2nd/10_Wiki/Topics/Frontend/에일리어싱 (Aliasing).md

---
id: wiki-2026-0508-에일리어싱-aliasing
title: 에일리어싱 (Aliasing)
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Aliasing, 계단현상, Jaggies]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [graphics, rendering, frontend, antialiasing]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: CSS/JS
  framework: Canvas/WebGL
---

# 에일리어싱 (Aliasing)

## 매 한 줄
> **"매 sampling rate 가 signal frequency 의 절반 미만일 때 발생하는 distortion"**. Nyquist theorem 위반 의 결과로, frontend 에서 매 jagged edges, moiré patterns, shimmer 형태로 나타남. 매 antialiasing (AA) 기법으로 완화.

## 매 핵심

### 매 정의
- **Spatial aliasing**: 매 jagged edges (계단 현상) — pixel grid 가 매 diagonal/curved line 의 표현 부족.
- **Temporal aliasing**: 매 frame rate 부족 의 결과 — wagon-wheel effect, stutter.
- **Texture aliasing**: 매 minification 시 매 moiré pattern.

### 매 원인
- **Discrete sampling**: 매 continuous signal 을 discrete pixel 로 sampling.
- **Sub-pixel detail**: 매 single pixel 보다 작은 detail 의 미손실 표현 불가.
- **Nyquist criterion**: 매 sampling_rate ≥ 2 × max_frequency 충족 X.

### 매 응용 (frontend)
1. **Canvas/WebGL rendering**: 매 line, polygon, font 의 smooth rendering.
2. **CSS transforms**: 매 rotated/scaled element 의 edge.
3. **SVG icons**: 매 small size 매 shimmer 방지.

## 💻 패턴

### Canvas 2D antialiasing 활성화
```javascript
const canvas = document.querySelector('canvas');
const ctx = canvas.getContext('2d');

// imageSmoothingEnabled: 매 default true
ctx.imageSmoothingEnabled = true;
ctx.imageSmoothingQuality = 'high'; // 'low' | 'medium' | 'high'

ctx.drawImage(img, 0, 0, 100, 100);
```

### WebGL MSAA (Multi-Sample Anti-Aliasing)
```javascript
const gl = canvas.getContext('webgl2', {
  antialias: true, // 매 MSAA 활성화 (browser 가 sample count 결정)
});

// 매 explicit sample count (offscreen framebuffer)
const fb = gl.createFramebuffer();
gl.bindFramebuffer(gl.FRAMEBUFFER, fb);
const rb = gl.createRenderbuffer();
gl.bindRenderbuffer(gl.RENDERBUFFER, rb);
gl.renderbufferStorageMultisample(
  gl.RENDERBUFFER, 4, gl.RGBA8, width, height
);
```

### CSS — 매 transform 시 jagged edge 완화
```css
.rotated {
  transform: rotate(15deg);
  /* 매 GPU 가속 + subpixel AA */
  will-change: transform;
  backface-visibility: hidden;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* 매 image scaling 시 quality */
img {
  image-rendering: auto; /* 매 default — browser AA */
  /* image-rendering: pixelated; — 매 retro pixel art */
  /* image-rendering: crisp-edges; — 매 sharp without AA */
}
```

### SVG — 매 sub-pixel rendering
```html
<!-- 매 매끈한 line: shape-rendering -->
<svg viewBox="0 0 100 100">
  <line
    x1="10" y1="10" x2="90" y2="50"
    stroke="black"
    shape-rendering="geometricPrecision"
  />
  <!-- "geometricPrecision" | "crispEdges" | "auto" -->
</svg>
```

### Three.js — 매 FXAA postprocessing
```javascript
import * as THREE from 'three';
import { EffectComposer } from 'three/addons/postprocessing/EffectComposer.js';
import { ShaderPass } from 'three/addons/postprocessing/ShaderPass.js';
import { FXAAShader } from 'three/addons/shaders/FXAAShader.js';

const composer = new EffectComposer(renderer);
const fxaa = new ShaderPass(FXAAShader);
fxaa.material.uniforms.resolution.value.set(
  1 / window.innerWidth, 1 / window.innerHeight
);
composer.addPass(fxaa);
```

### Devicepixelratio 보정
```javascript
function setupHiDPICanvas(canvas) {
  const dpr = window.devicePixelRatio || 1;
  const rect = canvas.getBoundingClientRect();

  canvas.width = rect.width * dpr;
  canvas.height = rect.height * dpr;
  canvas.style.width = `${rect.width}px`;
  canvas.style.height = `${rect.height}px`;

  const ctx = canvas.getContext('2d');
  ctx.scale(dpr, dpr);
  return ctx;
}
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| 매 SVG icon, vector | shape-rendering="geometricPrecision" |
| 매 retina display | devicePixelRatio scaling |
| 매 WebGL game | MSAA 4x or FXAA postprocess |
| 매 pixel art | image-rendering: pixelated (AA 끄기) |
| 매 rotated text | -webkit-font-smoothing: antialiased |

**기본값**: 매 antialias: true 활성화 + DPR scaling 적용.

## 🔗 Graph
- 부모: [[Computer Graphics]]
- 변형: [[FXAA]]
- 응용: [[WebGL]] · [[SVG]]

## 🤖 LLM 활용
**언제**: 매 Canvas/WebGL rendering 매 jagged edge 의 완화, retina display 의 sharp output.
**언제 X**: 매 pixel art (의도적 jagged), 매 ultra low-end GPU (AA 비용 부담).

## ❌ 안티패턴
- **DPR 무시**: 매 retina 매 blurry — devicePixelRatio scaling 누락.
- **AA 항상 max**: 매 mobile GPU 매 fps 저하 — adaptive quality 필요.
- **transform 후 sub-pixel position**: 매 0.5px offset 매 blur — translateZ(0) hack.

## 🧪 검증 / 중복
- Verified (MDN Canvas API, WebGL spec, Three.js docs).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — aliasing, AA techniques (MSAA/FXAA), Canvas/WebGL/SVG/CSS 패턴 정리 |