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CD-Graphics
and CD TEXT
CDs can include CD-Graphics for karaoke
applications and CD-Text, for text information |
This is an extension to CD Audio (the Red Book) to include data for graphics and text. It
allows the addition of very simple CD-ROM like features to a normal CD
Audio disc.
The additional data is contained in the subcode channels R to W, which
provide only about 3% of the capacity of a normal CD-ROM, but do allow graphics and text
to be displayed while the music is being played. The available maximum data rate in the subcode channels R to W is 5.4 kB/s (cf
150kB/s for mode 1 CD-ROM).
CD-Graphics modes
The R to W data can be in any of the following
modes defined within the subcode channels. The table shows the
number of pixels per line, the number of lines and the number of colours.
| Mode |
Pixels |
Lines |
Colours |
| Line-graphics |
288 |
24 |
2 |
| TV-graphics (CD-G) |
288 |
192 |
16 |
| Extended-TV-graphics (CD-EG) |
288 |
192 |
256 |
One application of CD-G is for Karaoke and there are CD-G Karaoke versions of portable CD hifi audio
equipment available. They only need
a television set to see the graphics and text which are the song lyrics and the owner has
a portable self-contained Karaoke system.
CD-Graphics also defines two additional modes, MIDI and
User:
- MIDI mode provides a
3.125kb/s maximum data channel for the Musical Instrument Digital Interface (MIDI) data as
specified by the International MIDI Association.
- User mode is intended for
professional applications. The meaning of the data is application specific.
The R to W channels can also be used for CD TEXT.
CD TEXT
CD TEXT adds disc and
track related information to standard audio CDs for playback on suitably
equipped CD audio players. The CD TEXT information, coded as characters for maximum
efficiency, is contained in the R to W subcode channels in the lead-in and/or program area
of a CD.
- Lead-in
area: text information about the whole disc and individual tracks.
- Program
area: text information for the current track including track title, composer,
performers etc. The CD TEXT data is repeated throughout each track to reduce the delay in
retrieving the data.
CD TEXT is compatible with the ITTS (Interactive Text Transmission
System) standard.
Players
CD TEXT equipped players can provide a range of display formats from
one or two line, 20 character display to 21 lines of 40 colour
alphanumeric or graphics characters. The specification also allows for
future additional data such as JPEG coded images.
Some DVD players and new CD players support CD Text, usually with a
single-line scrolling display.
In-car players often support CD Text, particularly as they include text
displays for RDS station names.
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