SLR 12 - Coding Text & Graphics Flashcards
(24 cards)
What is a character set?
A defined list of characters recognised by software and hardware, with each character represented by a unique binary code.
How many characters can be stored with 1 bit? Give an example.
2 characters. Example: 0 = A, 1 = B
How many characters can be stored with 2 bits? Give an example.
4 characters. Example: 00 = A, 01 = B, 10 = C, 11 = D
What is ASCII?
An early standard 7-bit character set representing 128 characters.
What is Extended ASCII?
An 8-bit character set representing 256 characters.
What is Unicode and why was it introduced?
A multilingual character set covering characters in every language, emojis, and symbols. Introduced to support global and multilingual use.
How many bits did Unicode originally use and how many now?
Originally 16-bit, now typically 24-bit (over 16 million characters).
Compare ASCII and Unicode in terms of file size.
Unicode uses more bits per character, so files take more space compared to 7-bit ASCII.
What is the difference between character code and pure binary representation of digits?
Character code represents a digit using binary values of characters (e.g. ‘5’ as binary of ASCII), while pure binary is the binary value of the number itself (5 = 101)
Why is error checking needed in data transmission?
To detect errors caused by interference or packet switching, where 0s and 1s may be lost or altered.
Name four error checking methods.
Parity Bits, Majority Voting, Checksums, Check Digits.
What is a parity bit?
A bit added to binary data to make the number of 1s either even (even parity) or odd (odd parity).
What is majority voting?
A method where data is sent multiple times, and the most common value for each bit is assumed to be correct.
What is a checksum and how does it work?
- Sender calculates checksum using algorithm, appends it to data.
- Data + checksum is sent.
- Receiver recalculates checksum using same algorithm.
- If checksum matches, data is correct; else, a resend is requested.
What is a check digit?
A final digit calculated from others in a code (e.g. barcodes, ISBN) to detect data entry errors like mistyping or scanning errors.
What are the two main ways of storing images in binary?
Bitmap and Vector.
What is a bitmap image?
An image made of pixels, each pixel having a binary value representing its colour
What is a vector image?
An image stored as shapes with mathematical properties like coordinates, colour, radius etc.
Define resolution in bitmaps.
Number of dots (pixels) per inch (dpi).
Define colour depth.
Number of bits used to store each pixel. More bits = more colours.
Give an example of colour depth values.
1-bit = 2 colours
2-bit = 4 colours
24-bit = ~16 million colours
How is file size of a bitmap calculated?
Colour depth × height (px) × width (px)
What is metadata in a bitmap file?
Data about the image e.g. width, height, colour depth, format info.
How are vector graphics stored?
As lists of objects with properties, e.g. Circle(Centre=9,13, Radius=6, Stroke=Blue, StrokeWidth=10px)
