Question 1

Why use Base64 for images?

Accepted Answer

Base64-encoded images can be embedded directly in HTML, CSS, or JSON without hosting the image as a separate file. This eliminates one HTTP request per image and is particularly valuable in HTML email where external image hosting may be blocked.

Question 2

Does Base64 increase file size?

Accepted Answer

Yes, Base64 encoding increases the raw string size by approximately 33% compared to the binary image file. For this reason, Base64 embedding is most appropriate for small images like icons, logos, and decorative elements under 10 KB.

Question 3

What is the difference between the data URL and the raw Base64 string?

Accepted Answer

The data URL includes the MIME type prefix (e.g., data:image/png;base64,) followed by the Base64 data. The raw Base64 string is just the encoded data without that prefix. Use the full data URL in HTML src attributes and CSS url() values; use the raw string when an API expects Base64-only input.

Question 4

Is there a file size limit?

Accepted Answer

There is no server-side limit since all encoding happens in your browser. The practical limit depends on your browser's available memory. Images up to 10 MB encode reliably on modern devices. Very large images may slow down or crash the browser tab.

Question 5

Which image formats are supported?

Accepted Answer

Any format your browser can load: PNG, JPG, WEBP, GIF, SVG, BMP, and ICO are all supported. The MIME type is detected automatically from the file and included in the data URL prefix (e.g., data:image/png;base64,).

Question 6

Can I use the Base64 output in CSS?

Accepted Answer

Yes. Use the full data URL as the value of a CSS background-image property: background-image: url("data:image/png;base64,..."). This technique is useful for small decorative images and icons to eliminate extra HTTP requests, especially in critical CSS.

Question 7

Can I use the Base64 output in a JSON API?

Accepted Answer

Yes. Copy the raw Base64 string (without the data URL prefix) to use as the value of an image field in a JSON payload. Many APIs that accept image data expect Base64 without the MIME prefix — check your API documentation to confirm which format is required.

Question 8

What happens to transparency in the Base64 output?

Accepted Answer

Transparency is fully preserved in the Base64 output when the source is a PNG or WEBP with an alpha channel. The MIME type in the data URL prefix (data:image/png;base64,) tells the browser to render it with transparency intact.

画像をBase64に変換