Methods of watermarking documents
AssigneeXerox Corporation
InventorsYonghui Zhao, Shen-ge Wang
Life of this patent
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Abstract
Methods are provided for creating a fluorescent watermark within an image on a substrate, such as paper. The method involves creating a halftone image using two different halftone strategies. The halftone method is combined with a binary watermark mask to form two color patterns (e.g., one in a background region of the image and one in a watermark region of the image) and two successive-filling halftone algorithms, such that the ink droplets deposited by one color pattern cover more of the substrate than the ink droplets deposited by the other color pattern, with the two color patterns having approximately the same reflectance under normal light. However, under UV illumination, a visible difference (e.g., the watermark) is seen in the two patterns.
Claims20
A method of generating an ultraviolet (UV) fluorescent watermark in an image, comprising:
- selecting an electronic continuous-tone color image in an input color space for a document;
- generating a binary watermark mask that divides the continuous-tone color image into two regions including a watermark region and a background region;
- performing a first color transformation that converts the continuous-tone color image in the watermark region from the input color space to a first CMY color space;
- executing a successive-filling halftoning algorithm with a dot-on-dot strategy on the continuous-tone color image in the watermark region to generate a first binary output image in the watermark region;
- performing a second color transformation that converts the continuous-tone color image in the background region from the input color space to a second CMY color space;
- executing a successive-filling halftoning algorithm with a dot-off-dot strategy on the continuous-tone color image in the background region to generate a second binary output image in the background region;
- generating a watermarked binary output image embedded with UV fluorescent watermark by combining the first binary output image in the watermark region with the second binary output image in the background region;
- and
- printing the watermarked binary output image on a fluorescent substrate.
A method of generating an ultraviolet (UV) fluorescent watermark in an image, comprising:
- selecting an electronic continuous-tone color image in an input color space for a document;
- performing a first color transformation that converts the continuous-tone color image from the input color space to a first CMY color space;
- generating a binary watermark mask that divides the continuous-tone color image into two regions including a watermark region and a background region;
- executing a successive-filling halftoning algorithm with a dot-on-dot strategy on the continuous-tone color image in the watermark region to generate a first binary output image in the watermark region;
- performing a second color transformation that converts the continuous-tone color image in the background region from the first CMY color space to a second CMY color space;
- executing a successive-filling halftoning algorithm with a dot-off-dot strategy on the continuous-tone color image in the background region to generate a second binary output image in the background region;
- generating a watermarked binary output image embedded with UV fluorescent watermark by combining the first binary output image in the watermark region with the second binary output image in the background region;
- and
- printing the watermarked binary output image on a fluorescent substrate.
A system that facilitates generating UV fluorescent images using the successive-filling halftoning algorithms with both dot-on-dot and dot-off-dot strategies, comprising:
- a memory that stores, and a processor that executes, computer-executable instructions for:
- selecting an electronic continuous-tone color image in an input color space for a document;
- generating a binary watermark mask that divides the continuous-tone color image into two regions including a watermark region and a background region;
- performing a first color transformation that converts the continuous-tone color image in the watermark region from the input color space to a first CMY color space;
- executing a successive-filling halftoning algorithm with a dot-on-dot strategy on the continuous-tone color image in the watermark region to generate a first binary output image in the watermark region;
- performing a second color transformation that converts the continuous-tone color image in the background region from the input color space to a second CMY color space;
- executing a successive-filling halftoning algorithm with a dot-off-dot strategy on the continuous-tone color image in the background region to generate a second binary output image in the background region;
- generating a watermarked binary output image embedded with UV fluorescent watermark by combining the first binary output image in the watermark region with the second binary output image in the background region;
- and
- a printer that prints the watermarked binary output image on a fluorescent substrate.
Dependencies are inferred from the claim text.