DIGITAL WATERMARKING FOR FEW-COLOR IMAGES
Systems and methodologies for embedding a watermark in a few-color image are provided herein. A digital watermarking algorithm named Spatial Unified Key Insertion (SUKI) can be utilized, wherein adaptive threshold halftoning can be performed in combination with contour shaping and modification to embed a binary logo into a digital image. Watermarking can be performed for an image using SUKI without introducing “salt-and-pepper” artifacts into the image. Further, watermarking techniques described herein can embed data into an image with a considerably high payload while providing excellent resistance against JPEG compression and other attacks and introducing no additional colors into an image.
1 . A system for watermarking a few-color image, comprising:
a halftoning component that generates a binary halftoned image based on a few-color image, the binary halftoned image distinguishes between edge pixels and content pixels in the few-color image;
a block management component that utilizes the binary halftoned image to identify one or more candidate pixel blocks for embedding watermark data in the few-color image; and
a contour shaping component that embeds a binary watermark in the few-color image to create a watermarked image by modifying contours of respective candidate pixel blocks in the few-color image.
2 . The system of claim 1 , further comprising a segmentation component that divides an input image into one or more few-color image segments, wherein the halftoning component, the block management component, and the contour shaping component are utilized for respective few-color image segments.
3 . The system of claim 1 , wherein the halftoning component generates a binary halftoned image based on a few-color image at least in part by determining a pixel value threshold, assigning a first halftone value to respective pixels in the few-color image having a pixel value equal to or greater than the pixel value threshold, and assigning a second halftone value to respective pixels in the few-color image having a pixel value less than the pixel value threshold.
4 . The system of claim 1 , wherein the block management component comprises:
a boundary block detection component for detecting respective pixel blocks in the binary halftoned image corresponding to boundaries between edge pixels and content pixels; and
a candidate block identification component that identifies respective pixel blocks detected by the boundary block detection component that are candidate pixel blocks for embedding watermark data.
5 . The system of claim 1 , wherein the contour shaping component comprises:
a contour measurement component that determines respective contours of candidate pixel blocks corresponding to a few-color image received by the block management component; and
a contour modification component that embeds a binary watermark in the few-color image by modifying respective contours of the candidate pixel blocks based at least in part on the binary watermark.
6 . The system of claim 5 , wherein the contour modification component modifies respective contours of the candidate pixel blocks by toggling a center pixel in the respective candidate pixel blocks between an edge color and a content color.
7 . The system of claim 1 , further comprising an extraction component that receives the watermarked image and extracts the binary watermark from the watermarked image.
8 . The system of claim 7 , wherein the watermarked image is communicated to the extraction component using a communication channel, an image compression operation is performed on the watermarked image in the communication channel, and the extraction component obtains a binary watermark from a resulting compressed image that is substantially similar to the binary watermark embedded in the watermarked image.
9 . The system of claim 7 , wherein the extraction component comprises:
a halftoning component that generates a binary halftoned image based on the watermarked image;
a block management component that utilizes the binary halftoned image to identify one or more candidate blocks in which the binary watermark was embedded in the watermarked image; and
a contour measurement component that obtains the binary watermark from the watermarked image at least in part by determining respective contours of edge pixels in the candidate blocks.
10 . The system of claim 1 , wherein a color palette of the watermarked image is substantially identical to a color palette of the few-color image.
11 . A method for embedding a logo in an image, comprising:
obtaining a halftone image from the image based at least in part on adaptive threshold halftoning;
identifying candidate blocks for watermarking from the halftone image; and
embedding a logo in the image to create a watermarked image by performing contour shaping on the candidate blocks for watermarking.
12 . The method of claim 11 , further comprising dividing the image into one or more few-color image segments, wherein the obtaining, identifying, and embedding are respectively performed for respective few-color image segments.
13 . The method of claim 11 , wherein the obtaining includes:
forming a histogram based on respective pixel values in the image, the histogram comprises a peak for an edge color and one or more peaks for content colors;
determining a halftoning threshold by selecting a pixel value between the peak for the edge color and a peak for a content color;
assigning pixels in the image having a pixel value below the halftoning threshold a first halftone value; and
assigning pixels in the image having a pixel value equal to or above the halftoning threshold a second halftone value.
14 . The method of claim 11 , wherein the identifying includes:
dividing the halftone image into a plurality of blocks of a predetermined size;
identifying boundary blocks in the halftone image from the plurality of blocks; and
selecting candidate blocks for watermarking from the identified boundary blocks.
15 . The method of claim 11 , wherein the embedding includes:
determining respective contours of candidate blocks for watermarking; and
modifying respective contours of the candidate blocks for watermarking based at least in part on the logo.
16 . The method of claim 15 , wherein the logo comprises information bits having a first value and information bits having a second value, and the modifying includes:
setting respective contours of candidate blocks for watermarking to one of a first set of contours to represent respective information bits in the logo having the first value; and
setting respective contours of candidate blocks for watermarking to one of a second set of contours to represent respective information bits in the logo having the second value.
17 . The method of claim 11 , further comprising extracting the logo from the watermarked image.
18 . The method of claim 17 , wherein the extracting includes:
obtaining a halftone image from the watermarked image based at least in part on adaptive threshold halftoning;
identifying blocks in the watermarked image in which the logo was embedded based on the halftone image; and
extracting the logo from the watermarked image based at least in part on respective contours of the blocks in watermarked image in which the logo was embedded.
19 . A computer-readable medium having stored thereon computer-executable instructions for performing the method of claim 11 .
20 . A system that facilitates embedding a watermark in a few-color image, comprising:
means for generating a binary halftoned image based on the few-color image;
means for identifying candidate pixel blocks for watermarking in the few-color image based at least in part on the binary halftoned image; and
means for embedding a watermark in the few-color image by modifying respective contours of the candidate pixel blocks for watermarking in the few-color image.