Encoding Methods for Characters, Images, and Audio

Comprehensive vocabulary flashcards reviewing character encodings (ASCII, GB2312, GBK, GB18030, Unicode, UTF-8, UTF-16, UTF-32), digital image representation and formats (sampling, quantization, bitmap, vector, BMP, JPEG, PNG, SVG, GIF), and audio encoding standards (PCM, CELP, G.729, MP3, FLAC).

Character Encoding

The process of establishing a mapping relationship between characters and binary numbers, serving as the foundation for computer processing of text information.

ASCII (American Standard Code for Information Interchange)

The United States standard code for information interchange that uses 7-bit binary numbers to represent a total of 128 characters.

ASCII Control Characters

Characters within the ASCII range 0–31 and 127 (such as line feed and carriage return) used for device control and data flow rather than displayable symbols.

ASCII Printable Characters

Characters within the ASCII range 32–126, consisting of displayable text including English letters, digits, and punctuation symbols.

GB2312

A Chinese national standard character set that uses a double-byte ($16\,\text{bit}$) representation, containing 6,763 Chinese characters and 682 symbols to facilitate Chinese text processing.

Level 1 Chinese Characters (GB2312)

A subset of 3,755 Chinese characters within the GB2312 standard that are ordered alphabetically by pinyin.

Level 2 Chinese Characters (GB2312)

A subset of 3,008 Chinese characters within the GB2312 standard that are ordered by radical.

GBK

An extension of GB2312 that includes 21,003 Chinese characters, provides support for Traditional Chinese, and maintains backward compatibility with GB2312.

GB18030

China's latest national standard for Chinese character encoding, encompassing over 70,000 Chinese characters using mixed single-byte, double-byte, and four-byte encodings to cover all scripts in China, including ethnic minority scripts.

Unicode

A globally unified character encoding standard designed to eliminate "garbled text" by assigning a unique numeric identifier (code point) to every character, script, and symbol across world languages.

Code Point

A unique numeric identifier assigned to a specific character in the Unicode standard, typically expressed in hexadecimal notation with the prefix $U+$.

Basic Multilingual Plane (BMP)

The primary plane of Unicode (Plane 0) containing 65,536 code points that accommodate the commonly used characters for almost all modern languages.

UTF-8

A variable-length encoding implementation of Unicode using 1 to 4 bytes per character; it is backward compatible with ASCII (1 byte), typically encodes Chinese characters in 3 bytes, and is the dominant encoding on the Internet.

UTF-16

A Unicode character encoding that allocates either 2 or 4 bytes per character; characters in the Basic Multilingual Plane (BMP) occupy 2 bytes, while supplemental characters require 4 bytes.

UTF-32

A fixed-length character encoding for Unicode that allocates exactly 4 bytes ($32\,\text{bits}$) per character, corresponding directly to Unicode code points, offering simple processing but low storage efficiency.

Pixel

The fundamental picture element and smallest individual component of a digital image, carrying specific color and intensity information.

Sampling (Image)

The step in image digitization of spatially discretizing a continuous image by dividing it into a discrete matrix of pixels; the dimension of this matrix determines image resolution.

Quantization (Image)

The step in image digitization of converting continuous color values of each pixel into a finite set of discrete numerical levels (for instance, an $8\,\text{bit}$ channel represents 256 discrete levels).

Image Encoding

The process of converting a 2D pixel matrix and its quantized color values into 1D binary data organized in a standardized file format.

Bitmap (Raster Image)

An image structured as a grid of discrete pixels, capable of representing rich colors and photographic detail, but susceptible to jagged edges and blurriness when enlarged.

Vector Image

A digital graphic defined mathematically via geometric primitives (points, lines, curves, shapes), allowing infinite scaling without distortion while preserving small file sizes.

BMP (Bitmap File Format)

An uncompressed or losslessly compressed raster file format that preserves original image quality but produces large file sizes, making it less suitable for network transfer.

JPEG

A lossy compressed raster image format characterized by high compression ratios and compact file sizes, widely used for digital photos and web imagery.

PNG (Portable Network Graphics)

A lossless raster graphics file format that supports transparent backgrounds and maintains high visual fidelity, making it ideal for web graphics, logos, and icons.

SVG (Scalable Vector Graphics)

An XML-based vector image format that can be rendered, scaled infinitely without quality loss, edited with text editors, and programmed for interactivity and animation.

GIF (Graphics Interchange Format)

A lossless raster image format restricted to a maximum palette of 256 colors that supports simple frame-based animation and transparency.

Pulse Code Modulation (PCM)

The foundational method of converting continuous analog audio waves into uncompressed digital signals through periodic sampling and discrete amplitude quantization.

PCM Audio Data Volume Formula

$\text{Data volume} = \frac{\text{Sampling rate} \times \text{Quantization bits} \times \text{Duration}}{8}$, calculating uncompressed raw audio size in bytes.

Parametric Encoding (CELP)

A voice compression approach that extracts human vocal tract parameters to achieve extremely low bitrates ($8\,\text{kbps}$) suitable for severely limited bandwidth at the cost of lower audio fidelity.

Hybrid Encoding (G.729)

A speech coding technique that integrates the audio quality of waveform coding (PCM) with the high compression ratio of parametric coding, widely deployed in VoIP.

Perceptual Encoding (MP3)

A lossy audio compression technique that applies a psychoacoustic model to discard sound frequencies and nuances imperceptible to human hearing, dramatically reducing file size while preserving high perceptual quality.

Masking Effect

A psychoacoustic phenomenon where the presence of a louder or dominant sound makes simultaneous softer or adjacent frequencies undetectable by the human auditory system.

FLAC

A lossless audio compression format designed to preserve complete acoustic fidelity without data loss, preferred for high-quality music archiving.