Discussion on "Push" theory and "reverse lookup" theory in permutation law

This article has referred to "ignorant Zhai" and "hoodlum" teacher wrote the relevant information.

There are two ways to explain the substitution rule (I call it a theory here). One is called "push", and one is called "reverse lookup", which is not contradictory.

I used the "push" theory in the previous post to explain. Because the "reverse lookup" theory to explain, more abstract, the use of language is more difficult to express.

Explain some of the rules of substitution, sometimes using the "reverse lookup" theory, but better understanding.

What do you mean by "push" theory?

1. Pixels in the original selection (without a selection, the whole picture is a selection) of the displaced are proportional to the pixels in the permutation channel (red, green).

2. For each pixel in the original selection, it will be in the horizontal direction and vertical direction (according to the corresponding gray-scale values in the replacement channel), according to the replacement principle, the replacement.

3. According to the permutation principle, if the pixel on the original artwork should move 100 pixels horizontally to the left. Then the pixel will be moved 100 pixels to the left. The vertical direction is similar.

This is the so-called "push" theory.

What is the "reverse lookup" theory? It's going to cost a lot of breath! Don't worry, listen to me slowly! (Please don't worry too!) ）

1. Pixels in the original selection (without a selection, the whole picture is a selection) of the displaced are proportional to the pixels in the permutation channel (red, green).

2. For each pixel in the original selection, it will be in the horizontal direction and vertical direction (according to the corresponding gray-scale values in the replacement channel), according to the replacement principle, the replacement.

3. According to the permutation principle, if the pixel on the original artwork should move 100 pixels horizontally to the left. According to the "reverse lookup" theory, it performs the following procedure:

4. Select the pixel on the original image, copy horizontally to the right (this is the "reverse lookup" meaning) the pixel in the 100 pixel position, then paste it back (this is the meaning of "permutation").

This is like using the "harnesses rod" harnesses, from the right side of the Ma Geo pull back. The length of the harnesses rod is equal to the gray-scale value -128]* permutation ratio of the pixel (corresponding pixel in the permutation channel) of the original image being displaced. Positive, vertical up, horizontal to left, negative to vertical, horizontal to right.

It's kind of like grabbing the right pixel back with your right hand. Leprous and harnesses the same method of calculation.

The horizontal direction is the same, and the vertical direction is similar.

5. As for horizontal displacement, vertical displacement, the sequence is not related.

The theory of "push" and "reverse lookup" are different in the description of permutation process, but the expression of permutation result is the same. For some phenomena, "push" theory can not be explained, but the "reverse lookup" theory could be explained. It is obvious that the "reverse lookup" theory is more applicable. For the better understanding of the replacement principle of friends, it is advisable to use the "reverse lookup" theory to observe the replacement of the law. For beginners, you might as well try both theories.