Session4 Images and Graphics

Raster and Vector
Computers have two different ways to represent graphic information such as photographs, diagrams, illustrations, maps and charts.
The first one is raster which is grid based information. Information is stored in a sequence of square pixels. The other one is vector data which store and manipulate information defined with a series of point and boundaries. In both ways, geometric information is stored and manipulated numerically. One of the most important differences between raster information and vector information is that vector images never become blocky when they are zoomed and raster images may appear blocky as they are zoomed.

Raster geometry is represented by binary data which consist of two parts. The first part represent width and height of the raster image and the flowing part defines presence or absence of colors for each cells ( In the simple two color raster ). For example, 001001100010001 represent a figure below.


The first part of 001 001, means 3(width) by 3(height) and flowing 9 binary digits 100010001 demonstrate shape on the 3-by-3 raster geometry.
In order to manipulate more colorful data, there are two systems to represent colors. The RGB color system uses three basic colors which are red, green, blue. This is called additive model and used in TV and computer monitor. Cyan, magenta and yellow are used in the CMYK color system( K means black ). This is called subtractive model and used by print media.

Color data represented by using binary
Computers interpret color information by using binary data based on RGB color system. Different colors are represented by six figures. The first two figures represent the amount of red, the second pair of figures represent the amount of green and the last two figures represent the amount of blue. For instance, red is represented #FF0000. Orange which consist of a lot of red, some green and a few blue is represented #FF6633.