fig1 is a block diagram of a spray performance analysis system 100 in accordance with an exemplary embodiment of the present invention . as shown in fig1 , analysis system 100 includes a wc image capture unit 102 , a calibration image analysis unit 104 , a wc image analysis unit 105 , a calibration unit 106 and a statistics unit 108 . wc image capture unit 102 captures witness card images that are submitted to either unit 104 or unit 105 depending on the type of image being processed . wc images of calibration witness cards are submitted to unit 104 . wc images of as - sprayed witness cards are submitted to unit 105 . the image analysis units 104 and 105 preferably include the same core image preprocessing control parameters , but are configured to perform different functions . the calibration image analysis unit 104 generates stain area information from calibrated drops of one or several stains as directed by the user . the wc image analysis unit 105 automatically identifies as many as all of the stains within a witness card image and may determine stain areas for each identified stain and physical attributes of the stain image space . calibration unit 106 , receives calibration witness card stain dimension data from calibration image analysis unit 104 and known droplet volume information to generate a calibration curve equation , or set of linear and / or non - linear equations , capable of accurately estimating a droplet dimension ( e . g ., droplet diameter or mmd ) as a function of a determined stain dimension ( e . g ., stain diameter ) for an identified fluid at an identified temperature upon an identified paper stock . statistics unit 108 receives and stores one or more calibration equations generated by calibration unit 106 . upon receiving as - sprayed witness card stain dimension data from wc image analysis unit 105 , statistics unit 108 may select a stored calibration equation , or set of equations , based upon the fluid , fluid temperature and type of witness card used to produce the as - sprayed stains . statistics unit 108 then uses the selected calibration equation ( s ) to estimate spray droplet diameters ( i . e ., mmd values ) and spray density for each as - sprayed witness card . in addition , based upon the number of droplets , spray density , and mmd values determined for each as - sprayed witness card retrieved from a known location within a sprayed target area , statistics unit 108 is capable of generating statistical data that characterizes spray performance within any or all portions of the sprayed target area . fig2 a depicts an exemplary embodiment of the present invention in which a spray performance analysis system 200 is implemented in a stand - alone configuration . as shown in fig2 a , such an embodiment may include a scanner 202 ( or more generally , a wc image capture unit 102 including a digital camera 640 as will be discussed more fully in connection with fig6 ), and a conventional computer processing unit 204 with conventional user input / output devices such as a display 206 , keyboard 208 and mouse 210 . the computer system may use any of the major platforms such as windows , linux , macintosh , unix or os2 . further , computer processing unit 204 includes components ( e . g . processor , disk storage or hard drive , etc .) having sufficient processing and storage capabilities to effectively execute spray performance analysis system processes . in such an embodiment , a user interfaces with the spray performance analysis system executing upon computer processing unit 204 via a command line or graphical user interface to process witness cards in accordance with the present invention . wc image capturing , image analysis , generation of calibration equations , and the generation of as - sprayed statistics may , accordingly , be performed from a single location . fig2 b presents an alternate exemplary embodiment of the present invention in which spray performance analysis system functions are performed in a distributed networked environment . as shown in fig2 b , a scanner 212 ( or , again , any wc image capture mechanism , e . g ., camera 640 ), computer processing unit 214 and storage device 216 are connected by communication network 218 . in such an environment , scanner 212 ( or , e . g ., a camera ) is typically used to generate images of calibration witness cards and / or as - sprayed witness cards and to store the images to networked storage device 216 . in this manner , images can be generated , stored and later retrieved by processing unit 214 in order to develop calibration equations and / or generate as - sprayed analysis statistics . as described in u . s . pat . no . 7 , 277 , 570 , paper stock may be used as witness cards . such paper stock is preferably selected to avoid paper speckle ( i . e ., single or small clusters of pixels within a witness card image caused by the grain and / or structure of the paper stock ) and to avoid paper imperfections ( i . e ., larger groups of image pixels caused by paper stock local area imperfections or lack of homogeneity in the grain structure of the paper ). although paper stock may be used in connection with the instant witness card analysis methodology , it has been determined that other forms of witness cards and related witness card image capturing techniques may be more suitable or desirable in certain situations . referring now to fig5 a , one other type of witness card in accordance with the present invention that may be employed is a semiopaque wc 500 . such a wc 500 may include a transparent or semiopaque sheet or substrate 510 that is covered by a coating 520 that may be designed to chemically react or be altered upon contact / interaction with a sprayed simulant or other substance . such a wc 500 may be made from , e . g ., a material known as flexible tlc plates available from whatman plc ( united kingdom ). these plates are available in 20 cm × 20 cm sheets and can be cut with scissors ( or with any other appropriate cutting tool ) to desired dimensions . a particular variety of these plates suitable for wc analysis in accordance with the present invention is known as tlc pe sil g / uv , which contains , as a coating , 60 å of silica gel . fig5 b shows an alternative witness card 501 in which a chemical reactant or marker is actually integrally formed or mixed with the material that forms the sheet 525 itself . that is , as a result of the card manufacturing process , the “ coating ” is indistinguishable from what might be considered a carrier sheet or substrate . depending on the type of coating 520 ( including , e . g ., the coating on the tlc pe sil g / uv sheets ) or chemical reactant / marker , a droplet of simulant ( and particularly an un - dyed stimulant ) may not be immediately visible to a human eye or electronic imaging device such as a scanner or digital camera . accordingly , to facilitate detection or viewing of stains on semiopaque wc 500 , an image enhancing apparatus 600 may be provided , as shown in fig6 . such an apparatus may comprise a light table 610 having a light source 625 that is preferably capable of emitting light in an evenly distributed manner so as to avoid , to the extent possible , uneven lighting of a wc 500 . the light source may comprise any suitable form of illumination at any suitable wavelength and is not restricted to white light or light in the visible waveband . light table 610 preferably has a semiopaque or semi - transparent platform 630 through which light from light source 625 passes . platform 630 may comprise glass , crystalline and / or plastic structures that help to evenly distribute light . in accordance with an embodiment of the instant invention , wc 500 is placed on platform 630 in view of , for example , a camera 640 . camera 640 may be a conventional film camera , but is preferably an electronic digital camera that can quickly generate digital wc image data 650 . light source 625 illuminates wc 500 in such a way as to make the stains or droplets thereon visible to , e . g ., camera 640 . the resulting captured wc image data 650 is the data that , as shown in fig1 , may be supplied to either calibration image analysis unit 104 or witness card image analysis unit 105 . further , it should be appreciated by those skilled in the art that the light table 610 and camera 640 arrangement described herein is merely an example of one approach to practicing the instant invention and that other implementations of a wc image capture unit 102 are possible and still within the scope of the invention . with the wc data 650 in hand , either by way of a scanner or the light table 610 and camera 640 arrangement of fig6 , analysis of the witness card data can proceed as explained in detail in u . s . pat . no . 7 , 277 , 570 and as outlined next . fig3 depicts a process flow diagram for the development of calibration equations used to calibrate a spray performance analysis system in accordance with an exemplary embodiment of the present invention . as shown in fig3 , a spray fluid and witness card type is selected ( e . g ., paper stock , transparent / coated / semiopaque ) at step 302 , and calibration witness card sample stains are produced at step 304 , upon the selected wc with known volumes of the selected fluid . next , at step 306 , the calibration witness card is scanned or digitally imaged by wc image capture unit 102 ( see fig1 ) to produce an electronic image containing images of the calibration witness card stains . image processing of the respective stain images is performed , at step 308 , by image analysis unit 104 to determine stain area and / or dimension measurements of the sample stains . examples of such dimension measurements may include a diameter of an identified stain , a radius of an identified stain , and a circumference of an identified stain . stain area and / or dimension measurement information and droplet volume information is passed to calibration unit 106 to develop , at step 310 , a calibration equation , or set of linear and / or non - linear equations , using conventional techniques capable of approximating droplet volume as a function of droplet stain area and / or dimension measurements . the generated calibration equation is validated , at step 312 , by calculating stain volume approximations for each of the calibration droplets based upon the measured calibration stain measurements . if the approximated volumes are determined , at step 314 , to be within a predetermined percentage error of the known droplet volumes , the generated calibration equation information is stored , at step 316 , for later access by the spray performance analysis system statistics unit 108 . if the approximated volumes are determined , at step 314 , to not be within the predetermined percentage error of the known droplet volumes , the calibration process described above is iterated or repeated until a set of validated calibration equations is achieved . still additional detail regarding the calibration process of depicted in fig3 may be found in u . s . pat . no . 7 , 277 , 570 . fig4 is a process flow diagram depicting use of the spray performance analysis system of fig1 to generate as - sprayed performance statistics in accordance with an exemplary embodiment of the present invention . as shown in fig4 , a spray fluid and witness card type is selected at step 402 , witness cards are positioned at step 404 throughout an area to be sprayed , and as - sprayed witness card stains are produced at step 406 as a result of spraying the test area with a spray device in a prescribed manner using the selected fluid or simulant . for example , the manner of spraying is typically representative of a proposed agricultural , military , industrial or other use , as described above . next , at step 408 , an electronic image of each as - sprayed witness card is produced using wc image capture unit 102 ( e . g ., scanner or digital camera ) and stored . image processing of the respective stain images is performed , at step 410 , by wc image analysis unit 105 to identify stains within the as - sprayed witness card image that exceed a pre - determined threshold and to determine an approximate area and / or dimension of each detected stain . examples of such dimension measurements may include a diameter of an identified stain , a radius of an identified stain , and a circumference of an identified stain . preferably , such as - sprayed witness card stain area and / or dimension information is stored in a manner that associates the witness card with a unique test ( e . g ., a unique test identifier , etc .). at step , 412 , statistics unit 108 , retrieves as - sprayed witness card stain area measurement and / or dimension information associated with a common test from storage and further retrieves a set of calibration equations for use in approximating the mass of the droplet that produced each identified as - sprayed witness card stain . next , at step 414 , statistics unit 108 generates and stores spray density and droplet mass data for an as - sprayed witness card associated with the selected test . if the statistics unit 108 determines , at step 416 , that additional as - sprayed witness card stain area and / or dimension information remains to be processed , step 414 is repeated , otherwise , statistics unit 108 proceeds to generate , at step 418 , statistics data that summarizes as - sprayed performance based upon the spray density and droplet mass data generated , at step 414 , for each of the respective as - sprayed witness cards . additional detail related to steps identified in fig4 may be found in u . s . pat . no . 7 , 277 , 570 . in positioning , at step 404 , witness cards within a target spray area , care should be taken to place the witness cards in positions that may capture appropriate spray information . for example , witness cards may be placed at strategically selected and / or evenly spaced locations from a stationary spray distribution point , or a ground zero detonation point , to form one or more representative grids and / or cross - sections of the target area . if the spray device is mobile , witness cards may be placed at strategically selected locations and / or evenly spaced intervals along the spray path . for example , to sample spray performance of a spray device moving along a spray path , a set of witness cards may be positioned along a perpendicular cross - section of the spray path . such cross - sectional sampling may be established at various points along the spray path to obtain information related to performance of the spray device over time . in producing as - sprayed witness cards , at step 406 , care should be taken to monitor the as - sprayed operational conditions and any deviations from the operational conditions under which the calibration witness card was created should be duly noted . such notable changes may include , as - sprayed fluid temperature , as sprayed viscosity , color intensity , wind conditions , ambient temperature / humidity , etc . preferably , the as - sprayed operational conditions can be matched at step 412 with a set of calibration equations based upon calibration witness card data produced under the same operational conditions . this matching may be conveniently done post - spraying as noted above . the systems and methods described herein may be embodied in other specific forms without departing from the spirit or essential characteristics thereof . the foregoing embodiments are therefore to be considered in all respects illustrative and not meant to be limiting .
a system for and method of assessing fluid spray using image processing techniques of a calibration and one or more as - sprayed witness cards . calibration and as - sprayed witness cards are exposed to a backlight sufficient to make a plurality of stains thereon electronically visible . at the same time an image of the stains is captured by , e . g ., a digital camera . resulting image data is processed to assess characteristics of the stains of the fluid on the as - sprayed witness card and thereby assess characteristics of the spray , e . g ., volume of fluid delivered . in one embodiment , the witness card is a chemically coated semiopaque plate .