About

Data URLs embed binary image data directly into text using base64 encoding. The format data:image/gif;base64, followed by encoded bytes allows GIFs to exist within HTML, CSS, or JSON without external file references. This converter decodes that base64 payload back into a native GIF file. Incorrect decoding produces corrupted files that fail to render. The tool validates the GIF87a or GIF89a header signature before processing, extracts the Logical Screen Descriptor for width × height dimensions, and counts image descriptor blocks to estimate frame count for animations.

Processing occurs entirely client-side. No data leaves your browser. Base64 encoding increases file size by approximately 33% due to the 6-bit to 8-bit conversion ratio. A 100KB GIF becomes roughly 133KB when encoded. Reverse conversion restores the original binary exactly. Invalid base64 characters or truncated strings trigger validation errors before any Blob creation attempt.

Formulas

Base64 encoding converts every 3 bytes of binary data into 4 ASCII characters from a 64-character alphabet. The encoded size relates to original size by:

S_encoded = 4 × ceil(S_original3)

Where S_encoded is the base64 string length in characters and S_original is the binary file size in bytes. Padding characters (=) are appended when the input length is not divisible by 3.

GIF dimensions are stored in the Logical Screen Descriptor as 16-bit little-endian unsigned integers:

width = byte₆ + (byte₇ × 256)

height = byte₈ + (byte₉ × 256)

Frame count estimation scans for image descriptor bytes (0x2C) throughout the file. Each occurrence marks the start of a new frame in an animated GIF sequence.

Reference Data

Property	GIF87a	GIF89a	Notes
Magic Bytes	47 49 46 38 37 61	47 49 46 38 39 61	ASCII: "GIF87a" / "GIF89a"
Max Width	65,535px	65,535px	16-bit unsigned integer
Max Height	65,535px	65,535px	16-bit unsigned integer
Color Depth	1 - 8bits	1 - 8bits	Max 256 colors per frame
Animation	No	Yes	Uses Graphic Control Extension
Transparency	No	Yes	Single color key transparency
Interlacing	Yes	Yes	4-pass Adam7-like scheme
Image Descriptor	0x2C	0x2C	Marks frame start
Extension Block	N/A	0x21	Comments, delays, disposal
Trailer Byte	0x3B	0x3B	End of file marker
Compression	LZW	LZW	Lempel-Ziv-Welch algorithm
Min Code Size	2bits	2bits	For 2-4 color images
Max Code Size	12bits	12bits	LZW dictionary limit
Frame Delay	N/A	0 - 65,535	In centiseconds (10ms units)
Loop Count	N/A	0 - 65,535	0 = infinite loop
Base64 Overhead	~33%		6-bit encoding adds padding
MIME Type	image/gif		Required in data URL
Data URL Prefix	data:image/gif;base64,		Standard format

Frequently Asked Questions

Corruption typically occurs from truncated base64 strings or invalid characters. Valid base64 uses only A-Z, a-z, 0-9, +, /, and = for padding. Line breaks or whitespace within the encoded portion cause parsing failures. Ensure the data URL is complete and unmodified from its source. The converter validates the GIF header bytes (GIF87a or GIF89a) before processing.

Browser limits vary. Chrome supports approximately 2MB in data URLs. Firefox handles larger strings but performance degrades. For GIFs exceeding 1MB encoded, consider direct file transfer instead. The converter processes data entirely in memory using Uint8Array buffers, so available RAM is the practical limit.

In browser DevTools (F12), inspect the image element. Check the src attribute for inline data URLs. For CSS backgrounds, examine computed styles for background-image. Copy the entire string starting from data:image/gif;base64, through the final character. Some developers use build tools that inline small GIFs automatically.

Yes. Base64 encoding is lossless and reversible. The decoded binary is byte-for-byte identical to the original GIF file. All frames, delays, disposal methods, and loop counts remain intact. The converter simply reverses the encoding without modifying pixel data or animation metadata.

Frame detection counts image descriptor blocks (0x2C bytes) in the file. Some GIFs store all animation data in a single frame using disposal methods and transparent overlays. The reported count reflects structural image descriptors, not necessarily visual frames. True animated GIFs using GIF89a extensions will show accurate frame counts.