Editing Apple Display Card 8•24 (section)

== Interlaced video and NTSC ==
The card produces RS-170-A interlaced video. It uses Apple Convolution, which averages each line with the lines above and below in a 1:2:1 ratio to stop thin horizontal lines flickering; convolution works up to 8 bits per pixel and switches off in 24-bit mode.<ref name="til5205" /><ref name="til5860">Apple Computer, "Display Card 8/24: RS-170 External Sync", Tech Info Library article 5860 (TA44002), last reviewed 5 July 1990, file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: the 8•24 and 8•24 GC not accepting external sync; production cards meeting RS-170-A; interlaced output black and white without a converter.</ref> For an overscanning monitor, such as a television, the card can be switched to an overscan mode of 512 × 384 so that the whole image stays visible.<ref name="til5205" /> No software switch is involved: a correctly wired cable puts the card into its interlaced mode. The interlaced signal is black and white unless an RGB-to-NTSC converter such as the RasterOps Video Expander or Truevision VIDI/O Box is used, and the card does not accept external sync.<ref name="til5859">Apple Computer, "Macintosh Display Card 8/24: NTSC Video Encoding", Tech Info Library article 5859 (TA43998), file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: no software switch to NTSC interlaced mode, a configured cable being all that is needed; colour NTSC needing an RGB-to-NTSC converter such as the RasterOps Video Expander or Truevision VIDI/O Box, which accept the cards' RS-170-A output; convolution only to 8 bits.</ref><ref name="til5860" />