Editing CD+G (section)

== Design ==
The CD+G format takes advantage of the six [[Compact Disc subcode]] channels R through W (which are unused in standard [[Compact Disc Digital Audio]]), to provide 6 extra bits in CD+G for graphics information per 24 bytes of audio data. When a disc is read at normal speed, these six channels provide only 28.8 [[Bit rate|kbit/s]] for graphics, which is enough to provide primitive visuals but which is dwarfed by modern bitrates (for comparison see {{Section link|bit rate|Video}}).<ref name="jbum" />{{efn|The document does contain a number of errors, later discovered.}}

In the CD+G system, 16-color (4-bit) [[raster graphics]] are constructed using [[tiled rendering]] with 6×12 [[pixel]] tiles (6 pixels wide and 12 lines high). These tiles are typically font definitions for text (such as for karaoke or info about the music). But the tiles can be used in any manner that tile rending permits, such as for fragments which combine together to represent a picture, or simply for patterns to decorate the background. These tiles are displayed in the main central 288×192 pixel area which is surrounded by a 1-tile thick border (for a total raster field of 300×216 pixels). The 16 colors are defined in a [[Palette (computing)|color table]], which can be manipulated to change the color scheme and simulate primitive animations.

=== Instruction set ===
The main [[Machine code|instructions]] for manipulating graphics are:
* Memory Preset: Set the screen to a particular color.
* Border Preset: Set the border of the screen to a particular color.
* Tile Block (Normal): Load a 12×6 tile, 2 color tile and display it normally.
* [[Scrolling|Scroll]] Preset: Scroll the image, filling in the new area with a color.
* Scroll Copy: Scroll the image, rotating the bits back around.
* Define Transparent Color: Define a specific color as being transparent.
* Load Color Table (entries 0–7): Load in the lower 8 entries of the color table.
* Load Color Table (entries 8–15): Load in the upper 8 entries of the color table.
* Tile Block ([[Exclusive or|XOR]]): Load a 12×6 tile, 2 color tile and display it using the XOR method.