mix two images
mixedImage=eimgmix(image1,image2[,fraction[,offset]])
image1 :
first RGB-image-matrix
image2 :
second RGB-image-matrix
fraction :
scalar, mixing fraction of image2, (0<=fraction<=1)
or vector 1x3, mixing fractions of RGB-Channels
or matrix with size of image2, mixing fraction for each pixel
default:fraction=0.5
offset :
vector [x y], position of NW-Corner of image2, default [0 0]
mixedImage :
mixed RGB-image-matrix