Online Color Research Articles

On-line Colour Measurement Using Laser-based Abridged Spectrophotometry

Carefully constructed colour relationships and subtle colour choice are central to design inspiration. When the designer's ideas are transferred to production, loss of the original colour inspiration is potentially very damaging to the ultimate success of the design. Reliable on-line colour measurement may prove to be an important part of the technology needed to faithfully reproduce original design ideas. A demonstration laser photometer, intended to measure colorant concentrations during production, has been constructed at UMIST. It has proved capable of a level of measurement sensitivity and reflectance measurement accuracy comparable to a reference bench spectrophotometer at the three wavelengths used. The intent is to provide an instrument technology with which the output of a coloration system can be monitored and potentially controlled, on-line. The availability of abundant monochromatic light from lasers, and flbre-optic delivery, makes cheap multi-head measuring systems feasible. The predicted reflectance values for the laser wavelengths are provided by the match prediction system. The colorimeter compares the required with the actual reflectance at three wavelengths, and can generate an unambiguous control signal for up to three colorants in the recipe. Additional laser lines can be added if more than three colorant concentrations need to be controlled.

On-line 3-chromatic graphs - II critical graphs

On-line coloring of a graph is the following process. The graph is given vertex by vertex (with adjacencies to the previously given vertices) and for the actual vertex a color different from the colors of the neighbors must be irrevocably assigned. The on-line chromatic number of a graph G, χ ∗(G) is the minimum number of colors needed to color on-line the vertices of G (when it is given in the worst order). A graph G is on-line k-critical if χ ∗(G)=k , but χ ∗(G′) < k for all proper induced subgraphs G′ ⊂ G. We show that there are finitely many (51) connected on-line 4-critical graphs but infinitely many disconnected ones. This implies that the problem whether χ ∗(G) ⩽ 3 is polynomially solvable for connected graphs but leaves open whether this remains true without assuming connectivity. Using the structure descriptions of connected on-line 3-chromatic graphs we obtain one algorithm which colors all on-line 3-chromatic graphs with 4 colors. It is a tight result. This is a companion paper of [1] in which we analyze the structure of triangle-free on-line 3-chromatic graphs.

An optoelectronic sensor system for industrial multipoint and imaging spectrometry

The paper presents a compact integrated sensor system for industrial multipoint and imaging optical spectrometry applications. The sensor consists of a compact prism-grating-prism spectrograph combined with a matrix detector and signal preprocessing electronics. All the optical components are on a single optical axis, resulting in ease of assembly and adjustment, small size and low cost. The spectrograph can be used in the wavelength range 380–820 nm, with a resolution of 3 nm. In imaging spectrometry one axis of the matrix detector is used for the wavelength spectrum and the other for spatial location. The built-in microcontroller-based signal-preprocessing electronics compresses the CCD data before transfer. Test results for a 16-channel spectrometer demonstrate the suitability of the system for on-line multipoint colour measurement.

On-Line Coloring of Sparse Random Graphs and Random Trees

The performance of the greedy coloring algorithm “first fit” on sparse random graphsGn,c/nand on random trees is investigated. In each case, approximatelylog2logncolors are used, the exact number being concentrated almost surely on at most two consecutive integers for a sparse random graph and on at most three consecutive integers for a random tree.

On-line coloring of perfect graphs

Lovasz, Saks, and Trotter showed that there exists an on-line algorithm which will color any on-linek-colorable graph onn vertices withO(nlog(2k−3) n/log(2k−4) n) colors. Vishwanathan showed that at least Ω(log k−1 n/k k ) colors are needed. While these remain the best known bounds, they give a distressingly weak approximation of the number of colors required. In this article we study the case of perfect graphs. We prove that there exists an on-line algorithm which will color any on-linek-colorable perfect graph onn vertices withn 10k/loglogn colors and that Vishwanathan's techniques can be slightly modified to show that his lower bound also holds for perfect graphs. This suggests that Vishwanathan's lower bound is far from tight in the general case.

ENHANCING HORTICULTURAL EDUCATION THROUGH WORLD WIDE WEB TECHNOLOGY

The World Wide Web and other emerging information technologies are bringing about a quiet revolution in higher education. Networked computers deliver high-quality educational enhancements to students at little per unit cost to the teacher. Slide presentations, course handouts, on-line color photographs, and interactive modules are accessible from the computer desktop via high-speed Ethernet or modem connections. Aggie Horticulture, the Web server of the Texas Horticulture Program, will be used as a model to demonstrate the impact of Web technology on delivery of enhancements to “traditional” lecture-format courses and its potential for delivery of “nontraditional” courses to large audiences independent of space and time constraints.

On-line color monitoring in continuous textile dyeing

This paper describes how on-line color monitoring could be used as part of an ultrasound enhanced continuous textile dyeing system. The current state-of-the-art of color measurement and control in textile manufacturing is reviewed. The use of ultrasound in a closed-loop dyeing system is proposed. The current status of on-line color monitoring which would be required is presented. Some possible solutions to measuring the color of wet fabric have been developed.

SOME ASPECTS OF RGB VISION AND ITS APPLICATIONS IN INDUSTRY

RGB machine vision overlaps both colorimetry instrumentation and gray scale machine vision, and offers advantages over both. Proper calibration of the color camera which makes measurements independent of changes in illumination is essential for the reliability of color machine vision. A practical approach to on-line color camera calibration under unstable illumination conditions is presented and the performance of the procedure is evaluated. New potential applications of RGB machine vision are discussed from the perspective of physics-based vision and the calibration procedure developed here.

Efficient approximation algorithms for domatic partition and on-line coloring of circular arc graphs

We exploit the close relationship between circular arc graphs and interval graphs to design efficient approximation algorithms for NP-hard optimization problems on circular arc graphs. The problems considered here are maximum domatic partition and on-line minimum vertex coloring. We present a heuristic for the domatic partition problem with a performance ratio of 4. For on-line coloring, we consider two different on-line models. In the first model, arcs are presented in the increasing order of their left endpoints. For this model, our heuristic guarantees a solution which is within a factor of 2 of the optimal (off-line) value; and we show that no on-line coloring algorithm can achieve a performance guarantee of less than 4 3 . In the second on-line model, arcs are presented in an arbitrary order; and it is known that no on-line coloring algorithm can achieve a performance guarantee of less than 3. For this model, we present a heuristic which provides a performance guarantee of 4.

On-Line and First-fit Coloring of Graphs that Do Not Induce $P_5 $

For a graph H, let ${\text{Forb}}( H )$ be the class of graphs that do not induce H, and let $P_5 $ be the path on five vertices. In this article, we answer two questions of Gyárfás and Lehel. First, we show that there exists a function $f( \omega )$ such that for any graph $G \in \,{\text{Forb}}( P_5 )$, the on-line coloring algorithm First-Fit uses at most $f( \omega ( G ) )$ colors on G, where $\omega ( G )$ is the clique size of G. Second, we show that there exists an on-line algorithm A that will color any graph $G \in \,{\text{Forb}}( P_5 )$ with a number of colors exponential in $\omega ( G )$. Finally, we extend some of our results to larger classes of graphs defined in terms of a list of forbidden subgraphs.

Optimal on-line coloring of circular arc graphs

We show that a certain optimal on-line coloring algorithm for interval graphs given independently by Kierstead and Slusarek can be applied to a wider class of circular arc graphs. We prove that the competitive ratio of the algorithm is equal to 3 which improves a previous result by Marathe, Hunt and Ravi.

Colour matching with cadmium- free pigments

This paper describes how on-line color monitoring could be used as part of an ultrasound enhanced continuous textile dyeing system. The current state-of-the-art of color measurement and control in textile manufacturing is reviewed. The use of ultrasound in a closed-loop dyeing system is proposed. The current status of on-line color monitoring which would be required is presented. Some possible solutions to measuring the color of wet fabric have been developed.

On-Line Coloring and Recursive Graph Theory

An on-line vertex coloring algorithm receives the vertices ofa graph in some externally determined order, and, whenever a new vertex is presented, the algorithm also learns to which of the previously presented vertices the new vertex is adjacent. As each vertex is received, the algorithm must make an irrevocable choice of a color to assign the new vertex, and it makes this choice without knowledge of future vertices. A class of graphs $r$ is said to be on-line $\chi$-bounded if there exists an on-line algorithm $A$ and a function $f$ such that $A$ uses at most $f(\omega(G))$ colors to properly color any graph $G$ in \Gamma. If $H$ is a graph, let Forb($H$) denote the class of graphs that do not induce $H$. The goal of this paper is to establish that Forb($T$) is on-line $\chi$-bounded for every radius-2 tree $T$. As a corollary, the authors answer a question of Schmerl's; the authors show that every recursive cocomparability graph can be recursively colored with a number of colors that depends only on its clique number.

Coloring inductive graphs on-line

In this paper we consider the problem of on-line graph coloring. In an instance of on-line graph coloring, the nodes are presented one at a time. As each node is presented, its edges to previously presented nodes are also given. Each node must be assigned a color, different from the colors of its neighbors, before the next node is given. LetA(G) be the number of colors used by algorithmA on a graphG and letx(G) be the chromatic number ofG. The performance ratio of an on-line graph coloring algorithm for a class of graphsC is maxG ∈C(A(G)/χ(G)). We consider the class ofd-inductive graphs. A graphG isd-inductive if the nodes ofG can be numbered so that each node has at mostd edges to higher-numbered nodes. In particular, planar graphs are 5-inductive, and chordal graphs arex(G)-inductive. First Fit is the algorithm that assigns each node the lowest-numbered color possible. We show that ifG isd-inductive, then First Fit usesO(d logn) colors onG. This yields an upper bound ofo(logn) on the performance ratio of First Fit on chordal and planar graphs. First Fit does as well as any on-line algorithm ford-inductive graphs: we show that, for anyd and any on-line graph coloring algorithmA, there is ad-inductive graph that forcesA to use Ω(d logn) colors to colorG. We also examine on-line graph coloring with lookahead. An algorithm is on-line with lookaheadl, if it must color nodei after examining only the firstl+i nodes. We show that, forl<n/logn, the lower bound ofd logn colors still holds.

Use of a process colorimeter in industrial processing of tomatoes

A system to provide on-line colour monitoring of tomato products was investigated. The tristimulus colorimeter used can supply hundreds of recordings per second to a remote PC, which elaborates the data in real time and shows the trend of all colorimetric data with respect to any scale. By using the linear regression equation obtained by processing the experimental data it is also possible to predict values for measurements carried out in quality control laboratories during the concentration phase.

Three-dimensional, on-line color graphics representation in complex decision-making tasks

Three-dimensional, on-line color graphics representation in complex decision-making tasks

Fermentation control with personal computers

A cheap but efficient computer network system for advanced fermentation control is described. Two Commodore C-64 computers are connected to a single-drive floppy disk; possible bus conflicts are avoided by software programming. The first computer is dedicated to data acquisition and process control with conventional parameters whereas the second computer unit utilizes previously stored parameter values for on-line high-resolution color graphics and for the evaluation of derived process variables such as growth rate and productivity. These variables can then be used for more refined process control.

A computer system for aircraft flyover acoustic data acquisition and analysis

A mini‐computer‐based system housed in a mobile trailer was designed for field measurements of aircraft flyover noise. The system was used to accomplish recent Federal Aviation Regulation Part 36 noise certification testing for the new Boeing model 757 and 767 aircraft. The multi‐user system performed acoustic and telemetered data acquisition, analysis, and data storage. All data were made available to online color monitors and on hardcopy. One‐third octave band acoustic data were acquired and analyzed via microcomputer controlled digital frequency analyzers. Ground weather data and telemetered data, which includes upper air weather and airplane position and performance information, was received, stored and displayed automatically. By integrating all of the data, fully corrected acoustic time histories, spectra, and EPNL values were calculated within minutes of an airplane flyover. Online data output were used to make test operational decisions and evaluate aircraft noise level predictions. This computer system increased test efficiency by providing high quality data to personnel for real time decision making.

New On-Line Colour and Brightness Measurement and Control System

In recent years, the on-line measurement and control of colour and brightness has stimulated great interest in the paper industry. The monitoring and control of paper quality in the paper mill is becoming increasingly important as the capacity and quality requirements of both the paper mills and the printing houses continue to rise. The continuous on-line measurement and control system described in this paper is noteworthy for the production of even colour, the reduction of colour broke, and tne snortening of the time required for grade and colour changes.

An on-line spectrophotometer for color measurement of moving samples

The development of a reflectance spectrophotometer designed specifically for on-line non-contact measurement of color is discussed. The on-line spectrophotometer utilizes two concepts new to the field of color measurement:1. A pulsed-xenon flashtube light source2. A diffraction grating spectrometer and detector array for parallel wavelength sensing.Both of these concepts result in an instrument with improved performance capabilities compared with the tristimulus colorimeters previously used for on-line color measurement. These capabilities include improved accuracy, non-contact measurement of moving samples, long term stability, and agreement of measurements made with multiple instruments. The on-line spectrophotometer is presently used as a key element in the measurement and control of color in the textile, plastics and paper industries. Several applications will be described.