Computer Science

Introductory Activity

Observe the picture below and answer the following questions:

1. Describe what you see.

2. Describe how the pictures inside are arranged.Are these pictures

created using the same material?

3. How can you measure the size of each picture?

4. Is it easy to modify these pictures? Explain.

5. Explain the areas where pictures are used.

6. Why is it important to have good pictures in business advertisement?

7. Nowadays, youth like posting their nakedness pictures on social media.

Discuss the inconvenience.

12.1 Definition of Computer graphics terms

Activity 12.1

By using different mobile phones, take pictures of the same group of students in

your classroom. After saving those pictures in one folder and observing carefully,

give the difference between them. Explain what could be the cause of that

difference.

12.1.1 Introduction

The human perception of the world is done through the five senses among which

the view is very important. Our brain recognizes the faces of people and the shapes

of things because they retain their pictures.

Currently, the use of computers has helped to digitalise the images and the work

of drawing became easier than before. Consequently, a new area of application

of computer science called computer graphics was born and hence pictures and

images are used in different areas of the human life for its development. Computer

Graphics involves the ways in which images can be displayed, manipulated and

stored using a computer. Computer graphics provides the software and hardware

techniques or methods for generating images.

 12.1.2.Definition of different terms

Computer graphics can be defined in two ways depending on the circumstances:

Computer Graphics is an art of drawing pictures, lines, charts, etc, using computers

with the help of programming. Computer graphics are made up of number of pixels.

A pixel is the smallest graphical picture or unit represented on the computer screen.

or

Computer graphics are pictures and films created by using computers. Usually, the

term refers to computer-generated image data created with help from specialized

graphical hardware and software.

 Computer graphics can be classified into two categories: Raster or Bitmap graphics

and Vector or Object-oriented graphics.

1. Raster (Bitmap) Graphics

These are pixel based graphics and the pixels can be modified individually.

• The images are easy to edit in memory and display on TV monitors owing to

the arrangement of the pixels in a rectangular array.

• The image size is determined on the basis of image resolution.

• These images cannot be scaled easily; resizing do not work very well and

can significantly distort the image.

• Bitmap graphics are used for general purpose images and in particular

photographs.

2. Vector (Object-oriented) Graphics

These graphics are mathematically based images.

• Vector based images have smooth edges and therefore used to store images

composed of lines, circles and polygons.

• These images can easily be re-scaled and rotated.

• They can not easily accommodate complex images such as photographs

where colour information varies from pixel to pixel.

• Vector graphics are well suited for graphs, e.g. in spreadsheets and for

scalable fonts, e.g. postscript fonts

3. A model of an object is a physical representation that shows what it

looks like or how it works. The model is often smaller than the object it

represents

4. The computer resolution is the number of pixels (individual points of

color) contained on a display monitor, expressed in terms of the number

of pixels on the horizontal axis and the number on the vertical axis.

5. A pixel is the smallest element of a picture that can be represented on

the screen of a device like a computer. Pixels per inch (PPI) or pixels per

centimeter (PPCM) are measurements of the pixel density (resolution)

of an electronic image device, such as a computer monitor or television

display, or image digitizing device such as a camera or image scanner.

6. 2D (2Dimensional) images are objects that are rendered visually on

paper, film or on screen in two planes representing width and height (X

and Y). Two-dimensional structures are also used in the construction of 3D

objects. 

7. 3D computer graphics or three-dimensional computer graphics,

(in contrast to 2D computer graphics) are graphics that use a threedimensional representation of geometric data (often Cartesian) that is

stored in the computer for the purposes of performing calculations and

rendering 2D image.

8. A color scheme is the choice of colors used in design for a range of media.

For example, the use of a white background with black text is an example

of a basic and commonly default color scheme in writing.

9. 8-bit color graphics is a method of storing image information in a

computer’s memory or in an image file, such that each pixel is represented

by one (8-bit) byte. The maximum number of colors that can be displayed

at any one time is 28=256.

10. 16-bit color graphics also called High color is a method of storing

image information in a computer’s memory or in an image file where

computerand monitors can display as many as 216=65,536 colors,

which is adequate for most uses. Each pixel is represented by two

bytes i.e 16 bits, but some devices also support 15-bit high color.

However, graphic intensive video games and higher resolution video can

benefit from and take advantage of the higher color depths.

11. 32-bit color graphics is a method of storing image information in a

computer’s memory or in an image file where computer and monitors can

display as many as 232=4,294,967,296 colors, which is adequate for most

uses. Each pixel is represented by four (4) bytes i.e 32 bits.

a. Image compression

Image compression is minimizing the size in bytes of a graphic file without degrading

the quality of the image to an unacceptable level. The reduction in file size allows

more images to be stored in a given amount of disk or memory space. It also reduces

the time required for images to be sent over the Internet or downloaded from web

pages. Know an image’s file size and dimensions before or after uploading it into the

Library

b. Determination of an image’s file size and dimensions

The determination of an image’s file size and dimensions differs according to the

Operating System being used.

On MS Windows computers, Open the image in Windows Explorer to check

dimensions and file size by clicking the Windows Start button on the taskbar. After

opening the folder containing the image, right clicking the icon of the image file,

and in the pop up menu, click on property and details. The result will look like below.

The wanted information are circled with red line

c. Calculating size of an uncompressed image file 

byte is a unit of storage in computing, and unfortunately, a byte isn’t big enough

to hold a pixel’s worth of information. It actually takes 2 to 3 bytes to store one pixel

of a color image.

So the pixels in the image store a color at a given point in the image, but it takes 2

to 3 bytes of storage to record this value. If we consider 3 bytes of storage, the file

size of a color image is: width * height * 3 = 36,636,672 which gives us the file size

in bytes.

But this is a big number, so we want to convert it to megabytes. There are 1,024

bytes in a kilobyte. There are 1,024 kilobytes in a megabyte. So the file size of a color

image in megabytes is: width * height * 3 / (1024 * 1024) = 34.9MB

d. Graphics file format/image file format:

Image file formats are standardized means of organizing and storing digital images.

Image files are composed of digital data in one of the formats that can be rasterized

for use on a computer display or printer. An image file format may store data in

uncompressed, compressed, or vector formats. Once rasterized, an image becomes

a grid of pixels, each of which has a number of bits to designate its color equal to the

color depth of the device displaying it.

There are 5 main formats in which to store images including TIFF, JPEG, GIF, PNG and

Raw image files. Their differences are given in the table below:

Application Activity 12.1.

1. Define an image.

2. Define vector graphics and raster graphics.

3. Define a pixel.

4. What is computer resolution?

5. How an image size is calculated?

6. Briefly describe two basic types of Graphics file formats.

7. List two categories of images in computer graphics.

8. In which graphic system are images easily scalable?

9. By using image taken with your camera or retrieved in your computer,

determine its size. 

12.2 Images capturing tools

Activity 12.2

1. Describe what you see

2. What are the roles of the above devices?

3. Which device is most useful in our days in photo capturing? Why?

4. Describe the functioning of each device and describe the parts of each 

12.2.1 Digital camera

a. Definition

A digital camera is a camera which produces digital images that can be stored in

a computer and displayed on screen.It records and stores photographic images in

digital format.

These stored images can be uploaded to a computer immediately or stored in the

camera to be uploaded into a computer or printer later.

Digital cameras use an image sensor instead of photographic film.

2. Digital camera parts

There are 10 basic camera parts to identify in today’s digital world. These parts will

inevitably be found on most cameras being digital compact or single-lens reflex

camera (SLR)

• Lens

The lens is one of the most vital parts of a camera. The light enters through the lens,

and this is where the photo process begins. Lenses can be either fixed permanently

to the body or interchangeable. They can also vary in focal length, aperture, and

other details.

• Viewfinder

The viewfinder can be found on all digital single-lens reflex cameras (DSLR) and some

models of digital compacts. On DSLRs, it will be the main visual source for imagetaking, but many of today’s digital compacts have replaced the typical viewfinder

with Liquid Crystal Display (LCD) screen.

• Body

The body is the main portion of the camera, and bodies can be a number of different

shapes and sizes. DSLRs tend to be larger bodied and a bit heavier, while there are

other consumer cameras that are a conveniently smaller size and even able to fit into

a pocket.

• Shutter Release

The shutter release button is the mechanism that “releases” the shutter and therefore

enables the ability to capture the image. The length of time the shutter is left open 

or “exposed” is determined by the shutter speed.

• Aperture

The aperture affects the image’s exposure by changing the diameter of the lens

opening, which controls the amount of light reaching the image sensor. Some digital

compacts will have a fixed aperture lens, but most of today’s compact cameras have

at least a small aperture range.

• Image Sensor

The image sensor converts the optical image to an electronic signal, which is then

sent to the memory card. There are two main types of image sensors that are used

in most digital cameras: complementary metal-oxide-semi conductor (CMOS) and

charge-coupled device (CCD) Both forms of the sensor accomplish the same task,

but each has a different method of performance.

• Memory Card

The memory card stores all of the image information, and they range in size and

speed capacity.

• LCD Screen

The LCD screen is found on the back of the body and can vary in size. On digital

compact cameras, the LCD has typically begun to replace the viewfinder completely.

On DSLRs, the LCD is mainly for viewing photos after shooting, but some cameras do

have a “live mode” as well.

• Flash

The on-board flash will be available on all cameras except some professional grade

DSLRs. It can sometimes be useful to provide a bit of extra light during dim, low light

situations.

• User Controls

The controls on each camera will vary depending on the model and type. The

basic digital compacts may only have auto settings that can be used for different

environments, while a DSLR will have numerous controls for auto and manual

shooting along with custom settings.

Those parts can be seen on the following picture.

c. Importing pictures using USB cable

The images taken by using a camera are stored automatically in its memory. However,

for different purposes, the images can be printed or inserted in documents for

illustrations. The camera is then connected to the printer or the computer by using

a USB cable appropriately designed for such action. The fact of taking pictures from

the camera to the computer is called importing pictures.

The following steps are followed to successfully import a picture from camera to

computer by using a USB cable.

Step1

Connect one end of the USB cable to the port in your camera.

Step2

Connect the other end of the USB cable to the USB port in the computer. This may

be in the front or back of the computer.

Step3

Turn on the camera

Step4

A dialog box may appear on the screen. If it does, select “View Files” or “Open Folder.”

If the dialog does not appear, click the Windows “Start” menu, select “Computer” and

then choose the drive labeled for the connected camera.

Step5

The pictures are probably located in a particular photo folder on the camera. Open

that folder. Drag individual photos from the folder to the desktop or some other

folder on the computer. All the photos can be selected by pressing “Ctrl-A” and then

pasted into a folder on the computer by pressing “Ctrl-V.”

12.2.2 Scanner

a. Definition

A scanner is an electronic device which can capture images from physical items

(printed text, handwriting, photographic prints, posters, magazine pages, and

similar sources) and convert them into digital formats, which in turn can be stored in

a computer, and viewed or modified using software applications.

Very high resolution scanners are used for scanning for high-resolution printing, but

lower resolution scanners are adequate for capturing images for computer display.

b. The different parts of scanner

A scanner has the following five (5) parts visible externally:

(1)Start button, (2) Copy button, (3) Scan to E-mail button, (4) Scan to Web button,

(5) Scanner cover

Application Activity 12.2.

1. Compare digital camera to scanner? List the importance of digital

camera in computer graphic.

2. With your camera, take a picture of the school computers, import it in

your computer and insert it in one of your text documents created in

MS Word.

3. At your school, what are the advantages and disadvantages of keeping

scanned documents?

4. By using your scanner in computer laboratory, scan your student card

and insert it in one text document created in MS Word.

5. Give the names of the 3 scanner parts indicated in the following image.

Area of graphics use

Computer graphics can be applied in various areas. Examples are such as follows:

12.3 Computer-Aided Design

Activity 12.3

After visiting the school library take different books and magazines and answer

the following questions:

1. Describe how the books and magazines covers look.

2. What is importance of having attractive picture on first page of any

magazine?

3. Which ways can be used to advertise your school?

4. List other fields where the photo are important to use

In engineering and architectural systems, the products are modeled using computer

graphics commonly referred as CAD (Computer Aided Design). In many design

applications like automobiles, aircraft, spacecraft, etc., objects are modeled in a

wireframe outline that helps the designer to observe the overall shape and internal

features of the objects.

12.3.2 Computer Art:

A variety of computer methods are available for artists for designing and specifying

motions of an object. The object can be painted electronically on a graphic tablet

using stylus with different brush strokes, brush widths and colors. The artists can also

use combination of 3D modeling packages, texture mapping, drawing programs

and CAD software to paint and visualize any object.

12.3.3 Entertainment:

Computer graphics methods are widely used in making motion pictures, music

videos and television shows. Graphics objects can be combined with live actions or

can be used with image processing techniques to transform one object to another.

12.3.4 Education and training:

Computer graphics can make better the understanding of the functioning of a

system. In physical systems, biological systems, population trends, etc., models make

it easier to understand. In some training systems, graphical models with simulations

help a trainee to train in virtual reality environment. For example, practice session or

training of ship captains, aircraft pilots, air traffic control personnel.

12.3.5 Image processing:

Image processing provides techniques to modify or interpret existing images. One

can improve picture quality through image processing techniques. For instance,

in medical applications, image processing techniques can be applied for image

enhancements and is been widely used for CT (Computer X-ray Tomography) and

PET (Position Emission Tomography) images.

12.3.6 Graphical User Interface:

GUI is commonly used to make a software package more interactive. There are

multiple window systems, icons, menus, which allow a computer setup to be utilized

more efficiently.

a. Logo (abbreviation of logotype, from Greek: is a graphic mark, emblem,

or symbol used to aid and promote public recognition. It may be of an

abstract or figurative design or include the text of the name it represents

as in a logotype or wordmark.

b. Advertising is communicated through various mass

media, including traditional media such as newspapers,

magazines, television, radio, outdoor advertising or direct mail; and new

media such as search results, blogs, social media, websites or text

messages. The actual presentation of the message in a medium is referred

to as an advertisement

c. An illustration is a decoration, interpretation or visual explanation of a

text, concept or process, designed for integration in published media,

such as posters, flyers, magazines, books, teaching materials, animations,

video games and films.

d. A magazine is a publication, usually a periodical publication, which is

printed or electronically published (sometimes referred to as an online

magazine). Magazines are generally published on a regular schedule and

contain a variety of content.

Conclusion

Computer Graphics involves ways in which images can be displayed, manipulated

and stored using computers. Computer graphics images can be categorised into

raster graphics, which as pixel-based graphics, and vector graphics, which are

mathematically represented. Computer graphics is applicable in various areas such

as computer-aided design, computer art, entertainment, as well as in education and

training. 

Application Activity 12.3.

5. Why is it important to use graphics in advertisement?

6. In Rwanda, how computer graphics is used in entertainment?

7. How your school logo is designed? Explain how can you modify it using

computer graphic

8. Differentiate computer art to computer aid design

9. Discuss how computer graphics is used in entertainment in our country

12.4 Graphics software, features and editing tools

Activity 12.4

1. Describe what you see on the pictures below

2. How is it the appearance of those pictures?

3. In which way a picture can be modified?

4. Which tools can you use to modify or to create a picture?

12.4.1 Graphic softwares

Computer graphics is mostly mastered by practicing; such as by writing and testing

programs that produce a variety of pictures. An environment that allows one to

write and execute programs is required. The environment should generally include

hardware for display of pictures, and software tools that written programs can use

to perform the actual drawing of pictures. This part presents the commonly used

software for producing graphics.

a. Microsoft Paint

Microsoft Paint or ‘MS Paint’ is a basic graphics/painting utility that is included in

all the Microsoft Windows versions. MS Paint can be used to draw, colour and edit

pictures, including imported pictures from a digital camera for example. MS Paint is

found in the windows start menu within the Accessories Folder.

The primary features of MS Paint are simple drawing tools that you can use to easily

draw on a blank canvas or existing image. Beyond that, Paint includes cropping,

resizing, rotating, skewing, and selection tools to further.

b. Microsoft Office Picture Manager

Microsoft Office Picture Manager (code named Microsoft Picture Library) is a raster

graphics editor introduced in Microsoft Office 2003 and included up to Office 2010.

The Basic image editing features include colour correct, crop, resize, and rotate.

With Microsoft Office Picture Manager, you can manage, edit, share, and view your

pictures from where you store them on your computer. There are picture editing

tools to crop, expand, or copy and paste.

Microsoft Office Picture Manager allows easily managing and editing. Picture

Manager is used to adjust the brightness and contrast of an image.

c. Adobe Photoshop

Adobe Photoshop is a raster graphics editor developed and published by Adobe

Systems for MacOS and Windows.

Adobe Photoshop is the predominant photo editing and manipulation software on

the market. Its uses range from full featured editing of large batches of photos to

creating intricate digital paintings and drawings that mimic those done by hand. 

12.4.2 Graphic features

12.4.2.1 Definition

Graphic features are pictures and other images that accompany a piece of text to

improve its meaning for the reader. Some examples of graphic features include

photographs, drawing, maps, charts and diagrams. While graphic features may

sometimes be purely decorative, they are more often used to make the meaning of

a text clearer.

12.4.3 Graphic editing tools

a. Tools in MS-Paint

Starting the Microsoft Paint program in Windows

1. Choose Start->All Programs->Accessories->Paint.

c. Tools in Ms Office picture manager

Step1.

Starting the Microsoft office picture manager

Microsoft Office comes with its own Picture Manager. You can open the Picture

Manager by clicking Start, choosing All Programs (or Programs), choosing the

Microsoft Office folder, choosing Microsoft Office Tools, and clicking Microsoft

Picture Manager. 

Step2.

Using Picture Manager editing tools for adjustment:

• Brightness and contrast: Select the brightness and contrast menu entry.

The task pane will display a range of control sliders; you can use these to

adjust any exposure issues (too bright, too dark etc).

• Color: Select the Color option from the Edit Pictures menu. Use the sliders

to adjust the Hue and Saturation.

• Crop: Select the Crop option. You will notice the crop is previewed on the

image; you can click and drag the crop area to reposition it. Grab the little

black crop marks in the corners or on the edges to scale the image.

 Red-eye removal: Select Red eye removal from the Edit Pictures menu.

Click the mouse curser several times over all the red eye areas you want to

remove, and then click OK.

 Resize your picture: On the Edit Pictures menu select Re-size to display the

resize.

Choose the Predefined setting of Document – Small (800 x 600), this is perfect for

working in Word without slowing it down. This will also reduce the size of the file,

perfect if you intend on emailing the document as an attachment.

After editing a picture, you can either File > Save to save the photo in its modified

format, or File > Save As… to give it a new filename (allowing you to keep the original

source file intact).

1. Photoshop editing tools

To change the image size, go through these steps:

Start->photoshop->File->open (choose an image where it is stored)->image

(in menu bar)

->image size->fill the new width and height in pixel dimension->ok

For this exercice, consider the image below which is with its original dimensions:

In Photoshop, Adobe introduced the Color Picker to make the selection of a color

even easier. (To access the Color Picker with a painting tool selected, click anywhere

in the image area and drag to select a color.

Magic wand

The Magic Wand Tool, known simply as the Magic Wand, is one of the oldest selection

tools in Photoshop. Unlike other selection tools that select pixels in an image based

on shapes or by detecting object edges, the Magic Wand selects pixels based color

Eraser

An eraser is an article of stationery that is used for removing writing from paper or

skin. Erasers have a rubbery consistency and come in a variety of shapes, sizes and

colours.

Gradient tool

A gradient is a set of colors arranged in a linear order, sometimes known as the

“gradienttool” or “gradient fill tool”: it works by filling the selection with colors

from a gradient. 

Paint bucket

The paint bucket tool generally comes along with image editing software. What

it does is fill an area on the image with a selected color. The tool usually fills to the

boundaries of a solid color. As an example if you have a black box and apply red with

the paint bucket tool it will convert the entire box to red.

Smudge

The smudge tool is used to smear paint on your canvas. The effect is much like

finger painting. You can use the smudge tool by clicking on the smudge icon and

clicking on the canvas and while holding the mouse button down, dragging in the

direction you want to smudge.

Clone stamp tool

Clone stamp is used in digital image editing to replace information for one part of

a picture with information from another part. In other image editing software, its

equivalent is sometimes called a clone brush.

Shape

A shape is the form of an object or its external boundary, outline, or external surface,

as opposed to other properties such as color, texture or material composition

Rectangle: is a quadrilateral with four right angles a plane figure with four straight

sides and four right angles, especially one with unequal adjacent sides, in contrast

to a square

Lasso tool: it is used to create a selection area within or around a particular object.

The difference is that it allows the user to more easily select along individual short

paths on difficult object limit where the tool can’t be used

Polygon lasso

The Polygonal Lasso Tool is hiding behind the standard Lasso Tool in the Tools

panel. Once you’ve selected the Polygonal Lasso Tool, it will appear in place of the

standard Lasso Tool in the Tools panel.

Rotate

This tool is used to rotate the active layer, a selection or a path. When you click on

the image or the selection with this tool, a grid or an outline is superimposed and a

rotation information dialog is opened. There, you can set the rotation axis, marked

with a point, and the rotation angle.

Application Activity 12.4.

1. What is the importance of Ms Paint in computer graphics?

2. Differentiate Photoshop from MS office picture manager

3. Discuss the use of Ms Office picture manager in graphics

4. Differentiate Paint from Photoshop

5. What is the use of Lasso tool in Photoshop

6. Distinguish image size to canvas size

7. What is the use of Gradient Tool?

12.5 Basic Graphic elements

Activity 12.5

Observe the picture above and answer the following questions:

1. Describe what you see on the picture

2. What are the elements which make this picture?

3. how can you put different parts of this image

12.5.1 Graphic elements

Graphic elements are the simplest building blocks of graphics. Just as bricks are the

basic elements of a building, graphic elements are used to create graphics.

12.5.2 Basic graphic element types

The basic graphic elements are the following:

Line is probably the most fundamental of all the elements of design. A more usable

definition might be that line is the path of a dot, point etc. through space and that

is always has more length than thickness. Lines are not all the same, especially in art

A brush is a tool with bristles, wire or other filaments, used for cleaning, grooming

hair, make up, painting, surface finishing and for many other purposes.

Polyline

A polyline is a connected sequence of straight lines. To the eye, a polyline can appear

as a smooth curve. Simple polyline attributes are colour and thickness. The simplest

polyline is a single straight line segment. A line segment is specified by its two

endpoints, such as (x1, y1) and (x2, y2). When there are several lines in a polyline,

each one is called an edge, and two adjacent lines meet at a vertex.

The edges of a polyline can cross one another but a polyline does not have to be

closed. A polygon has its first and last points connected by an edge. If no two edges

cross, the polygon is called a simple polygon. An example of a polyline is shown in

figure 12.60 and a polygon is shown in figure 12.61

The polygon element defines a closed shape consisting of a set of connected straight

line segments. The last point is connected to the first point.

Text

Some graphics devices have two distinct display modes: text mode and graphics

mode. In text mode, text is generated using a built-in character generator. Text in

graphics mode is drawn. Text attributes are such as colour, size, font, spacing and

orientation.

Filled Regions

A filled region is a shape filled with some colour or pattern. An example is a filled

polygon as shown in figure.

Application Activity 12.5.

1. Describe the graphic element?

2. Describe basic elements in computer graphics

3. Differentiate an oval to a circle

4. Describe the use of brush in computer graphic?

END UNIT ASSESSMENT

A. Written assessment

Define the following terms:

• Brush

• Shape

• Lasso tool

• Bitmap

• Advertisement

1. Match the following tools in column A with their corresponding use in

2. What is polygon? Give an example

3. Explain the importance of computer graphic in decoration service

4. Write in full words the following abbreviation and explain them:

 JPEG - TIFF - PNG

5. Distinguish 8-bit colour to high colour graphics

6. What is the use of USB port on digital camera

7. Differentiate 2D image to 3D image

8. Discuss the difference between Ms Paint and Adobe Photoshop

9. In Rwanda, computer graphics are used in advertising and entertainment.

Discuss

B. Practical work

Create a simple image using some of the drawing tools in Paint(Pencil, brush and shapes)

a. Selecting and moving parts of an image

b. Selecting and copying parts of an image

c. Save the image in JPG format

d. Copy that image in a word document

1. Using Adobe Photoshop, draw a ball as shown bellow

2. Create a line, polygon and a square using Paint. Make the shape outlines

coloured and filled with effects where possible. Save the file as SHAPES

3. Take a picture of yourself using a digital camera and edit the photo in

a way you wish using various tools on the toolbox and menu. In case

of absence of camera, use any available photo on your computer and

perform editing functioning to crop, resize, rotate and change the light of

the picture.