3.3 Fundamentals of data representation

Decimal (base 10)

Binary (base 2)

Hexadecimal (base 16)

What do computers use to represent all data and instructions?

Computers use binary.

A bit pattern could represent different types of data, including text, image, sound, integer

Why is hexadecimal often used in computer science?

How can binary be used to represent whole numbers?

How can hexadecimal be used to represent whole numbers?

How do you convert numbers from binary to decimal?

How do you convert numbers from decimal to binary?

How do you convert numbers from binary to hexadecimal?

How do you convert numbers from hexadecimal to binary?

How do you convert numbers from decimal to hexadecimal?

How do you convert numbers from hexadecimal to decimal?

What is the fundamental unit of information? What is a byte?

A bit is the fundamental unit of information. (either a 0 or 1, represented by a ‘b’)

A byte is a group of 8 bits. (represented by ‘B’)

Order bits - terabytes from smallest to largest

1 bit, b

1 byte, B (8 bits)

1 kilobyte, kB (1000 bytes)

1 megabyte, MB (1000 kilobytes)

1 gigabyte, GB (1000 megabytes)

1 terabyte, TB (1000 gigabytes)

What is a pixel?

A pixel is a single point in an image.

What is the word pixel short for?

Pixel is short for Picture Element.

Describe how pixels relate to an image and the way images are displayed.

Describe what image size is for a single BITMAP (not a file).

W x H = image size (pixels)

What is colour depth?

Colour depth is the number of bits used to represent each pixel.

Describe how a bitmap represents an image using pixels and colour depth.

explain how bitmaps are made from pixels

Describe using examples how the number of pixels and colour depth can affect the file size of a bitmap image.

Calculate bitmap image file sizes based on the number of pixels and colour depth.

Size = (bits) = W x H x D

Size = (bytes) = (W x H x D)/8

• W = image width

• H = image height

• D = colour depth in bits

Convert binary data into a bitmap image.

Convert a bitmap image into binary data.

Understand that sound is analogue and that it must be converted to a digital form for storage and processing in a computer.

What is a sample?

A sample is a measure of amplitude at a point in time.

Understand that analogue signals are sampled to create the digital version of sound.

What is sampling rate?

Sampling rate is the number of samples taken in a second and is usually measured in hertz (1 hertz = 1 sample per second).

What is sample resolution?

Sample resolution is the number of bits per sample.

Describe how sound is represented digitally using the terms sampling rate and sample resolution.

How do you calculate sound file sizes?

File size (bits) = rate x res x secs

• rate = sampling rate

• res = sample resolution

• secs = number of seconds

Explain what data compression is.

Understand why data may be compressed and that there are different ways to compress data.

Explain how data can be compressed using Huffman coding.

Be able to interpret Huffman trees.

Be able to calculate the number of bits required to store a piece of data compressed using Huffman coding.

Be able to calculate the number of bits required to store a piece of uncompressed data in ASCII.

Explain how data can be compressed using run length encoding (RLE).

Represent data in RLE frequency/data pairs