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 FAX images to PAM format. This tool works for both professionals and casual users. Convert your images to PAM in seconds.
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.
Portable Arbitrary Map
The 'universal' bitmap format of the Netpbm toolkit.
PAM (Portable Arbitrary Map) is the newest and most flexible member of the Netpbm format family (which includes PBM, PGM, and PPM). While earlier formats were strictly strictly black/white, grayscale, or RGB, PAM was designed to be generic. It can handle images with any number of channels, including transparency (alpha) channels, which the older formats lacked.
A PAM file starts with a text header defining width, height, maximum component value (depth), and 'TUPLTYPE' (describing what the channels mean, e.g., 'RGB_ALPHA' or 'CMYK'). The data follows as a raw binary stream of tuples. It unifies the parsing logic: instead of writing separate parsers for PBM/PGM/PPM, a program can just implement a PAM parser to handle everything.
Introduced with the Netpbm library updates to solve the 'Alpha Channel Problem'. The older formats (PPM) had no standard way to store transparency, leading to hacky non-standard extensions. PAM standardized this by allowing arbitrary tuple types.
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