How Does Quick Selection Tool in Photoshop Works?

Now the question is that how does it work? How does it automatically detect edges?

If I go to the proper explanation, I need to write the whole mathematical algorithm here. I am certainly not going to do that. Instead I can explain it in simpler words. What Quick Selection Tool does is that it measures the contrast among the adjacent pixels. If there’s a huge change in value, it’ll know by itself that an edge is present out there.

4 - Day 10: What is Quick Selection Tool in Photoshop

Fig. 4

Let’s understand this with the help of Fig. 4. Suppose I am dragging my cursor from the baby’s right hand towards his left hand. I am making sure that my cursor doesn’t cross the baby’s body. While I am dragging my mouse, Photoshop, in the background, calculating the difference in the RGB values of the nearby pixels. If there’s a huge jump, Photoshop knows that there’s an edge present out there. For example the RGB values of skin color is quite different than the RGB values of the white background.

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Suggest one tutorial that I MUST write.

Here Ya Go!
Give it a try at least.