Convert PGM to G3

The Portable Graymap (PGM) file extension, originating in the late 1980s as part of the Netpbm project, stands for "Portable Gray Map". It serves as a simple, versatile format for grayscale images, enabling easy reading and writing by various programs. Due to its straightforward structure and plain text encoding, it's often used in academic and research settings where ease of parsing and accessibility are crucial. PGM files store grayscale images in a compact, efficient manner, making them an essential tool for image processing tasks.

The G3 file extension refers to the CCITT Group 3 Fax Image, a standardized format developed by the Consultative Committee for International Telegraphy and Telephony (CCITT), now known as ITU-T. This format was created to efficiently compress black-and-white fax documents for transmission over telephone lines. It employs a method called Modified Huffman Coding for data compression, enabling reduced transmission time and bandwidth usage. G3 was widely adopted in the 1980s and 1990s as the primary standard for fax transmissions, ensuring compatibility across different fax machines and systems.