Chapter 1

Question 1

What is the Denary Number System?

Answer 1

A system that uses ten digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.

Also known as the ‘base 10’ system.

Question 2

What is the Binary Number System?

Answer 2

A system that only uses two digits: 1 and 0.

Also known as the ‘base 2’ system.

Question 3

What is Ones’ Complement?

Answer 3

Represents positive numbers.

128 64 32 16 8 4 2 1

Question 4

What is Two’s Complement?

Answer 4

Represents negative numbers.

-128 64 32 16 8 4 2 1

Question 5

What is Overflow?

Answer 5

The number produced in the previous example is outside the range of values which can be represented by the 8 bits ➔ This causes overflow.
For -128 64 32 16 8 4 2 1: +127 is the largest value
For 128 64 32 16 8 4 2 1: +256 is the largest value

Question 6

Binary Subtraction Steps:

Answer 6

For example: 93 - 66
We have a positive number, 93, and a negative number, -66:
1. Convert the two numbers into binary (93 and 66)
2. Find the two’s complement of 66
3. Add the two binary numbers

Question 7

What is the Hexadecimal Number System?

Answer 7

A number system that uses 16 digits:
0 1 2 3 4 5 6 7 8 9 A B C D E F
Also known as the ‘base 16’ system.

Split it into groups of 4 bits (starting for right to left) and then find the equivalent hex digits

Question 8

When is the Hexadecimal System used and why?

Answer 8

1. When developing new software
2. When trying to trace errors in programs
3. Memory dump (the contents of a computer memory output to screen or printer)

Because it is easier to work with hex than it is to work with binary.

Question 9

What is the Binary-Coded Decimal (BCD) System?

Answer 9

A system that uses a 4-bit code to represent each denary digit (0-9).
Stored either as:
◦Half a byte
◦Two codes stored together to form one byte

Question 10

When is the BCD System used?

Answer 10

To represent decimal/monetary values accurately.

For example on a: calculator, digital clock.

Question 11

What are ASCII Codes?

Answer 11

To represent text, a character set is required.

ASCII (American Standard Code for Information Interchange) is a system code representing letters, numbers, characters and control codes.
Standard ASCII character set consists of 7-bitcodes:
2^7 = 128 different characters (0 to 127 denary)

Question 12

What are Extended ASCII Codes?

Answer 12

Extended ASCII consists of 8-bit codes.
2^8 = 256 different characters (0 to 255 denary).
128 - 255 denary are non-English and drawing characters.
Use of 1 byte per character.

Question 13

What is Unicode?

Answer 13

Allows characters of all the languages of the world; supporting many OS, search engines and internet browsers used globally.
First 128 characters the same as ASCII.
Use of up to 4 bytes per character.

Question 14

How can images be stored either as?

Answer 14

Bit-map image or Vector image

Question 15

What is a bit-map image?

Answer 15

Image that is made up of a two-dimensional matrix of pixels (picture elements).

Question 16

What is image resolution?

Answer 16

The number of pixels that make up an image.

E.g.: 4096x3192=12738656 pixels

Question 17

What is bit depth?

Answer 17

The number of bits used to represent a pixel (the colour).

E.g.: 8 bits

Question 18

What is colour depth?

Answer 18

The number of possible colours which can be represented.

E.g.: 2^8 = 256 colours

Question 19

What is screen resolution?

Answer 19

The number of horizontal pixels and the number of vertical pixels that make up a screen display.

Question 20

What will happen if the screen resolution is smaller than the image resolution?

Answer 20

The whole image cannot be shown on the screen (cropped image).
The image will be a lower quality (pixels will be removed).

Question 21

What is pixel density?

Answer 21

The number of pixels per square inch.
(If you zoom in an image, the pixel density will be lower and the image will become pixelated; deterioration in the image quality).

Question 22

How to calculate the pixel density for a given screen:

Answer 22

1. Add together the squares of the resolution size
2. Find the square root
3. Divide by screen size

For example:
iPhone 8, 5.5-inch screen size, 1900x1080 pixels resolution; 
19202+10802=4852800
4852800 = 2202.907
2202.907/5.5 = 401 ppi

Question 23

How to calculate bit-map image file sizes:

Answer 23

1. Calculate the number of pixels (length*width)
2. Check how many bits each colour requires
3. Divide bits into required size (ex KB/MB etc)

Question 24

When saving a bitmap image what is included (which increases the file size)?

Answer 24

A file header: 
◦ File type
◦ File size
◦ Image resolution
◦ Bit depth
◦ Type of data compression

Question 25

What are vector graphics?

Answer 25

Images that use 2D points to describe lines and curves and their properties that are grouped to form geometric shapes. Can be produced by a CAD software.

Question 26

Vector graphics Vs. Bit-map images

Answer 26

VECTOR GRAPHIC IMAGES 1. Made up of geometric shapes which require attributes 2. To edit the design, it is necessary to change each of the geometric shapes 3. They do not require large file sizes since it is made of simple geometric shapes 4. They are not usually very realistic because the number of geometric shapes is limited. 5. File formats: .svg, .cgm, .odg BIT-MAP IMAGES 1. Made up of tiny pixels of different colours 2. Each pixel can be edited 3. The file size is very large because of the use of pixels 4. The mage is usually very realistic, because of the pixels 5. File formats: .jpeg, .bmp, .png

Question 27

How is a sound wave sampled? How does Analogue to Digital converter (ADC) digitise sound?

Answer 27

Sound is an analogue value. Need to convert it into digital form in order to store it in the computer. SO, The amplitude of the sound wave is measured at set/regular time intervals. Each sample is then converted into the equivalent binary number. The whole collection of data is then stored in a digital file. Frequencies outside the range of human hearing are removed.

Question 28

What is the sampling rate?

Answer 28

The number of sound samples taken per second. Measured in Hz. The higher the number of samples the higher the accuracy of the sampled sound.

Question 29

What happens when we reduce the sample rate?

Answer 29

Fewer samples (per unit time). File size will decrease. Larger gaps / spaces between samples. Sound accuracy will reduce.

Question 30

What happens when we increase the sampling | resolution?

Answer 30

More bits per sample ➔ Larger file size. | More accurate representation of sound.

Question 31

Advantages of using higher sampling rate and larger resolution?

Answer 31

Larger dynamic range. Better sound quality. Less sound distortion.

Question 32

Disadvantages of using higher sampling rate and larger resolution?

Answer 32

Produces larger file size. Takes longer to transmit/download sound files. Requires greater processing power.

Question 33

What are some features when using sound editing software?

Answer 33

``` ◦ Edit start/stop and duration ◦ Extract & save (or delete) a part ◦ Alter frequency/amplitude ◦ Fade in/fade out ◦ Mix and/or merge multiple sound tracks ◦ Remove ‘noise’ ◦ Convert between different audio formats ```

Question 34

How is a digital video created?

Answer 34

From a series of static photos (frames) played at a high speed.

Question 35

What is frame rate?

Answer 35

Frame rate: the number of frames recorded/displayed per second.

Question 36

What is video resolution?

Answer 36

The number of lines per frame and the number of pixels per line.

Question 37

What is interlaced encoding?

Answer 37

1. Each frame contains half the number of lines of the complete image. 2. Each frame is divided into two fields: ◦ One field contains the data for the even numbered lines and the other has the data for the odd numbered lines. 3. Data from two frames is displayed simultaneously. 4. The rate of picture display is twice the rate of image frame display (the frame rate). 5. Half the frame is refreshed. 6. It halves the transmission bandwidth requirements.

Question 38

What is progressive encoding?

Answer 38

1. Each frame contains all the lines for the complete image. 2. Frames are not divided into fields. 3. Complete frames are displayed in sequence. 4. The rate of picture display is the same as the frame rate. 5. The entire frame is refreshed each time. 6. It has high bandwidth requirements.

Question 39

What is done to prevent "flickering"?

Answer 39

There needs to be compatibility between the resolution of the stored image and the resolution of the display screen. Traditional solution to this problem → use interlaced encoding Alternative approach → use progressive encoding

Question 40

What is lossless file compression?

Answer 40

File compression method where the original file can be restored following decompression. No loss of data and the file is exactly like the original. For files where loss of data would be disastrous.

Question 41

What is lossy file compression?

Answer 41

File compression method where parts of the original file cannot be recovered during decompression, so some of the original data is lost.

Question 42

Applications of File Compression?

Answer 42

MPEG-3 (MP3) MPEG4 (MP4) JPEG Run-Length Encoding (RLE)

Question 43

MPEG-3 (MP3)

Answer 43

Audio compression to convert sounds into an MP3 file format; uses perceptual music shaping. The music file size is reduced by about 90%. MP3 quality can never match the ‘full’ version of a CD, but it is satisfactory

Question 44

What is perceptual music shaping?

Answer 44

Used in file compression algorithms to remove: ◦ Frequencies that are outside the human hearing range. ◦ If two sounds are played at the same time, the softer sound is eliminated. Without affecting the quality too much.

Question 45

MPEG4 (MP4)

Answer 45

``` It can store ◦ Music ◦ Videos ◦ Photos ◦ Animation Compressed into codecs E.g. .avi, .mov, .mp4, .ogg, .rm ```

Question 46

JPEG

Answer 46

◦ Uses lossy compression ◦ The raw bit-map image will be reduced by a factor of 5-15 (Vector graphics can also undergo some form of file compression)

Question 47

Run-Length Encoding (RLE)

Answer 47

Lossless file compression technique used to reduce text and photo files. ◦ Reduces the size of a string of adjacent, identical data. (e.g.: characters in a text string or repeated colours in an image) ◦ A repeated string is encoded into 2 values.

Question 48

Video compression: Inter-frame compression

Answer 48

◦ It removes neighboring frames which are similar. ◦ Some change in image data is redundant. ◦ How redundant the change in image between frames determines the amount of compression possible.