Student Resource: In this lesson you are going to learn about the difference between bitmap and vector graphics. Bitmap graphics are everywhere there is a computer screen, from your smart phone to the gigantic images that appear in Times Square New York. Vector graphics are increasingly used to create print materials because as you increase size, the quality of the picture doesn’t change. You will also see that a graphics buffer knows how to construct an image by using a coordinate system. You are also going to learn about how scheduling a task can accomplish a lot of work in a small amount of time.
Until very recently, almost all of the images you saw on a computer were made by loading an image made up of pixels, or points of light, into computer memory. This is called raster graphics, and was based on the way old television technology worked. When you take a picture with a phone or digital camera you are producing an image made up of millions of pixels. The pixels are stored in memory starting with the one in the upper left corner, then the one to the right of that one, until the right edge is reached. Then the next row of pixels is loaded.
Even with modern computers, loading pixels takes time. Computer scientists study how to make things faster and take up less space, and often use math to help them. Vector graphics was invented to produce a picture in less time. Rather than keep track of all the points in a line or curve, vector graphics uses vectors. A vector is just a point in space. To keep it simple, we will stay in 2D(two dimensions). We need two numbers to keep track of a point: we need the horizontal position and the vertical position. (How many numbers do you think we need for 3D?).
To determine where a point is, we need a coordinate system. In math class you may have learned about Cartesian coordinates. Computer graphics is based on a different coordinate system, where the upper left corner is the origin, or starting position. You count positions across to the right just like in the Cartesian system, but to find a position in the vertical, you count down from the top, rather than up from the bottom.
Vector graphics are stored as a collection of instructions to draw lines and curves, with specific colors, based on the fewest number of points. Lines require two points - a start and an end. A rectangles and ellipse (egg shaped thing) also requires only two points. Other kinds of curves are a bit more complicated, but still need much less computer memory than bitmaps.
In this activity, you are going to create a bitmap mural where the points are large rectangles of color. Very old video games called ‘low res’ used this kind of bitmap images. You are also going to create a vector mural using lines.
This activity will require you to schedule who in your group will do what, and when. Modern computers do a lot of scheduling to create images, videos, and animation.
Although the type of scheduling computers do is very different from the actual schedule you will learn to do, you will get an idea of how complicated computer graphics is.
Graphics: Bits and Points Student Worksheet 1: A Bitmap Drawing Using this grid, create a drawing to contribute to your class mural.
Using a pencil, draw along the edges of the blocks that will be part of your contribution. Erase or start over if you need to.
When you have a drawing you like, use at most three colors to fill in the bricks.
Follow the directions your teacher gives you to cut out a bounding box.
As a group, lay out your bounding boxes to create a draft of the mural.
Fill out a Post-It with your name, your position on the mural, and your group.
Graphics: Bits and Points
Student Worksheet 2: A Vector Drawing Now that you are familiar with the coordinates of bitmap, let’s see how a vector drawing happens. A vector drawing is made up entirely of lines and curves that can be colored in (filled) when a region is closed. A square can be filled. A rectangle with one side missing cannot. Although vector drawings contain lines, curves and points, in this activity you will use painters’ tape to draw lines.
Whenever there is a closed region, it can be filled with color.
Your teacher will show you the boundaries of the drawing.
In groups assigned by your teacher, spend five minutes putting lines on the vector mural:
Distribute about a yard (meter) of tape to everyone in the group.
Start a timer and spend 5 minutes using your tape to draw lines within the drawing boundaries.
If you use up your tape, get more.
When the timer stops, distribute chalk to everyone in the group and spend at most 10 minutes coloring any closed regions. You may find all kinds of interesting polygons.
Think a bit about what you want to add to the mural with your tape.
Cooperate within your group and help each other create something interesting.
Cooperate with other groups by not covering what they’ve done, and leave room for the next group.
Consider leaving some open regions for the next group.
Consider creating closed regions from regions left by the previous group.