Principle:Puppeteer Puppeteer Screenshot Capture
| Knowledge Sources | |
|---|---|
| Domains | Browser_Automation, Visual_Testing, Rendering |
| Last Updated | 2026-02-11 23:00 GMT |
Overview
A technique that captures the visual rendering of a web page or a specific region as an image file.
Description
Screenshot Capture produces a raster image (PNG, JPEG, or WebP) of the current visual state of a rendered web page. This is fundamental to visual regression testing, page archiving, thumbnail generation, and debugging.
Key capabilities include:
- Full-page screenshots: Capture the entire scrollable content, not just the visible viewport
- Region clipping: Capture only a specific rectangular area of the page
- Format selection: Output as PNG (lossless), JPEG (lossy with quality control), or WebP
- Transparent backgrounds: Omit the default white background for compositing
- Base64 encoding: Return the image as a base64 string instead of binary data
- Element-level screenshots: Capture a specific DOM element by combining with ElementHandle
Usage
Use screenshot capture for visual regression testing (comparing screenshots across builds), generating page thumbnails, documenting UI states, or debugging rendering issues. Ensure the page has fully loaded and any dynamic content has settled before capturing.
Theoretical Basis
The browser's rendering pipeline produces a composited bitmap that the screenshot mechanism captures:
# Screenshot capture pipeline
1. Page content is fully rendered (HTML, CSS, JavaScript executed)
2. If fullPage: compute total scrollable dimensions
3. If clip: define target rectangle
4. Browser composites the target area into a bitmap
5. Bitmap is encoded into the requested format (PNG/JPEG/WebP)
6. Encoded bytes are transferred from browser to Node.js
7. If path specified: write to file system
8. Return binary data or base64 string
For full-page screenshots, the browser temporarily adjusts the viewport to encompass the entire page height before capturing.