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. |