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.