The filters we learned in the previous section use only one input source. There are other GEM pixel effects that combine two images together. The logic is similar to the layer option in Photoshop layers. They are the pix_add, pix_subtract, pix_multiply, and pix_diff objects.
The following first example uses the pix_add effect that combines two images together according to their pixels' color values:
Note that the object requires two input images. The patch has two gemhead objects. Each gemhead will use a pix_image object to load its image. In the end, there is only one pix_texture object to map the resulting image to the rectangle. The pix_add object adds the color pixel values of the two images, with result clamped between 0 and 1. The pix_subtract object subtracts the color pixel value of one image by the others. The pix_multiply object multiplies the color pixel value of the two images. The pix_diff object computes the absolute value of the color pixel value difference...
