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Prefiltering Antialiasing for General Vector Graphics

IP.com Disclosure Number: IPCOM000232657D
Original Publication Date: 2013-Nov-24
Included in the Prior Art Database: 2013-Nov-24
Document File: 6 page(s) / 1M

Publishing Venue

Linux Defenders

Related People

Juan M. Vuletich: AUTHOR

Abstract

The graphics engines commonly used to draw vector graphics apply the antialiasing technique known as pixel coverage. The quality of the results could be greatly improved through the application of sampling theory. This work presents a simple and practical technique for the rasterization of general vector graphics with correct prefiltering antialiasing: An appropriate antialiasing filter is applied to a continuous model of a shape, and the result is sampled at each pixel position, producing the rasterized output. The use of this technique can significantly enhance the visual quality of most computer applications.

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Prefiltering Antialiasing for General Vector Graphics

September 2013 Juan M. Vuletich juan@jvuletich.org www.jvuletich.org

Abstract

    The graphics engines commonly used to draw vector graphics apply the antialiasing technique known as pixel coverage. The quality of the results could be greatly improved through the application of sampling theory. This work presents a simple and practical technique for the rasterization of general vector graphics with correct prefiltering antialiasing: An appropriate antialiasing filter is applied to a continuous model of a shape, and the result is sampled at each pixel position, producing the rasterized output. The use of this technique can significantly enhance the visual quality of most computer applications.

Keywords

Vector Graphics, Antialiasing, Prefiltering, Sampling, Signal Processing, Nyquist-Shannon

Introduction

   Vector graphics form the basis of much of what a computer can display. They are used for almost all text, portable documents, many GUI elements, drawings, etc. Their importance will only grow, as users and developers become aware of the need to adapt applications and content to computer displays of varying size and resolution.

   Vector graphics are specified essentially as the path a pen is to follow over a piece of paper, to produce a drawing. The pen, the paper and the path are thought of as continuous. But computer displays are discrete, comprised of distinct elements or pixels. Because of this, in order to be shown on a computer, vector graphics need to be converted to pixel color values, a process called rasterization.

   Prefiltering antialiasing also called Signal processing approach to antialiasing ([1], [2]) is the mathematically correct way to compute the rasterization of 2D vector graphics. It is an application of the Nyquist-Shannon sampling theorem, and therefore it requires a prefiltering stage to satisfy the hypothesis that the original signal is bandlimited.

   Common 2D graphics engines, used by graphics libraries, operating systems, and video cards, almost universally employ the inferior pixel coverage antialiasing technique. Pixel coverage can be seen as an incorrect implementation of prefiltering, being limited to a step filter, with a fixed size of one pixel. A step filter is a poor choice, as it attenuates useful frequencies (producing a blurry result) while at the same time it allows too high frequencies

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(producing visible aliasing, in the form of "jaggies" or "staircase effects", and Moiré effects). In addition, the computation of pixel coverage is rather expensive. A few engines offer the possibility of the expensive super sampling to enhance quality somewhat, at an even higher computational cost. The main reason for this state of affairs might be that previously published algorithms for correct prefiltering only work on straight line segments.

   Disclosed is a simple and practical technique for the rasterization of general vector graphics (including s...