A new calibration target or Certified Reference Material (CRM) has been designed that uses violet, orange, green and cyan dyes ont cotton paper. This paper type was chosen because it has a relatively flat spectral response from 400 nm to 700 nm and good keeping properties. These specific dyes were chosen because the difference signal between the orange, cyan, green and purple dyes have certain characteristics that then a low the calibration of an instrument. The ratio between the difference readings is a direct function of the center wavelength of a given spectral band. Therefore, the radiometric and spectral calibration can be determined simultaneously from the physical properties of the reference materials.
The Hexachrome Hi-Fi colorant set has added Orange and Green to the normal Cyan, Magenta and Yellow inks used in the extant printing process. The new inks have been added to expand the gamut of printable colors. This new ink set maximizes the total volume of the printable gamut. Therefore, both lightness and chromaticity bounds were considered in the design of the new Hexachrome ink set. This method of adding extra inks is being explored by others to develop richer reds, greens and blues in other reproduction techniques. These new inking systems require new measurement standards to control ink density, dot gain and ink trap on press. Spectrophotometery is suggested as a new standard to control the complex interaction of these new ink combinations. The use of spectral tags is now possible because of the introduction of low cost spectrophotometers. These new instruments will allow inks to be completely described by their spectral signatures. The establishment of spectral signatures as the new standard instead of density will allow new inks to be used and controls to be specified without having to define yet another set of status filters. Tags are being employed to specify the targeted use of color images in a document. Recently the ability to add a PostScript colorant tag has been made possible with the ColorTron spectrometer and software developed by Light Source Computer Images. These colorant tags can be added to the image files to completely describe the preferred reproduction. These can indude the overprint ink spectra which better specify the interactions of the primary ink sets. The new specification should also include measurement conditions so that the control conditions can be accurately repeated at any location. The world of printing is no longer an isolated community where a single measurement instrument was used to control a press. In this production scenario, the repeatability of the instrument was more important than accuracy. With image files now being distributed widely over electronic networks , the need for accuracy, precision and known measurement method is becoming paramount in the control of printing dependent on the new extra-trinary processes.
Most spectrometers illuminate a dispersing grating with collimated light. This form of the instrument is optimum when high spectral resolution is required. There are many applications such as color matching and desktop publishing that require only 10 nm resolution over the limited spectral region of 390 nm to 700 nm. In addition, the design must lead to a configuration that is affordable. This paper describes a spectrometer design that uses divergent light incident on a grating. The grating is followed by a glass lens used to focus the light on the exit slit. This design uses a simple scanning mechanism that combines the motion of the grating with the chromatic aberrations of the lens to produce a linear-dispersion constant-bandwidth spectrometer. In this configuration the spectrometer is compact a light.
The ATD color space developed by Guth has shown that is can predict the response of human vision to a wide range of stimulus conditions. ATD is a good candidate for predicting the proper transforms under which the output of differing hard copy platforms can be made to have the same appearance. This paper will show how Guth's ATD model can be modified to produce appearance matches over the entire gamut of various ink sets. The paper will also discuss the many dimensions of gamut limits and gamut mapping.
The CIELab system of color coordinates is not optimal for use in desktop publishing (DTP) systems, because it is non-uniform, not well matched to human visual dynamics, and computationally inconvenient. CIELab uses cube roots of differences of color matching functions. In complex scenes, perceived lightness varies quadratically, not cubically, with intensity. Chroma varies in a more complex way but is also not well represented by cubic polynomials. As a result, CIELab exaggerates highlights and compresses shadows. It distorts the concentric circles and radii of the Munsell chart into ellipses and curves. This makes it difficult to achieve appearance equivalence during gamut compression. Gamut compression is an essential element in working with the variety of inexpensive DTP devices. Users expect DTP operations to proceed rapidly on inexpensive equipment. This dictates heavy reliance on integer arithmetic and lookup tables. These techniques do not mesh well with the computational complexities of CIELab.
Companion papers show why the CIELab system of color coordinates is not optimal for use in desktop publishing (DTP) systems and how ATD remedies most of the problems of CIELab. Since DTP deals primarily with the reproduction of images, DTP applications do not need to model human vision. They need only reproduce accurately in the image the reflective properties of the original. The eye does the rest. Linear arithmetic is adequate for this task. An intermediate color space decouples scanner calibration from printer control, leading to a system that is nearly device independent. Plots of Munsell and other color grids show the intermediate space to be uniform. The uniformity of the intermediate space and the linearity of the model lead to accurate gamut compression and negligible transformation errors using integer arithmetic operations on the 8-bit quantities associated with inexpensive DTP equipment. The resulting images are substantially better than those produced by current DTP programs.
A vision model is presented that combines a model for human color perception and visual adaptation with a model for the achromatic and chromaticity modulation transfer functions of the visual system. The combined models produce a uniform color space that can be described as a function of spatial frequency. This model may be useful in developing and optimizing image compression algorithms to reduce bit rate and to increase the quality of color images.
This paper addresses the shortcomings of trying to achieve device independence through colorimetry. These color models do not take into account the fundamental problems of the printing process and that there is a need for a true graphic arts color exchange space. A new meta printing space is proposed for color exchange that will offer a single exchange standard. This standard will allow the blind interchange of data between elements of the color reproduction process. The meta representation is based on human vision and able to encompass the gamuts of the dye sets used in the reproduction of images.
Many groups today are researching the characteristics of beryllium, in an attempt to find ways of producing high quality (low scatter) stable beryllium optics. This paper discusses a two-part study in which (1) an attempt is being made to determine the best, raw beryllium mixture and preparation, machining and polishing processes, test and analysis methods, and (2) a proposed model for the prediction of scatter from beryllium surfaces (based on a knowledge of surface and subsurface interactions with incident wavelengths) will be refined against empirical data. We discuss design of the experiment, the model, and some of the early results.