Optimizing optical scanners for digital watermark detection
The present disclosure relates generally to digital watermarking for retail product packaging. A digital watermark can be carried in different color channels, and at with different signal polarities. Detection can utilize different illumination sources or image sensors with various filters to highlight signal in one or more of the channels.
1. A method comprising:
illuminating a substrate with a first LED, the first LED providing illumination in a red spectrum, in which the first LED provides illumination having a peak in a range between 630 nm-710 nm;
illuminating the substrate with a second LED, the second LED providing illumination in a blue spectrum, in which the second LED provides illumination having a peak in a range between 410 nm-490 nm;
illuminating the substrate with a third LED, the third LED providing illumination in a green spectrum, in which the third LED provides illumination having a peak in a range between 500 nm-565 nm;
capturing imagery with a 2D monochrome image sensor, in which the captured imagery comprises a first image capture corresponding to illumination by the first LED and the second LED, in which the first image capture comprises data representing a cyan channel and a yellow channel, with each of the cyan channel and the yellow channel comprising a digital watermark embedded therein at a first signal polarity, and in which the captured imagery comprises a second image capture corresponding to illumination by the third LED, in which the second image capture comprises data representing a magenta channel, the magenta channel comprising a digital watermark embedded therein at a second signal polarity that is inversely related to the first signal polarity;
transforming the first image capture by subtracting the second image capture therefrom to yield transformed image data;
analyzing the transformed image data with a digital watermark detector to detect a digital watermark.
2. A point of sale system comprising an image sensor and one or more processors, said one or more processors configured to perform the method of claim 1 .
3. The method of claim 1 further comprising introducing a delay between illuminating the substrate with the first LED and illuminating the substrate with the second LED, and illuminating the substrate with the third LED, in which the first LED and the second LED are concurrently illuminated.
4. The method of claim 3 in which the delay comprises a delay in the range of 1/40 Hz to 1/80 Hz.
5. The method of claim 1 in which the 2D monochrome image sensor comprises a first 2D image sensor and a second 2D image sensor, in which the first 2D image sensor captures the first image capture, and in which the second 2D image sensor captures the second image capture.
6. The method of claim 1 in which the captured imagery represents product packaging including an encoded signal printed thereon.
7. A method comprising:
capturing image data with an image sensor, the image sensor comprising rows and columns of photo-detectors, the image sensor comprising a first set of photo-detectors arranged with a first set of green filters, and a second set of photo-detectors arranged with a first set of magenta filters, in which for at least four co-located blocks of photo-detectors, there are two magenta filters diagonally arranged, and two green filters diagonally arranged within each 2×2 block of photo-detectors;
processing the captured image data by subtracting image data captured by the first set of photo-detectors from image data captured by the second set of photo-detectors, said processing yielding processed image data; and
analyzing the processed image data to detect a digital watermark therein.
8. A point of sale system comprising an image sensor and one or more processors, said one or more processors configured to perform the method of claim 7 .
9. The method of claim 7 in which the captured image data represents product packaging including digital watermarking.
10. The method of claim 7 in which the digital watermark comprises a signal with a first polarity which is included in the image data captured by the first set of photo-detectors, and a second signal which is included in the image data captured by the second set of photo-detectors, in which the second signal includes a second polarity that is inversely related to the first polarity.
11. A method comprising:
capturing image data with an image sensor, the image sensor comprising rows and columns of photo-detectors, the image sensor comprising a first set of photo-detectors arranged with a first set of green filters, and a second set of photo-detectors arranged with a first set of magenta filters, in which for at least a 4×4 block of photo-detectors the first set of green filters comprises a 1:3 ratio relative to the first set of magenta filters;
processing the captured image data by subtracting image data captured by the first set of photo-detectors from image data captured by the second set of photo-detectors, said processing yielding processed image data; and
analyzing the processed image data to detect a digital watermark therein.
12. A point of sale system comprising an image sensor and one or more processors, said one or more processors configured to perform the method of claim 11 .
13. The method of claim 11 in which the captured image data represents product packaging including digital watermarking.
14. The method of claim 11 in which the digital watermark comprises a signal with a first polarity which is included in the image data captured by the first set of photo-detectors, and a second signal which is included in the image data captured by the second set of photo-detectors, in which the second signal includes a second polarity that is inversely related to the first polarity.
15. A method comprising:
capturing image data with an image sensor, the image sensor comprising rows and columns of photo-detectors, the image sensor including a first set of photo-detectors arranged with a first set of green filters, the image sensor also including a second set of photo-detectors arranged with a first set of magenta filters, in which for at least four co-located blocks of 2×2 photo-detectors there are three (3) magenta filters arranged per one (1) green filter within each 2×2 block of photo-detectors;
processing the captured image data by subtracting image data captured by the first set of photo-detectors from image data captured by the second set of photo-detectors, said processing yielding processed image data; and
analyzing the processed image data to detect a digital watermark therein.
16. A point of sale system comprising an image sensor and one or more processors, said one or more processors configured to perform the method of claim 15 .
17. The method of claim 15 in which the captured image data represents product packaging including digital watermarking.
18. The method of claim 15 in which the digital watermark comprises a signal with a first polarity which is included in the image data captured by the first set of photo-detectors, and a second signal which is included in the image data captured by the second set of photo-detectors, in which the second signal includes a second polarity that is inversely related to the first polarity.