Huanzhao Zeng

Printing anaglyph maps optimized for display

Although anaglyphs have a big advantage that they can be presented using traditional single channel media such as print, film, display, etc., a media type must be determined as a pair of views is combined into a single image to minimize retinal rivalry and stereo crosstalk. Most of anaglyph maps and map tools are optimized for display and assumed using red-cyan filtered glasses for viewing. Due to the large difference between a display gamut and a printer gamut, red and cyan colors that are used to separate the left view and the right view are changed considerably as they are mapped from a display color space to a printer color space for printing and results in serious retinal rivalry. A solution using a special gamut mapping method to preserve the relative relationship of cyanish and reddish colors was developed to gamut map colors from display to printer. And the color characterization to balance neutral colors for specific red/cyan glasses is applied to further improve the color appearance.

Modelling memory colour region for preference colour reproduction

Colour preference adjustment is an essential step for colour image enhancement and perceptual gamut mapping. In colour reproduction for pictorial images, properly shifting colours away from their colorimetric originals may produce more preferred colour reproduction result. Memory colours, as a portion of the colour regions for colour preference adjustment, are especially important for preference colour reproduction. Identifying memory colours or modelling the memory colour region is a basic step to study preferred memory colour enhancement. In this study, we first created gamut for each memory colour region represented as a convex hull, and then used the convex hull to guide mathematical modelling to formulate the colour region for colour enhancement.

Ink limit control for ink-jet printer color calibration

Ink limit is an important parameter for printer color calibration, especially for inkjet printers. A GCR approach is often used to control the total ink amount for CMYK printers. However, a tradition GCR approach has the following limitations: 1) it can not reduce the total ink amount to less than 200 percent for CMYK printers; 2) it can not be applied to reduce ink for CMY printers; 3) to achieve highest image quality, ink amount may be limited to different values in different regions, in which the GCR approach fails. In this paper, a new approach is presented to control ink limit. It controls ink limit globally as well as locally. An algorithm was developed to construct a gamut boundary for gamut mapping that guarantees that the constructed gamut surface covers only colors within the ink limit. If the ink limit needs to be modified, the gamut surface is reconstructed based on the original measured data. Therefore redoing and remeasuring a target is avoided. It greatly simplifies the ink limit control and color calibration.

A new method for skin color enhancement

Skin tone is the most important color category in memory colors. Reproducing it pleasingly is an important factor in photographic color reproduction. Moving skin colors toward their preferred skin color center improves the skin color preference on photographic color reproduction. Two key factors to successfully enhance skin colors are: a method to detect original skin colors effectively even if they are shifted far away from the regular skin color region, and a method to morph skin colors toward a preferred skin color region properly without introducing artifacts. A method for skin color enhancement presented by the authors in the same conference last year applies a static skin color model for skin color detection, which may miss to detect skin colors that are far away from regular skin tones. In this paper, a new method using the combination of face detection and statistical skin color modeling is proposed to effectively detect skin pixels and to enhance skin colors more effectively.

Preferred skin color enhancement for photographic color reproduction

Skin tones are the most important colors among the memory color category. Reproducing skin colors pleasingly is an important factor in photographic color reproduction. Moving skin colors toward their preferred skin color center improves the color preference of skin color reproduction. Several methods to morph skin colors to a smaller preferred skin color region has been reported in the past. In this paper, a new approach is proposed to further improve the result of skin color enhancement. An ellipsoid skin color model is applied to compute skin color probabilities for skin color detection and to determine a weight for skin color adjustment. Preferred skin color centers determined through psychophysical experiments were applied for color adjustment. Preferred skin color centers for dark, medium, and light skin colors are applied to adjust skin colors differently. Skin colors are morphed toward their preferred color centers. A special processing is applied to avoid contrast loss in highlight. A 3-D interpolation method is applied to fix a potential contouring problem and to improve color processing efficiency. An psychophysical experiment validates that the method of preferred skin color enhancement effectively identifies skin colors, improves the skin color preference, and does not objectionably affect preferred skin colors in original images.

Color schemes for encoding information in digital maps

Color schemes have been used in maps to visually distinguish different regions or to approximately represent the magnitude of a property. Since human eyes are not able to translate a color to a numerical scale, colors on a traditional map can only be used to visually estimate magnitudes. As maps are represented more and more digitally, a properly designed color scheme may be able to use color to encode numbers and to accurately translate colors into numerical scales of a property. As a mouse (or other pointers) points to a location, the color of the location can be translated into the original encoded number and therefore the numerical property of the location may be displayed. In this paper, method to encode information in digital maps using color schemes is investigated. A hue-based color scheme was developed to encode and decode numerical scales for digital maps. Color gamut issues between display and print are investigated as well.

A method to improve the invertibility of ICC profiles that use lookup tables

Traditionally, the AToB0 tag of an ICC printer profile, containing the perceptual transform from device specific to PCS Lab or XYZ values, has been generated directly from measurement data without considering the color re-rendering included in the PCS to device-specific transform found in the corresponding BToA0 tag. In this case, the AToB0 color conversion will often not be the inverse of the color conversion in the BToA0 tag. However, with ICC version 4, the AToBn and BToAn transforms are in general supposed to be inverses of each other, to the extent possible. This feature supports the re-purposing of color data within an ICC color management workflow. This inversion is a challenge for profile generation due to issues with either directly inverting 3-D interpolations or inverting every step applied in generating the BToA0 tag. Directly inverting a 3-D LUT may not be feasible because the forward mapping is usually not a one-to-one mapping. Mathematically, inverting every operation for generating a BToA0 tag may also be extremely difficult if not impossible. Consequently, a closed-loop method has been developed which iteratively adjusts AToBn tags to improve the invertibility of ICC profile transforms. The test results are very encouraging.