Images

Learning objectives

When you have completed this session, you should be able to

• define term "image",

Images, Illustrations in the Electronic Syllabus

Comprehension in the electronic syllabus can be aided by the integration of visual elements (motion pictures, still pictures and animations). Possibilities offered by technology are just about unlimited, however proper application is not a simple task. The quality of electronic syllabus is fundamentally determined by the correct and moderate application of visual elements.

This chapter is a brief professional overlook of the theoretical basics of digital picture construction. This may be important to anyone even if participating as a content editor or methodological expert and not as an information technologist in the development.

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Exercise

Let's have a look at your favourite website. Turn off the appearance of pictures in your webbrowser. Which one is better?

Displaying Images on the Screen

In order to decide what sort of picture or illustration to be used for a given part of lesson many standpoints must be taken into consideration during the planning process. First of all how that will look like on the screen or in printing. We must be aware that the picture appearing on the screen basically depends on two things:

• the quality of the graphic card ,
• the quality of the monitor .

How?

The graphic card communicates to the monitor what and how to display. The monitor makes the picture draw from different pixels in a grid. Each of the pixels can have a unique color. We can say that the screen of the monitor is a mosaic. In the picture to the left you can see the same image zoomed by 16.

Picture Definition

The density of dots defines the purity of the picture. In case of smaller size but higher number of pixels purer, larger size but fewer number of pixels rougher quality picture can be observed. The number of lines and columns of the bitmap results the definition of the picture.

The widest-spread picture definitions are the following:

• 640x480
• 800x600
• 1024x768
• 1152x864
• 1280x1024
• 1600x1200

There are higher definitions than the above listed ones as well but those can only be displayed with very good quality monitors.

In order to see the proper picture resolution on the screen both the graphic card and the monitor must be able to produce it. There is no use to send a 1280x1024 definition picture by the graphic card to the monitor if that is not able to display it and so is the other way around.

These days almost all graphic cards are suitable for 160x1200 definition. Usually monitors mean the narrow end.

The larger the definition is the smaller the pixels are and the more information can be displayed on the screen so images look smaller. Take a look of the same picture fraction with a 1024x768 and with a 640x480 definition.

Color Depth and Picture Refreshing

Pictures shown on the screen are effected by two more things:

• the number of colors,
• the frequency of picture refreshing.

The number of colors tells that how many colors can define the value of a pixel According to this a picture can be:

• 2 color (black and white, 1 bit),
• 16 color (vga, 4 bit),
• 256 color (svga, 8 bit),
• 65536 color (16 bit),
• 16 777 216 color (24 bit).

The number of colors that can be displayed is called the color depth and usually is given in bits (8 bit color depth, etc.). This comes from the fact that 8 bits are needed to store 256 colors (1. The measurements of data storage).

The quality of a true picture is highly influenced by the number of colors applied.

The characteristics of the different types of pictures:

2color picture:

In this case the only possibility we have is to define for each dot which color out of two they should be. This type of picture is simply called bitmap picture.

Monochrome picture:

Typically black and white photos are made with this method. Each dot has some gray shade. All together there are 256 shade variations from white to black.

256 color picture:

There are 256 colors all together to use which can be selected by the user. For each pixel it can be defined which color of the 256 to be used.

True color picture:

This is the perfect solution for displaying color pictures because practically all shades can be displayed. Today most pictures are made this way.

The displayed image disappears after a short time therefore it must be displayed again. The frequency of picture refreshing tells how many times in a second the monitor must display the image. The higher this value is the more stable the image is so the less vibration it produces.

The number of colors that can be displayed and the image refreshing frequency is given with the resolution as the following:

640x480 24 bit 100Hz,

which means that besides a 640x480 resolution, the device (a monitor or a graphic card) can perform with a 24 bit color depth and a 100 Hz image refreshing.

Summary:

Images are produced by a graphic card and displayed by a monitor. The monitor displays the pictures in dots (in a grid). The density of the dots results the purity of fineness of the picture. All pixels can have different colors. The quality of the image is also determined by the number of colors and by the frequency of image refreshing.

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Exercise

1. Look at the resolution, the color depth and refreshing rate of your screen. You can change the values to see the differences.

2. Search for a picture (a photo, e.g. on Internet) and zoom in as long as you can with the help of a picture viewer application. Can you see the pixels?