Oriented Modulation for Watermarking in Direct Binary Search Halftone Images

Abstract

In this paper, a halftoning-based watermarking method is presented. This method enables high pixel-depth watermark embedding, while maintaining high image quality. This technique is capable of embedding watermarks with pixel depths up to 3 bits without causing prominent degradation to the image quality. To achieve high image quality, the parallel oriented high-efficient direct binary search (DBS) halftoning is selected to be integrated with the proposed orientation modulation (OM) method. The OM method utilizes different halftone texture orientations to carry different watermark data. In the decoder, the least-mean-square-trained filters are applied for feature extraction from watermarked images in the frequency domain, and the naïve Bayes classifier is used to analyze the extracted features and ultimately to decode the watermark data. Experimental results show that the DBS-based OM encoding method maintains a high degree of image quality and realizes the processing efficiency and robustness to be adapted in printing applications.

Orientation Modulation for Data Hiding in Chrominance Channels of Direct Binary Search Halftone Prints

“…Using orientation modulation for data embedding during iterative DBS halftoning of grayscale images was originally proposed by Guo et al 23 The main idea of this technique is to use a point-spread function (in Eq. (6)) which is modified (oriented) according to the data which is to be embedded in the M × N block.…”

“…For the luminance channel Y we use the same point-spread function which was proposed in the original DBS/CDBS; it is derived from the luminance contrast sensitivity function proposed by Nasanen. 32 For the pointspread function used for the two chrominance channels C b and C r , we start with a Gaussian function 23,33 and add two parameters to control its orientation and eccentricity:…”

“…depending on the chrominance channel and the actual data to be embedded. In contrast to the originally proposed approach, 23 the error minimization is not performed in parallel for all the blocks, but in the usual raster-scan order. The update of an accepted change using Eq.…”

“…Guo et al used the orientation modulation approach to hide data in DBS halftoned images. 22,23 The data is embedded by modulating the orientation of the point-spread function which is used as an HVS-based filter in the DBS halftoning process. The detector is using trained filters and naive Bayesian classifier to detect the orientation features in frequency domain.…”

“…25 The proposed technique for data embedding is an extension of the previously described grayscale approach 23 to color halftones. There are several possible ways to extend the original DBS-based orientation modulation to color; in this work we are using only the chrominance channels for data embedding as this results in improved capacity and print-and-scan robustness while keeping the visual degradation almost imperceptible.…”