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.
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.