📄 7_3_01.txt
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A.3 facsimile (Series T)
The process of scanning a document (page), converting the
image scanned into electrical signals for transmission to a remote
receiver and the conversion of the received signals to produce a
copy of the image originally scanned.
A.4 factor of cooperation (Recommendation T.1)
The product of the total scanning line length and the scanning
density.
A.5 flat-bed transmitter (Recommendation T.1)
Apparatus in which the original document is placed flat and
scanned line by line.
A.6 index of cooperation (Recommendations T.1, T.2, T.3)
Quotient of the factor of cooperation divided by the quan-
tity ~~. In the case of a drum apparatus, the index of cooperation
is also equal to the product of the drum diameter and the scanning
density.
A.7 judder, longitudinal (Recommendation T.1)
Effect due to the irregular rotation of the drum or helix
causing, on the reproduced picture, slight waviness or breaks in
lines that are regular on the original document.
A.8 judder, transverse (Recommendation T.1)
Effect due to irregularity of the scanning pitch resulting in
concurrent overlapping and underlapping in the reproduced picture.
A.9 lost time (Recommendation T.3)
The portion of the scanning line period which cannot be used
for picture signal transmission.
Note - In the case of drum apparatus, this is the same as the
dead sector scanning time.
A.10 nominal black (white) (Recommendation T.1)
Level or frequency of the signal corresponding to a pure black
(white).
A.11 pel (Series T)
A contraction of "picture element".
A.12 phasing (Recommendations T.1, T.2, T.3)
At the receiver, ensuring the exact coincidence of the mid-
point of the scanning field, with the corresponding point at the
transmitter so as to ensure the correct positioning of the picture
on the recording medium.
A.13 phasing signal (Recommendations T.1, T.2, T.3)
A signal sent by the transmitter for phasing purposes.
Note - Phasing is known as "phase white (black)" if the phas-
ing signal is a black (white) signal of which a short interruption
corresponding to the white (black) is sent during the lost time.
A.14 phototelegraphy (Recommendation T.1)
Method of reception of facsimile telegraphy which is chiefly
intended for the reproduction of graded tonal densities and in
which a photographic process is used at the receiver.
A.15 picture element (Recommendations T.3, T.4)
a) at transmission:
The part of the area of the original document which coincides
with the scanning spot at a given instant and which is of one
intensity only, with no distinction of the details that may be
included.
b) at reception:
The area of the finest detail that can be effectively
reproduced on the recording medium.
A.16 reproduction ratio (Recommendation T.1)
The ratio of the linear dimensions of the reproduced document
to the corresponding dimensions of the original document.
A.17 resolution (Series T)
A measure of the capability for delineating picture detail. In
Group 3 and Group 4 facsimile transmission resolution is expressed
as picture elements or pels per mm (horizontal resolution) and
lines per mm (vertical resolution).
A.18 scanning density (Recommendations T.1, T.2, T.3)
Number of scanning pitches per unit length.
A.19 scanning line (Recommendations T.1, T.2, T.3)
The area explored by the scanning spot in one sweep from one
side to the other of the scanning field.
A.20 scanning pitch (Recommendation T.1)
The distance between the corresponding edges of two consecu-
tive scanning lines.
A.21 skew (Recommendation T.3)
A defect in reproduction in which lines that should be at
right-angles to the scanning direction are inclined to it, owing to
a difference between the scanning speeds at transmission and recep-
tion.
A.22 synchronization (Recommendation T.1)
The establishment of equal scanning line frequencies at the
transmitter and receiver.
Recommendation T.1
STANDARDIZATION OF PHOTOTELEGRAPH APPARATUS
(former CCIT Recommendation D.1; amended at
New Delhi, 1960; Geneva, 1964; Mar del Plata, 1968;
Malaga-Torremolinos, 1984 and Melbourne, 1988)
The CCITT,
considering
that the transmission of pictures is possible only if certain
characteristics of the transmitting and receiving equipments are
identical,
unanimously declares the view
that phototelegraph apparatus and the associated modulating
and demodulating equipment should be constructed and employed
according to the following standards:
1 Scanning track
At the transmitting apparatus the message area should be
scanned in a "negative" direction. The orientation of the document
in relation to the scanning plane will depend upon its dimensions
and is of no consequence.
At the receiving apparatus scanning takes place in a "nega-
tive" direction for "positive" reception and in a "positive" direc-
tion for "negative" reception.
2 Index of cooperation
The normal index is 352 (corresponds to a factor of coopera-
tion of 1105).
The preferred alternative index, for use when less dense scan-
ning is required, or when the characteristics of circuits (and par-
ticularly combined radio and metallic circuits) so demand, is 264
(a factor of cooperation of 829). The admissible tolerances on the
above-mentioned values are _ | %.
3 Dimensions of apparatus
3.1 Apparatus with drum scanning
The most currently used drum diameters are 66, 70 and 88 mm.
The drum factor of the sending apparatus shall not be more
than 2.4.
The drum factor of the receiving apparatus shall not be less
than 2.4.
The width of the picture-retaining device (dead sector) may
not exceed 15 mm. An allowance of 3% of the total length of a scan-
ning line is also made for phasing. Thus, since the total cir-
cumference of a drum of the diameter of 66 mm is about 207 mm, the
usable circumference will be at least 186 mm.
3.2 Apparatus with flat-bed scanning
The total lengths of the most current scanning lines are 207,
220 and 276 mm of which 15 mm are not used for effective transmis-
sion, because of the possibility that the receiving station may use
a drum apparatus.
Before transmitting a picture to a receiving station using a
drum apparatus, it is necessary to ensure that the value of ratio:
otal length of a scanning line
____________________________________ x ~~
is less or at most equal to the drum factor of the receiver used.
3.3 Table 1/T.1 gives corresponding values of index of
cooperation M , factor of cooperation C , drum diameter D , total
length of scanning line L , scanning pitch P and scanning density F
for apparatus in most common use.
H.T. [T1.1]
TABLE 1/T.1
_________________________
Measured in the direction perpendicular to the scanning
line.
_________________________________________________________
M C D (mm) L (mm) P (mm) F (lines/mm)
_________________________________________________________
264 829 66 207 1/4.77 4.77
264 829 70 220 1/3.77 3.77
264 829 88 276 1/3.77 3.77
350 1099 70 220 1/5.77 5.77
352 1105 66 207 3/16 7 16/3
352 1105 88 276 1/4.77 4.77
_________________________________________________________
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