Deep Dive: Base64 Image Decoder
Base64 decoding converts encoded ASCII text strings back to binary image data. Paste a data URI or raw base64 string, and this tool extracts the image in its original format (PNG, JPG, WebP, GIF). All processing happens in your browser for complete privacy.
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Privacy Architecture
This tool uses client-side WebAssembly to ensure your data never touches a server. Secure, fast, and privacy-focused by design.
Core Capabilities
- Decode base64 to image
- Supports data URI format
- Accepts raw base64 strings
- Auto-detects image format
- Download decoded image
- Preview before download
- Shows image size info
- 100% Client-side processing
Why It Matters
- Extract: Get images embedded in HTML/CSS back
- Download: Save base64 images from emails or code
- Verify: Check what an encoded string contains
- Convert: Get usable image files from base64
- Privacy: No server uploads—all local processing
Quick Start Guide
Paste base64 string (with or without data URI prefix)
Click 'Decode to Image'
Preview the decoded image
Download in original format (PNG, JPG, etc.)
Clear and decode another!
Usage Examples
Data URI Format
Scenario 01Decode complete data URI
data:image/png;base64,iVBORw0KGgo...
decoded-image.png (downloadable)
Raw Base64
Scenario 02Decode without data URI prefix
iVBORw0KGgoAAAANSUhEU...
decoded-image.png (default PNG format)
From Email
Scenario 03Extract embedded email logo
<img src="data:image/jpeg;base64,/9j/4AAQ...">
logo.jpeg - downloaded and usable!
Common Scenarios
Extract Email Images
Get images embedded in HTML emails
Debug Web Code
Check what base64 string contains
Questions?
Technical Architecture
How Base64 Decoding Works
Base64 represents binary data using 64 ASCII characters (A-Z, a-z, 0-9, +, /). Decoding reverses this: every 4 Base64 characters are converted back into 3 bytes of binary data. The tool strips metadata headers (like `data:image/png;base64,`) and parses the remaining string. Padding characters (`=`) at the end indicate the byte alignment. Browser's `atob()` function or `Buffer` (in Node) handles this conversion, turning the string back into a Blob (Binary Large Object) representing the original image file.
MIME Types and Data URIs
**Data URI Scheme**: `data:[<media type>][;base64],<data>` - **Media Type**: Tells the browser what file it is (e.g., `image/png`, `image/jpeg`). - **Base64**: The encoding method. - **Data**: The actual encoded string. Our decoder looks for this media type in the header to set the correct file extension for download. If missing, we analyze the binary signature (magic numbers) to guess: `89 50 4E 47` = PNG, `FF D8 FF` = JPEG.
Base64 Efficiency
**Size Increase**: Base64 encoded images are roughly 33% larger than the original binary file. This is because 3 bytes (24 bits) are represented by 4 characters (32 bits). **Performance**: Decoding strictly large Base64 strings (10MB+) on the client side can freeze the main thread. We use optimized Blob handling to minimize memory impact, but extremely large strings might still cause browser lag.
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