Colorimetric Characterization Research Articles

Adaptive Colorimetric Characterization of Camera for the Variation of White Balance

The RGB signals generated by different cameras are not equal for the same scene. Therefore, cameras are characterized based on a CIE standard colorimetric observer. One method of deriving a colorimetric characterization matrix between camera RGB output signals and CIE XYZ tristimulus values is least squares polynomial modeling. Yet, this involves tedious experiments to obtain a camera transfer matrix under various white balance points for the same camera. Accordingly, the current paper proposes a new method for obtaining camera transfer matrices under different white balances using a 3 x 3 camera transfer matrix under a specific white balance point.

Calibrated color mapping between LCD and CRT displays: A case study

AbstractThe primary goal of a color characterization model is to establish a mapping from digital input values di (i = R,G,B) to tristimulus values such as XYZ. A good characterization model should be fast, use a small amount of data, and allow for backward mapping from tristimulus to di. The characterization models considered here are for the case of an end user who has no direct knowledge of the internal properties of the display device or its device driver. Three characterization models tested on seven different display devices are presented. The characterization models implemented in this study are a 3D look up table (LUT) (Raja Balasubramanian, Reducing the Cost of Lookup Table Based Color Transformations, Proc IS&T/SID 7th Color Imaging Conference 1999;44:321–327), a linear model (Fairchild MD, Wyble DR. Colorimetric Characterization of the Apple Studio Display (Flat Panel LCD). Munsell Color Science Laboratory Technical Report, 1998), and the masking model (Tamura N, Tsumura N, Miyake. Masking Model for accurate colorimetric characterization of LCD. Proc IS&T/SID 10th Color Imaging Conference 2002;312–316). The devices include two CRT monitors, three LCD monitors, and two LCD projectors. The results of this study indicate that a simple linear model is the most effective and efficient for all devices used in the study. A simple extension to the linear model is presented, and it is demonstrated that this extension improves white prediction without causing significant errors for other colors. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 438–447, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.

End-to-end self-assembly and colorimetric characterization of gold nanorods andnanospheres via oligonucleotide hybridization

We report end-to-end assembly for tuning the optical properties of a gold nanorod/spherebased on oligonucleotide hybridization. The rationale behind the selection of themercaptoalkyloligonucleotide molecule is based on the fact that the thiol group binds to theends of the nanorods, which further assemble in an end-to-end fashion throughhybridization with the target oligonucleotide. A highly selective, colorimetricpolynucleotide detection method based on mercaptoalkyloligonucleotide-modified goldnanorod/sphere probes is also reported.

Colour parameters, whiteness indices and physical features of marking paints for horizontal signalization

The present paper describes the assessment of colour parameters of industrial paints for horizontal signalization (designed as POM S1 and POM S2 / ZEB 1 and ZEB 2) of white colour hue, coming from two different producers ("Pomoravlje" and "Zorka") with reference to an independent sample (IND 0) and some physical properties of each sample. Colorimetric characterization of samples was performed using a reflectance spectrophotometer "Update Colour Eye 3000". Standard and modified test methods (ASTM) were performed to establish physical properties of the paints. The industrial paints show better values for the investigated parameters and properties and satisfy standards prescribed by law. POM S2 sample with dry film thickness, similar to the same of other samples, provides the best physical features maximizing quality and minimizing protection cost.

High-Accuracy Digital Imaging of Cultural Heritage without Visual Editing

At Rochester Institute of Technology, a research program is near completion aimed at benchmarking the quality of direct digital imaging of cultural heritage in American museums, libraries, and similar institutions. The current practice at nearly all institutions surveyed includes visual editing. Digital masters incorporate camera spatial processing, ICC-type color management including encoding in a large-gamut RGB space, and global and local visual editing. Also at RIT, a research program is underway aimed at developing a high-quality digital camera that incorporates spectral imaging. The hypothesis is that when using the new camera system, visual editing is unnecessary, greatly improving workflow efficiency and color accuracy. An experiment was performed to test this hypothesis. The experiment included spectral-based imaging of both color targets and small paintings and rendering the spectral images for a colorimetrically-characterized computer-controlled LCD display. The targets and paintings were viewed adjacent to the display in a laboratory lit by ceiling-mounted daylight-balanced fluorescent lights. A variety of quantitative comparisons were performed including: reflectance spectrophotometry vs. insitu spectroradiometry, reflectance spectrophotometry vs. spectral-based imaging, forward and inverse model accuracy of the LCD colorimetric characterization, and in-situ spectroradiometric comparison of targets and paintings compared with their LCD renderings. Using the GretagMacbeth Color-Checker as an independent verification target, average color differences varied between 1.0 and 2.9 ΔE00. For two paintings, the average accuracy was 4.2 and 5.1ΔE00. This level of accuracy exceeded that achieved by museums and libraries, even following global and local image editing, confirming our hypothesis that it is possible to create a digital archive of cultural heritage without the need for visual editing.

Colorimetric Characterization of Digital Cameras Preserving Hue Planes

Colorimetric Characterization of Digital Cameras Preserving Hue Planes

Structural, compositional, optical and colorimetric characterization of TiN-nanoparticles

We present results of an investigation of TiN nanoparticles, which were produced by laser ablation/evaporation and adiabatic expansion with the nanoparticle beam apparatus LUCAS. Compositional and structural characterization, using secondary ion mass spectrometry (SIMS), electron energy loss spectroscopy (EELS), X-ray diffraction (XRD) and selected area electron diffraction (SAED), revealed that crystalline and almost stoichiometric particles were formed and that they are susceptible to oxidation. Furthermore, transmission electron microscopy (TEM) analysis showed that TiN nanoparticles exhibit cuboid shapes. The size distributions were obtained using the edge length as parameter. They are fairly broad and the mean particle diameter depends on the seeding gas flow (the pressure) that is applied to the ablation chamber during production. In situ optical transmission spectra of the TiN nanoparticles deposited on a quartz substrate indicate a pronounced single Mie resonance at around 1.7 eV and an absorption flank starting at approximately 3.0 eV. The experimental optical extinction spectra of different samples were fitted using Mie theory calculations. The dielectric function of bulk TiN was modified to account for size and interface damping of the Mie resonance. Due to the distinct absorption band, TiN may be used as a color pigment. The dependence of the color stimulus on the extinction cross-section as well as on the product of the particle concentration and the sample thickness were examined. Chromaticity coordinates were derived according to the CIE 1976 (L * a * b *) color space from the in situ optical transmission spectra.

Colorimetric characterization of a computer‐controlled liquid crystal display

AbstractA new method was used to characterize computer‐controlled liquid crystal displays (LCDs). The characterization, which was performed to enable colorimetric image display, included channel independence, spatial independence, screen uniformity, and colorimetry. The colorimetric model consisted of three one‐dimensional look‐up tables (LUTs) describing each channel's optoelectronic transfer function and a 3 × 4 matrix transformation that included black‐level flare. The matrix coefficients were estimated statistically by minimizing the average CIEDE2000 color difference for a data set sampling the display's colorimetric gamut. The LUTs were recreated dynamically throughout the optimization of the matrix coefficients. The characterization was implemented with three different instruments to evaluate the robustness of the method with respect to measurement uncertainty. The average performance ranged between 0.1 and 0.4 ΔE00 and was well correlated with instrument precision. The optimization approach improved performance by a factor of two compared with direct measurements. Despite differences in instrument design, the chromaticities of each primary following optimization and black‐level flare compensation were very similar. This excellent performance was a result of the display's optoelectronic properties well matching the model assumptions. The technique was also used to characterize three additional LCD displays ranging in their matching of the model assumptions. In this case, performance worsened. For one display, more complex models would be required for colorimetric characterization. Finally, a colorimetric characterization based on measurements at the center of the display and perpendicular to the face was used to predict measurements at the edges and at different angles. The results indicated that characterizations would be required at multiple positions and angles in order to achieve sufficient accuracy. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 365–373, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20046

Design and performance of a color chart based in digitally processed images for sensory evaluation of piquillo peppers (Capsicum annuum)

AbstractA chart of color standards for visual color evaluation of the piquillo pepper (Capsicum annuum) has been designed. The chart comprises six rectangular regions of digitally processed images of piquillo peppers covering the observed visual range of variability in this product. Colorimetric characterization of piquillo peppers and the color chart has been made using instrumental color measurements. Both trained and untrained sensory panels tested the reliability of the designed color chart. The Pearson correlation coefficient between color chart scores and subjective color quality scores is 0.831 (P < 0.01). Correlation between all instrumental color coordinates, with the exception of CIELAB a*, and visual color chart scores are significant at P< 0.001 and Pearson correlation coefficients range from −0.747 with CIELAB chroma C* to −0.926 with CIELAB hue angle h. Repeatability of visual color chart scores is completely satisfactory, having found no statistically significant differences between color chart scores in samples evaluated twice by panelists. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 305–311, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20026

Optical and Colorimetric Characterization of a Micro Mirror Based Spectral Image Capturing System

Optical and Colorimetric Characterization of a Micro Mirror Based Spectral Image Capturing System

Color measurements for pearlescent coatings

AbstractThis article describes recent developments at the National Institution of Standards and Technology in the colorimetric characterization of pearlescent coatings. The goal of this research is to develop a measurement protocol for the accurate color characterization of these coatings using an understanding of their scattering mechanism as a guide. A large ensemble of bi‐directional reflectance measurements on a series of pearl interference pigmented coatings show general trends in the color variations with illumination and viewing angles. These measurements were used to define a set of geometries (illumination angles of 15°, 45°, and 65° and aspecular angles of 15°, 35°, 45°, 70°, and 85°) to characterize the angle dependent color travel observed in these coatings. © 2003 Wiley Periodicals, Inc. Col Res Appl, 29, 38–42, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10210

Estimating black‐level emissions of computer‐controlled displays

AbstractIt is quite common for computer‐controlled displays to emit light in image areas set to digital values of zero, referred to as their black level. This is expected for liquid–crystal displays and also can occur for cathode‐ray tube displays when the “brightness” (gun‐amplifier offset) is set excessively high. For either display, the light emission at the black level results in color channels whose chromaticities vary with luminance level. Consequently, typical methods of colorimetric characterization result in large error. When this black‐level emission is measured and accounted for suitably, characterization accuracy is dramatically improved. Unfortunately, many instruments used to measure displays have too low a sensitivity to measure black‐level emission with sufficient precision and accuracy. A method of estimating black‐level emissions was derived and tested. Because the optimal black‐level results in channel chromaticities that are invariant to the greatest extent with luminance level, an objective function was defined as the sum of chromaticity variances of each channel over a range of measurements. Minimizing this objective function resulted is an estimate of a display's black level. The estimated black level resulted in equivalent or superior performance to direct measurements. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 379–383, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10181

Comparison of three algorithms in the classification of table olives by means of computer vision

The classification of table olive in different quality categories is performed depending on the defects in the surface of the fruits. However, the characteristics of every category are not defined. Then, it is necessary to apply learning algorithms that allow the extraction of quality information from batches previously classified by expert workers. In this research, a colorimetric characterisation of the more common defects has been carried out. An image analysis system has been used to segment the parameter set with the information from the olives quality. Three different algorithms have been applied to classify the olives in four quality categories. The results show that a neural network with a hidden layer is able to classify the olives with an accuracy of over 90%, while partial least squares discriminant and Mahalanobis distance are over 70%.

Characterization of a Digital Camera as an Absolute Tristimulus Colorimeter

An algorithm is proposed for the spectral and colorimetric characterization of digital still cameras (DSC) which allows them to be used as tele-colorimeters with CIE–XYZ color output, in cd/m2. The spectral characterization consists in the calculation of the color-matching functions from the previously measured spectral sensitivities. The colorimetric characterization consists in transforming the raw RGB digital data into absolute tristimulus values CIE–XYZ (in cd/m2) under variable and unknown spectroradiometric conditions. Thus, in the first stage, a gray balance was applied over the raw RGB digital data to convert them into RGB relative colorimetric values. In the second stage, an algorithm of luminance adaptation versus lens aperture was inserted in the basic colorimetric profile. Capturing the ColorChecker chart under different light sources, and comparing the estimated XYZ data according to the developed color model in relation to the measured XYZ data (in cd/m2) using a tele-spectroradiometer, we verified that the proposed characterization model may be broken down into two portions. Firstly, there is the basic colorimetric profile in combination with the new luminance adaptation algorithm. Secondly, there is the linear correction term due only to the mismatch of the color matching functions of the camera. Although the linear color correction term works relatively well, despite the imposed initial conditions (unknown spectral content of the scene), the separation of the proposed characterization model into two portions (raw and corrected performance) would allow the future comparison of various commercial cameras.

Masking model for accurate colorimetric characterization of LCD

Abstract— A color management system (CMS) such as ICC profile or sRGB space have been proposed for color transformation and reproduction of cross media. In such a CMS, accurate colorimetric characterization of a display device plays a critical role in achieving device‐independent color reproduction. In the case of a CRT, colorimetric characterization based on a GOG model is accurate enough for this purpose. However, there is no effective counterpart in liquid‐crystal displays (LCDs) since the characterization of an LCD has many difficulties, such as channel interaction and non‐constancy of channel chromaticity. In this paper, a new method of display characterization is proposed which is applicable to the assessment of color reproduction of LCDs. The proposed method characterizes an electro‐optical transfer function considering both channel interaction and non‐constancy of channel chromaticity. Experimental results show that the proposed method is very effective in the colorimetry of LCDs.

Colorimetric characterization of LCD and DLP projection displays

Abstract— Successful color‐management of projection systems depends on knowledge of their characteristics. In this study, two typical portable projectors were characterized. The projectors are based on different technologies, liquid‐crystal display (LCD) and digital light‐processing (DLP). Measurements were made with a spectroradiometer. The properties measured were spectral characteristics and the intensity of the primary and white colors, basic colorimetric characteristics, inter‐channel dependency, tone characteristics, color‐tracking characteristics, spatial non‐uniformity, dependency on background, and temporal stability. Based on the characterization results, the possibility of color‐management of the tested projectors is discussed.

Colorimetric Characterization Model for DLP™ Projectors

Colorimetric Characterization Model for DLP™ Projectors

A Practical Approach to Measuring and Modelling Paper Fluorescence for Improved Colorimetric Characterisation of Printing Processes

Paper Fluorescent Whitening Agent combined with differences in relative Ultra Violet levels between instrument illuminants, and real world viewing illuminants, can be a significant source of error in characterising a printing process, and hence in the ability to accurately reproduce colored images in print. These errors can be dealt with using bi-spectral measurements, but a simpler approach that significantly reduces paper whitening agent induced errors is possible, while using more practical print characterisation instruments and procedures.

Colorimetric characterization of negative film for digital cinema post-production

Colorimetric characterization of negative film for digital cinema post-production

Masking Model for Accurate Colorimetric Characterization of LCD

Masking Model for Accurate Colorimetric Characterization of LCD