IP Library › Granted Patent US 6,993,150
Granted Patent B2
US 6,993,150 · App. 10/052,895 · Granted Jan 31, 2006

Halftone primitive watermarking and related applications

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Quick Facts
Patent No.
US 6,993,150
App. No.
10/052,895
Filed
Jan 17, 2002
Granted
Jan 31, 2006
Kind
B2
Art Unit
2625
USPC
358/3.28
Abstract

The present invention relates to a method for embedding a digital watermark into a halftone image comprised of clusters of halftone dots, which are referred to as geometric primitives. This method embeds a watermark image signal including an array of multilevel per pixel delta values by increasing or decreasing the size of a corresponding cluster of halftone dots. In particular, each delta value represents a change in luminance in one implementation, but this delta value could correspond to other color planes of a monotone or color halftone image. The watermark embedder subtly changes the halftone primitives by toggling boundary pixels on or off in a manner that grows or shrinks the primitive.

Claims (10)

1. A method of embedding a watermark into a halftone image, said method comprising:

providing a watermark to alter the halftone dots by toggling boundary pixels of the halftone dots, wherein the halftone dots are represented as primitives comprising contiguous clusters of halftone pixels; and

embedding the watermark in the image by growing or shrinking the primitives through the toggling of the boundary pixels.

2. The method according to claim 1 , wherein the step of embedding comprises the step of gradually changing the halftone dots.

3. A method of embedding a watermark into a halftone image, said method comprising:

providing a watermark to alter a cluster of halftone dots by toggling boundary pixels of the halftone dots; and embedding the watermark in the image, including toggling boundary pixels on or off to grow or shrink the halftone dots.

4. An apparatus to embed a watermark in a halftone image, said apparatus comprising:

means for receiving an image including primitives comprising contiguous clusters of halftone pixels; and

an encoder to toggle halftone data values at an outer boundary of a cluster of halftone pixels of the image, the encoder operable to grow or shrink the cluster at the outer boundary to embed an element of the watermark in the image.

5. The apparatus according to claim 4 , wherein said encoder effects a change in the image's luminance.