IFF-DEEP (or DEEP) is a raster image and animation format, originally associated with the TVPaint and XiPaint applications. It supports various "truecolor" formats. It uses the IFF metaformat.
It should not be confused with truecolor ILBM images, which are also sometimes called "deep", and also use IFF.
DEEP files begin with bytes
'F' 'O' 'R' 'M' ?? ?? ?? ?? 'D' 'E' 'E' 'P'.
- DEEP IFF Chunky Pixel Image, from the AmigaOS Documentation Wiki