This enumeration determines the algorithm used to improve the quality of the image.
Values:
| IG_TW_IF_AUTO | Auto. |
| IG_TW_IF_BANDPASS | Bandpass algorithm. Good for improving text. |
| IG_TW_IF_FINELINE | Fineline algorithm. |
| IG_TW_IF_HIGHPASS | Highpass algorithm. Good for improving fine lines. |
| IG_TW_IF_LOWPASS | Lowpass algorithm. Good for halftone images. |
| IG_TW_IF_NONE | No algorithm |
| IG_TW_IF_TEXT | Text algorithm. |