CCITT draft recommendation T.4 (RFC0804)
Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2019-Feb-14
Internet Society Requests For Comment (RFCs)
This is the CCITT standard for group 3 facsimile encoding. This is useful for data compression of bit map data.
CCITT Draft Recommendation T.4
As Defined In: CCITT STUDY GROUP XIV, CONTRIBUTION No.25-E
SOURCE: DRAFTING GROUP ON DRAFT RECOMMENDATION T.4 TITLE: DRAFT RECOMMENDATION T.4 - STANDARDIZATION OF GROUP 3 FACSIMILE APPARATUS FOR DOCUMENT TRANSMISSION (as amended and agreed by Working Party XIV/2)
Draft Recommendation T.4
STANDARDIZATION OF GROUP 3 FACSIMILE APPARATUS FOR DOCUMENT TRANSMISSION
The CCITT, considering
a. that Recommendation T.2 refers to Group 1 type apparatus for ISO A4 document transmission over a telephone-type circuit in approximately six minutes; b. that Recommendation T.3 refers to Group 2 type apparatus for ISO A4 document transmission over a telephone-type circuit in approximately three minutes: c. that there is a demand for Group 3 apparatus which enables an ISO A4 document to be transmitted over a telephone-type circuit in approximately one minute; d. that for a large number of applications black and white reproduction is sufficient; e. that such a service may be requested either alternatively with telephone conversation, or when either or both stations are not attended; in both cases, the facsimile operation will follow Recommendation T.30,
(unanimously) declares the view that Group 3 facsimile apparatus for use on the general switched telephone network and international leased circuits should be designed and operated according to the following standards:
1. Scanning track
The message area should be scanned in the same direction in the transmitter and receiver. Viewing the message area in a vertical plane, the scanning direction should be from left to right and subsequent scans should be adjacent and below the previous scan.
2. Dimensions of apparatus
CCITT Draft Recommendation T.4 PAGE 2
The following dimensions should be used:
a. A normal definition standard and an optional higher definition standard of 3.85 and 7.7 line/mm respectively in vertical direction; b. 1728 black and white picture elements along the scanned line; c. A scanning line length of 215 mm. Other scanning line lengths may be employed in which case the scanning density should be changed to maintain the correct picture proportions; d. Input documents up to a minimum of ISO A4 size should be accepted.
3. Transmission time per scanning line
A total scanning line is defined as the sum of DATA bits plus any required FILL bits plus the EOL bits. The minimum transmission times of the total scanning line should conform to the following:
a. 20 milliseconds recommended standard with an optional fall-back to the 40 milliseconds option; b. 10 milliseconds recognized option with a mandatory fall-back to the 20 milliseconds standard; c. 5 milliseconds recognized option with a mandatory fall-back to the 10 milliseconds option and the 20 milliseconds standard; d. 40 milliseconds recognized option.
The identification and choice of this minimum transmission time is to be made in the pre-message (Phase B) portion of the T.30 control procedure. The maximum transm...