Apparatus and method for embedding electronic watermark

Abstract

An electronic watermark embedding apparatus for embedding watermark information as digital information into a document image includes a background eliminating unit that determines whether pixels on an input image are pixels composing a background image and eliminates the pixels determined as the pixels composing the background image from the input image, and a watermark embedding unit that embeds a watermark into a background eliminated image from which the background is eliminated by the background eliminating unit so as to form a watermark image. A readable watermark can be embedded into a multi-valued image including a halftone/gradation portion on the background of the input image.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram illustrating a constitution of an electronic watermark embedding apparatus according to a first embodiment;

FIG. 2 is an explanatory diagram illustrating an input image;

FIG. 3 is an explanatory diagram illustrating a background eliminated image in the first embodiment;

FIG. 4 is an explanatory diagram illustrating a watermark image;

FIG. 5 is a flowchart illustrating an operation of a background eliminating unit 102 in the first embodiment;

FIG. 6 is a flowchart illustrating a labeling process (step S102);

FIGS. 7A to 7C are explanatory diagrams illustrating the labeling process (step S102);

FIGS. 8A and 8B are explanatory diagrams illustrating a foreground/background determining method (1);

FIGS. 9A and 9B are explanatory diagrams illustrating the foreground/background determining method (2);

FIGS. 10A to 10D are explanatory diagrams illustrating the foreground/background determining method (3);

FIG. 11 is an explanatory diagram illustrating the foreground/background determining method (4);

FIG. 12 is an explanatory diagram illustrating a constitution of the electronic watermark embedding apparatus according to a second embodiment;

FIGS. 13A to 13C are explanatory diagrams illustrating foreground and background images and watermark images in the second embodiment;

FIG. 14 is an explanatory diagram illustrating enlarged FIG. 13C;

FIG. 15 is a flowchart illustrating an operation of a background separating unit 201 in the second embodiment;

FIGS. 16A to 16C are explanatory diagrams illustrating the foreground and background images and the watermark images in a third embodiment; and

FIG. 17 is a flowchart illustrating an operation of the background separating unit 201 in the third embodiment.

Claims

1. An electronic watermark embedding apparatus that embeds watermark information as digital information into a document image, the apparatus comprising: a background determining unit that determines whether pixels on the document image are pixels composing a background image;a background eliminating unit that eliminates the pixels determined as the pixels composing the background image by the background determining unit from the document image; anda watermark embedding unit that embeds a watermark into a background eliminated image from which the background is eliminated by the background eliminating unit.

2. The electronic watermark embedding apparatus according to claim 1, wherein the background determining unit determines halftone, gradation or photograph in a multiple-valued image as the background.

3. The electronic watermark embedding apparatus according to claim 1, wherein the background determining unit includes: a region extracting unit that groups adjacent pixels with the same feature in the image as a region; anda region determining unit that determines whether the pixels on the document image compose the background image on the basis of the feature of the region extracted by the region extracting unit.

4. The electronic watermark embedding apparatus according to claim 3, wherein the feature of the pixels grouped as one region by the region extracting unit is such that a luminance level or a color of the pixels are the same or are within a range of predetermined thresholds.

5. The electronic watermark embedding apparatus according to claim 1, wherein the region determining unit makes a determination on the basis of at least one of a luminance level, color information, a size, an area, a boundary length and a wavelength after frequency conversion of the region.

6. The electronic watermark embedding apparatus according to claim 1, wherein the region determining unit measures a size of a circle or a polygon which is maximally inscribed in the region and makes a determination on the basis of the size of an inscribed graphic.

7. The electronic watermark embedding apparatus according to claim 1, wherein the region determining unit measures a difference in luminance or color information between the region and a region adjacent to the region, and makes a determination on the basis of the difference in the luminance or the color information.

8. The electronic watermark embedding apparatus according to claim 1, wherein the region determining unit extracts a region including the region and makes a determination on the basis of luminance or color information between the region and the inclusion region.

9. An electronic watermark embedding apparatus that embeds watermark information as digital information into a document image, the apparatus comprising: a background determining unit that determines pixels on the document image are pixels composing a background image;a background separating unit that separates the document image into a foreground image and the background image on the basis of the determined result of the background determining unit; anda watermark embedding unit that embeds a watermark into the foreground image output by the background separating unit,wherein the watermark embedding unit changes concentration or density of the watermark to be embedded into the foreground image according to contents of the background image.

10. The electronic watermark embedding apparatus according to claim 9, wherein the background separating unit includes a limit level adjusting unit that separates a portion on the background image with a concentration level not less than a limit level to a foreground image side when the watermark concentration level changeable by the watermark embedding unit has a limit.

11. The electronic watermark embedding apparatus according to claim 9, wherein the background determining unit determines halftone, gradation or photograph on a multiple-valued image as the background.

12. The electronic watermark embedding apparatus according to claim 9, wherein the background determining unit includes: a region extracting unit that groups pixels with the same feature in the image as a region; anda region determining unit that determines whether the pixels on the document image compose the background image on the basis of the feature of the region extracted by the region extracting unit.

13. The electronic watermark embedding apparatus according to claim 12, wherein the feature of the pixels grouped as one region by the region extracting unit is such that a luminance level or a color of the pixels are the same or are within a range of predetermined thresholds.

14. The electronic watermark embedding apparatus according to claim 9, wherein the region determining unit makes a determination on the basis of at least one of a luminance level, color information, a size, an area, a boundary length and a wavelength after frequency conversion of the region.

15. The electronic watermark embedding apparatus according to claim 9, wherein the region determining unit measures a size of a circle or a polygon which is maximally inscribed in the region and makes a determination on the basis of the size of an inscribed graphic.

16. The electronic watermark embedding apparatus according to claim 9, wherein the region determining unit measures a difference in luminance or color information between the region and a region adjacent to the region, and makes a determination on the basis of the difference in the luminance or the color information.

17. The electronic watermark embedding apparatus according to claim 9, wherein the region determining unit extracts a region including the region and makes a determination on the basis of luminance or color information between the region and the inclusion region.

18. An electronic watermark embedding method for embedding watermark information as digital information into a document image, comprising the steps of: determining whether pixels on the document image are pixels composing a background image;eliminating the pixels determined as the pixels composing the background image from the document image; andembedding a watermark into a region of the eliminated background image.

19. An electronic watermark embedding method for embedding watermark information as digital information into a document image, the method comprising the steps of: determining whether pixels on the document image are pixels composing a background image;separating the document image into a foreground image and the background image; andchanging concentration or density of the watermark according to contents of the background image so as to embed the watermark into the foreground image.