# Grey-Scale Connectivity

Regardless of how the image was segmented, the same technique is used to connect pixels into blobs.

A blob is defined as a group of connected object pixels, where an object pixel is any pixel with a nonzero weight. The Blob tool defines object connectivity in terms of 8-connectedness; that is, all object pixels bordering a given pixel's edges, as well as those touching its corners, are considered to be connected to that pixel.

Because object pixels are 8-connected, background pixels are 4-connected; that is, background pixels are not considered to be connected diagonally. The following figure illustrates 4-way and 8-way connectivity.

Defining connectivity in this way has appealing topological properties, as demonstrated in the following figure. If you interpret object pixels (black) as 8-connected, they are considered to be a single blob. If they were 4-connected, there would be eight blobs, because diagonally adjacent pixels would not be considered connected.

Interpreting the object pixels in as a single 8-connected blob is more useful than interpreting them as eight 4-connected blobs.

All features in the image, whether they are blobs or holes, are stored in their own RLE images. These images can then be used for other purposes.