10.3 Data

Bit mapping is the relationship between the image on the screen and the bits in memory.

Resolution is the number and size of the display pixels. It is expressed as

Number of horizontal pixels x Number of vertical pixel lines = total pixels

For example,

Low resolution

                                                                                                            320 x 200 = 64 000

                                                                                                            This results in a chunky picture

High resolution

                                                                                                            1024 x 768 = 786 432

                                                                                                            More detail

640

If we had a display of 640 x 480 pixels then…………..

There is a total of 640 x 480 = 307 200 pixels.

480

If this is monochrome, black and white,

we only need to know if the pixel is ON or OFF (1 or 0).

This is stored in a bit (Binary Digit) and we need one bit per pixel.

So, we need 307 200 bits.

307 200 bits     =          307 200 ¸ 8                 bytes                (8 bits in a byte)

                        =          307 200 ¸ (8x1024)     kilobytes           (1024 bytes in a kilobyte)

                        =          38                                kilobytes

Shades of grey can be achieved by having more bits per pixel.

            2 bits give four shades               (2²=4)

            4 bits give sixteen shades          (2⁴=16)

            6 bits give sixty four shades       (2⁶=64)

Memory needed is

            2 x 38 = 76 kilobytes

            4 x 38 = 152 kilobytes

            6 x 38 = 228 kilobytes

Memory needed dramatically increases if colour and shades are used.

Write out the sentence and fill in the missing word

 

The smallest part of the screen that can be controlled by the computer is ?????.

The movement of a graphic, as in a cartoon is ?????.

Animation that involves drawing and displaying individual frames in a particular sequence or path is ?????.

The smooth change between two images of similar shapes ?????

Animation that involves displaying the movement of objects onto a fixed background is ?????.

The smooth change between two images that have completely different shapes is ?????.

The measurement of detail of an image produced on a monitor, or output from a printer is ?????.

The relationship between the image on the screen and the bits in memory is ?????.

Graphics created by a painting program are ?????.

Graphics created by a drawing program are ?????.