# What does it mean “derivative of an image”?

I am reading a book about OpenCV, it speaks about some derivative of images like sobel. I am confused about image derivative! What is derived from? How can we derived from an image? I know we consider an image(1-channel) as a n*m matrix with 0 to 255 intensity numbers. How can we derive from this matrix?

A piece of text of the book:

One of the most basic and important convolutions is computing derivatives (or approximations to them). There are many ways to do this, but only a few are well suited to a given situation.

In general, the most common operator used to represent differentiation is the Sobel derivative operator. Sobel operators exist for any order of derivative as well as for mixed partial derivatives (e.g., ∂ 2 /∂x∂y).

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( 2018-06-09 09:36:43 -0600 )edit

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You can think an image as a function--f(x),which the x is the pixels and the f() is how the piexls are arranged on the image. And when we talk about the derivative of an image is actually find the most obvious change of the pixels intensity .

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Yes, but how does it work?

( 2018-06-11 03:16:54 -0600 )edit

Your question is off topics. It is not an opencv problem. An example in french is here

( 2018-06-11 03:25:34 -0600 )edit

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