Specifies the dropout type.

Values:

IG_ISIS_DROPOUT_NONE	No dropout.
IG_ISIS_DROPOUT_RED	Red dropout.
IG_ISIS_DROPOUT_GREEN	Green dropout.
IG_ISIS_DROPOUT_BLUE	Blue dropout.
IG_ISIS_DROPOUT_CUSTOM	Custom dropout.
IG_ISIS_DROPOUT_GREY_CCD	Used in HP Tulip driver.
IG_ISIS_DROPOUT_NTSC	Used in HP Tulip driver.