Optimal nonnegative color scanning filters

In this correspondence, the problem of designing color scanning filters for multi-illuminant color recording is considered. The filter transmittances are determined from a minimum-mean-squared orthogonal tristimulus error criterion that minimizes the color error in estimates obtained from noisy recorded data. Nonnegativity constraints essential for physical realizability are imposed on the filter transmittances. In order to demonstrate the significant improvements obtained, the resulting filters are compared with suboptimal filters reported in earlier literature.     

Problems in publishing accurate color in IEEE journals

To demonstrate the performance of color image processing algorithms, it is desirable to be able to accurately display color images in archival publications. In poster presentations, the authors have substantial control of the printing process, although little control of the illumination. For journal publication, the authors must rely on professional intermediaries (printers) to accurately reproduce their results. Our previous work describes requirements for accurately rendering images using your own equipment. This paper discusses the problems of dealing with intermediaries and offers suggestions for improved communication and rendering.     

Rapid computation of the continuous wavelet transform by obliqueprojections

We introduce a fast simple method for computing the real continuous wavelet transform (CWT). The approach has the following attractive features: it achieves O(N) complexity per scale, the filter coefficients can be analytically obtained by a simple integration, and the algorithm is faster than a least squares approach with negligible loss in accuracy. Our method is to use P wavelets per octave and to approximate them with their oblique projection onto a space defined by a compactly supported scaling function. The wavelet templates are expanded to larger sizes (octaves) using the two-scale relation and zero-padded filtering. Error bounds are presented to justify the use of an oblique projection over an orthogonal one. All the filters are FIR with the exception of one filter, which is implemented using a fast recursive algorithm     

Filter considerations in color correction

The quality of color correction is dependent on the filters used to scan the image. This paper introduces a method of selecting the color filters using a priori information about the viewing illuminants. Color correction results using the derived filters are compared with color correction results using filters that are optimal for individual viewing and recording illuminants. The comparison is performed using the CIE PEL (L*a*b*) perceptual color difference measure. Applications of this work are found in the design of scanners, copiers, and television systems.     

Color image generation and display technologies

The goal of this article is to provide an overview of the transformations and limitations that occur in color imaging input and output devices. We concentrate on two common recording devices and three common output devices. First we provide an overview of digital scanners and cameras, and then we discuss inkjet and laser printers. Finally, liquid crystal display (LCD) devices are presented.     

Color device calibration: a mathematical formulation

The mathematical formulation of calibrating color image reproduction and recording devices is presented. This formulation provides a foundation for future research in areas of characterization of devices and display of color images. The importance of calibration is demonstrated by real examples. The procedure outlined in this paper should become standard for displaying color images for the image processing community.     

Color correction using principal components

The problem of color correction for changes in illumination is briefly reviewed. A new method using the spectral reflectance distribution in the image is introduced and compared to a white-point mapping method. The new method is based on principal component analysis and thus is dependent upon the characteristics of the images that are to be viewed. These two methods are compared using chromaticity plots and the CIE L*a*b* ΔE measurement, for test samples which include color copiers, thermal writers, ink-jet printers, and lithography.     

Projection based prefiltering for multiwavelet transforms

We introduce a method for initializing the multiwavelet decomposition algorithm. The initialization procedure is the orthogonal projection of the input signal into the space defined by the multiscaling function. The approach will always have a solution, places no restrictions on the input (except that it be contained within L₂ ), and can be implemented in a fast algorithm. We present the details of our approach and compare it with another proposed method of prefiltering     

Color imaging for multimedia

To a significant degree, multimedia applications derive their effectiveness from the use of color graphics, images, and video. However, the requirements for accurate color reproduction and for the preservation of this information across display and print devices that have very different characteristics and may be geographically apart are often not clearly understood. This paper describes the basics of color science, color input and output devices, color management, and calibration that help in defining and meeting these requirements     

Measurement and Analysis of Object Reflectance Spectra

Recent algorithms developed in the field of color vision make assumptions based on the spectral reflectance curves of Munsell chips and natural materials. Some of them rely on data collected many years ago. which is partially incomplete in the visible spectrum. or contains many occurrences of the same material in it. In this article. we present a set of new measurements of different materials. In particular. we measured the spectral reflectance of Munsell chips, paints. and various natural materials in the 390–730-nm range. In addition, we have analyzed. through principal-component analysis, the possibility of representing the data collected with a set of basis functions. We show the implications of varying the number of principal components used (from 7 down to 3) on the errors introduced using this method.