Representing Images

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Bitmap

Most digital images are stored as bitmaps.

Bitmap

A bitmap image is split up into tiny squares called pixels.
The colour of each pixel is stored as a binary number.

Colour-depth

The amount of bits used to store the colour of each pixel is known as the colour depth.
The greater the number of bits used to represent each pixel, the more unique colours can be stored.
Common colour depths are 1-bit, 8-bit, 16-bit, and 24-bit.

Resolution

Resolution represents the number of pixels in an image.
The number of pixels is found by multiplying the width by the height of the image.
An example resolution is 1080p which is 1920x1080.

Metadata

Metadata is extra information that is added to an image file such as:
- The resolution.
- The colour-depth.
- The encoding format.
- The time and date of taking the photo.

File size

The size (in bits) of an image file is calculated as follows:
- File size (in bits) = image width x image height x colour depth (in bits)
The size of the image file in bytes is equal to:
- File size (in bytes) = file size (in bits) ÷ 8

Converting Binary and Images

All images are stored as binary. It's important to be able to convert between an image and its binary representation.

Binary to image

In a black and white image, each pixel is represented by 1 bit:
- A 0 will represent a black area.
- A 1 will represent a white area.
The image will be represented by a binary string. Use the value of each bit to colour each pixel in the right colour.
The binary string starts at the top-left of the image, and represents the first row, followed by the second row, and continues until the end of the image.

Image to binary

Each pixel of the image will be represented by one bit of the binary string.
Starting at the top left, and working across the first row:
- Write a 0 if the pixel is black.
- Write a 1 if the pixel is white.
Continue this process until the end of the image.

1Computer Systems

1.1Systems Architecture

1.1.1Architecture Introduction

1.1.2Von Neumann Architecture

1.1.3Fetch-Execute Cycle

1.1.4Factors Affecting CPU Performance

1.1.5Elements of Computer Systems

1.1.6Exam-Style Questions - Von Neumann Architecture

1.2Memory & Storage

1.3Computer Networks, Connections & Protocols

1.4Network Security

1.4.1Forms of Attack

1.4.2Malware

1.4.3Social Engineering

1.4.4Phishing

1.4.5Common Active Attacks

1.4.6Information Security

1.4.7SQL Injection

1.4.8Network Administration

1.4.9Protecting Against Malware

1.4.10Authentication & Passwords

1.4.11Encryption

1.4.12End of Topic Test - Networks

1.5Systems Software

1.5.1Types of System Software

1.5.2Operating Systems

1.5.3Operating System Managers

1.5.4File Management

1.5.5Device Management

1.5.6User Management

1.5.7Utility Software: Encryption & Defragmentation

1.5.8Utility Software: Data Compression & Backup

1.6Ethical, Legal, Cultural & Environmental Concern

1.6.1Open Source vs Proprietary Software

1.6.2Licensing Issues

1.6.3Ethical Issues

1.6.4Ethical Issues 2

1.6.5Exam-Style Questions - Ethical Issues

1.6.6Legal Issues

1.6.7Legal Issues 2

1.6.8Freedom of Information Act (2000)

1.6.9Cultural Issues

1.6.10Environmental Issues

1.6.11Positive Environmental Impact

1.6.12Privacy Issues

1.6.13Stakeholders

1.6.14End of Topic Test - Software & Issues

2Computational Thinking, Algorithms and Programming

2.1Algorithms

2.1.1Computational Thinking

2.1.2Algorithmic Thinking

2.1.3Pseudocode & Flow Diagrams

2.1.4Interpreting & Correcting Algorithm

2.1.5Completing Algorithms

2.1.6Search Algorithms

2.1.7Binary Search

2.1.8Overview of Sort Algorithms

2.1.9Bubble Sort & Insertion Sort

2.1.10Merge Sort

2.1.11Exam-Style Questions - Sorting Algorithms

2.2Programming Fundamentals

2.2.1Fundamentals

2.2.2Program Flow 1

2.2.3Program Flow 2

2.2.4Arithmetic & Relational Operators

2.2.5Boolean Operators

2.2.6Data Types

2.2.7Arrays

2.2.8Strings

2.2.9File Handling

2.2.10Structuring Data

2.2.11End of Topic Test - Programming

2.2.12Exam-Style Questions - Translation

2.3Producing Robust Programs

2.3.1Defensive Design Considerations

2.3.2Defensive Design Considerations 2

2.3.3Maintainability

2.3.4Testing

2.3.5Test Plans

2.3.6Error Types

2.3.7End of Topic Test - Programming

2.3.8Exam-Style Questions - Testing

2.4Boolean Logic

2.4.1Computational Logic

2.4.2Boolean Logic

2.4.3Boolean Operators

2.4.4Grade 9 - Logic

2.5Programming Languages & IDEs

2.5.1High-Level vs Low-Level Languages

2.5.2Translation - Compliers & Interpreter

2.5.3Translation - Assemblers

2.5.4Integrated Development Environments

2.5.5Exam-Style Questions - Translation

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