Methods and arrangements for enhancing detection of digital watermark signals
AssigneeDigimarc Corporation
InventorsVojtech Holub, Tomas Filler
Life of this patent
Estimating the term…
Abstract
In an illustrative embodiment, watermark decoding reliability is increased, for images of watermarked objects captured at close distances, by reducing influence of pixel noise (e.g., shot noise). In the same or different embodiment, watermark decoding reliability is increased, for images of watermarked objects captured from far distances, by reducing image under-sampling. A particular implementation down-samples input imagery twice—a first time by a fixed factor, preparatory to performing an FFT, and a second time by a variable factor, preparatory to submitting the image for decoding, where the variable factor is determined using results from the FFT. A number of other features and arrangements are also detailed.
Claims18
A method comprising the acts:
- capturing imagery depicting a packaged retail item, using a 2D image sensor having at least 256 rows by 256 columns of photodetectors;
- down-sampling unfiltered data from the 2D sensor by a scale factor k, to produce a first set of down-sampled imagery;
- performing an FFT on the first set of down-sampled imagery, transforming the captured imagery into frequency domain image data;
- determining affine transformation of a digital watermark signal within the frequency domain image data, including an affine scale factor j;
- down-sampling the unfiltered data from the 2D sensor, said down-sampling comprising first upsampling by a factor q, and then down-sampling by a factor p using box-filtering, wherein a ratio p/q differs from a product jk by 5% to 25%;
- and
- providing the second set of down-sampled imagery to a digital watermark decoder to extract plural-bit payload data conveyed by the digital watermark signal;
- wherein pixel noise in the second set of down-sampled imagery has a lower standard deviation than pixel noise in the first set of down-sampled imagery.
A point of sale scanner apparatus for a retail checkout, comprising:
- first means for estimating a scale of a digital watermark signal within captured imagery;
- and
- second means, responsive to scale data produced by the first means, for producing transformed image data to be provided to a digital watermark decoder, wherein noise in the transformed image data has a smaller standard deviation than noise in the captured imagery.
A method comprising the acts:
- capturing 2D image data from a substrate region that is mostly unprinted, said substrate region bearing a dot pattern that encodes plural bits of information, the captured 2D image data depicting the substrate region from an unknown distance, resulting in an unknown pixels-of-imagery-per-inch-of-substrate scale;
- down-sampling the captured 2D image data by a first factor, yielding first down-sampled 2D image data;
- determining a scale factor for the dot pattern depicted in the first down-sampled 2D image data;
- down-sampling the captured 2D image data by a second factor based on said determined scale factor, yielding second down-sampled 2D image data;
- and
- decoding said plural bits of information from the dot pattern depicted in said second down-sampled 2D image data.
Dependencies are inferred from the claim text.