AmigaOS 3.9 came with SYS:Prefs/PictDT. With it, you could explicitly set which application supports the V43 mode of the datatype. This mode offers support for screens with more than 256 colors. In addition, you can specify whether pictures should be dithered on high color screens (65,536 colors) or not. Disabling dithering decreases image quality on these screens, but improves the speed of the datatype considerably.
In AmigaOS 3.1.4 the ENV variable
Classes/DataTypes/picture/ForceV43
holds a list of all programs that should be forced to v43 mode. In particular, this list should contain the string
« IPrefs »
including the double angle brackets to avoid dithering on the Workbench. If you leave the environment variable empty, it means that there is a list of programs to be promoted, and this list is empty. If the environment variable does not exist, however, the known well-working Os components receive full truecolor images. So it is easiest just to delete
ENVARC:Classes/DataTypes/picture/ForceV43.
Dithering of the picture.datatype can be set or unset by the ENV variable
Classes/DataTypes/picture/DitherHiColour
which can hold either a 0 or 1 value (0 = OFF and 1 = ON).
