Chapter 1 Flashcards
What is the Denary Number System?
A system that uses ten digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
Also known as the ‘base 10’ system.
What is the Binary Number System?
A system that only uses two digits: 1 and 0.
Also known as the ‘base 2’ system.
What is Ones’ Complement?
Represents positive numbers.
128 64 32 16 8 4 2 1
What is Two’s Complement?
Represents negative numbers.
-128 64 32 16 8 4 2 1
What is Overflow?
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
Binary Subtraction Steps:
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
What is the Hexadecimal Number System?
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
When is the Hexadecimal System used and why?
- When developing new software
- When trying to trace errors in programs
- 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.
What is the Binary-Coded Decimal (BCD) System?
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
When is the BCD System used?
To represent decimal/monetary values accurately.
For example on a: calculator, digital clock.
What are ASCII Codes?
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)
What are Extended ASCII Codes?
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.
What is Unicode?
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.
How can images be stored either as?
Bit-map image or Vector image
What is a bit-map image?
Image that is made up of a two-dimensional matrix of pixels (picture elements).
What is image resolution?
The number of pixels that make up an image.
E.g.: 4096x3192=12738656 pixels
What is bit depth?
The number of bits used to represent a pixel (the colour).
E.g.: 8 bits
What is colour depth?
The number of possible colours which can be represented.
E.g.: 2^8 = 256 colours
What is screen resolution?
The number of horizontal pixels and the number of vertical pixels that make up a screen display.
What will happen if the screen resolution is smaller than the image resolution?
The whole image cannot be shown on the screen (cropped image).
The image will be a lower quality (pixels will be removed).
What is pixel density?
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).
How to calculate the pixel density for a given screen:
- Add together the squares of the resolution size
- Find the square root
- 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
How to calculate bit-map image file sizes:
- Calculate the number of pixels (length*width)
- Check how many bits each colour requires
- Divide bits into required size (ex KB/MB etc)
When saving a bitmap image what is included (which increases the file size)?
A file header: ◦ File type ◦ File size ◦ Image resolution ◦ Bit depth ◦ Type of data compression
What are vector graphics?
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.
Vector graphics Vs. Bit-map images
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
How is a sound wave sampled? How does Analogue to Digital converter (ADC) digitise sound?
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.
What is the sampling rate?
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.
What happens when we reduce the sample rate?
Fewer samples (per unit time).
File size will decrease.
Larger gaps / spaces between samples.
Sound accuracy will reduce.
What happens when we increase the sampling
resolution?
More bits per sample ➔ Larger file size.
More accurate representation of sound.
Advantages of using higher sampling rate and larger resolution?
Larger dynamic range.
Better sound quality.
Less sound distortion.
Disadvantages of using higher sampling rate and larger resolution?
Produces larger file size.
Takes longer to transmit/download sound files.
Requires greater processing power.
What are some features when using sound editing software?
◦ 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
How is a digital video created?
From a series of static photos (frames) played at a high speed.
What is frame rate?
Frame rate: the number of frames recorded/displayed per second.
What is video resolution?
The number of lines per frame and the number of pixels per line.
What is interlaced encoding?
- Each frame contains half the number of lines of the
complete image. - 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. - Data from two frames is displayed simultaneously.
- The rate of picture display is twice the rate of image frame display (the frame rate).
- Half the frame is refreshed.
- It halves the transmission bandwidth requirements.
What is progressive encoding?
- Each frame contains all the lines for the complete
image. - Frames are not divided into fields.
- Complete frames are displayed in sequence.
- The rate of picture display is the same as the frame
rate. - The entire frame is refreshed each time.
- It has high bandwidth requirements.
What is done to prevent “flickering”?
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
What is lossless file compression?
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.
What is lossy file compression?
File compression method where parts of the original file cannot be recovered during decompression, so some of the original data is lost.
Applications of File Compression?
MPEG-3 (MP3)
MPEG4 (MP4)
JPEG
Run-Length Encoding (RLE)
MPEG-3 (MP3)
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
What is perceptual music shaping?
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.
MPEG4 (MP4)
It can store ◦ Music ◦ Videos ◦ Photos ◦ Animation Compressed into codecs E.g. .avi, .mov, .mp4, .ogg, .rm
JPEG
◦ 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)
Run-Length Encoding (RLE)
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.
Video compression: Inter-frame compression
◦ 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.
