Lessons 1 · 1 lessons · N. I. Taylaqov (general editor), A. B. Akhmedov, M. D. Pardayeva, A. A. Abdug‘aniyev, U. M. Mirsanov. Informatics and Information Technologies, Grade 11, 1st edition. “Extremum-press”, Tashkent, 2018
1
Graphic objects and how they are shown on a computer
Textbook: pp. 4–6
GoalExplains the roles of the pixel, the display and the video card, calculates screen size in pixels and tells the classes of computer graphics apart.
New words
pixel: the smallest dot of a screen image; it has its own address and colour · pikselvideo card (graphics adapter): the device that builds the picture and sends it to the screen · videokartadisplay: the part of a monitor, laptop, tablet or phone on which the picture appears · displeyaspect ratio: the width of a screen compared with its height, for example 16:9 · tomonlar nisbati
Explanation
Humans receive most of their information about the world through sight, so a computer also spends a great deal of effort on creating, storing and showing pictures. The picture on the screen is built by the video card: it contains a special video processor (GPU) that refreshes the image dozens of times a second (60 times a second on a 60 Hz screen). The device that shows the picture is the monitor and the surface on which the picture appears is the display; a laptop, tablet or phone has no separate monitor, only a display. A display is divided into rows and columns, and the smallest picture dot where a row and a column cross is the pixel; it has its own address and its colour is controlled separately. Each pixel is built from three small parts that give red, green and blue light; mixing their brightness produces almost any colour. In a 24-bit (“true colour”) picture each pixel gets 3 bytes and can take one of 16 777 216 colours. According to the kind of picture produced, graphics is divided into static graphics, computer animation and multimedia; according to the field of use, scientific, business (tijorat), design (konstruktorlik), illustrative and artistic graphics are distinguished.
Worked examples
A phone display is 1280×720 pixels: 1280·720 = 921 600 pixels. In 24-bit colour one uncompressed frame takes 921 600·3 = 2 764 800 bytes, about 2.8 million bytes.
A photo of a school building is static graphics; a short cartoon is computer animation; a study site with video, sound and buttons is multimedia. A wiring-diagram drawing is design (konstruktorlik) graphics; a diagram of rainfall by region is business or scientific graphics.
Class activity
“Pixel counter”: students find the screen size of their own device (phone or laptop) in the settings, work out the number of pixels and write it in a shared table; the device with the most pixels is identified.
Practice
1
What is the job of the video card?
It creates the picture and sends it to the screen; it has its own video processor for this.
2
A display is 2560×1440 pixels. How many pixels does it have?
3686400
3
Classify (static graphics, animation or multimedia): a) scanning a passport photo; b) a ten-second cartoon clip; c) a study site with buttons and sound.
a) static graphics; b) animation; c) multimedia.
4
Why does a computer send the screen picture again dozens of times a second even when it is idle?
The display receives the picture as a stream of frames from the video card; if the frames come fast enough the eye sees no flicker and changes such as the cursor or clock appear at once.