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WO2016001339A1 - Communication de données de code à barres - Google Patents

Communication de données de code à barres Download PDF

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Publication number
WO2016001339A1
WO2016001339A1 PCT/EP2015/065049 EP2015065049W WO2016001339A1 WO 2016001339 A1 WO2016001339 A1 WO 2016001339A1 EP 2015065049 W EP2015065049 W EP 2015065049W WO 2016001339 A1 WO2016001339 A1 WO 2016001339A1
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WO
WIPO (PCT)
Prior art keywords
light
barcode
rolling
pattern
image
Prior art date
Application number
PCT/EP2015/065049
Other languages
English (en)
Inventor
Frederik Jan De Bruijn
Original Assignee
Koninklijke Philips N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips N.V. filed Critical Koninklijke Philips N.V.
Publication of WO2016001339A1 publication Critical patent/WO2016001339A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/114—Indoor or close-range type systems
    • H04B10/116—Visible light communication

Definitions

  • the present disclosure relates to barcodes, and particularly to an alternative method of communicating barcode data.
  • a barcode is a visibly-displayed, binary spatial pattern of light and dark stripes (typically black and white) that conveys data according to one of a number of predetermined barcode formats.
  • a barcode may be physically printed, e.g. on the packaging of a product or sticker to be applied to a product or its packaging, or on a printed document; or alternatively a barcode may be displayed on a graphical display, i.e. a computerized or electronic display, for instance as part of an electronic document.
  • the barcode may for example be used to identify a product to which it is applied, or in a document as proof of purchase, or to identify, verify or authenticate a holder of the document.
  • a barcode is formatted according to a barcode format, which is one of a number of predetermined, standardized formats for conveying data in the pattern of the barcode.
  • the barcode can read by a barcode reader based on a visible-light based technology, and a suitable algorithm or equivalent circuitry configured to recognize the barcode format.
  • the barcode reader may take the form of a dedicated laser-based barcode scanner, or a general purpose camera and a suitable application configured to read the barcode from an image captured by the camera based on image recognition techniques.
  • barcodes can also take the form of a two dimensional pattern, and need not necessarily even be limited to a binary pattern (e.g. the format could be based on three colors).
  • the present disclosure is primarily concerned with one-dimensional binary barcodes according to conventional, pre-existing formats.
  • barcodes are fixed to the surface on which they are printed.
  • Printed barcodes are relatively cheap and simple, e.g. being printed directly onto a product or document, or on a sticker applied to the product. However, they are also inflexible. If the barcodes are to be used to provide a temporary or changeable label, an image display is required to create the striped pattern, but this is more complex and costly.
  • Coded light is a technology whereby information is embedded into the visible light emitted by light sources such as everyday luminaires, using high-frequency light modulation at frequencies beyond human perception such that the primary function of illumination is not affected.
  • Coded light can be detected using rolling-shutter cameras such as are typically found in many mobile devices like smartphones and tablets.
  • a rolling-shutter camera is one in which the camera's image capture element is divided into lines (i.e. parallel rows or columns of pixels, typically horizontal rows) which are exposed one-after-another in a sequence.
  • the fast time- varying modulation in the light causes a striped spatial modulation over the lines in the images captured with a rolling-shutter camera.
  • this phenomenon is used to detect coded light using rolling-shutter cameras, but only based on formats such as line-coding formats (e.g. Manchester coding) that are not also designed for visible display or reading as are barcodes.
  • line-coding formats e.g. Manchester coding
  • coded light can in fact be used to cause a striped pattern in the lines of a rolling shutter camera that takes substantially the same form as a printed or graphically displayed barcode format. I.e. the modulation in the light can be used to send a "virtual barcode" that will form into a barcode pattern when captured in the lines of the rolling-shutter camera. The data then can be read by inputting the pattern from the rolling shutter image sensor into a conventional barcode-reader algorithm or circuit.
  • coded light thus broadens the applicability of existing barcode formats beyond printed or graphically displayed media; or conversely broadens the applicability of existing barcode- reader algorithms or circuits to the detection of coded-light.
  • the disclosed idea may extend the use of such embedded barcode 'scanning' applications to the detection of coded light.
  • a light- emitting apparatus for emitting light to be detected by a rolling-shutter camera, the rolling- shutter camera having an image capture element divided into a plurality of lines which are exposed in a sequence.
  • the light-emitting apparatus comprises a light source for emitting the light, and a controller for modulating the light emitted by the light source.
  • the controller is configured to encode data into the light using a time-varying binary modulation in the intensity of the light, formatted such that when detected by the rolling-shutter camera the time-varying binary modulation will form a binary pattern of light and dark stripes over the lines of the rolling-shutter camera according to a one-dimensional barcode format, this being pre-existing format that is also used for printed or graphically displayed one-dimensional barcodes.
  • the controller is configured to receive an input signal comprising data formulated for display according to said one-dimensional barcode format for printed or graphically displayed one-dimensional barcodes, and to convert to said input signal into said one-dimensional binary modulation of the light from the light source.
  • the controller can take a signal that was intended to generate a printed or graphically displayed barcode, and convert this instead to a coded light signal, but one which can still ultimately be read according to the same format by a conventional or existing barcode-reader algorithm or circuit.
  • the apparatus may comprising a barcode reader
  • the controller may be configured to receive said input signal by using the barcode reader to read a printed or graphically displayed barcode comprising said data.
  • the controller may thus convert the printed or graphically displayed barcode to said one-dimensional binary modulation of the light for detection using the rolling-shutter camera according to said same format.
  • the apparatus may comprise a diffuser arranged to diffuse said light before the detection by the rolling shutter camera. This can make the light flood a larger area of the camera's image capture element, enabling more reliable detection of the barcode image in the lines of the image capture element.
  • the controller may be configured to adapt the data such that the levels and/or spacing of the stripes in said binary pattern deviate from the barcode format within a tolerance of said barcode format; the data being adapted to reduce a visible flicker in the light caused by the data, reduced relative to a strict adherence to said format.
  • Existing barcodes will not result in a DC-free signal when converted to light modulation, which may lead to visible flicker in the light.
  • Embodiments of the present disclosure exploit the tolerance of existing barcode formats and their corresponding readers (originally designed to accommodate for factors such as imperfect reflection, faded or imperfect printing, damaged packaging, etc.) to deliberately vary the modulation of the light within the tolerance of the barcode format, to give a modulation that is closer to being DC- free (and therefore flicker free).
  • a corresponding receive-side device comprises a barcode-reader module for reading printed or graphically displayed one-dimensional barcodes according to a one- dimensional barcode format, and a rolling-shutter camera for receiving light emitted by a light source.
  • the rolling-shutter camera is arranged to capture an image over a plurality of lines, each line of the image representing the received light captured at a successive time, and the device further comprises an image processing module for processing said image.
  • Data is encoded into the light using a time- varying binary modulation in an intensity of the light, formatted such that when detected by the rolling-shutter camera the time- varying binary modulation forms a binary pattern of light and dark stripes over the lines of the rolling- shutter camera according to said one-dimensional barcode format; and the image processing module is configured to perform one or more coded-light processing operations on the image in order to prepare said pattern for reading by the barcode-reader module according to the barcode format, and, following said processing, to output the pattern to the barcode-reader module for reading the data from said pattern according to said format.
  • said one or more coded-light processing operations may comprise: applying a Wiener filter or other filter to mitigate a filtering effect of an exposure time of the camera.
  • said one or more coded-light processing operations comprise: producing an average background by averaging a plurality of frames captured by the camera at a frame rate, and subtracting the averaged background from said image, wherein the barcode pattern is repeated in said modulation with a repetition rate, and wherein each of said plurality of frames experiences the barcode pattern at a different spatial offset due to the repetition rate not matching the frame rate, said averaging thereby generating the averaged background image with the modulation substantially removed.
  • the barcode-reader module may be a barcode reader application (i.e. software), for example embedded in an operating system of the device, or running on the operating system.
  • a barcode reader application i.e. software
  • the image processing module may be configured to de-focus the camera from the light source to obtain a greater coverage of the light over the image than if focused on the light source. This may be used as an alternative to (or even in addition to) the diffuser between the light source and camera.
  • the device may be a mobile device (e.g. smartphone or tablet), and may comprises a user interface configured to output directions to a user to hold the device in a suitable orientation for capturing said pattern in the lines of the rolling-shutter camera according to said barcode format.
  • a mobile device e.g. smartphone or tablet
  • the device may comprises a user interface configured to output directions to a user to hold the device in a suitable orientation for capturing said pattern in the lines of the rolling-shutter camera according to said barcode format.
  • the image processing module may comprise an image processing application for processing the pattern prior to being output to the barcode- reader module for reading; and the device may be operable to communicate via a first medium, other than time- varying binary modulation of light being used to form a barcode in the lines of the rolling-shutter camera.
  • the first medium may comprises an RF channel, or the use of said camera or another camera of the device to read a printed or graphically displayed barcode.
  • the device may then be configured to obtain a link for downloading the image processing application or an update thereto via the first medium, to download the image processing application or update based on said link as obtained via the first medium, and to subsequently use the image processing application or update to detect said pattern and output the pattern to the barcode-reader module. For instance if a user has a device not already equipped to obtain the barcode formatted data from the coded light, the user can exploit the existing barcode-reader functionality in the more conventional manner in order to obtain the software for the new way of obtaining barcode data.
  • the device may comprise a transmitter (e.g. RF) for sending messages to the light source.
  • a controller of the device may then be configured to send a message to the light source via said transmitter requesting that the light source switches to a mode in which it modulates the light with said time- varying binary modulation.
  • a method comprising: controlling a light source to emit light to be detected by a rolling-shutter camera, the rolling-shutter camera having an image capture element divided into a plurality of lines which are exposed in a sequence; and encoding data into the light using a time- varying binary modulation in an intensity of the light, formatted such that when detected by the rolling-shutter camera the time-varying binary modulation will form a binary pattern of light and dark stripes over the lines of the rolling-shutter camera according to a one-dimensional barcode format, being a same format as used for printed or graphically displayed one- dimensional barcodes.
  • the method may further comprises steps in accordance with any of the emitting or receive side operations disclosed herein.
  • a computer program product comprising code embodied on at least one computer-readable storage medium and configured so as when executed on one or more processors, to perform operations of the emit-side controller, image processing module and/or receive-side controller according to any of the embodiments disclosed herein.
  • the computer-program product may be stored locally at the apparatus or device, and/or on a server comprising one or more server units at one or more sites (being downloadable from the server to the apparatus or device), and/or any other storage medium or media or combination.
  • Fig. 1 is a schematic block diagram of a system comprising a light emitting apparatus and a device with a camera;
  • Fig. 2 is another schematic block diagram of a system comprising a light emitting apparatus and device with camera;
  • Fig. 3 is a schematic block diagram of a mobile device
  • Fig. 3a is a schematic block diagram of an emit-side apparatus comprising light source, controller and input barcode scanner;
  • Fig. 4 schematically illustrates an image capture element of a rolling-shutter camera
  • Fig. 5 schematically illustrates a barcode pattern formed in the lines of a rolling-shutter camera
  • Fig. 6 is a timing diagram of a rolling-shutter capture process
  • Fig. 7 is a picture of a product with barcode
  • Figs. 8a and 8b show images captured by a rolling-shutter camera comprising a barcode pattern formed by modulation in the captured light;
  • Figs. 9a and 9b show an example of a barcode pattern and an example of a modified barcode pattern
  • Figs. 10a and 10b show an example of a signal associated with a barcode pattern and an example of a signal associated with a modified barcode pattern
  • Fig. 11 shows an example of magnitude responses associated with a barcode pattern and a modified barcode pattern
  • Fig. 12 is a schematic block diagram, illustrating an example barcode signal modification method.
  • light is modulated so that when captured by a rolling-shutter camera, it forms a spatial pattern that conforms with one of the pre-existing barcode formats used for printed or graphically displayed barcodes, such that the captured pattern can be read by a conventional barcode reader application or circuit.
  • the modulation in the light is used to send a "virtual barcode" that will form on the image sensor of the rolling-shutter camera.
  • the detected pattern is the same; and as the pattern is the same, there is in principle no need for additional detectors other than the barcode scanner application or circuit.
  • Figures 1 and 2 schematically illustrate examples of a system set-up for implementing the encoding of barcodes via the modulation of light (as used by the inventor to demonstrate the concept).
  • the system comprises a light source 4, for example an LED-based lamp comprising one or more LEDs.
  • the light source 4 is connected to a controller 2 via a driver (not shown) allowing the controller to control the emission of light from the light source 4, at least in that the controller 2 is able to modulate the light 5 emitted by the light source 4 with a time-varying modulation.
  • the system also comprises a device 6 which in embodiments takes the form of a user terminal, preferably a mobile user terminal such as a smartphone or tablet. This device 6 comprises a rolling-shutter camera 8.
  • the light source 4 is arranged so that at least some of the light 5 it emits can be captured by the camera 8.
  • Figure 1 shows an alternative arrangement in which the camera 8 captures a reflection of the modulated light 5 via an illuminated surface 10.
  • the controller 2 comprises a function generator that is arranged to repeatedly transmit, by means of this modulation, a binary pulse train that corresponds to the binary pattern of a barcode. I.e. it modulates the light with a signal such that the rolling shutter capture by the camera 8 results in a spatial barcode pattern with the same characteristics as a printed barcode, as will be discussed in more detail below.
  • the controller may be
  • the light source's controller 4 is implemented in software stored on a memory and arranged to be executed on a processor of the light source 4, or connected to the light source 4. Alternatively it is not excluded that some or all of the functionality of the light source's controller 4 is implemented in dedicated hardware circuitry, or in configurable or reconfigurable circuitry such as a PGA or FPGA.
  • a “rolling shutter” camera is the type of camera usually integrated into a mobile phone or tablet.
  • the camera's image capture element is divided into a plurality of lines (typically horizontal lines, i.e. rows) which are exposed in sequence line-by-line.
  • lines typically horizontal lines, i.e. rows
  • sequence typically in order across the frame, e.g. in rows top to bottom, hence the name “rolling shutter”.
  • Figure 4 represents the image capture element 20 of an example rolling-shutter camera, as used in the camera 8.
  • the image capture element 20 comprises an array of pixels for capturing signals representative of light incident on each pixel, e.g. typically a square or rectangular array of square or rectangular pixels.
  • the pixels are arranged into a plurality of lines, e.g. horizontal rows 22.
  • T exp To capture a frame each line is exposed in sequence, each for a successive instance of the camera's exposure time T exp .
  • the exposure time is the duration of the exposure of an individual line.
  • a sequence in the present disclosure means a temporal sequence, i.e. so the exposure of each line starts at a slightly different time. For example first the top row 221 begins to be exposed for duration T exp , then at a slightly later time the second row down 22 2 begins to exposed for T exp , then at a slightly later time again the third row down 22 3 begins to be exposed for T exp , and so forth until the bottom row has been exposed. This process is then repeated to expose a sequence of frames.
  • Figure 6 shows a timing diagram an example rolling shutter process, each line being exposed in turn for time T exp , at a line rate fii ne .
  • the exposure times may overlap, i.e. the next line 22 2 starts being exposed after its preceding line22i but not necessarily before that preceding line 221 has finished being exposed, and so forth (also therefore T exp is not necessarily equal to 1 / fiine) -
  • the process may repeat over multiple frames at a rate f fra me, thus providing continuous video capture. Alternatively a single still image may be used.
  • the light 5 is coded with a binary modulation (on-off or high- low intensity), with the timing of the modulation being tuned relative to the line rate j ine of the target camera 8 (or a range of target cameras). If the momentary modulation level of the light 5 is on or high when a given line 22 is being exposed, then then line will record a light stripe in the captured image, corresponding to a "white” stripe of the barcode format. If on the other hand the momentary modulation level of the light 5 is off or low when a given line 22 is being exposed, then that line will record a dark stripe in the captured image, corresponding to a "black" stripe of the barcode format.
  • a binary modulation on-off or high- low intensity
  • each barcode stripe covers one or a few lines 22 of the image capture element 20, and the pattern of at least one whole barcode fits into the image capture element 20.
  • the condition is "at least one", as the barcode pattern is preferably transmitted from the light source 4 in a repetitive fashion (repeated instances of the pattern are concatenated, with a small space between them).
  • the detection by a conventional barcode scanner application or circuit will stop after one detection, which is standard behavior of barcode scanners to avoid bursts of multiple detections from the same barcode.
  • the condition "at least one” is added here to ensure that each image of video stream always contains at least one single, not-truncated barcode. If two or more instances of the barcode pattern are transmitted in the space of one frame, this means one barcode including idle interval will occupy less than half an image height.
  • L the number of channel symbols of a single barcode including possible leading and or trailing guarding symbols
  • r idle the time interval between consecutive barcode repetitions to create the required spatial separation within a captured image (a "quiet zone")
  • H the number of lines in a captured image.
  • the shutter time (i.e. line exposure time) r exp of a rolling shutter camera produces a filtering effect which can cause inter- symbol interference in coded light detection.
  • this filtering effect manifests itself in lack of "sharpness" in the captured barcode pattern.
  • the exposure time of the camera 8 is locked to a very small value in order to cause a sufficiently "sharp" appearance of the modulated light signal.
  • the exposure time is the temporal equivalent of the spatial "measuring aperture" for printed barcodes, which according to ISO/IEC 15416 is chosen to be smaller than 80% of the spatial symbol size. Therefore by analogy, the condition: can for example be used as condition for the exposure time. Alternatively longer exposure times can be accommodated by applying a suitable filter such as Wiener filter to mitigate the filtering effect of the camera's exposure time (to at least some extent).
  • a diffuser screen or layer 9 may be placed between the light source 4 and the camera 6. This helps ensure the light 5 more fully floods the whole area of the image capture element 20, as the aim is to capture the time- varying modulation in the light rather than to capture a picture of the light source (i.e. there is no need for any details of the light source to be identifiable in the image).
  • the reflecting surface 10 may act as a diffuser if it predominantly causes diffusive reflection rather than mirror reflection.
  • a diffuser 9 or 10 may not be required at all.
  • the controller 17 may be configured 17 to defocus the camera 8, so that it is not focused on the light source 4 and hence the image capture element 20 is flooded with light from the light source. Another possibility is that no diffuser or defocussing is used, and instead the device 6 is held close to the camera 8, or the light source 4 has a large emitting area.
  • Figure 7 shows an example of a barcode printed on the packaging of a product
  • Figures 8a and 8b show a detail of the corresponding pattern (from an actual capture) seen by a rolling-shutter camera 8 in an example experiment performed by the inventor using the disclosed techniques (in this example with use of a diffuser 9).
  • Figure 8a shows a detail of the captured pattern under relatively non-uniform illumination of the sensor and using an exposure time T exp that is larger than the duration of a single channel symbol, such that the pattern appears smeared along the vertical direction.
  • Figure 8b shows a detail of the captured pattern under relatively uniform illumination of the sensor and using an exposure time that is shorter than the duration of a single channel symbol, such that the pattern appears sharp along the vertical direction.
  • FIG. 3 shows more detail of the receiving device 6.
  • the receiving device 6 comprises: the rolling-shutter camera 8, optionally an image processing module 14 coupled to the camera 8, and a barcode reader module 16 coupled to the image processing module 14 or directly to the camera 8.
  • the device 6 also comprises a controller 17 and a transmitter 18 coupled to the controller 17.
  • each of the image processing module 14, barcode reader module 16 and controller 17 is implemented as a portion of code stored on a memory of the device 6 and arranged for execution on a processor of the device 6.
  • modules 14, 16, 17 is implemented wholly or partially in dedicated hardware circuitry, or configurable or reconfigurable circuitry such as a PGA or FPGA.
  • the barcode reader module 16 is configured to read barcodes according to one or more conventional barcode formats, i.e. the same format as already used for printed and/or graphically displayed barcodes.
  • the barcode reader module 16 takes the form of a barcode reader application (i.e. software), either included as part of the device's operating system or as a separate application running on the operating system. It may have been originally included on the device 6 (e.g. phone or tablet) for the purpose of reading barcodes from images of visibly-displayed barcodes captured by the camera 8.
  • no special coded-light processing is required, and image formed directly by the modulation on the image sensor 20 can be output straight to a conventional barcode reader module 16.
  • T exp exposure time
  • ISO sensitivity
  • the fact that the pattern has been formed from time-varying modulation in the light falling on the rolling-shutter image sensor 20 may introduce some artefacts that need to be mitigated before the image can be supplied to the barcode reader 16, and/or this fact may provide opportunities for further enhancing the image before being read by the barcode reader 16 . In these cases some extra signal processing may be required or desired in order to prepare the pattern for input to the barcode reader module 16.
  • the receiving device 6 is provided with an image processing module 14 configured to receive the image formed in the lines of the image capture element 20 of the camera 8 due to the invisible modulation of the light 5, and to process the image based on one or more coded- light image processing techniques in order to enhance the barcode pattern into a form suitable for reading by the barcode reader module 16 based on the same, conventional barcode format as used for reading printed or graphically displayed barcodes.
  • the image processing module 14 then outputs at least a portion of the processed image comprising the pattern (or even the pattern represented as a ID digital signal) to the barcode reader 16 to be read according to aid barcode format.
  • image processing may be required to remove the non-uniformity before the barcode pattern can be detected by the barcode reader module 16. This can be performed by taking an average image resulting from multiple captured images, on the basis of the repeated barcode pattern being repeated with a timing such that the light modulation has a different spatial vertical offset in each image.
  • the image processing module 14 is arranged to receive a plurality of frames captured by the rolling-shutter camera, e.g. a sequence of contiguous frames, thus forming a "stack" of images. Further, the modulation encoding the barcode pattern is repeated multiple times. Each repetition can be thought of as a packet having a duration T pac k e t. E.g.
  • T pac k e t niT sym b 0 i + Tidie-
  • 1/ T pac k e t is not equal to an integer multiple of the frame rate ff rame (and preferably not a simple ratio such as a half integer multiple) then each of the frames in the stack will experience the barcode pattern at a different respective spatial offset within the respective frame (e.g. different vertical offset in the case of horizontal rows 22). I.e. the pattern "rolls" across the image over multiple frames.
  • the image processing module 14 obtains an averaged background image with the effect of the modulation substantially removed.
  • the image processing module then subtracts the averaged background image from the image that is to be supplied to the barcode reader module 16 ("substantially removed” meaning to a sufficient degree to allow reading of the barcode pattern by the barcode reader module).
  • the skilled person may also be aware of other coded light processing techniques which may be used to improve a pattern formed by light modulation in a rolling shutter-camera.
  • the processing by the image processing module 14 may be performed with the images in two-dimensional form or one-dimensional form.
  • the individual pixel samples of each line 22 are first averaged over the respective line to produce an average sample representative of the line, such that the image is represented by a ID set samples with one sample per line 22, e.g. per row.
  • the image processing module 14 may supply the output pattern to the barcode reader module 16 in 2D form or ID form.
  • the image processing module 14 may output the pattern to the barcode reader module 16 also in ID form (if the barcode reader is arranged to accept a digital ID signal representation of a barcode as an input).
  • ID form if the barcode reader is arranged to accept a digital ID signal representation of a barcode as an input.
  • the image processing module 14 may use the resulting ID form of the pattern to artificially re-generate a 2D image of the barcode pattern (with each ID sample simply being extended uniformly across the respective line it represents), and supply this re-generated 2D pattern to the barcode reader 16 (which will never need to know this was not a directly captured image).
  • the image processing module 14 may perform one or more general image processing operations such as:
  • the image processing module 14 detects the presence of the barcode pattern in the image and then, in response to the detection, decides to forward the image to the reader 16 unmodified (possibly with some processing such as contrast adjustment and/or rotation rotation); or
  • the image processing module 14 detects where the barcode pattern is located in the image, and extracts a portion of the image comprising the barcode pattern from the image (optionally with extra processing such as contrast adjustment and/or rotation) then forwards the extracted barcode pattern to the reader 16.
  • the barcode reader module 16 then reads and decodes the barcode from the image or pattern it receives from the image processing module 14, based on conventional barcode reading techniques.
  • any one both of (i) and (ii) may be intrinsic features of the barcode reader module 16 (designed to be used on an image of a printed or graphically displayed barcode captured in the conventional fashion, but which may equally work on the virtual barcode formed from the time- vary light modulation).
  • a user or application at the emitting side may simply provide the unencoded data that is desired to be communicated (e.g. a message or product identifier) to the controller 2 as its input.
  • the controller 2 then automatically formulates this into a digital barcode signal suitable for representation as a barcode (i.e. a sequence of Is and 0s coded to digitally represent the pictorial pattern of light and dark stripes according to the relevant barcode format), then modulates the light based on this signal.
  • the data may be generated by a device (e.g. mobile device at the emit-side) on the basis of a source of identification, validation or authorization information (e.g. for identifying validating or authenticating a user of the device).
  • This identification, validation or authorization data may be part of a database that is stored remotely or on the device 6.
  • the controller 2 may receive, as its input, data that has already been formulated into a digital barcode signal (i.e. that already digitally represents the pattern of light and dark stripes of a barcode).
  • the barcode signal may have been designed or intended by a user or application for printing on a physical surface, or for generating a barcode to be visibly shown on a graphical display.
  • the controller 2 of the lighting apparatus converts this into the light-encoded form disclosed herein.
  • the disclosed system is able to take barcode data originally intended or designed to generate a visible barcode and make this available in an alternative or additional form with little or no extra effort by the user.
  • the emit-side apparatus further comprises a barcode-scanner 1 (camera or laser based) for generating the input signal by reading an actual printed or graphically displayed barcode.
  • the barcode scanner 1 reads the actual physical barcode in order to determine the digital barcode signal represented by that barcode and then supplies this signal as an input to the controller 2 where it is converted into a modulated light signal 5 that will mimic the same spatial pattern when captured with a rolling-shutter camera 8.
  • the barcode reader 1 may be operable to read a nonlinear or 2D printed or graphical barcode (e.g. a QR-code), and the controller 2 may be configured to convert this into a modulated light signal that will mimic another, ID spatial barcode pattern representing the same data when captured with a rolling-shutter camera 8 (note that the use of modulated light with rolling-shutter capture cannot mimic 2D barcodes).
  • a nonlinear or 2D printed or graphical barcode e.g. a QR-code
  • the controller 2 may be configured to modulate the emitted light 5 so that the pattern it forms on the image capture element 20 of the rolling- shutter camera 8 will in fact deviate slightly from the barcode format, but nonetheless within a tolerance of that format (and therefore the tolerance of the barcode reader module 16 designed to read that format). Particularly, this deviation is controlled by the controller 2 in order to reduce a visible flicker caused by the coding in the emitted light 5.
  • Some dedicated coded light formats have the property that the signal average over the duration of a packet always adds up to zero, so each packet is DC-free. This property is desirable in many scenarios as it ensures the coding does not cause a visible flicker in the light, or at least substantially reduces visible flicker compared to other schemes (in fact complete imperceptibility of coded light follows from sufficient absence of low frequency contributions in the perceptible range from DC to about 200 Hz).
  • the barcode patterns could be encoded in the light 5 without concern for the non-DC-free property.
  • Light flicker perception thresholds are higher in cases where the luminous modulated structures are smaller, particularly where the light does not fill the periphery of the user's vision.
  • flicker will be much more noticeable, and so the encoding of traditional non-DC-free barcode formats in the light may not be so desirable without further measures being taken.
  • the controller 2 is configured to adapt the modulation in such a way that the packet containing the barcode is substantially DC-free (or at least has a lower DC content that it would otherwise), but nonetheless will still form a pattern in the captured image that will be recognized by the barcode reader module 16 at the receive side.
  • the DC-free property can be achieved by adaptation of symbol amplitudes (representing the printed '0' or ⁇ ').
  • the controller 2 is configured to exploit the fact that for printed (or graphically displayed) barcodes a certified detector has to be able to deal with variations in printed reflectivity (e.g. there are ISO guidelines on this).
  • the DC-free property may also be achieved by manipulation of the leading and trailing space around the code.
  • the system exploits the fact that the tolerances for detection of printed codes are broader than the tolerances for visible imperceptibility of light- embedded codes. An advantage therefore is that existing camera-based barcode readers require little or no adaptation to the system.
  • Figures 9a and 9b show examples of the barcode associated with the product barcode in Figure 7.
  • Figure 9a shows the original bi-level (black- and-white) pattern of the original barcode including the quiet zones left and right of the pattern, following the minimal requirements for robust detection as prescribed by ISO/IEC 15416.
  • Figure 9b shows an example of a modified barcode, which is based on the barcode in Figure 9a.
  • the modified barcode is not bi-level, but rather is modified into a multi-level code, such that intermediate grey-levels appear when printed. In Figure 9b these grey levels are depicted in a dithered fashion for reproducibility.
  • Figure 9b the modified barcode in Figure 9b is still compliant to ISO/IEC 15416 and it allows proper detection by a regular barcode scanner.
  • Figures 10a and 10b show examples of modulation signals associated with the product barcode in Figure 7.
  • Figure 11 shows an example of a magnitude response associated with the signals in Figures 10a and 10b and in this example based on a symbol-rate / sym boi of 4 kHz.
  • the modulation amplitude relative to the average light level can be expressed as a percentage of the average light level and can in principle be chosen at any value up to 100%, causing the light output to switch between 0 and a maximum level that is twice the average level.
  • the choice of a relative modulation depth smaller than 100% can be a compromise between visibility of light-flicker and detectability of the data embedded in the modulation.
  • Figure 10a shows an example of a signal associated with the original bi-level barcode of Figure 9a.
  • the channel- symbol value ⁇ ' is associated with the white spaces of the printed barcode and the channel- symbol value '-1 ' is associated with the black bars.
  • the signal in Figure 10a is not DC-free such that its application as a light- modulation signal can give rise to visible light flicker each time that a single packet (i.e. barcode) is transmitted in the light. In case of a repetitive transmission, the lowest light flicker frequency will be equal to the packet repetition frequency.
  • the magnitude response of a single packet is depicted in Figure 11 and indicated by the solid curve.
  • the solid curve shows the appearance of relatively strong signal magnitudes for the lower frequency range, part of which is in the range of perceptual flicker frequencies. This, in contrast to the dashed curve which is associated with the modified modulation signal depicted in Figure 10b.
  • Figure 10b shows an example of a modified modulation signal, and associated with the modified barcode in Figure 9b. Note that in this example this has been achieved by changing the signal levels associated with a bar and a space, "-1" and "1". In addition, each run of three or more equal channel symbols, have been replaced by sequence containing a variation in signal levels.
  • the modified signal is DC-free and has also been modified to exhibit a suppressed signal magnitude in the same lower- frequency range such that requirements for absence of visible light flicker are more easily met.
  • the modulation signal in Figure 10b exhibits jumps between a limited set of possible signal levels, which has a benefit in that the modulation-signal can be readily implemented through generation by an LED driver.
  • FIG. 12 shows a block diagram, schematically illustrating an example barcode signal modification algorithm for implementation in software and/or hardware of the emit-side controller 2, for generating a DC-free or substantially DC-free version of the barcode signal for modulation into the light 5 emitted by the light source.
  • the algorithm comprises: an input stage 24 for receiving an input signal in the form of an unmodified barcode signal, a convolution stage 26, a kernel (h) 28, a weighting (a) 30, a multiplication stage 32, a first subtraction stage 34, a signal averaging stage 36, a second subtraction stage 38, and an output stage for outputting the modified version of the barcode signal.
  • the convolution stage 26 receives an instance of the input signal from the input stage 24 and convolves it with the kernel (h) 28. The result of this is output to the multiplication stage 32 where it is multiplied with the weighting (a) 30. The result of this is output to the first subtraction stage 34 where it is subtracted from an instance of the input signal from the input stage 24.
  • the resulting output of the first addition stage 34 is supplied to the signal averaging stage 36 where it is averaged of the duration of a single packet.
  • the second subtraction stage 38 subtracts this averaged signal with the instantaneous version of the output of the first subtraction stage 34. The result of this second subtraction forms the output signal which is output via the output stage 40.
  • the input signal of the algorithm is the original bi-level barcode signal composed of a sequence of channel symbols valued or "1".
  • the output signal of the algorithm is a modified, multi-level barcode signal that is DC-free and exhibits less low- frequency signal energy relative to the input barcode signal.
  • the input signal is convolved with kernel and after multiplication with a weighting factor subtracted from the input signal to create an intermediate multi-level signal that exhibits suppressed low- frequency signal energy. Subsequently, after subtraction of the signal average, an output signal is composed that is also DC-free.
  • the signal average is a fixed value equal to the average of the intermediate barcode signal calculated over one single packet, i.e. one single barcode duration including the quiet zone of ten symbols between packets.
  • the symbol values may be varied randomly by a small amount within the tolerance of the relevant barcode standard. This will not result in a perfect DC-free signal, but the DC component can nonetheless be reduced relative to strict values of "-1" and "1".
  • the modifications to the symbol values may be determined empirically by testing trial modifications and observing the resulting DC component.
  • the coded light transmitter 2, 4 is broadcasting the barcode pattern
  • the top of the scan may correspond to the tail of the barcode pattern.
  • the detection of a barcode start need not be a problem, and in embodiments fractional barcode patterns are not misinterpreted.
  • barcodes can carry redundancy; for example in the EAN-13 barcode format, the last digit is in fact a decimal checksum that needs to match the checksum of the twelve preceding digits.
  • the barcode reader 16 can use this to check that a full barcode pattern (corresponding to one full instance of a barcode) has been successfully received.
  • the controller 2 at the transmit side obeys the minimal requirements for a quiet zone following the ISO/IEC15416 standard (or other barcode standard).
  • the quiet zone may also in fact be modulated, but this will still be within the standard tolerance of the barcode format.
  • the symbol clock such that at least two full barcode patterns fit inside in one image height (one frame), then at least one complete barcode pattern will always be visible (especially if the entire image or most of the image is filled with coded light).
  • a normal image-based barcode detection algorithm can detect the coded light without any need to stitch fractional messages before input to the barcode algorithm.
  • the image processing module 14 could use a coded- light stitching algorithm to stitch together partial barcode patterns from different frames.
  • the device 6 is a mobile device such as a smartphone or tablet
  • its controller 17 may be configured to output instructions to the user to hold the device 6 in an orientation that is most beneficial for capturing the pattern, e.g. so that the camera 8 faces the light source 4, and/or the light from the light source 4 more fully fills the view of the camera 8 in the case where no diffuser 9 is used.
  • the instructions may be output via a display (not shown) of the device 6, and/or audibly.
  • the device 6 may be equipped with a mechanism for bootstrapping itself, in case the device 6 comes pre-equipped with a barcode-reader application 16 but not the necessary image processing software 14 for obtaining the light- encoded barcodes from the light 5.
  • the device 6 may comprise an alternative communication means by which it can obtain a link (e.g. Internet link) from which it can download the image processing software 14 (or an update to existing image processing software).
  • the controller 17 may use the camera 8 and barcode reader application 16 to read a printed or graphically displayed barcode in the conventional fashion, and this barcode may communicate the link allowing the controller 17 to download the software 14 for adapting the device to be able to read light-encoded barcodes.
  • the device 6 does not have to rely on printed barcodes and can instead use their light-encoded equivalents.
  • the separate communication means could be an RF channel communicating to the device 6, e.g. an RF tag based on a near- field communication (NFC) technology, or a channel based on a short-range (unlicensed) RF transmission technology such as Wi-Fi, ZigBee or Bluetooth.
  • customers in a supermarket may be presented with a printed or graphically displayed barcode, an RF tag, or a Wi-Fi, ZigBee or Bluetooth signal; informing them via their devices 6 that they can scan LEDs on shelves to obtain more information.
  • the controller 17 of the device 6 is configured to use its transmitter 18 to communicate a trigger to the light emitting apparatus 2,4, requesting the controller 2 to switch to barcode output.
  • the trigger may be transmitted over a visible light communication link (in the opposite direction to the barcode data) or over an RF channel (with possible bidirectional communication).
  • An example use case could be where a user wants to obtain barcode data, but can't get physical access to the product. For instance, consider a scenario where the user wishes to check what type of light bulb is in a socket (e.g. which of multiple different types of LED-based bulb). During commissioning and/or assembly this is quite often done using barcodes, which works well if the bulb is in the user's hand where it can be easily scanned. If the bulb is an existing light in a ceiling and not readily accessible, another possibility would be to use a coded light ID, but that works only if a database or document is available linking the coded light ID to the barcode. Using embodiments of the present disclosure however, if this is not available, the device 6 could instead ask the bulb to output its barcode via the light it emits.
  • a socket e.g. which of multiple different types of LED-based bulb.
  • Another option would be to obtain barcode data from a product that is on display in a retail environment but not easily accessible, e.g. if the product is in a display case. If the product is illuminated with a light that can emit the barcode in accordance with embodiments of the present disclosure, the user may use his or her device 6 to ask the light to transmit the product's barcode in light-encoded form in order to see details of the product.
  • a light bulb or product may instead continuously emit a light-encoded version of its own barcode, or a product on display may be continuously be illuminated by or associated with light encoding the product's barcode.
  • a product on display may be continuously be illuminated by or associated with light encoding the product's barcode.
  • the same barcode pattern is simultaneously made available in two different alternative forms, both the printed or graphically displayed form of an actual barcode, and a light-encoded form in accordance with the techniques disclosed herein. The user may then detect the barcode pattern however he or she finds most convenient or feasible depending on factors such as the capability of his or her device 6 and/or the accessibility of the bulb or product.
  • a computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Image Input (AREA)

Abstract

L'invention concerne un appareil émetteur de lumière servant à émettre de la lumière destinée à être détectée par une caméra à obturateur déroulant, la caméra à obturateur déroulant possédant un élément de capture d'image divisé en une pluralité de lignes qui sont exposées dans une séquence. L'appareil émetteur de lumière comprend une source de lumière destiné à émettre de la lumière et un contrôleur destiné à moduler la lumière émise par la source de lumière. Le contrôleur est configuré pour coder des données dans la lumière à l'aide d'une modulation binaire variable dans le temps dans l'intensité de la lumière, formatée de telle sorte que lorsqu'elle est détectée par la caméra à obturateur déroulant, la modulation binaire variable dans le temps formera un motif binaire de bandes claires et sombres sur les lignes de la caméra à obturateur déroulant conformément à un format de code à barres unidimensionnel, celui-ci étant un format pré-existant qui est également utilisé pour les codes à barres unidimensionnels imprimés ou affichés sous forme graphique.
PCT/EP2015/065049 2014-07-03 2015-07-02 Communication de données de code à barres WO2016001339A1 (fr)

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US10491297B2 (en) 2016-07-21 2019-11-26 Signify Holding B.V. Detecting signals embedded in visible light
CN107800477A (zh) * 2017-10-12 2018-03-13 漳州立达信光电子科技有限公司 一种基于摄像头的可见光通信接收方法
FR3074383A1 (fr) * 2017-11-27 2019-05-31 Oledcomm Procede de reception d’un signal lumineux module de type signal vlc
WO2019120052A1 (fr) * 2017-12-19 2019-06-27 北京外号信息技术有限公司 Procédé et appareil de décodage d'informations transmises par une source optique
CN108023640A (zh) * 2018-01-09 2018-05-11 华南理工大学 一种基于平板灯和移动终端摄像头的可见光通信系统
CN108023640B (zh) * 2018-01-09 2024-02-13 华南理工大学 一种基于平板灯和移动终端摄像头的可见光通信系统
WO2020048635A1 (fr) * 2018-09-04 2020-03-12 Sew-Eurodrive Gmbh & Co. Kg Système et procédé pour faire fonctionner un système, comprenant une première unité de communication et une deuxième unité de communication
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FR3095726A1 (fr) * 2019-05-05 2020-11-06 Ellipz Smart Solutions Europe procédé de décodage d’un signal de communication lumineuse et système optoélectronique
WO2020225495A1 (fr) * 2019-05-05 2020-11-12 Ellipz Smart Solutions Europe Procédé de décodage d'un signal de communication lumineuse et système optoélectronique

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