Color adaptive watermarking
AssigneeDigimarc Corporation
InventorsAlastair M. Reed, Geoffrey B. Rhoads
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Abstract
A color mapping process enhances a watermark by computing a change in colors that is less visible for a given watermark strength. The mapping process provides smooth transitions from one color region to another, and may be implemented efficiently with a 3D look up table. A user interface scheme enables the user to control encoding of the watermark in desired color regions.
Claims18
In a watermark encoder, a method of encoding auxiliary information in an image comprising:
- computing a change in an attribute of an image sample to encode auxiliary information in the image;
- and
- changing color values of the image sample to effect the change in the image sample attribute with minimized impact on visibility;
- wherein the color values are changed in a direction in color space that depends on original color values of the image sample such that the change in color values is adapted to the color of the image sample and the direction is selected to minimize impact on visibility.
In a watermark encoder, a method of encoding auxiliary information in an image comprising:
- computing a change in an attribute of an image sample to encode auxiliary information in the image;
- and
- changing color values of the image sample to effect the change in the image sample attribute with minimized impact on visibility;
- wherein the change in the image sample attribute is a change in chrominance, and the changes in the color components are made to have an equivalent change in chrominance.
In a watermark encoder, a method of encoding auxiliary information in an image comprising:
- computing a change in an attribute of an image sample to encode auxiliary information in the image;
- and
- changing color values of the image sample to effect the change in the image sample attribute with minimized impact on visibility;
- wherein the change in the image sample attribute is a change in a first vector in a color space for a first set of colors, and is a change in a second vector in the color space for a second set of colors;
- and the change in the image sample attribute is mapped to a change in color components of the image sample to effect the change in the first vector for image samples in the first set of colors, and to effect the change in the second vector for image samples in the second set of colors.
A method for assessing whether a watermark in an image is valid comprising:
- decoding a watermark using a color key that indicates how an attribute of an image sample is changed in watermark encoding based on color of the image sample, wherein the color key indicates colors in which the watermark is expected to be embedded, and the colors of watermark embedding vary depending on colors of the image;
- based on the decoding, determining whether the watermark is valid.
A method for assessing whether a watermark in an image is valid comprising:
- decoding a watermark using a color key that indicates how an attribute of an image sample is changed in watermark encoding based on color of the image sample;
- based on the decoding, determining whether the watermark is valid;
- for image samples in the image, using the color key to select a color channel or channels in which the watermark signal is expected to be the strongest;
- measuring a figure of merit of the watermark signal in the selected color channel or channels;
- and
- assessing validity of the watermark signal based on the measured figure of merit of the watermark signal in the selected color channel or channels.
A method for encoding auxiliary data into an image comprising:
- transforming blocks of the image into transform coefficients;
- altering the transform coefficients to encode the auxiliary data;
- determining a characteristic color of the blocks;
- wherein the transform coefficients are altered such that the auxiliary data is embedded in each block depending on the characteristic color of the block and the auxiliary data is embedded in a selected color that has reduced visibility for the characteristic color of the block.
Dependencies are inferred from the claim text.