run-length compressed bitmaps that are overlayed ontop of the
MPEG reconstructed video.
Applications include: Menus, sub-titles, karaoke, and simple animation.
Pixels are divided into four types:
1. background 2. Foregound 3. Empahsis-1 4. Emphasis-2
4 colors out of 16 color palette (4 colors are determined once per PGC).
4 out of 16 contrast values
up to a maximum of 32 sub-picture bitstreams. Each subpicture stream
could, for example, could contain text from a particular language.
subpicture buffer size is restricted to 62 Kbytes. This means
a maximum of 62 KB per GOP/cell. 32 Kbytes of this is control data.
Maximum number of bits per run-length coded line is 1440 bits.
Display area maximum: 720x480 (525/60) and 720x576 (625/50)
area, content, color, and contrast can be changed every video field
Sub-Picture Display Control Sequences (SP_DCSQ) control the
presentation of Sub-pictures.
Presentation effects include: scroll up/down, fade in/out, etc.
Structure of Sub-picture Decoding Unit (SPU):
[ SPUH ][ PXD ][ DCSQT ]
SPUH: Sub-picture Unit Header (size of SPU, start address of DCSQT)
PXD: Pixel Data (variable length run-length coded)
DCSQT: Display Control Sequence Table (one or more display control
DCSQT: [DCSQ 0][DCSQ 1][DCSQ 2] ... [DCSQ n]
DCSQ: [Start time] [ Pointer to next DCSQ] [Command Sequence]
Command Sequence: [DCC 0][DCC 1]... [DCC m]
Display Control Commands (DCC):
Set start address in PXD
Set SP screen position
Set CHG_COLCON areas.