Gametamer

Never in History have Time and Space been bent so severely as with the advent of the microprocessor. In a matter of months, personal computers become twice as fast, twice as powerful. The World Wide Web has gone from its birth to maturity (and possibly overpopulation!) in less than 2 years. Nearly every medium of communication is now augmented?and sometimes replaced?by digital equivalents. Email has created the term ?Snail Mail?, desktop publishing has made movable type obsolete, and optical effects in television commercials are now accomplished with software. To track the impact that technology has had even in the past five years would merit a book, but that?s not the point of this post Let?s just concern ourselves with a niche within the expanding niche of the personal computer?how it is used, and sometimes misused, by today?s artist to communicate. Let?s presume that every person who sits before a personal computer is bound to map some hencetoforth unchartered territory?technically and creatively, because today?s designer is one who got into technology by bootstrapping them self. Only recently have colleges and trade schools begun to address the very real need for formal education in computer arts, and those teaching the courses are bootstrappers? they hold no specific degree in computer graphics and are themselves graphic pioneers. This forum comprises a generalized toolkit designed to remove some of the mystique from computer graphics, and to fill in some of the missing holes in the designer?s self-education. Even the best of pioneers take a leap over a rock or two to arrive at a new place, and graphics pioneers sometimes are thwarted in their adventures due to a missing piece of information in their education. For example, most of us are familiar with the term pixel?we?ve heard it used to describe part of an image, and many of us toss the term around as we would the terms ?dime? or ?muffler?. But what is a pixel good for, how do we accurately measure pixels, and how do we weave pixels to create a photorealistic image? Good questions? This thread will attempt to answer them in a way that integrates with your work and play at the personal computer.

Anti-Aliasing and Resampling Artwork
In order to understand anti-aliasing better, it?s useful to explain what the term aliasing means first in your work. ?Aliasing? is the false presentation of visual data, and is the result of an application rendering an image area without enough visual information. In figure 1, you can see a spaceship at top whose outline is aliased?there are supposed to be curved and smooth diagonal lines around its outline, but instead there are stairsteps. Anti-aliasing ?shown applied to the same spaceship at the bottom of figure 2.1?is a method for accurately representing image data, and this chapter takes you through both a working definition, and the methods by which anti-aliasing is added to your work.

Image Resolution and Granularity
To better demonstrate the effects of aliasing and anti-aliasing, let?s choose a visual example of a checkerboard that extends into the horizon. To remove user input and simply show how an application handles anti-aliasing, let us say that this checkerboard scene is being rendered in a modeling application?you define the scene, and the application does the rendering work. The squares that are closest to the viewer are white or black; there is no ambiguity about the color of the large squares. However, as the squares diminish in size towards the horizon, each square is perceived using a smaller amount of photo-receptors in the eye, until the horizon appears to be a solid tone instead of alternating colors. Your eye cannot distinguish clearly which squares are white and which are black because the granularity?the number of photoreceptors in your eye?is a fixed amount. When this checkerboard scene is rendered by a computer application to bitmap format, the application performing the rendering has two choices to make: to alias the horizon?to choose either white or black at any given pixel, or to anti-alias, to average the color for a given pixel, to create an image area closer to the way a human eye would see the actual scene. In figure 2, you can see a checkerboard extending into the horizon. Let?s imagine that the square next to the call-out is a single pixel, a pixel whose size cannot change and can contain only one color. The visual content at this point in the picture, however, consists of more than one color?there can be a number of white and black squares close to the horizon?with only a single image pixel to represent them. So, what?s it going to be: a black or a white pixel? To make such a decision is called aliasing; if you fill this pixel with white, you?re negating the black squares within this sample area. To reconcile the impossibility of filling a single pixel with more than one color, anti-aliasing of the scene fills the pixel with a shade of black, because in reality the pixel sample area should contain a blend of both black and white sample information. Anti-aliasing can be added to artwork by most graphics applications on three occasions: When you make a brush stroke. When a brush stroke is made for you, as with a modeling/rendering application. When pixels are added or deleted from an image. This is called resampling. Anti-aliasing does more than simply reconcile pixel colors when the image information is too large to fit in a single pixel. Let?s take a look now at how curves and diagonal lines?geometry that cannot realistically be displayed on a monitor?can be made smooth in appearance by anti-aliasing.

Note: Super-sampling is a term used in modeling applications to describe yet another type of anti-aliasing. The mechanism for super-sampling works like this: the user defines a specific size for the scene to be rendered. The application images the scene 2 times the requested size, holds the image in memory, and then creates the image at the requested size while averaging tones for the image?s pixels from the larger image in memory. This super- sampling process can use more than one image in memory; you could request that an 8x image, a 4x and a 2x image should be used to average and calculate final pixel colors.

...to be continued.
--Gare