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CCITT Group 4 Fax Image (.g4)

The G4 file extension signifies a CCITT Group 4 Fax Image, a format endorsed by the International Telecommunication Union (ITU) for encoding and transmitting bitonal images, consisting of two colors, typically black and white. This format utilizes a lossless compression technique to ensure the integrity of the original image data, which is paramount for legal documents and archival needs. Known as Modified Modified READ (MMR), this advanced compression method surpasses the previous Group 3 standard, focusing on the efficient compression of text and line art. This makes it ideal for fax machines compliant with the ITU-T T.6 standard.

The G4 algorithm compresses images by interpreting them as sequences of black lines against a white backdrop, encoding patterns and redundancies more succinctly. In contrast to the one-dimensional approach of Group 3, Group 4 employs a two-dimensional coding strategy, leveraging both horizontal and vertical patterns to attain superior compression rates. This is especially beneficial for documents with ample white space and uniform text, which is common in fax communications. Consequently, G4 compression can realize compression ratios of up to 20:1, markedly diminishing file sizes and the time required to transmit fax documents.

G4 Specifications

Name CCITT Group 4 Fax Image
File Extension(s) .g4
Category Raster Images
Use For Encoding bitonal images for fax transmissions, which ensures efficient data compression without compromising quality.
Developer International Telegraph and Telephone Consultative Committee (CCITT); now known as ITU-T.
MIME Type(s) image/g4fax
License N/A
File Sample(s) N/A
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