This enumeration specifies types of blending of two images.

Values:

IG_BLEND_OVER	Blend the first image over the second image.
IG_BLEND_IN	Blend the first image into the second image.
IG_BLEND_HELD_OUT	The first image is held out by the second image.
IG_BLEND_LINEAR	The first and second images are combined in a linear fashion.