Patrick G. Herzog

Stacked amorphous silicon color sensors

Color sensors based on vertically integrated thin-film structures of amorphous silicon (a-Si:H) and its alloys were realized to overcome color moire or color aliasing effects. The complete color information of the color aliasing free sensors is detected at the same spatial position without the application of additional optical filters. The color separation is realized in the depth of the structure due to the strong wavelength dependent absorption of a-Si: H alloys in the visible range. The sensors consist of three stacked p-i-n diodes. The spectral sensitivity of the sensors can be controlled by the optical and electronic properties of the materials on one hand and the design of the devices on the other hand. In order to investigate the optical wave propagation within the device and to optimize the color separation we have developed an optical model, which takes the optical properties of the individual layers and the device design into account. The optical model has been combined with a colorimetric model, which facilitates the benchmarking of the color sensors and the reduction of the color error of the sensors. Finally, an improved device design is presented.

Further development of the analytical color gamut representation

This paper describes the analytical representation of the color gamut surfaces of arbitrary print processes. Such a method was published earlier, but has now been improved and tested against a number of different print processes. Moreover, an algorithm to determine the model parameters that reflect the characteristics of a considered print process is described.

Gamut mapping using an analytical color gamut representation

In this study, gamut mapping between real print processes was investigated. The processes were supposed to have equal lightness ranges, hence no lightness mapping applied. Several chroma mapping methods modifying and not modifying lightness were systematically evaluated. Pure clipping of chroma resulted as the best technique when lightness was left untouched. However, a few images required adjustments of lightness in order to retain higher chroma. These investigations were used to gain practical experience with anew, analytical color gamut representation recently published. THE new representation method displayed no kind of anomalies and hence proved to be fully practical.

Multi-channel sensors with reduced metameric errors

Abstract Novel 4-channel sensors for the detection of the components of visible and the near infrared light have been developed. The sensors are based on stacked amorphous and microcrystalline silicon pin diodes. The color separation is performed in the depth of the structure which prevents the color moire or color aliasing effect. Due to the vertical integration of the diodes the four channels can be read-out simultaneously. To gain optimization criteria the sensors are colorimetrically analyzed. The presented model facilitates the quantification of color errors with regard to human perception. The evaluated color errors of the 4-channel sensors are compared with an amorphous 3-channel sensor and a commercial color CCD camera. Based on the colorimetric analyses the 4-channel sensors have a reduction of the color error in comparison with the amorphous 3-channel sensors and the commercial CCD camera.

Spectral scanner characterization using linear programming

Today, the characterization of scanners combines properties of both the scanner and the medium. A different method is proposed here. If the characterization of the scanner is carried out spectrally, it is not specific to a medium and the medium properties can be acquired separately. The drawback of this approach is the lack of a simple solution to determine spectral properties of a scanner. Therefore, a method to estimate the spectral properties of a scanner by scanning a single test chart is proposed.

Performance of amorphous-siliçon based multiple-channel color sensors

The purpose of this study was to identify the performance of novel realized color sensors manufactured in thin film technology and to compare the results with simulations. In a previous study, a novel technology of three- and six-channel color sensors was presented. The performance of the sensors was tested in simulations and compared to other sensors for different characterization methods (polynomial regression and smoothing inverse). Now, these method are supplemented by a new linear programming method. Moreover, practical experiments with real color capture have been conducted.

Quality evaluation of current ICC-profile generation tools for CMYK-output devices

ICC-color Management tools claim to give both accurate and consistent results. However, using these tools of distinct manufacturers, different results are likely to occur even if the same parameters are given. Obviously the manufacturers do not focus on the same criteria doing their optimizations, which leads to the fact that each tool has its own strengths and weaknesses. In this study, new methods for comparing ColorManagement tools were evaluated, and with these methods, ICC profiles generated by five CM tools of current leaders on the market were investigated in order to point out their weaknesses and strengths. In addition, the influence of using various ColorMatchingModules (CMM) was tested. For the generation of each ICC profile, the same measurements (ISO 12642 equals ANSI IT8. 7/3 target of Iris InkjetPrinter) were used. Since the standardized ISO 12642 file format, in which the measurement data are stored, was not accepted by each of the tools, the data-file had to be converted to proprietary formats. The investigated quality aspects were accuracy, consistency and smoothness, with ΔEab2 and ΔE943 taken as the criteria. For each aspect, performance was visualized by mapping the ΔE values to pseudo colors, giving a very intuitive view on the investigated subject. Results showed that ColorManagement tools indeed achieved good color fidelity, especially if generated as large profiles.

Design and Modeling of Optical Sensors in Multi-Channel Technology

We have realized color sensors based on vertically integrated thin film structures to overcome color moire or color aliasing effects. The complete color information of the color aliasing free sensors can be detected at the same position of a sensor array without optical filters. The color separation is realized by the wavelength dependent absorption of amorphous silicon and its alloys. The sensors consist of three amorphous silicon pin diodes. The spectral sensitivity of the sensors can be controlled by the optical and optoelectronic properties of the materials on one hand and the design of the devices on the other hand. In order to investigate the optical wave propagation within the device and to optimize the color separation we have developed an analytical optical model, which takes the optical properties of the materials and the device design into account. The optical model has been combined with a colorimetrical model, which facilitates the benchmarking of the color sensors and the reduction of the color error of the sensors. The analytical colorimetric/optical model and an improved device design will be presented.

Multichannel sensors in thin film technology

A novel sensor concept for the detection of the fundamental components of visible light has been developed. The multi- channel sensors (3-, 4- and 6-channel detectors) based on three and four stacked amorphous thin film detectors are color moire or color aliasing free due to their vertical integration. The color separation is performed in the depth of the structure without using optical filters. The developed 3- and 4-channel detectors can be read-out with one shot whereas the color information of the 6-channel detector can be read- out with two shots. The sensors are colorimetrically characterized in order to gain further optimization criteria concerning the improvement of the sensor performance. The presented characterization model facilitates the quantification of color errors with regard to the human perception. Furthermore, the color errors of amorphous thin film sensors are compared with a commercial color CCD camera and a BiCMOS color-sensor.

Three and six channel sensors : realization and colorimetrical characterization

A novel sensor concept for detecting the fundamental components of the visible light has been developed. The multi-channel sensors based on three stacked amorphous thin film detectors are color moire or color aliasing free due to their vertical integration. The four terminal devices enable the generation of three or six linearly independent spectral response curves at the same spatial position. The 3-channel sensor based on three stacked pin-diodes generates a red-green- blue signal with one shot, whereas the 6-channel sensor with three stacked pinip structures allows the detection of up to six linearly independent spectral response curves. The reproducibility of the complex layer sequences is enhanced by introducing a textured TCO-layer in the rear part of the device, which leads to a distinct scattering of the incoming light for longer wavelengths. In order to gain information on how to improve the sensor performance, the sensors are characterized. The presented characterization model facilitates the quantification of color errors with regard to the human perception. Furthermore, the color errors of amorphous thin film sensors are compared with a commercial color CCD camera and a BiCMOS color-sensor.