Photoshop repeat edge pixel and retrace filter detailed

Many friends do not understand "repeat edge pixels" and "retrace" in the "Undefined region" option in the Photoshop replacement filter. Below I do a more detailed diagram to analyze and explain, for friends to refer to.

Description

Duplicate edge pixels are an option that is part of the set undefined area. It is related only to undefined regions (areas outside the selection).

Notice the meaning of "edge" in "repeat edge pixels" while observing.

I'm making a horizontally moving displacement map size 40*40. In addition, three 40*40 sizes were produced for demonstration purposes.

There are two ways to explain the substitution rule. One is called "push", and one is called "reverse lookup", which is not contradictory.

I explained it in the previous post with the "push" method. Because the "reverse lookup", the method to explain, more abstract, the use of language more difficult to express.

With the "Reverse lookup" method, the replacement of some of the rules, it is easier to understand the explanation.

The two are not contradictory, I now understand. Whether it is right or not, awaits further study.