Shen-ge Wang

Moiré-based auto-stereoscopic images by duplex printing on transparencies

In this paper we describe a method using duplex printing on transparencies to create auto-stereoscopic images viewed in a “see-through” manner. By choosing different halftone structures, differing by having different spatial frequencies for each of the two sides of a transparency, a moiré 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 f. 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 frequency f plus some Δf, while a desired image partition is printed using a halftone with a spatial frequency equal to the median frequency f minus the same Δf. The spatial frequency difference between the halftones on two sides creates a corresponding shift-magnification factor M. The moiré produced by the two partition print images as visually located appear in two separate spatial planes as separated by the transparency, with an amplified total depth of the shift-magnification factor M times the thickness of the transparency. This yields a moiré stereoscopic pattern for the desired image partition as clearly discernable to the human eye with out aid of lenses or other means.

Color correction of smartphone photos with prior knowledge

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 owners 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 owners 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.

Moire-free color halftoning using 2x2 printer modeling

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.

Moiré-free color halftoning using hexagonal geometry and spot functions

A halftone configuration is presented that utilizes three or four rotated hexagonal screens, or more precisely, screens with hexagonally tiled clusters, for moiré-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 moiré-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.

Parametrically controlled, stochastically seeded clustered halftones

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.

UV fluorescence encoded image using two halftoning strategies

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.