Patent Publication Number: US-11039028-B2

Title: Visual privacy protection system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 15/616,386 filed Nov. 5, 2019 hereby incorporated by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under 1506657 awarded by the National Science Foundation. The government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a system for controlling the use of cameras to record visual images in given locations and in particular to a privacy protection system that may work with standard rolling shutter cameras. 
     Electronic cameras are pervasive, being found on common consumer devices including smart phones, tablets, drones, smart glasses, and the like. The ubiquity of these cameras, paired with widely available wireless access, raises significant visual privacy issues including individual privacy, for example, in locker rooms and the like, the prevention of copying of visual works such as art or the like, and the protection of other visual information such as trade secrets. 
     A variety of privacy enhancing systems have been proposed that require the cameras to sense and abide by signals indicating that the camera is in a “no photography zone” or is focused on a subject that should not be photographed. The signals may be visual, for example, a QRS code. Currently very few, if any, cameras respect such signals and accordingly these “bilateral” visual privacy systems, requiring coordination between the holder of privacy rights and the camera owner, are limited in use. 
     A desire to enforce visual privacy against a wide variety of cameras without special modification to those cameras (“unilateral” visual privacy systems) has been addressed, for example, using camera-blinding light sources, for example, in the infrared or near infrared region. Such systems only work if the light sources are in the camera&#39;s field of view and therefore special hardware must be placed in close proximity to every object to be visually protected. Such systems are relatively costly when there are many objects to protect, for example, multiple pictures in a museum, or impractical for moving objects or in situations where a premeditated location of camera-blinding lights would be difficult, for example, in a factory. 
     SUMMARY OF THE INVENTION 
     The present invention provides a unilateral visual privacy system that can be implemented to protect an arbitrary number of items in a given area at low cost by making use of LED lights that may also provide for area illumination. The LED lights are modulated within a frequency range designed to interact with the rolling shutter electronics of common electronic cameras to “print” obscuring bands or colors over the image. The system can cooperate with authorized cameras allowing them to work freely in the protected area and, in cases where there is substantial ambient light that cannot be controlled, can switch to a “watermarking” mode which embeds a “barcode” in the image that can be detected automatically if the image is posted or published. 
     Specifically, in one embodiment, the invention provides a visual privacy system providing a privacy-enforced environment having a floor area of at least 100 square feet containing a plurality of LED light fixtures synchronously modulatable to provide at least 50 percent of the ambient illumination of the environment and its contents. A modulator communicates with the light fixtures to synchronously modulate the light of the light fixtures between on and off values at a frequency above the flicker fusion rate to impose a banding in images taken by rolling frame shutter cameras relying on the ambient illumination for image acquisition, the banding completely obscuring portions of the image. 
     It is thus a feature of at least one embodiment of the invention to provide a “unilateral” privacy enforcement mechanism that does not require coordination with the unauthorized camera and that can operate to protect an entire region. 
     The modulator may synchronously modulate the light of the light fixtures between on and off values at a frequency in excess of 400 Hz. 
     It is thus a feature of at least one embodiment of the invention to provide a simple modulation system (binary) that can be readily implemented with existing LED hardware used for ambient lighting without degrading the ambient light experience through perceivable flicker. 
     The modulator may alternatively or in addition synchronously modulate the light of the light fixtures between on and off values at a frequency of less than 2,000 Hz. 
     It is thus a feature of at least one embodiment of the invention to provide thick obscuring bands in an acquired image that prevent ready visual interpolation and thus which substantially obscure the image. 
     In addition, the modulator may synchronously modulate the light of the light fixtures between on and off values with a duty cycle greater than 40 percent. 
     It is thus a feature of at least one embodiment of the invention to provide a balance between producing ambient illumination and wide obscuring bars in the image. 
     The ambient illumination may provide an illumination within the environment of no less than 2000 Lux. 
     It is thus a feature of at least one embodiment of the invention to provide substantial ambient illumination and to maximize the ability of the invention to block picture taking in the environment between the limits of under and over exposure. 
     The modulation may vary modulation among different frequencies in a nonrepeating pattern over an interval less than 1 second so that time adjacent different frequencies are not related by an integer multiple. 
     It is thus a feature of at least one embodiment of the invention to prevent simple defeat of the privacy system of the present invention through adjustment of the exposure of the unauthorized camera. While a given exposure setting may defeat the ability to obscure the image at some modulation frequencies, shifting modulation frequencies makes this exposure adjustment strategy impractical. 
     The LED light fixtures may provide separate red, green, and blue light sources that are independently modulatable, and the modulator provides different modulation frequencies to the red, green, and blue light sources. 
     It is thus a feature of at least one embodiment of the invention to separately modulate different color channels to greatly increase the difficulty of defeating the privacy system. 
     The visual privacy system may include at least one authorized camera positioned to view contents of the environment, the authorized camera intercommunicating with the modulator to exchange a timing signal controlling timing of an image acquisition. The timing signal may synchronize the modulation of the light fixtures and the image acquisition by the authorized camera to eliminate banding in images acquired by the authorized camera. For example, when the authorized camera provides a rolling shutter in which rows of an image are sequentially exposed, the timing signal may allow the authorized camera to coordinate an exposure of each row with a time period to produce an exposure spanning a constant cumulative on-time of the plurality of light fixtures. 
     It is thus a feature of at least one embodiment of the invention to prevent interference with authorized cameras, for example, security cameras in the environment. 
     The timing signal may indicate at least one of a frequency and a period of repetition of a modulation pattern or at least one of a beginning of a period of repetition and a phase of a modulation pattern. 
     It is thus a feature of at least one embodiment of the invention to provide a relatively simple communication between the modulator and the authorized camera (e.g., frequency) requiring only low bandwidth or to permit phase locking of the modulator and authorized camera, for example, when transmitting obscuring data during the interframe blanking period of the camera. 
     The modulator may further provide a barcoding modulation pattern when an illumination in the environment is below a predetermined percentage, the barcoding modulation pattern imposing a non-obscuring banding in images taken by rolling frame shutter cameras relying on the ambient illumination for image acquisition and encoding a predetermined data pattern. 
     It is thus a feature of at least one embodiment of the invention to provide “bilateral” type privacy protection when “unilateral” type protection is not available because of adverse environmental conditions. 
     The predetermined data pattern may be a ratio between a first and second frequency of the barcoding modulation pattern. 
     It is thus a feature of at least one embodiment of the invention to provide an encoding in an image taken by an unauthorized camera that does not require synchronization with that camera. 
     These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified perspective view of a room holding an object for which visual privacy is desired and holding an authorized and unauthorized camera, the room having LED lights communicating with a modulation system to block the use of an unauthorized camera but allowing an authorized camera to provide imaging; 
         FIG. 2  is a timing diagram showing a modulation of the lighting system of  FIG. 1  with respect to exposure periods for a rolling shutter of the unauthorized camera of  FIG. 1  such as provides a banding in the acquired image; 
         FIG. 3  is a simplified representation of an image obtained from the camera of  FIG. 1  as blocked by the lighting system; 
         FIG. 4  is a timing diagram similar to that of  FIG. 2  showing a multifrequency modulation pattern together with a coordination of image acquisition by an authorized camera to allow standard imaging; 
         FIG. 5  is a timing diagram similar to that of  FIG. 4  showing use of a frame separator time for additional obscuring techniques; 
         FIG. 6  is a flowchart of the modulation system of  FIG. 1  such as may respond to external ambient light sources to convert from an obscuring mode to a barcode mode; 
         FIG. 7  is a program executed by the authorized camera for providing unobsecured images; and 
         FIG. 8  is a representation of an imprinting of barcodes on unauthorized images for later identification. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a privacy system  10  of the present invention may establish visual privacy in a room  12  or other illuminated area where individuals  14  carrying unauthorized cameras  16  may be present. The unauthorized camera  16  may be a rolling shutter camera employing a CMOS detection element, for example, having a shutter speed of 1/24 of a second or faster and typically on the order of 1/30 of the second. Such an unauthorized camera  16  may be found, for example, in a standard cellular phone or tablet, and may be expected to be provided in other wearable or easily carried camera systems. 
     Typically, the room will have an area of greater than 100 square feet and ceiling heights ranging from 8 to 20 feet although no size limitation is contemplated by the present invention so long as an adequate ambient illumination level may be obtained. In this regard, the room will generally be illuminated by a set of light fixtures  18  to provide a lighting level equal to or greater than that of a standard office (700 Lux) and preferably at a higher level in excess of 2000 Lux to provide the invention with greater efficacy. 
     The room  12  may contain contents  20  including both objects or people for which visual privacy is desired, for example, a painting in a museum where no photograph should be taken, although it is contemplated that the invention may be used in any environment where ambient lighting may be controlled. 
     Each of the light fixtures  18  may provide a monochrome (white) LED array or preferably a three-color LED array  22  providing red, green, and blue LEDs that may be independently modulated by a control circuit  24  according to a received signal-over-signal channel  26  as will be discussed below. The control circuit  24  may provide for controlled current to the LEDs according to techniques well known in the art, for example, for color balancing, as well as to allow the LEDs to be turned to either an on or off state according to the signal channel  26 . In this regard, the control circuit  24  may make use of standard commercial technology providing LED control coupled with circuitry for receiving modulation patterns over signal channel  26 . The invention also contemplates operation in a monochrome mode using LEDs producing white light, for example, with a phosphor and ultraviolet source, as mentioned above. 
     A synchronizing modulator  30  may provide a modulation signal over signal channel  26  to each of the light fixtures  18 , for example, through a daisy-chained conductor system, carrier current communicating over the light fixture power supply lines, wireless signaling (including radiofrequency and light frequency communication), or the like. The signal-over-signal channel  26  may simply provide on and off state which the light fixtures  18  follow or may indicate at a higher level a timing and pattern providing instructions allowing the modulation patterns to be developed in a distributed fashion among each of the light fixtures  18 . Generally, each of the light fixtures  18  will be synchronized to provide their respective on and off states at the same time. 
     The synchronizing modulator  30  may also communicate with one or more authorized cameras  32  positioned in the room  12  and intended to provide for imaging of objects including contents  20  in the room  12  without interference. Such authorized cameras  32 , for example, may be security cameras where unobscured imaging is essential. In this regard, the modulator  30  may provide a signal-over-signal channel  26  coordinating acquisition by the authorized camera  32  and providing either the on and off pattern directly or frequency and phase information necessary for the authorized camera  32  to coordinate acquisition of visual information without interference. In some embodiments, the signal-over-signal channel  26  may be identical to that provided over channel  26  to the light fixtures  18 . This signal on channel  26  may be encrypted or otherwise protected against unauthorized interception. 
     The central modulator  30  may, for example, provide for a processor  36  executing a stored program  38  as will be discussed below. Each of the unauthorized camera  16  and authorized camera  32  may provide for a similar computer processing system. 
     Referring still to  FIG. 1 , generally an unauthorized camera  16  held by an individual  14  will provide for a CMOS array  40  having light sensors each sensing one pixel of an image. These light sensors will be arranged in rows  42  and rectilinear columns  44  and are usually scanned in a row by row basis (termed a rolling shutter) shown by dotted line  39  in which a first row is exposed and then read out by an associated camera processor  48 , followed by exposure and read out of the next row and so on. Sequential rows may have periods of overlapping exposure but generally the exposure times of successive rows are increasingly delayed. 
     The camera processor  48  will include a memory  49  holding image files  51  collected from the CMOS array  40  and may communicate with the display and user controls or the like (not shown) depending on the camera application. 
     Referring now to  FIGS. 1 and 2 , in a simple example, each of the light fixtures  18  will be illuminated periodically as indicated by the waveform  50  at a periodicity  62  during illumination periods  52  of duration  63 . These durations  63  of illumination periods  52  are adjusted so that the illumination periods  52  will fall into the exposure windows  54  of some CMOS rows  42  and not others. Thus, for example, an exposure window  54  of a first row  42   a  may occur before an illumination period  52   a  thus providing for a low exposure for the light sensors of that row  42  and a corresponding dark row  58   a  in the resulting image  60 . 
     In contrast, a next row  42   b  may have an exposure window  54  fully aligned with the illumination period  52   a  producing a bright row  58   b  in the resulting image  60  caused by a full exposure of the light sensors of that row  42   b . A next row  42   c  may provide an exposure window  54  partially aligned with illumination period  52   a  thereby providing a somewhat darker row  58   c.    
     Generally, each of the exposure windows  54  of succeeding rows  42  will be staggered in time (either at disjoint times or overlapping times) so as to continue in this pattern to produce a set of dark and light rows  58  in the image  60 . The speed of the scanning through the rows  42  will be such that the exposure of the camera will be essentially constant in this time meaning that the rows  58  will include over and underexposed regions blocking or significantly reducing information in the image  60 . The exposure separation in the over and underexposed regions, such as controls the obscuring quality of the bands, may be accentuated through the use of high-intensity LEDs in the light fixtures  18 . High-intensity LEDs tend to produce overexposure in rows  42  having alignment of the illumination periods  52  and exposure windows  54  by increasing the average exposure of all rows  42 , and tend to create severe underexposure when the illumination periods  52  are unaligned with a given exposure window  54 . 
     Referring now to  FIGS. 2 and 3 , generally when the camera exposure window  54  is equal to or shorter than the dark time between illumination periods  52  (periodicity  62  minus duration  63 ) there will be completely dark bands  55 . Likewise, depending on the strength of the light during illumination periods  52  (its peak value and the length of illumination periods  52 ) and the sensitivity of the unauthorized camera  16 , the space in the image between the dark bands  55  may also be overexposed providing a set of bright bands  57  also obscuring data. The invention contemplates that for a given exposure setting of the unauthorized camera  16 , there will be either completely dark bands  55  with intelligible image showing between the dark bands  55  or completely overexposed bands  57  with the dark bands  55  revealing some intelligible image, although there can be situations where the image is completely obscured by both bands  55  and  57 . The bands  55  and  57  are shown vertically reflecting the fact that the rows of the CMOS sensor, and hence the scanning direction, can be oriented arbitrarily. 
     The bands  55  and  57  in the image not only redact image information in the same way that black lines (or erasures) would work in text, but the banding may also upset the camera&#39;s autofocus function because of the variations in exposure which upset the focusing algorithm and/or because the sharpness of the bands does not depend on the lens focus (being a time domain phenomenon) suggesting to the autofocus circuit that the camera is in focus even when the image scene is blurred. 
     In order to maximize the obscuring effect of the dark bands  55  and  57 , the periodicity  62  of the illumination periods  52  should be much shorter than the response time of a camera auto exposure circuit but long enough to provide a limited number of bands  55  or  57  of substantial width within the image  60 . Larger bands  55  and  57  prevent the missing image information from being visually interpolated when some information is visible in the dark bands  55  or light bands  57 . Desirably the modulation frequency of the light fixtures  18  (the inverse of the periodicity  62 ) will be low enough to produce a limited number of bands  55  and  57  within a single scan of the CMOS array  40  but also high enough to be above the flicker fusion rate typically being at a frequency above 100 Hz. When the duty cycle of the illumination period  52  is approximately 50 percent, three to ten bands may be desired in an image. 
     Lower duty cycles of the illumination periods  52  (duration  63  divided by periodicity  62 ) provide increased degradation of the image  60  by generating fully black bands but reduce the ability of the system to provide for overexposure bands  57  during the on time of the illumination periods  52  which can also obscure the image. In one embodiment, the invention may adopt a relatively modest duty cycle (between 0.4 and 0.6) and high peak intensity of the light during illumination period  52 , for example, greater than typical office illumination of 700 Lux and desirably above 2000 Lux. 
     Desirably the frequency provided by the modulation of the illumination at periodicity  62  will be such as to produce multiple bands within a single scan of the CMOS array  40  as well as to be above the flicker fusion rate typically being at a frequency above 100 Hz. This lower frequency bound prevents modulation of the light fixtures  18  (which also provide ambient illumination) from being visible or distracting to a human observer. The flicker fusion rate is a rate of flicker for a given brightness above which a human observer no longer perceives a flashing. For most people, frequencies above 400 Hz are free from flicker and thus are above the flicker fusion rate. Lower frequencies may be accommodated under particular illumination conditions that may be empirically determined. 
     Referring again to  FIG. 2 , it will be appreciated that when exposure window  54  is long enough to equal an integer multiple of the periodicity  62  of the illumination periods  52 , the camera will effectively integrate or average the waveform  50  and in this way, eliminate the bands  55  and  57  preventing the system from obscuring the image  60 . For this reason, it is possible that a user could adjust the unauthorized camera  16  to eliminate banding problem, for example, by adjusting the exposure time of that unauthorized camera  16  to match an integer multiple of the periodicity  62 , for example, by observing banding in the image and adjusting the exposure setting accordingly. 
     Referring now to  FIG. 4 , in order to prevent this circumvention of the present privacy system through simple exposure rate control in the unauthorized camera  16 , the invention contemplates varying the time periodicity  62  between illumination periods  52  to increase the difficulty to the user of an unauthorized camera  16  in selecting a static exposure rate that will defeat the present invention. In this regard, the modulator  30  may switch between two (or more) different periods, for example, periodicity  62  and longer periodicity  62 ′, essentially changing the frequency at which the LEDs of the light fixtures  18  are illuminated. Ideally these different frequencies are not integer multiples of each other, avoiding the possibility that an exposure time adjusted to be equal to one time periodicity  62  would likewise defeat the second time periodicity  62 ′. 
     Preferably, switching between the different periodicities  62  and  62 ′ occurs at a rate selected to prevent the formation of strong low-frequency side bands that might be below the flicker fusion rate mentioned above. In one embodiment, for example, the modulation rate may be approximately 200 Hz meaning that a new periodicity  62  is selected every 0.005 seconds. The central modulator  30  may communicate the new frequencies to each of the light fixtures  18  or may communicate a schedule to the individual light fixtures  18  that may then be used to generate the frequency pattern on a distributed basis. 
     Referring still to  FIG. 4 , the operation of this frequency switching can be understood by considering, for example, an unauthorized camera  16  having an exposure window  54   a  at a first time during modulation periodicities  62   a  where the exposure window  54   a  coincidentally equals an integer multiple of the modulation periodicity  62   a . In a first time interval (I) during exposure window  54   a , the unauthorized camera  16  may receive and integrate light from two illumination periods  52  indicated by cumulative exposure  59  which climbs a fixed amount for each illumination period  52  for each imaging row  42 , ultimately providing, in this example, an exposure that is neither underexposed (as indicated by level  70   a ) or over exposed (as indicated by level  70   b ) during scanning of a single row  42  in the image (shown in  FIG. 1 ). By coincidence, this could be an acceptable exposure level on the unauthorized camera  16  to effectively decode the obscured image. This small exposure window  54   a , however, when applied to a later modulation periodicity  62   b  at time interval (II) may receive light from no illumination periods  52  for rows  42 ′ providing no exposure of the resulting image row  42 ′ (at level  70   a ) or underexposure at intervening rows  42 ″. The result is the banding described with respect to  FIG. 3  with black bands  55  and a general underexposure of the image  60 . 
     Referring still to  FIG. 4 , conversely, it will be understood that if the unauthorized camera  16  coincidentally selects an exposure window  54   c  equal to the latter modulation periodicity  62   b , then during time interval (I) the exposure window  54   c  will capture so many illumination periods  52  so as to drive the cumulative exposure  59  into overexposure level  70   b  as it integrates an additional illumination period  52 . 
     Additional robustness to the above-described banding system may be obtained by applying different and independent periodicities  62  to each different color channel of red, green, and blue of the image  60 . This approach provides a set of obscuring bands of different colors and may further affect the image by interfering with the color balance system of the unauthorized camera  16 . 
     Referring now to  FIGS. 1 and 4 , the present invention permits an authorized camera  32 , for example, shown mounted in the room  12  but conceivably held by another individual, to take images without interference by the system  10  of the present invention. This may be done most simply when there is a constant periodicity  62  (in the case of  FIG. 2 ) by ensuring that the exposure window  54  of the authorized camera  32  exactly equals an integer multiple of the periodicity  62 . This information may be communicated from the modulator  30  to the authorized camera  32  either in the form of exposure time value, or start and stop signals having a separation of that time. It will be appreciated that the authorized camera  32  may conversely control the modulator  30  to similar effect. 
     Referring to  FIG. 4 , in the case of a varying modulation frequency, the authorized camera  32  may receive a set of different values for periodicity  62   a  and periodicity  62   b  as those periodicities change under control of the modulator  30 . That is, the authorized camera  32  may receive periodicity period  62   a  during time period (I) and set its exposure window  54   b  to equal in length to a predetermined integer multiple of this periodicity  62   a  and may receive periodicity period  62   b  during time period (II) setting its exposure window  54 ′ b  equal to the same integer multiple of this periodicity period  62   b . In both time intervals (I) and (II), the cumulative exposures  59 ′ will be identical. Note that the authorized camera  32  need not align its exposure window  54   b  with the periodicity  62   a  and  62   b  (that is, phase alignment is not required) but rather only frequency matching is necessary. 
     In this way, the authorized camera  32  may provide for consistently exposed CMOS rows  42  despite the widely varying illumination frequencies. Again, it will be appreciated that this information can be communicated to the authorized camera  32  by a variety of means including a wire or wireless signal from the modulator  30  or maybe derived by observing the light fixtures  18 , for example, to count illumination periods  52  to provide consistent exposure for each CMOS row  42 . 
     Referring now to  FIG. 5 , after the exposure windows  54  have been completed for each row of the image  60  there may be a blanking interval  76  separating a second scan of each of the rows of the image  60 . This blanking interval  76  is a normal part of camera operation and is a time during which there are no exposures of any of the rows  42  and may be used by the camera for processing or data transfer. In one embodiment, the present invention contemplates that during this blanking interval  76 , the light fixtures  18  may be activated to provide a random or pseudorandom pulse sequence  78  (or any arbitrary pulse sequence) matching the duty cycle occurring during regular exposure of the sensor. The cumulative exposure  59 ′ of the authorized camera  32  will not be affected by this pulse sequence which occurs during its blanking interval  76 , but an unauthorized camera  16  out of phase with the authorized camera  32  will capture these pulses  78  driving its cumulative exposure  59 ″ into overexposure indicated by the crosshatched portion of the graph of cumulative exposure  59 ″. Coordination of the blanking interval  76  with the operation of the light fixtures  18  may be done by communication from the authorized camera  32  to the central modulator  30  or vice versa with either device acting as a master. 
     The invention is ideally suited for a closed environment where 40 percent or more and typically 50 percent or more, or desirably 80 percent or more, of the light in the room  12  is provided by the light fixtures  18 . In this way, high contrast between the on and off times of the light fixtures  18  is ensured. Nevertheless, the invention also contemplates use in environments that may not consistently provide this level of illumination control, for example, because of sunlight coming through windows or auxiliary light sources or the like. In such cases, the modulator  30  may move from an image blocking mode, in which the images acquired by the unauthorized camera  16  are blocked through dark or overexposed bands  55  and  57  as described above, to a barcode mode where the mechanism of producing the dark and overexposed bands  55  and  57  is used to produce low contrast and possibly non-obscuring bands in the image collected by the unauthorized camera  16 . In this latter mode, the bands  55  and  57  form a “barcode” that can be used later, after the images are displayed, to identify pictures taken in restricted areas either for policing or through automatic systems that refuse to display or transmit such pictures. 
     Referring to  FIG. 8 , this barcoding may be accomplished in one embodiment through a set of relatively low contrast bars  79  providing two regions  80   a  and  80   b  distributed across the image  60  and corresponding to different times during the acquisition of that image  60 . The bars  79  in the region  80   a  may have a first frequency that is in a first fixed frequency ratio to the frequency of the bars in region  80   b . This first fixed frequency ratio R may uniquely encode the fact that indicates that the image  60  was taken in a restricted area. 
     The bars  79  may be either slightly overexposed or under exposed and may be sensitively recovered from any image  60 , even in low contrast, through the use of a Fourier transform that averages all columns of data (rows in the depicted image of  FIG. 8 ) and analyzes frequency content to isolate particular frequencies. In this regard, the bars  79  may be created through extremely short duty cycles of illumination periods  52  of the light fixtures  18  such as enforces a high-frequency content on the image  60  that may exceed the optical bandwidth of the camera thus being readily distinguishable from the image  60  itself. 
     It will be appreciated that multiple different frequency pairs may be used for regions  80   a  and  80   b  encoding the same or a set of frequency ratios R i  to provide either greater noise immunity or to encode a series of values, for example, expressing text messages or the like. It will further be understood that the regions  80   a  and  80   b  may be distributed in any fashion in the image  60  and thus there is no need to coordinate this encoding with the acquisition timing of the unauthorized camera  16 . It will further be appreciated that because a ratio is being considered, this information is not lost when the unauthorized camera  16  employs a range of different exposure times which may affect the physical band size and spacing in the image  60  but not the frequency ratio. 
     Additional robustness can be obtained by encoding the same or independent frequencies in each of the different color channels of red, green, and blue of the image by separate modulation of the LEDs of the light fixtures  18 . Each of these different channels may be individually decoded to determine the necessary values of R or multiple values of R. 
     Using the barcoding system, the present invention may switch from a unilateral to a bilateral mode of operation that works even when the external light source greatly exceeds the power of the light fixtures  18 . Such a system could conceivably be used in daylight with a directed beam of light from a fixture  18  on the object to be barcoded for protective purposes. 
     Referring now to  FIG. 5 , the system  10  of  FIG. 1  may operate through a program executed on the modulator  30  to first check the ambient light as indicated by decision block  90 . This check may be done through a separate light detector or may make use of a signal from the authorized camera  32  to determine whether the ambient light is primarily provided by the fixtures  18  or whether there is additional unmodulated light from an external source that would corrupt the process of providing privacy protection. In this regard, the sensor or authorized camera  32  may measure light in the room at the time the light fixtures  18  are turned off. If there is an interfering light source illuminating the room beyond a predetermined value, the latter of which may be determined for each environment, such as would prevent obscuring of images taken by unauthorized camera  16  in the room  12 , the system  10  may move to a barcoding mode. 
     In the barcoding mode and at process block  92 , the barcoding frequencies and phase or the like may be provided to the authorized camera  32  so that the authorized camera  32  may coordinate acquisitions to eliminate any obscuring barcode in the images acquired. This coordination adjusts the exposure window  54  of the authorized camera  32  in a manner described above with respect to obscuring bands  55  and  57 . In some embodiments, the barcoding may be faint enough so that this step need not be performed. 
     After any updating of the authorized camera  32 , the central modulator  30  may modulate the light of the fixtures  18  to multiple frequencies as indicated by process block  94  and  96  producing the barcoding bands of regions  80   a  and  80   b  shown in  FIG. 8  and described above. These frequency pairs may then be cycled with new frequency pairs having the same or different ratios as indicated by process block  98  and this process repeated indefinitely (so long as the interfering external light signal detected at decision block  90  is present) to provide for continuous barcoding. The resulting low contrast bars  79  in the barcoding mode may allow greater than four bits of image information to be communicated through the bar  79 . 
     If at decision block  90 , the ambient light is primarily provided by the fixtures  18  (for example, in excess of 50 percent) then, again, authorized camera  32  may be updated with modulation information that will be used for blocking normal photography, as indicated by process block  100 , so that the authorized camera  32  can avoid having obscuring bands  55  and  57  in its image. Next, the modulation pattern may be imposed on the light fixtures  18  indicated by process block  102  as discussed above with respect to  FIGS. 2 and 4 . At least one of the obscuring bands  55  and  57  may prevent more than four bits of image information from being viewed through the bar over an area of at least 20 percent of the image  60 . 
     Referring to  FIG. 6 , the authorized camera  32  receiving the update information at either process block  92  or  100 , as indicated by process block  104 , may then synchronize its acquisition of image data as discussed with respect to  FIG. 4  as indicated by process block  106 . 
     Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
     When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     References to “a microprocessor” and “a processor” or “the microprocessor” and “the processor,” can be understood to include one or more microprocessors that can communicate in a stand-alone and/or a distributed environment(s), and can thus be configured to communicate via wired or wireless communications with other processors, where such one or more processor can be configured to operate on one or more processor-controlled devices that can be similar or different devices. Furthermore, references to memory, unless otherwise specified, can include one or more processor-readable and accessible memory elements and/or components that can be internal to the processor-controlled device, external to the processor-controlled device, and can be accessed via a wired or wireless network. 
     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.