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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.

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.

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 always performed in the presence of noise. A major part of this noise is due to the spatial non-uniformity of the printer. In many cases, the spatial non-uniformity does not repeat the same pattern page by page. Some calibration techniques use randomizing the locations of patches and averaging a large numbers of measurements to reduce the noise. Since the non-uniformity is a kind of systematic errors, it should be estimated and corrected in a more effective way. This presentation describes a method to provide a more accurate color calibration/characterization result by estimating the spatial non-uniformity presented on the printed target page and applying a correction to the very same page itself. Instead of defining the noise in the color measurement space, e.g. the CIE Lab space, the new method specifies the noise in the printer-dependent color space, e.g. the CMY space. After the first-round color calibration, an inverse transform, from CIE Lab to CMY, is derived from measurements of the entire printed target. The noise dC, dM, or dY is determined as the difference between the original CMY values and the output of the inverse transform with the measured Lab values as the transform input. Since color patch locations are stochastically arranged, any "noticeable" spatial pattern of the noise is most likely due to the printer non-uniformity in the corresponding channel. The nonuniformity can be estimated by spatially smoothing the noise terms and the result can be subtracted from the original CMY input for a second-round calibration to achieve higher color accuracy.

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.

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.

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.

Introduction of 2 X 2 centering can significantly reduce the number of dot patterns required in color calibration. As a result, local calibration can be performed using direct measurement and fast table lookup. In this paper, 2 X 2 calibration is applied to error diffusion. A novel concept for error diffusion is introduced. It matches the color increment instead of color. The concept makes integration of error diffusion and 2 X 2 calibration natural and free of causality issue.