Halftone primitive watermarking and related applications

• US 20020105679A1
• Filed: 01/17/2002
• Published: 08/08/2002
• Est. Priority Date: 01/24/2001
• Status: Active Grant

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Haynes, Mark E.
• Granted Patent: US 6,993,150 B2
• Time in Patent Office: Days
• US Class Current: 358/3.28
• CPC Class Codes: G06T 1/0064 Geometric transfor invariant watermarking, e.g. affine transform invariant
• CPC Class Codes: G06T 2201/0051 Embedding of the watermark in the spatial domain
• CPC Class Codes: H04N 1/32144 embedded in the image data, i.e. enclosed or integrated in the image, e.g. watermark, super-imposed logo or stamp
• CPC Class Codes: H04N 1/32256 in halftone data

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

1. A method of embedding a watermark into a halftone image, the image comprising a cluster of halftone dots, said method comprising the steps of:

providing a watermark to alter the cluster of halftone dots by toggling boundary pixels of the halftone dots; and

embedding the watermark in the image.

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

3. The method according to claim 1, further comprising the step of 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:

an encoder to toggle halftone data values at an outer boundary of a cluster of halftone dots of the halftone image.

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

6. A method of embedding a watermark into a halftone image comprising the steps of:

selecting a block of halftone dots in the halftone image; and

adding or subtracting halftone dots in the block to achieve a change in luminance.