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In this paper, a QR code is presented with a dual resolution structure. It contains a high resolution layer that is coded in luminance and is in consistency with the conventional QR code, and a low resolution layer providing additional error checking information, that is coded in chrominance and is robust to blurring. The proposed QR code is compatible to its underlying conventional black and white barcode as it can be read by their decoders. Its advantage is additional reliability when a color decoder is used. In particular, it enhances the decoding accuracy for devices such as mobile devices for barcodes printed in small sizes.

Embedded watermarks in printed halftone images, which can subsequently be detected using an visual aid or using a watermark detection algorithm on a scan of the image, are of interest in wide range of applications. For black and white halftone printing using stochastic screens, digital watermarks that are embedded as correlations in the halftone screen have been previously proposed. Here we present a novel extension of these watermarks to color that produces a high contrast watermark by using the colorant separations coherently with a single watermarked stochastic screen and performing detection coherently across the color separations. Compared with independent watermarking of the halftone separations, the resulting watermark offers significantly higher contrast in the detected image.

Human visual system has the property of perceiving the object color to remain constant regardless of the prevailing illumination. However, digital cameras usually lack this capability, and the captured images are digitally corrected to discount the color of the scene light based on the estimated illuminant. Illumination estimation might be erroneous in some artificial or chromatic lighting conditions. A method was proposed to correct digital photos captured with a smartphone camera using the smartphone owner's face as the reference. Taking the advantage of the latest smartphones with two build-in cameras, we could use the front camera to capture the smartphone owner's face and compare with the saved reference face image in order to estimate the scene illuminant. After that, we could properly adjust the capture setting for the main camera in order to take a decent target image; or we could automatically correct the target image based on the estimated illumination by comparing two face images. The method was implemented on the iOS mobile platform. Experimental result shows that the adjusted images using the proposed method are generally more favorable than the pictures taken directly by the default camera application.

We present a stochastically seeded halftoning method with parametric control of dot shapes as well as seed placement adaption to local image structure. While the literature on other randomly structured screens (blue noise, green noise, FM) is quite extensive, there is very little discussion on optimization of dot shape for robustness or preferred tile appearance. The halftoning method that we introduce defines dot centers as seeds that are placed, typically in a random high spatial frequency configuration. Spot functions are defined about these randomly placed seeds, where the spot function allows control of dot cluster growth, touch points, cluster angle, and eccentricity. The spot function can also be applied to regular and irregular polygonal halftone tiling. The seed adaption aspect of the halftoning method allows for better edge rendition than conventional isotropic methods.

A method is provided for embedding a UV fluorescent watermark in a color halftone image printed on paper. The described method implements two different strategies to halftone a watermark region and a background region. One strategy uses dot-on-dot halftoning to maximize the usage of black ink and minimize ink dispersion, while the other strategy uses successive-filling halftoning to maximize ink dispersion. An accurate color look-up-table (LUT) is built to directly transform the colorant values for one halftoning strategy to the colorant values for the other strategy. With the color transformation applied on one region, the binary outputs in both watermark and background regions halftoned with different strategies exhibit similar color appearance under normal lighting condition. However, under UV illumination, due to the fluorescent effect caused by different paper coverages in two regions, the embedded watermark becomes clearly visible.

A halftone configuration is presented that utilizes three or four rotated hexagonal screens, or more precisely, screens with hexagonally tiled clusters, for moire-free color printing. Halftone designers consider many options to deliver a screen with desirable characteristics, and often must settle for less than desirable results. The present method presents a new option with several beneficial properties compared to conventional square-cell-based screens. Hexagonal screens can appear to have smoother texture. Due to differences in packing geometry and touch point geometry, hexagons have the potential to possess different tone reproduction characteristics, which may be favorable for some marking processes. A fourth screen (e.g., yellow) can be included moire-free, thereby avoiding problems associated with stochastic solutions for yellow. We also present a corresponding parametrically controlled hexagonal halftone spot function that allows for optimization of dot touch points and provides compact growth. The optimized touch points can prevent a tone reproduction bump, while the compact growth throughout the gray range ensures maximum stability. Examples are provided.

While diffraction-pattern sampling has been widely applied in the classification of patterns, still its usage has been limited somewhat by the need to devise rather sophisticated algorithms. In this paper we describe sorting or classification of a variety of patterns with commercially available neural-network software together with the ring-wedge photodetector to supply optical transform data for the input neurons. With this combination of neural networks and diffraction-pattern sampling it is no longer necessary to write specialized software. The training and testing methodology is carried out for this new system, and excellent results are obtained for sorting thumbprints. In sorting thumbprints the neural network can be trained for orientation-independent or wide-scale size-independent classifications by use of ring-only or wedge-only input neurons, respectively. Separate experiments are described for the sorting of particulates. Again, these are cases in which writing appropriate software based on diffraction theory would be extremely difficult. Two interesting novel neural networks are obtained: one is for real-time control of a submicrometer colloidal suspension of CdS, and the second is for concentration measurements of 2.02-µm polyvinyltoulene spheres in methyl alcohol. Widespread new applications are predicted for this hybrid system that combines diffraction-pattern sampling and the neural network.

Method for duplex printing on transparencies to create auto-stereoscopic images. By choosing different halftone structures, differing by having different spatial frequencies for each of the two sides of a transparency, a moire pattern resulting due to halftone overlapping can be observed. On one side of the transparency is provided a uniform halftone with a selected median spatial frequency as printed. On the other side, the printing consists of two partitions: what is to be perceived as the background is printed using a halftone with spatial frequency equal to the median plus some delta x, while a desired image partition is printed using a halftone with a spatial frequency equal to the median minus the same delta x. The spatial frequency difference creates a corresponding shift-magnification factor M with an amplified total depth of the shift-magnification factor M times the thickness of the transparency.

A monochromatic binary printer model at the cluster level defined by the halftone frequencies is presented in this paper. The halftone process using a cluster halftone screen creates halftone structures with aligned clusters within halftone cells tiled to fill the image plane. Each halftone cell, or each tile, can be treated as a "primary color", which can be calibrated, or macroscopically measured, from a corresponding halftone pattern. The cluster-based printer model estimates the average color of a halftone pattern containing different halftone cells using a modified Neugebauer spectral (colorimetric) color mixing model incorporating the Yule-Nielsen effect. A method based on the proposed clusterbased printer model for quickly and accurately characterizing the complete tone reproduction curve (TRC) for multicenter halftone screens is also described with the experiment result.

Color printer calibration is the process of deriving correction functions for device CMYK signals, so that the device can be maintained with a fixed known characteristic color response. Since the colorimetric response of the printer can be a strong function of the halftone, the calibration process must be repeated for every halftone supported by the printer. The effort involved in the calibration process thus increases linearly with the number of halftoning methods. In the past few years, it has become common for high-end digital color printers to be equipped with a large number of halftones thus making the calibration process onerous . We propose a halftone independent method for correcting color (CMY/CMYK) printer drift. Our corrections are derived by measuring a small number of halftone independent fundamental binary patterns based on the 2×2 binary printer model by Wang et. al. Hence, the required measurements do not increase as more halftoning methods are added. The key novelty in our work is in identifying an invariant halftone correction factor (HCF) that exploits the knowledge of the relationship between the true printer response and the 2×2 predicted response for a given halftoning scheme. We evaluate our scheme both quantitatively and qualitatively against the printer color correction transform derived with the printer in its "default state". Results indicate that the proposed method is very successful in calibrating a printer across a wide variety of halftones.

By selecting halftone frequencies from high-order harmonics of two common rosette fundamentals for all color separations, a true moire-free color halftoning can be achieved. With such screen configurations, the interference between any two frequency components, fundamentals or high-order harmonics, of different colors will also result in a linear combination of the two rosette fundamentals. Thereby, no visible interference, or moire, at all will be shown in the output. The halftone outputs are two-dimensionally repeated patterns, as visually pleasant uniform rosettes. The uniform-rosette configurations can be implemented by single-cell non-orthogonal halftone screens for digital halftoning. Unlike "dot-on-dot" screening, or using one screen for all colors, uniform-rosette halftoning is robust to mis-registration between color separations. Several designs of uniform-rosette halftone screens have been successfully applied to Xerox iGen3 color printers for high-quality color reproduction.

Reflective displays that rely on ambient light as opposed to an internal light source have been making inroads for a variety of important applications, especially those involving mobility where power usage must be aggressively controlled. The underlying color rendering strategies for both reflective and emissive displays have largely been the same, combining three fixed, primary color subpixels to compose the rich gamut that users expect. The result, for reflective color displays, is unfavorable brightness/gamut performance since each of the color subpixels absorbs roughly 2/3 of the incident white light. We demonstrate a new technology that we call the single mirror interferometric display that overcomes such limitations with pixels whose reflectance properties can tune through a continuum of colors, including high contrast black and white reflectance states. We use an effect that we call interferometric absorption in which a thin absorbing metal layer in front of a highly reflective mirror surface selectively absorbs different colors, depending on the gap that separates the two. The gap is controlled by electrostatic actuation in a relatively simple micro-electro-mechanical-system structure. We describe this elegant and powerful color rendering principle and present experimental results for the basic pixel device as well as early system demonstrations.

Glossmark technology is a halftone-based digital imaging process to embed visible watermarks into xerographic color prints. The gloss of a xerographic print depends not only on surface roughness of paper and toner, but also on the microscopic structure created by the halftone process. The surface relief of a halftone image can be treated as a two-dimensional phase grating. The shape, or profile, of the surface relief determines the reflected pattern of the illumination. A strong angular differential gloss can be obtained by employing two anisotropic halftone screens in the halftone process. A careful design of these screens enables embedding Glossmark images while maintaining the high quality of the color reproduction. The printing process, that simultaneously creates high quality primary and Glossmark images in a single step, requires neither special equipment nor special paper or toner. Glossmark images, shown in a high contrast of gloss, provide a perfect simulation of the traditional paper watermarks, while their digital implementation makes it easy to embed variable data as digital watermarks into individual documents.

A new technique for design of stochastic screens is proposed that produces screens that are robust against mis-registration in multi-pass printing. Conventional stochastic screens are designed through an optimization process that minimizes low-frequency structure in halftone images under the assumption that the placement of pixels is accurate. In inkjet printing, however, a page is often printed in multiple passes to allow for better drying of inks and to minimize appearance of a head signature. Any potential mis-registration between the passes is typically not comprehended in the conventional stochastic screen design process. The mis-registration between the passes can therefore cause significantly increased graininess (low-frequency structure) in printed images produced with stochastic screens even though the corresponding electronic bitmaps are free from low-frequency structure. In this paper, we propose modifications to the stochastic screen design process that take the two pass printing into account and produce halftones that are robust to inter-pass mis-registration errors. This allows reduced tolerances and alignment requirements in manufacturing that translate to lower cost. The proposed technique works by modifying the screen design process to ensure that a majority of the minority pixels are concentrated in a single pass, which provides improved robustness to mis-registration between the passes. Experimental results demonstrate that the proposed design technique performs significantly better than conventional stochastic screens in the presence of mis-registration errors.

In color reproduction, the most troublesome moire pattern is the second-order moire, or the three-color moire, usually produced by mixing of cyan, magenta and black halftone outputs. A classical 3-color zero-moire solution is using three identical cluster halftone screens with different rotations: 15, 45 and 75°, respectively. However, for most digital printing devices, the size and shape of halftone screens are constrained by the "digital grid", which defines the locations of printed dots; and therefore, an exact 15 or 75° rotation of a cluster screen is impossible. Although there are many alternative approaches for moire-free color halftoning, most of them only provide approximate solutions and/or have a tendency to generate additional artifacts associated with halftone outputs. The difficulty to achieve moire-free color halftoning is greatly relieved by using non-orthogonal halftone screens, i.e., screens in general parallelogram shapes. In this paper, a general condition for 3-color zero-moire solutions is derived. A procedure using integer equations to search moire-free solutions for different applications is also described.

In most existing color reproduction systems, color correction is performed in an open-looped fashion. For multiple generation color copying, color fidelity cannot be guaranteed as the errors introduced in color correction may accumulate. In this paper, we propose a method of solving the error accumulation problem by embedding color information as invisible digital watermark in hardcopies. When the hardcopy is scanned, the embedded information can be retrieved to provide real-time calibration. As the method is close-looped in nature, it may reduce error accumulation and improve color fidelity, particularly when copies go through multiple generation reproduction.

We present a stochastically seeded, clustered halftoning method with parametric control of dot shapes as well as seed placement adaption to local image structure. While the literature on other randomly structured screens (blue noise, green noise, and stochastic halftoning) is quite extensive, there is very little discussion on optimization of dot shape for robustness or preferred tile appearance. The parametric control presented here can enable an imaging engineer to optimize robustness for a given printing system. The halftoning method that we introduce defines dot centers as seeds that are placed typically in a random, high spatial frequency configuration. Spot functions are defined about these randomly placed seeds, where the spot function allows control of dot cluster growth, touch points, cluster angle, and eccentricity. The spot function can also be applied to regular and irregular polygonal halftone tiling. The adaptability of the seed placement provided by the halftoning method allows for better edge rendition than conventional isotropic methods and enables the implementation of data-embedding techniques. The resulting monochromatic screens can be seamlessly integrated with novel successive filling techniques in order to provide dot-off-dot vector halftoning capabilities.

Colorimetric data can be readily computed from measured spectral data, however, as illustrated by metameric pairs, the mapping from spectral data to colorimetric values is many-to-one and therefore typically not invertible. In this paper, we investigate inversions of the spectrum-to-colorimetry mapping when the input is constrained to a single color reproduction medium. Under this constraint, accurate recovery of spectral data from colorimetric data is demonstrated for a number of different color reproduction processes. Applications of the spectrum reconstruction process are discussed and demonstrated through examples.

This paper introduces a moire-free color half toning algorithm. Moire patterns might appear in traditional halftone images. This could be caused by interference among halftone screens of different colors, or beating between he input image and the screens. In our algorithm, we adjust the halftone screens of different colors, or beating between the input image and the screens. In our algorithm, we adjust the halftone output in such a way that the low-frequency difference between the input and the appearance of the output is minimized. Due to non-linear color mixing, the appearance of a color print is not a simple combination of CMYK four channels, and is hence not easily predictable. We use the 2 by 2 printer model to estimate the pixel-level CIE-Lab values from the halftone output. Next we calculate the difference between the original CIE-Lab input image and the 2 by 2 estimation and run a low-pass filtering on the result. Then, we feed back the low-frequency difference into the input. The low-frequency-feedback process cancels the potential color moire patterns.

Invisible watermark images can be incorporated in printed halftone images using specially designed halftone screens. The watermark information is embedded into the image by varying the spatial correlation of the halftone texture. The halftone screen with embedded watermarks can be used exactly as a normal halftone screen, so there is no additional image processing required for processing individual images to embed watermarks. Once the binary output image is printed on the paper, the correlation of the binary image is converted into physical spatial correlation between neighboring areas of the printed image. This correlation relation is not visible to the eye but it can be detected by scanning the printed image on a desktop scanner and processing the scanned image. Printer and scanner distortions can interfere with the self-alignment of the scanned image, so localized adjustments are made to detect the embedded spatial correlation information in the watermarked image. The retrieval of this watermark is robust to copying and distortion and it can be detected in reproductions of the halftone image.

A method will be shown to incorporate digital watermarks in printed halftone images using stochastic screens. The watermark is not visible to the eye and introduces no loss in image quality. Although it cannot be seen, the watermark can be extracted at a later time with post processing. Watermarks of high contrast are incorporated in the image by varying the statistics of the stochastic screen. The watermark information can be made visible by comparing the relative changes in spatial correlation in the halftone texture of the image. Watermarking allows a printed image to be tested for the purposes of identifying the owner or the source of the image. Arbitrary customer information can be incorporated into the image, including variable information, such as the data or time of day. The technique is robust to copying of the printed image and the watermark can be detected in reproductions of the halftoned image.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Color printer calibration is the process of deriving correction functions for device signals (e.g., CMYK), so that the device can be maintained with a fixed known characteristic color response. Since the colorimetric response of the printer can be a strong function of the halftone, the calibration process must be repeated for every halftone supported by the printer. The effort involved in the calibration process thus increases linearly with the number of halftoning methods. In the past few years, it has become common for high-end digital color printers to be equipped with a large number of halftones, thus making the calibration process onerous. We propose a halftone independent method for correcting color (CMY or CMYK) printer drift. Our corrections are derived by measuring a small number of halftone independent fundamental binary patterns based on the 22 binary printer model by Wang et al. Hence, the required measurements do not increase as more halftoning methods are added. First, we derive a halftone correction factor (HCF) that exploits the knowledge of the relationship between the true printer response and the 22-model predicted response for a given halftoning scheme. Therefore, the true color drift can be accurately predicted from halftone-independent measurements and corrected correspondingly. Further, we develop extensions of our proposed color correction framework to the case when the measurements of our fundamental binary patches are acquired by a common desktop scanner. Finally, we exploit the application of the HCF to correct color drift across different media (papers) and for halftoneindependent spatial nonuniformity correction.

A printing apparatus and method for duplex printing a document having a show-through watermark wherein the watermark is comprised of first and second images on both sides of the document. The images comprise stoclustic halftone screens having a substantially common registration wherein the second image is relatively shifted from the first image for forming an associated overlay pattern between the first and second images resulting in a recognizable pattern comprising the watermark upon illumination by a show-through light source. The watermark is unrecognizable from either image alone upon illumination from a front light source. The relative shifting can be implemented by either phase, frequency or angle shifting between the front and back side images.

A novel sine-filter-cosine cascade is proposed that is realizable for either coherent or spatially incoherent illumination. Computer simulation is used to demonstrate effectively matched filter performance and elimination of deleterious background bias.