Dynapik offers a free online tool to change image types - no need to download anything. It's quick and easy to use. You can change your PNG8 images to FAX format. This tool works for both professionals and casual users. Convert your images to FAX in seconds.
PNG-8 (8-bit Indexed)
The lightweight champion for simple graphics, offering GIF-like sizes with PNG quality.
PNG-8 is a specific variant of the PNG format that uses an 8-bit indexed color palette, limiting the image to a maximum of 256 colors. This is the same color technique used by GIF, but PNG-8 uses the superior DEFLATE compression algorithm, resulting in files that are typically even smaller than GIFs. PNG-8 is the secret weapon of web optimization. For logos, icons, and simple illustrations that don't need millions of colors, converting a standard 24-bit PNG to PNG-8 can reduce file size by 60-80% with virtually no visual difference. It supports transparency, usually in binary form (like GIF), though some modern tools can create PNG-8 files with full alpha transparency.
In a PNG-8 file, each pixel is represented by a single byte (8 bits) which acts as an index into a palette (PLTE chunk) of up to 256 RGB colors. This is much more efficient than storing the full 3-byte RGB value for every pixel. Transparency in PNG-8 is typically handled by the `tRNS` chunk, which specifies a single color index as transparent (binary transparency). However, the PNG specification allows the `tRNS` chunk to contain alpha values for palette entries, enabling semi-transparency. Tools like `pngquant` exploit this to create 'Alpha PNG-8' files that have both small size and smooth transparency, though very old browsers (IE6) struggled with this.
PNG-8 has been part of the PNG specification since version 1.0 (1996). It was designed to replace GIF, offering better compression and being patent-free. However, due to Internet Explorer 6's poor support for alpha transparency in PNGs, PNG-8 (with binary transparency) was often used as a fallback for years. Today, with modern tools like TinyPNG and pngquant, PNG-8 has seen a resurgence as an optimization target, allowing developers to serve crisp graphics at tiny file sizes.
Group 3 FAX
The raw compressed data stream used by classic fax machines.
When we talk about the 'FAX' file format, we typically refer to a raw data stream compressed using the CCITT Group 3 (G3) or Group 4 (G4) algorithms. These are specialized compression methods designed for bi-level (black and white) images of text documents. In most modern contexts, you won't see a standalone `.fax` or `.g3` file. Instead, this compression data is wrapped inside a container like TIFF or PDF. A `.fax` file is essentially a headerless chunk of this compressed data, which makes it difficult for modern software to open without knowing the specific dimensions (width/height) beforehand.
Group 3 compression is based on Huffman coding and Run-Length Encoding (RLE). It scans a line of pixels and records the lengths of alternating runs of black and white pixels. Because most documents are largely white space, this results in significant compression. Group 4 is an improvement that uses 2D compression (referencing the previous line to predict the next), offering better ratios but requiring an error-free transmission channel (like a digital network), unlike G3 which had to survive noisy phone lines.
Standardized by the CCITT (Consultative Committee for International Telephony and Telegraphy), now ITU-T, in 1980 (Group 3) and 1984 (Group 4). These standards enabled the global fax boom of the 80s and 90s.
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