---
id: css-masking-with-svg
title: "CSS Masking with SVG"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["SVG mask", "svg mask element", "mask-image svg", "CSS masking SVG", "svg clip shapes"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.87
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["css", "web", "frontend", "w3schools", "masking", "svg", "mask-image"]
raw_sources: ["https://www.w3schools.com/css/css3_masking_svg.asp"]
applied_in: []
github_commit: ""
---

# [[CSS Masking with SVG]]

## 🎯 한 줄 통찰 (One-line insight)
An SVG `<mask>` element can act as a mask layer for an image, using SVG shapes (circle, ellipse, polygon) to define which parts of the image are revealed. [S1]

## 🧠 핵심 개념 (Core concepts)
- **SVG mask layer** — an SVG `<mask>` element can serve as the mask layer applied to an image. [S1]
- **Shape-driven** — the visible region is defined by SVG shapes (`<circle>`, `<ellipse>`, `<polygon>`) filled with `#ffffff` inside the mask. [S1]
- **Wiring** — the image references the mask via `mask="url(#svgmask1)"`, where the id matches the `<mask>` element's id. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Define-then-reference** — declare a `<mask id="...">` containing white-filled shapes, then point the `<image>`'s `mask` attribute at `url(#id)`. [S1]
- **Composite masks** — multiple shapes (e.g. several `<circle>`s) inside one `<mask>` reveal multiple regions at once. [S1]

## 📖 세부 내용 (Details)
This page demonstrates how to apply SVG mask layers to images using various SVG shapes. Each example defines an SVG `<mask>` with one or more white-filled (`#ffffff`) shapes, then applies it to an `<image>` via `mask="url(#svgmask1)"`. [S1]

**Circle mask** [S1]
```html
<svg width="600" height="400" xmlns="http://www.w3.org/2000/svg">
  <mask id="svgmask1">
    <circle r="150" cx="200" cy="200" fill="#ffffff" />
  </mask>
  <image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="img_5terre.jpg" mask="url(#svgmask1)"></image>
</svg>
```

**Ellipse mask** [S1]
```html
<svg width="600" height="400" xmlns="http://www.w3.org/2000/svg">
  <mask id="svgmask1">
    <ellipse cx="220" cy="150" rx="200" ry="100" fill="#ffffff" />
  </mask>
  <image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="img_5terre.jpg" mask="url(#svgmask1)"></image>
</svg>
```

**Triangle mask** [S1]
```html
<svg width="600" height="400" xmlns="http://www.w3.org/2000/svg">
  <mask id="svgmask1">
    <polygon fill="#ffffff" points="200 0, 400 400, 0 400"></polygon>
  </mask>
  <image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="img_5terre.jpg" mask="url(#svgmask1)"></image>
</svg>
```

**Star mask** [S1]
```html
<svg width="600" height="400" xmlns="http://www.w3.org/2000/svg">
  <mask id="svgmask1">
    <polygon fill="#ffffff" points="100,10 40,198 190,78 10,78 160,198"></polygon>
  </mask>
  <image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="img_5terre.jpg" mask="url(#svgmask1)"></image>
</svg>
```

**Multiple circles mask** [S1]
```html
<svg width="600" height="400" xmlns="http://www.w3.org/2000/svg">
  <mask id="svgmask1">
    <circle fill="#ffffff" cx="75" cy="75" r="75"></circle>
    <circle fill="#ffffff" cx="80" cy="260" r="75"></circle>
    <circle fill="#ffffff" cx="270" cy="160" r="75"></circle>
  </mask>
  <image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="img_5terre.jpg" mask="url(#svgmask1)"></image>
</svg>
```

**CSS masking properties reference** [S1]

| Property | Description |
|---|---|
| `mask-clip` | Specifies which area is affected by a mask image |
| `mask-composite` | Specifies a compositing operation used on the current mask layer with the mask layers below it |
| `mask-image` | Specifies an image to be used as a mask layer for an element |
| `mask-mode` | Specifies whether the mask layer image is treated as a luminance mask or as an alpha mask |
| `mask-origin` | Specifies the origin position (the mask position area) of a mask layer image |
| `mask-position` | Sets the starting position of a mask layer image (relative to the mask position area) |
| `mask-repeat` | Specifies how the mask layer image is repeated |
| `mask-size` | Specifies the size of a mask layer image |
| `mask-type` | Specifies whether an SVG `<mask>` element is treated as a luminance mask or as an alpha mask |

## 🛠️ 적용 사례 (Applied in summary)
The page's own examples are the applied cases: SVG `<mask>` layers (circle, ellipse, triangle, star, multiple circles) applied to the `img_5terre.jpg` image. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Reveal a circular region of an image with an SVG mask (language: HTML/SVG):
```html
<svg width="600" height="400" xmlns="http://www.w3.org/2000/svg">
  <mask id="svgmask1">
    <circle r="150" cx="200" cy="200" fill="#ffffff" />
  </mask>
  <image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="img_5terre.jpg" mask="url(#svgmask1)"></image>
</svg>
```

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
No contradictions found in the source.

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.87
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[CSS Tutorial]]
- **관련 개념:** [[CSS Masking PNG]], [[CSS Masking Gradients]], [[CSS Image Shapes]]
- **참조 맥락:** Referenced when masking an image to arbitrary shapes defined by SVG geometry.

## 📚 출처 (Sources)
- [S1] W3Schools — CSS Masking with SVG — https://www.w3schools.com/css/css3_masking_svg.asp

## 📝 변경 이력 (Change history)
- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Masking with SVG" page (Astra wiki-curation, P-Reinforce v3.1 format).