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Continuous Phase-Modulated Halftones

by Basak Oztan, Gaurav Sharma , 2009
"... A generalization of periodic clustered-dot halftones is proposed, wherein the phase of the halftone spots is modulated using a secondary signal. The process is accomplished by using an analytic halftone threshold function that allows halftones to be generated with controlled phase variation in diffe ..."
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A generalization of periodic clustered-dot halftones is proposed, wherein the phase of the halftone spots is modulated using a secondary signal. The process is accomplished by using an analytic halftone threshold function that allows halftones to be generated with controlled phase variation in different regions of the printed page. The method can also be used to modulate the screen frequency, albeit with additional constraints. Visible artifacts are minimized/eliminated by ensuring the continuity of the modulation in phase. Limitations and capabilities of the method are analyzed through a quantitative model. The technique can be exploited for two applications that are presented in this paper: a) embedding watermarks in the halftone image by encoding information in phase or in frequency and b) modulating the screen frequency according to the frequency content of the continuous tone image in order to improve spatial and tonal rendering. Experimental performance is demonstrated for both applications.
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Clustered-dot color halftone watermarks

by Basak Oztan, Gaurav Sharma - in [Proc. IS&T/SID Sixteenth Color Imaging Conference: Color Science and Engineering: Systems, Technologies, Applications], 99–104 (1015 , 2008
"... A framework for clustered-dot color halftone watermarking is proposed. Watermark patterns are embedded in the color halftone on per-separation basis. For typical CMYK printing systems, common desktop RGB color scanners are unable to provide the individual colorant halftone separations, which confoun ..."
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A framework for clustered-dot color halftone watermarking is proposed. Watermark patterns are embedded in the color halftone on per-separation basis. For typical CMYK printing systems, common desktop RGB color scanners are unable to provide the individual colorant halftone separations, which confounds per-separation detection methods. Not only does the K colorant consistently appear in the scanner channels as it absorbs uniformly across the spectrum, but cross-couplings between CMY separations are also observed in the scanner color channels due to unwanted absorptions. We demonstrate that by exploiting spatial frequency and color separability of clustered-dot color halftones, estimates of the individual colorant halftone separations can be obtained from scanned RGB images. These estimates, though not perfect, allow per-separation detection to operate efficiently. The efficacy of this methodology is demonstrated using continuous phase modulation for the embedding of per-separation watermarks.

Clustered-Dot Color . . .

by Basak Oztan, et al.
"... Spatial frequency separability is proposed as an attractive exploit for obtaining color halftone watermarking methods from monochrome clustered-dot halftone watermarking techniques. Detection of watermarks embedded in individual halftone channels is typically confounded by the cross-coupling between ..."
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Spatial frequency separability is proposed as an attractive exploit for obtaining color halftone watermarking methods from monochrome clustered-dot halftone watermarking techniques. Detection of watermarks embedded in individual halftone channels is typically confounded by the cross-coupling between colorant halftone separations and scan RGB channels caused by the so-called “unwanted absorptions”. This problem is resolved in the proposed framework by utilizing spatial filtering in order to obtain estimates of individual separation halftones that are suitable for watermark detection. The effectiveness of this methodology is experimentally demonstrated by utilizing continuous phase modulation for per-separation watermark embedding. The embedded watermark patterns in the halftone separations can be clearly detected from scans using the proposed spatial separability exploit. Continuous phase modulation based per-channel embedding with detection following spatial-filtering based separation thus provides an effective watermarking method for clustered-dot color halftones.
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Journal of Electronic Imaging 19(4), 043007 (Oct–Dec 2010)

by Basak Oztan, Gaurav Sharma
"... Per-separation clustered-dot color halftone watermarks: separation estimation based on spatial frequency content ..."
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Per-separation clustered-dot color halftone watermarks: separation estimation based on spatial frequency content
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unknown title

by Orhan Bulan, Orhan Bulan, Gaurav Sharma
"... Content authentication for printed images utilizing high capacity data hiding ..."
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Content authentication for printed images utilizing high capacity data hiding