This enumeration determines the color characteristic of the subtractive filter applied to the image data.

Values:

IG_TW_FT_BLACK	Black filter.
IG_TW_FT_BLUE	Blue filter.
IG_TW_FT_CYAN	Cyan filter.
IG_TW_FT_GREEN	Green filter.
IG_TW_FT_MAGENTA	Magenta filter.
IG_TW_FT_NONE	No filter.
IG_TW_FT_RED	Red filter.
IG_TW_FT_WHITE	White filter.
IG_TW_FT_YELLOW	Yellow filter.