Unit 10. Basic Level. Vector Graphics and Bitmaps.


How do represent graphics?

 

Probably you have seen multiple graphics with many different extensions: JPG, GIF, FLA, SWF, FH7... The extensions indicate the file type or format in which the graphics are saved. 

    There exist many programs in the market that allow us to display, to create and to modify graphics, and each manufacturer decides to represent the graphics as it's more convenient to him, or simply gives a certain extension to the graphics created with his own program to restrict its use to programs of the same company.

    In spite of all, the multiple formats, in which it's possible to find saved graphics, can be classified in two basic types: vector graphics and bitmaps.

Difference between Vector Graphics and Bitmap

 

Bitmaps and Vector Graphics are mainly differentiated in the size. Vector Graphics has an advantage of great importance: it takes much less disk space or in memory; and, therefore, it needs much less time to download it from an application or Web page.

    The explanation of this fact can be seen in the format in which they are created and represented:

 

The bitmaps or maps of bits are composed by huge "data rectangles" (matrix) that contain information about each one of the points (pixels) which form the graphics, and that roughly corresponds to the perception of what we see on our screen. 

At a glance we don't discern pixels due to their small size, but if we extend a Bitmap largely we can see them like color squares (see the left image).

The information stored in these matrices is the characteristics of each pixel. The characteristics stored on pixels are their coordinates within the graphics and its color.

So, our PC processes this information, and generates the image on the monitor or another output device, indicating what color must be applied to each coordinate of the image.

At a first glance pixels or smaller units that compose an image aren't noticeable on a quality image, but they are distinguished when extending the image.

     Pixels not always have the same size and there is no reason to find the equal number of pixels in images of equal dimensions. The quality of an image depends on the number of pixels in which we divide an image (normally it's measured in DPI or dpi) and the greater number of colors it can have.

Evidently, the higher the quality of the image, the more disc space it will take. As a result, it will be much more difficult to handle the graphics of higher quality and number of pixels. 

Among the bitmap file formats the more common are: JPG, PCX, PNG, TIFF,  GIF, BMP, ...

 

    As we've seen, to generate a bitmap graphic, our PC must store and work with a great amount of information due to the need of maintainig the data of each pixel.

To represent a vector image it's assumed that the graphics are formed by a set of vectors or lines.

This is a great advantage, since a line, which would be composed by many pixels in the case of a bitmap format, in a vector image will o nly needed to store information on its starting and ending points, its direction and its length.

In this way it also reduces any figure to a basic set of vectors, which is more complex. For example, we could represent a circle simply keeping the information about its center and its radius, besides the outline color and the background color. The secret of greatly reduced size of this type graphics resides here.

 

How does Flash 8 work?

 

Although Flash 8 allows us to also work with bitmaps, it uses vector graphics to make its animations. This allows one to generate animations of very high quality and dimensions, reducing significantly its load time in attempt to display them on our Web navigatior. In addition, there is no need in complete downloading the Flash 8 files to display them. As soon as exists a minimum information, the file can be shown while its downloading continues.

 



   
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January-2006.