Base64 to Image

Decode Base64 and display images in browser using native atob() + TextDecoder + Blob API.

// Base64 → Image (native browser implementation)
function base64ToImage(base64String, mimeType = 'image/png') {
  // 1. Strip Data URL prefix if present
  const clean = base64String.replace(/^data:image\/\w+;base64,/, '');

  // 2. Decode to binary string using native atob()
  const binary = atob(clean);

  // 3. Convert to Uint8Array
  const bytes = new Uint8Array(binary.length);
  for (let i = 0; i < binary.length; i++) {
    bytes[i] = binary.charCodeAt(i);
  }

  // 4. Create Blob URL for <img> tag preview
  const blob = new Blob([bytes], { type: mimeType });
  const url = URL.createObjectURL(blob);

  // 5. Set img.src to preview
  const img = document.createElement('img');
  img.src = url;
  img.onload = () => {
    console.log(`Image dimensions: ${img.width}x${img.height}`);
    console.log(`File size: ${bytes.byteLength} bytes`);
  };

  return { img, url, size: bytes.byteLength };
}

// Usage example:
const result = base64ToImage('iVBORw0KGgoAAAANSUhEUgAAAAUA...');
document.body.appendChild(result.img);

// Release Blob URL (avoid memory leaks)
setTimeout(() => URL.revokeObjectURL(result.url), 60000);

Decode Base64 data to image binary stream using Python standard library base64, then save with PIL/Pillow or built-in file operations.

import base64
from pathlib import Path

def base64_to_image(base64_string: str, output_path: str, mime_type: str = 'image/png'):
    """Decode Base64 string and save as image file"""

    # 1. Strip Data URL prefix
    if base64_string.startswith('data:image'):
        # Format: data:image/png;base64,iVBORw0...
        header, base64_string = base64_string.split(',', 1)
        # Auto-extract MIME from header
        if 'image/' in header:
            mime_type = header.split('data:')[1].split(';')[0]

    # 2. Decode
    image_bytes = base64.b64decode(base64_string)

    # 3. Save to file
    output_file = Path(output_path)
    output_file.parent.mkdir(parents=True, exist_ok=True)
    output_file.write_bytes(image_bytes)

    print(f"✅ Saved: {output_file}")
    print(f"   File size: {len(image_bytes):,} bytes")
    print(f"   MIME type: {mime_type}")

    return output_file


# Usage example:
# 1. Base64 string from API response
api_base64_response = "iVBORw0KGgoAAAANSUhEUgAA..."

# 2. Decode and save
base64_to_image(api_base64_response, 'output/captcha.png')

# 3. Optional: Further processing with PIL
try:
    from PIL import Image
    img = Image.open('output/captcha.png')
    print(f"Image dimensions: {img.size}")
    img.save('output/captcha.png', optimize=True)
except ImportError:
    print('Install Pillow for image processing: pip install Pillow')

Decode image binary stream using Java standard library Base64, with ImageIO / BufferedImage for metadata processing.

import java.io.*;
import java.util.Base64;
import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;

public class Base64ToImage {
    public static void main(String[] args) throws Exception {
        String base64String = "iVBORw0KGgoAAAANSUhEUgAA...";
        String mimeType = "image/png";

        // 1. Strip Data URL prefix if present
        if (base64String.startsWith("data:image")) {
            int commaIdx = base64String.indexOf(',');
            String header = base64String.substring(0, commaIdx);
            base64String = base64String.substring(commaIdx + 1);
            // Extract MIME from header
            if (header.contains("image/")) {
                mimeType = header.substring(header.indexOf("data:") + 5, header.indexOf(";"));
            }
        }

        // 2. Base64 decode
        byte[] imageBytes = Base64.getDecoder().decode(base64String);

        // 3. Save to file
        String extension = mimeType.substring("image/".length());
        File outputFile = new File("output." + extension);
        try (FileOutputStream fos = new FileOutputStream(outputFile)) {
            fos.write(imageBytes);
        }
        System.out.println("✅ Saved: " + outputFile.getAbsolutePath());
        System.out.println("   File size: " + imageBytes.length + " bytes");

        // 4. (Optional) Read image metadata
        ByteArrayInputStream bais = new ByteArrayInputStream(imageBytes);
        BufferedImage image = ImageIO.read(bais);
        if (image != null) {
            System.out.println("Image dimensions: " + image.getWidth() + "x" + image.getHeight());
        }
    }
}