Identifies the type of arithmetic operation (merge method) that is performed on the values of all intersecting pixels resulting from the merge.

For example, if you set IG_ARITH_ADD merge method, the resulting pixel values (of those pixels that intersected from the two images) equal the sum of the value of the pixel in the original image and the value of pixel in the image being merged.

Values:

IG_ARITH_ADD	Img1 = Img1 + Img2
IG_ARITH_ADD_SIGN_CENTERED	Img1 = Img1+ SC_Img2
IG_ARITH_AND	Img1 = Img1 & Img2
IG_ARITH_DIVIDE	Img1 = Img1 / Img2
IG_ARITH_MULTI	Img1 = Img1 * Img2
IG_ARITH_NOT	Img1 = ~Img1
IG_ARITH_OR	Img1 = Img1 | Img2
IG_ARITH_OVER	Img1 = Img2
IG_ARITH_SUB	Img1 = Img1 - Img2
IG_ARITH_XOR	Img1 = Img1 ^ Img2