c# Send operators inside method paramers

You need to understand that an operator can be considered as syntactic sugar over the concept of method. For example, you are talking about binary operators; functionally, they are equivalent to a function accepting two arguments (each representing an operant) and returning the value. In your case, they return Boolean. Therefore, your arguments should be delegate instances. Say, for int operands, the delegate type is delegate bool Comparison(int left, int right).

But you don't need to do even that. You already have such declaration as generic type System.Func<int, int, bool>. Moreover, you can make your own class generic and use this generic delegate; this way, you can abstract from the types of your operands to be compared. First, let's consider the method of your non-generic class. It could be something like

using System;

// ...

public void ChangeColor(
        Func<int, int, bool> lessThen,
        Func<int, int, bool> greaterOrEqualThen /* ... */) {
   // ...
   if (lessThen != null) {
        if (lessThen(myPixel, 0))
            DoDomething();
        else
            DoSomethingElse();
    } else
        DoSomethingByDefault();                
   // ...
}

// ...

// Here is how you can call it:
ChangeColor(
   new Func<int, int, bool>((a, b) => { return a < b; }),
   new Func<int, int, bool>((a, b) => { return a >= b; }));

I understand that this syntax of call is not as simple as you wanted, but this is what you have.

To to it in generic way, you can have something like

using System;

// ...

class GraphicProcessing<OPERAND> {
    public void ChangeColor(
            Func<OPERAND, OPERAND, bool> lessThen,
            Func<OPERAND, OPERAND, bool> greaterOrEqualThen /* ... */) {
        OPERAND myPixel = //...
        OPERAND compareTo = //...
        // ...
        if (lessThen != null) {
            if (lessThen(myPixel, compareTo))
                DoDomething();
            else
                DoSomethingElse();
        } else
            DoSomethingByDefault();                
        // ...
    }
}

Also note that you are trying to use very slow API, GetPixel, prohibitively slow. If you mean to use System.Drawing, such things can be done efficiently using System.Drawing.Bitmap.LockBits:
Bitmap.LockBits Method (System.Drawing)[^].

You will find a very informative code sample on the MDSN help page on one of the LockBits methods referenced above.

—SA