1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 4 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%2-).!,G0G0%15)0-%.4G0G0!.$G0G002/4/#/,3G0G0 Annex C, data syntax II. Rec. V.21: 300 bits per second duplex modem standardized for use in the general switched telephonenetwork. ISO 9281: Information processi
2、ng Identification of picture coding methods.4 Presentation functionalities4.1 This section describes a set of presentation functionalities. This set of functionalities is intended as a repertoire ofpresentation functionalities for telewriting in general. For a specific application a subset may be de
3、fined.4.2 In the description of presentation functionalities, the concept of TRACE is being used. A trace is a curve of anarbitrary shape, starting from a defined position, being completed incrementally and ending at a defined position.Handwritten information is considered to consist of traces.4.3 R
4、epresentation of the handwritten information is accomplished by the sequential reconstruction of the individualtraces. This implies that the effect of movement is retained during each reproduction.4.4 Telewriting information is to be displayed on the display area of some output device. The display a
5、rea isconsidered to be a two-dimensional surface.4.5 The display area is subdivided into an image area and a border area; see Figure 1-1/T.150.4.6 The border area surrounds the image area. External form and dimensions of the border area are not specified. Thepresence of a border area is not mandator
6、y. It is however inevitable in certain implementations.4.7 The image area is rectangular. The two shorter edges of the image area have a vertical orientation, the two longeredges have a horizontal orientation. The length ratio of shorter and longer edges is 3:4.Fascicle VII.5 - Rec. T.150 74.8 The p
7、osition of telewriting information on the display area is defined with respect to the edges of the image area.4.9 Information on the display area is composed of presentation elements of three categories: foreground, background, border area.4.10 Foreground and background presentation elements are def
8、ined in the image area only.Border area presentation elements are defined in the border area only. The use of the border area is not definedfor telewriting.4.11 Foreground presentation elements include trace, marker and closed area.4.12 The presentation elements have the following characteristics: T
9、race: This is the curve as defined in 2.6 of this part; the essence of the handwritten information isrepresented by one trace or by any combination of traces; the image area can contain an undefined number oftraces at a time. Marker: This is a marked representation of a single position; it behaves a
10、s if it is overlaid on the foreground;a moving marker does not create a trace; a marker can be switched on and off; one user can generate onlyone marker at a time. The image area can contain one locally generated marker and one remotely generatedmarker. Closed area: This is the area that is enclosed
11、 within a closed trace; this closed trace is the perimeter. A traceis a closed trace if it intersects itself; a trace that is nearly closed can be converted into a closed trace, by theaddition of the lacking part of the trace. Background: The background is a defined reference area on which foregroun
12、d information is to be imaged; ifthe full image area is filled with foreground information, the background is not visible. Border area : The border area is independent of the information in the image area.In case of a CRT display the border area is the remaining part between image area and edges of
13、the displayarea.In case of a cell-structured display device, the image area may coincide exactly with the display area. In thatcase no border area remains.4.13 The various presentation elements can have attributes assigned to them as defined in Table 1-1/T.150.TABLE 1-1/T.150Attributes of telewritin
14、g presentation elementsPresentation element AttributesTraceMarkerClosed areaBackgroundBorder areaLine thickness, line texture, colourShape, size, colourArea texture, colour (interaction or area attributes withbackground attributes to be defined)Area texture, colourNot definedNote The concept of colo
15、ur includes “intensity”.8 Fascicle VII.5 - Rec. T.1504.14 Once an image is displayed, subsequent modification of attributes is restricted as follows: trace: attributes unchangeable; marker: attributes can be changed at any instant; closed area: attributes unchangeable; background: attributes can be
16、changed at any instant.4.15 In case of intersection of two traces, the image of the older trace is interrupted as far as it coincides with thenewer trace.4.16 In case of intersection of a trace and a marker, the image of the trace is interrupted as far as it coincides with themarker. After removal o
17、f the marker, the image of the original trace is restored.4.17 With respect to erasure of foreground information, a distinction is made regarding the area in which erasure takesplace: full image area; defined part of the image area; individual traces.4.18 Erasure of the full image areaAll foreground
18、 information in the image area is removed; the background assumes a pre-defined appearance.4.19 Erasure of a defined part of the image areaAn area is identified either by means of a closed trace or as a defined square, within which all foregroundinformation is to be removed including the perimeter i
19、tself.4.20 Erasure of individual tracesAn existing trace is covered by a thicker trace with the same attributes as the background: this type of erasure isprocessed in the same way as a trace.4.21 Any modification of background information can take place for the full image area only.5 Principles of t
20、elewriting coding5.1 Telewriting coding relates to coding of telewriting information in foreground and background and to erasurefunctions.5.2 This section contains principles of telewriting coding. In Parts 3 and 4, details of telewriting coding are definedfor two methods, namely zone coding and dif
21、ferential chain coding, respectively.5.3 The coding is defined at the “telewriting coding interface”, TCI. This interface is introduced for ease ofreference, but need not exist physically.5.4 In the sending part of the telewriting terminal, the signal at the TCI contains all data originating from ha
22、ndwritteninput, selection of attributes and use of erasure functions.5.5 The signals at the TCI, both in sending and receiving parts, do not contain data pertaining to transmission orcommunication functions.5.6 In the receiving part of the telewriting terminal, the signal at the TCI contains all dat
23、a required to image theinformation in accordance with the intentions of the originator.Fascicle VII.5 - Rec. T.150 95.7 The concept of the TCI is illustrated in Figure 1-2/T.150.5.8 The signal at the TCI includes x and y coordinate information regarding telewriting presentation elements.5.9 The x an
24、d y coordinates are related to a unit area of 1 1. This implies that the respective values of x and yalways lie between 0 and 1 (0 included, 1 not included).5.10 The origin of the coordinate system is in the lower left corner. The x-axis is horizontal, the y-axis is vertical.5.11 The horizontal size
25、 of the telewriting image area corresponds with x = 1, the vertical size of this image areacorresponds with y = 0.75. See Figure 1-3/T.150.5.12 All coordinates of the telewriting information are quantized relative to a measurement grid in the unit area. Theresolution of this grid determines the accu
26、racy.5.13 The default resolution is 512 512 grid units. The telewriting coding can optionally also accommodate gridresolutions of 1024 1024 and 2048 2048 grid units.10 Fascicle VII.5 - Rec. T.150Part 2 - Telewriting together with telephony1 General1.1 This part of the Recommendation defines the use
27、of telewriting in combination with voice communicationthrough a telephone network (PSTN).1.2 For this application, both sides of the connection must have a combined telephone and telewriting terminal.1.3 The combined telephone and telewriting terminal should, as long as the telewriting transmission
28、function isswitched off, behave like a normal telephone set, both for incoming and outgoing calls. In this situation, the fullbandwidth is available for transmission of speech signals.1.4 During a telephone conversation, the telewriting transmission function at either side of the connection, may bes
29、witched on and off, manually or automatically.1.5 Remark that in this part of the Recommendation “switching on and off” of the telewriting function refers to thetelewriting transmission functions. Regardless of this, the telewriting equipment may be used locally, whether or not atelephone connection
30、 exists.1.6 By means of the telewriting terminal, the user can generate information. This includes: creation of traces, markerswitching on and off, movement of the marker, use of erasure functions.1.7 In this part, distinction is made between “basic terminal” and “enhanced terminal”.1.8 The enhanced
31、 terminal is not defined yet, but compared to the basic terminal it is anticipated to have additionalcapabilities regarding unattended operation, transmission facilities and presentation functionalities.2 Main characteristics of the basic terminal2.1 In this section, a basic terminal is defined.In t
32、he basic terminal a set of functions is implemented that is to be considered as a minimum requirement; thus abasic level of compatibility is defined.2.2 A basic terminal includes a telephone apparatus, a writing device and a display device. Circuitry to implementcontrol functions may be accommodated
33、 in a separate unit or may be included in one of the devices mentioned.2.3 Information generated at either side of the connection will be reproduced on the display devices at both sides ofthe connection.2.4 Both sides of the connection can contribute, one after another, to the same image.2.5 In the
34、basic terminal, transmission of telewriting signals is accomplished through a sub-channel, segregated fromthe speech channel. Transmission of speech signals and telewriting signals can take place simultaneously.2.6 Half-duplex transmission is used for conveying the telewriting signals through the su
35、b-channel, i.e. thetransmitter is prevented from sending as long as the associated receiver receives telewriting signals from the other side.2.7 The total power level of speech plus telewriting signals should conform to the limits normally applicable tospeech transmission and data transmission.2.8 T
36、he basic terminal can assume three modes of operation. The characteristics pertinent to each mode, aredescribed in Table 2-1/T.150.Fascicle VII.5 - Rec. T.150 11TABLE 2-1/T.150Modes of operation of the basic terminalSpeech only The telewriting function remains in the OFF condition.Speech plus telewr
37、iting The telewriting function can be switched ON after the establishmentof a connection. Speech signals and telewriting signals can be sentsimultaneously.Telewriting only This mode can be switched ON after the establishment of aconnection. The sending of speech signals is blocked, the power levelof
38、 the telewriting signals is increased correspondingly. Reception ofspeech signals is still possible.2.9 In this Recommendation, the expression “telewriting ON” is used as a common indication for either “speech plustelewriting” or “telewriting only”.2.10 A basic terminal may be able to continue trans
39、mission and reception of telewriting signals after termination ofthe human conversation. In this case, the telewriting transmission function will be switched OFF automatically aftercompletion of the telewriting transmission. (Defined in more detail later on.)2.11 For the coding of telewriting inform
40、ation, two methods are recognized for use at the sending side: tone coding(defined in Part 3) and differential chain coding (defined in Part 4).At the receiving side, the basic terminal should be able to properly accept telewriting signals coded according toeither method.3 Presentation functionaliti
41、es of the basic terminal3.1 The general description of presentation functionalities, as given in Part 1, 4, applies.With respect to this general description certain restrictions apply, as defined in the following points.3.2 The presentation functionalities as described for the basic terminal are to
42、be regarded as default capabilities.If required, characteristics of terminals with a higher level of sophistication will be described in a section onenhanced terminal.3.3 The basic terminal employs a monochrome display device. The writing device generates coded representations ofmonochrome images on
43、ly.3.4 The attributes applying to the basic terminal are given in Table 2-2/T.150.12 Fascicle VII.5 - Rec. T.150TABLE 2-2/T.150Attributes applying to the basic terminalPresentation elements AttributesImage sizeTraceHorizontal: 512 GUVertical: 0.75 512 GUOptions, the receiver must be able to accept:H
44、orizontal: 1024 and 2048 GUVertical: 0.75 1024 and0.75 2048 GU. thickness texture colourClosed areaUnit thickness, as used in the output device.Options: 2 and 3 unit thickness.Solid, no options.Monochrome, as used in the output device. The receiver must be able to accept thecodes of traces with colo
45、urs: red, green, blue, yellow, magenta, cyan, white, black.A black trace has the same colour as the background (used for erasure). texture colourBackgroundSolid.Same as background colour (used only for partial erasure). The receiver must beable to accept the codes of closed areas with colours: red,
46、green, blue, yellow,magenta, cyan, white, black. texture/colourNo information about the background is transmitted. Background can only beimagined as dark screen. This corresponds with colour black.Border areaMarkerBorder area is not specified, no information about the border area is transmitted. sha
47、pe sizePLUS sign; other shapes may be possible depending on terminal implementation.Not specified. colourMarker colour is not transmitted; on a monochrome device the marker appears inforeground colour; on a colour device the marker may assume a colour underlocal control.Full erasurePartial erasureBl
48、ack background is restored.1) closed area;2) overwriting with thicker black trace.GU Grid units4 Transmission for the basic terminal4.1 Transmission of the modulated telewriting signal takes place in a small frequency band, segregated from thespeech channel. This band is referred to as the sub-chann
49、el.4.2 The centre of the sub-channel is located at 1750 Hz. Details of the implementation are not given here, but therequirements of 4.6 and 4.7 should be met.Fascicle VII.5 - Rec. T.150 134.3 The binary telewriting signal is converted into a signal suitable for transmission, by means of frequency shiftmodulation. Details are the same as those specified in Recommendation V.21 for channel 2 (the high channel).4.4 The modulation rate is 300 Bd, the bit rate is 300 bit/s.4.5 The V.21 requirements for channel 2 are summarized as follows: The
