📚 Year 7 CAIE Media: Formula & Theorem Quick Reference Handbook | 7 年级 CAIE 媒体：公式定理速查手册
Welcome to your Year 7 CAIE Media quick reference guide. This handbook brings together the essential formulas, ratios and compositional theorems you will encounter when working with digital images, audio, video and design. Keep it handy as you complete projects, prepare for tests and explore creative media production.
欢迎使用这本 7 年级 CAIE 媒体速查手册。本手册汇集了你在处理数字图像、音频、视频和设计时将遇到的所有关键公式、比例和构图定理。在进行项目、准备测试和探索创意媒体制作时，请将它放在手边。
1. Pixels and Resolution | 像素与分辨率
A pixel, short for 'picture element' total number of pixels across the width and height of an image, written as width × height.
像素是“图像元素”的简称，是数字图像中最小的可寻址单位。分辨率指的是图像宽度和高度上的像素总数，记作宽 × 高。
Total Pixels = Width × Height
× 1080 contains 2,073,600 pixels, commonly referred to as approximately 2 megapixels (MP).
例如，一张 1920 × 1080 的图像包含 2,073,600 个像素，通常称为约 2 百万像素 (MP)。
The table below lists common screen and camera resolutions.
下表列出了常见的屏幕和相机分辨率。
| Common Resolution | 常见分辨率 | Megapixels (approx.) | 百万像素 (约) |
|---|---|---|---|
| 1280 × 720 (HD) | 1280 × 720 (高清) | 0.9 MP | 0.9 百万像素 |
| 1920 × 1080 (Full HD) | 1920 × 1080 (全高清) | 2.1 MP | 2.1 百万像素 |
| 3840 × 2160 (4K UHD) | 3840 × 2160 (4K 超高清) | 8.3 MP | 8.3 百万像素 |
2. Colour Depth and Number of Colours | 颜色深度与颜色数量
Colour depth, also called bit depth, tells you how many bits are used to store the colour information for each pixel. The greater the bit depth, the more colours can be represented.
颜色深度，也称为位深度，表示每个像素用于存储颜色信息的比特数。位深度越大，可以表示的颜色就越多。
Number of Colours = 2Bit Depth
For a 1-bit image, only 2 colours are possible (black and white). An 8-bit image allows 256 colours, while a 24-bit image (8 bits per red, green and blue channel) can display over 16.7 million colours.
对于 1 位图像，只能显示 2 种颜色（黑和白）。8 位图像允许 256 种颜色，而 24 位图像（红、绿、蓝通道各 8 位）可以显示超过 1670 万种颜色。
The formula highlights the power of binary: each extra bit doubles the number of available colours.
该公式凸显了二进制的力量：每增加一位，可用颜色数量就翻倍。
3. Calculating Image File Size | 计算图像文件大小
An uncompressed image file size depends on its resolution and colour depth. The fundamental formula gives the size in bits, which we usually convert to bytes.
未压缩图像的文件大小取决于其分辨率和颜色深度。基本公式以比特为单位给出大小，通常我们会转换为字节。
File Size (bits) = Width × Height × Bit Depth
File Size (bytes) = (Width × Height × Bit Depth) / 8
t 6.22 MB (megabytes). Remember that compressed formats like JPEG reduce this size significantly.
例如，一张 1920×1080、24 位颜色深度的图像将占用 1920 × 1080 × 24 = 49,766,400 位，约为 6.22 MB（兆字节）。请记住，JPEG 等压缩格式会大幅减小这一体积。
4. Understanding Aspect Ratio | 理解长宽比
Aspect ratio describes the proportional relationship between an image's width and height. It is expressed as two numbers separated by a colon, such as 16:9.
长宽比描述的是图像宽度与高度之间的比例关系。它表示为两个由冒号分隔的数字，例如 16:9。
Aspect Ratio = Width : Height
er. For a 16:9 ratio and a width of 1920 pixels, the height = 1920 × (9/16) = 1080 pixels.
如果已知一个尺寸和长宽比，就可以求出另一个尺寸。对于 16:9 的比例和 1920 像素的宽度，高度 = 1920 × (9/16) = 1080 像素。
Common aspect ratios include 4:3 (older TV), 16:9 (widescreen) and 1:1 (square). Understanding ratios helps when cropping or preparing media for different screens.
常见的长宽比包括 4:3（老式电视）、16:9（宽屏）和 1:1（正方形）。了解这些比例有助于在裁剪或为不同屏幕准备媒体时做出选择。
5. Audio Sampling and File Size | 音频采样与文件大小
Digital audio quality is determined by the sample rate, bit depth and number of channels. These three factors together dictate the amount of data stored per second of sound.
数字音频的质量由采样率、位深度和声道数决定。这三个因素共同决定了每秒声音存储的数据量。
Audio File Size (bits) = Sample Rate (Hz) × Bit Depth × Channels × Duration (s)
Audio File Size (bytes) = (Sample Rate × Bit Depth × Channels × Duration) / 8
, 16-bit) will be: 44100 × 16 × 2 × 180 = 254,016,000 bits, or about 30.3 MB uncompressed.
例如，一首 3 分钟的立体声曲目（2 声道）、CD 质量（44,100 Hz、16 位）的大小为：44100 × 16 × 2 × 180 = 254,016,000 位，约合 30.3 MB（未压缩）。
6. Video Bitrate and File Size | 视频比特率与文件大小
Video file size is most easily calculated using the bitrate, which tells you how many bits are processed per second. The bitrate is often measured in kilobits per second (kbps) or megabits per second (Mbps).
视频文件大小最易通过比特率计算，比特率表示每秒处理多少位。比特率通常以千比特每秒 (kbps) 或兆比特每秒 (Mbps) 计量。
Video File Size (bits) = Bitrate (bps) × Duration (seconds)
00 bits, which equals 300 MB (megabytes). Higher bitrates retain more detail but produce larger files.
例如，一段 5 分钟、恒定比特率为 8 Mbps 的视频大小为 8,000,000 × 300 = 2,400,000,000 位，等于 300 MB（兆字节）。较高的比特率能保留更多细节，但文件也更大。
7. Data Compression Ratio | 数据压缩比
Compression reduces file size to save storage space and speed up transfers. The compression ratio compares the original file size to the compressed file size.
压缩通过减小文件体积来节省存储空间并加快传输速度。压缩比比较的是原始文件大小与压缩后文件大小。
Compression Ratio = Uncompressed Size / Compressed Size
A ratio of 10:1 means the original file was ten times larger than the compressed version. Lossless compression preserves all original data, while lossy compression discards some information to achieve higher ratios.
10:1 的压缩比表示原始文件是压缩后文件的十倍大。无损压缩保留所有原始数据，而有损压缩则会丢弃部分信息以达成更高的压缩比。
8. DPI and Print Dimensions | DPI 与打印尺寸
DPI stands for dots per inch and describes the density of printed dots. When preparing images for print, you need enough pixels to match the desired physical size and resolution.
DPI 表示每英寸点数，用于描述打印点的密度。在准备打印图像时，你需要足够的像素来匹配所需的物理尺寸和分辨率。
Required Pixels = Print Size (inches) × DPI
800 pixels across the width. A higher DPI produces sharper prints but demands more pixels.
若想以 300 DPI 打印一张 6 英寸宽的照片，图像宽度就需要 6 × 300 = 1800 像素。较高的 DPI 可产生更清晰的打印效果，但对像素要求也更高。
Remember that screen displays typically use around 72 PPI (pixels per inch), while quality print often requires 300 DPI.
请记住，屏幕显示通常使用约 72 PPI（每英寸像素），而高质量打印往往需要 300 DPI。
9. The Golden Ratio in Composition | 构图中的黄金比例
The Golden Ratio is a mathematical proportion often found in nature, art and design. It appears when a line is divided such that the ratio of the whole length to the longer segment equals the ratio of the longer segment to the shorter segment.
黄金比例是一个在自然、艺术和设计中常见的数学比例。当一条线段被分成的两部分，整体与较长部分的比值等于较长部分与较短部分的比值时，就出现了黄金比例。
Golden Ratio φ = (1 + √5) / 2 ≈ 1.618
In media composition, placing a subject or key element using the golden ratio (or a golden spiral) is thought to create a naturally pleasing and balanced image. Many filmmakers and photographers use this as a foundational compositional theorem.
在媒体构图中，将主体或关键元素按照黄金比例（或黄金螺旋）放置，被认为能创造出自然悦目且平衡的画面。许多电影制作人和摄影师将其视为基础的构图定理。
10. Rule of Thirds Theorem | 三分法构法定理
The Rule of Thirds is one of the most widely taught composition theorems in photography and video. The frame is divided into nine equal rectangles by two equally spaced horizontal lines and two equally spaced vertical lines.
三分法是摄影和视频中教授最为广泛的
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