I have such image:

It is a binary image, I mean the pixel value is 0 or 1, but now, I hope to replace every pixel value with its distance from self to the image edges(edge can be one of the top edge, bottom edge, left edge or right edge), but I don’t care the distance is shortest or not. Such as the following red pixel, which have two or more paths to image edges. We can use any distance to replace its pixel value.

When the pixel have no any path to the image edge, I will replace the pixel value with -1. Is there any efficient method can implement this target? Sorry for no try but just a question. It seem it is hard to me. Can anyone give me some advice to do it?