Font Rasterization, the State of Art

Modern personal computers and workstations enable text, graphics and images to be visualized in a resolution independent manner. Office documents can be visualized and printed in the same way on displays, page-printers and photocomposers. Personal computers like the PC and the MacIntosh incorporate advanced rasterization algorithms for the rendering of outline characters and graphics. In the nineties, advanced workstations will provide facilities for the generation of finely tuned gray-scale characters. This tutorial provides a survey of the basic algorithms for representing and rendering outline characters. Fast scan-conversion and filling algorithms as well as basic and advanced character outline grid-fitting techniques are presented. The philosophy and functionality of Adobe's Type 1 and Apple's TrueType typographic rendering systems are discussed

Parallel storage and retrieval of pixmap images

To fulfill the requirement of rapid access to huge amounts of uncompressed pixmap image data, a parallel image server architecture is proposed, based on arrays of intelligent disk nodes, with each disk node composed of one processor and one disk. It is shown how images can be partitioned into extents and efficiently distributed among available intelligent disk nodes. The image server's performance is analyzed according to various parameters such as the number of cooperating disk nodes, the sizes of image file extents, the available communication throughput, and the processing power of disk node and image server processors. Important image access speed improvements are obtained by image extent caching and image part extraction in disk nodes. With T800 transputer-based technology, a system composed of eight disk nodes offers access to three full-color 512×512 pixmap image parts per second (2.4 megabytes per second). For the same configuration but with the recently announced T9000 transputer, image access throughput is eight images per second (6.8 megabytes per second

Vertical Scan-Conversion for Filling Purposes

Conventional scan-conversion algorithms were developed independently of filling algorithms. They cause many problems, when used for filling purposes. However, today's raster printers and plotters require extended use of filling, especially for the generation of typographic characters and graphic line art. A new scan-conversion algorithm, called vertical scan-conversion has been specifically designed to meet the requirements of parity scan line fill algorithms. Vertical scan-conversion ensures the selection of exactly one pixel per intersecting scan live between a local minimum and a local maximum of the shape outline. Pairs of selected pixels define horizontal spans. All horizontal spans contain the full set of pixels interior to the original shape. Vertical scan-conversion greatly simplifies traditional edge-tracking filling algorithms, such as ordered edge fill, flag fill and descriptive contour fill, removing the need for testinf and processing special cases

Parallel file striping on optical jukebox servers

In the near future, large digital media servers are expected to offer storage capacities in the order of petabytes. Servers made of clusters of PCs connected to jukeboxes may represent an interesting alternative compared with servers made of arrays of magnetic disks. However, due to disk exchange overhead, higher seek times and lower data transfer rates, access to data located on optical disks is significantly slower than access to data located on magnetic disks. In the present contribution, we analyze the benefits and limitations of striping files across multiple optical disks in order to speedup the retrieval of large pieces of information. We also show that server applications requiring both computer power and I/O bandwidth may be distributed over several processing nodes and access files striped over multiple optical disks. For such applications, as long as disk exchanges are not necessary, a predictable speedup can be obtained by ensuring a high enough number of server computers, optical disk drive units, and enough communication bandwidt

Analysing character shapes by string matching techniques

Preliminary attempts at automatic analysis and synthesis of typographic shapes are described. String matching techniques are used to recover implicit relationships between character parts. A knowledge base describing local character shape parts is created and is used in order to propagate local shape modifications across different character

Analysis of the superposition of periodic layers and their Moire effects through the algebraic structure of their Fourier spectrum

A new approach is presented for investigating the superposition of any number of periodic structures, and the Moire effects which may result. This approach, which is based on an algebraic analysis of the Fourier-spectrum using concepts from the theory of geometry of numbers, fully explains the properties of the superposition of periodic layers and of their Moire effects. It provides the fundamental notations and tools for investigating, both in the spectral domain and in the image domain, properties of the superposition as a whole (such as periodicity or almost-periodicity), and properties of each of the individual Moire generated in the superposition (such as their profile forms and intensity levels, their singular states, etc.). This new, rather unexpected combination of Fourier theory and geometry of numbers proves very useful, and it offers a profound insight into the structure of the spectrum of the layer superposition and the corresponding properties back in the image domai

Band Moire images

We propose a new powerful way of synthesizing moire images that enables the creation of dynamically moving messages incorporating text, symbols, and color elements. Moire images appear when superposing a base layer made of replicated base bands and a revealing layer made of a line grating comprising thin transparent lines. Each replicated base band contains the same image, e.g. text or color motifs. Since the base bands and the revealing line grating have similar periods, the revealed moire image is the image located within each base band, enlarged along one dimension. By considering the formation of the moire image as a line sampling process, we derive the linear transformation between the base layer and the moire image. We obtain the geometric layout of the resulting moire image, i.e. its orientation, size and displacement direction when moving the revealing layer on top of the base layer. Interesting moire images can be synthesized by applying geometric transformations to both the base and the revealing layers. We propose a mathematical model describing the geometric transformation that a moire image undergoes, when its base layer and its revealing layer are subject to different freely chosen non-linear geometric transformations. By knowing in advance the layout of a moire image as a function of the layouts of the base layer and of the revealing layer, we are able to create moire components running up and down at different speeds and orientations upon translation of the revealing layer. We also derive layer transformations which yield periodic moire images despite the fact that both the base and the revealing layers are curved. By offering a new means of artistic expression, band moire images can be used to create new designs and to synthesize visually appealing applications. © 2004 ACM

Modeling ink spreading for color prediction

This study aims at modeling ink spreading in order to improve the prediction of the reflection spectra of three ink color prints. Ink spreading is a kind of dot gain which causes significant color deviations in ink jet printing. We have developed an ink spreading model which requires the consideration of only a limited number of cases. Using a combinatorial approach based on Pbya's counting theory, we determine a small set of ink drop configurations which allows us to deduce the ink spreading in all other cases. This improves the estimation of the area covered by each ink combination that is crucial in color prediction models. In a previous study, we developed a unified color prediction model. This model, augmented by the ink spreading model, predicts accurately the reflection spectra of halftoned samples printed on various inkjet printers. For each printer, the reflection spectra of 125 samples uniformly distributed in the CMY color cube were computed. The average prediction error between measured and predicted spectra is about ΔE = 2.5 in CIELAB. Such a model simplifies the calibration of ink jet printers, as well as their recalibrations when ink or paper is change

Automatic synthesis of contrast controlled grayscale characters with component-based parametrisable fonts

A few years ago, a perceptually-tuned grayscale character generation technique was developed in order to automatically synthesize grayscale characters looking like manually-tuned pixmap characters. Weight and contrast controlled grayscale characters are obtained by grid-fitting the scaled character contours. However, this technique requires that hinting information be added to the outline font description. Adding hinting information to each outline character generally requires a considerable amount of human intervention. Our component-based parametrisable font system is a newly developed font description and reproduction technology. It incorporates for each basic character shape a software method responsible for the synthesis of an instance of that character. A given font is synthesized by providing appropriate font parameters to these character synthesis methods. Numerous concrete fonts can be derived by simply varying the parameters. Such variations offer high flexibility for synthesizing derived fonts (variations in condensation, weight and contrast) and enable saving a considerable amount of storage space. This paper shows that with component-based parametrisable fonts, high quality perceptually-tuned grayscale characters can be generated without requiring hinting information. Generating perceptually-tuned grayscale characters with parametrized component-based fonts consists in automatically adapting the phase of some of the character's parameters in respect to the underlying grid and in ensuring that thin character parts are strong enough not to disappear (weight-control

Parallel unfolding and visualization of curved surfaces extracted from large three-dimensional volumes

Although many three-dimensional (3D) medical imaging visualization methods exist, 3D volume slicing remains the most commonly used technique for visualizing medical data from modalities such as CT, MRI, and PET. We propose to extend the possibilities of oblique slicing to developable curved surfaces that can be flattened and displayed in two dimensions without deformation. Such surfaces can be used to follow curved anatomical structures while preserving distance metrics at visualization time. They may also be useful for the staging of tumors, i.e., to evaluate the spatial extension of a tumor. We propose an out of core algorithm that runs in parallel on a multi-PC architecture and is able to extract surfaces from very large 3D datasets such as the visible human data set (man: 13 GB, woman: 49 GB). Experimental performance results are presented which demonstrate that parallel surface extraction is scalable and has a reasonable overhead compared with traditional oblique planar slicing. Surface extraction is made available to the public as one of the services offered by EPFLs visible human web server (http://visiblehuman.epfl.ch