator bi-directional synchronization interface 
           20  test fixture bi-directional control interface 
           21  video interface 
           22  condenser lens 
           23  storage medium for calibration parameters 
           24  step—predetermined test algorithm 
           26  step—begin device test 
           28  step—set image capture device to exposing state 
           30  step—command LED illuminator to output desired SPD 
           32  step—read out image from image capture device 
           34  decision—last image or not 
           36  step—extract test and calibration parameters from test images 
           38  step—compare test parameters to specification limits 
           40  decision—image capture device performing acceptably or not