GammaCorrectionNode.cs

using System.Reflection;
using UnityEditor.ShaderGraph;

[Title("Custom", "Gamma Correction Node")]
public class GammaCorrectionNode : CodeFunctionNode
{
    public GammaCorrectionNode()
    {
        name = "Gamma Correction";
    }
    
    protected override MethodInfo GetFunctionToConvert()
    {
        return GetType().GetMethod("GammaCorrectionFunction",
            BindingFlags.Static | BindingFlags.NonPublic);
    }

    static string GammaCorrectionFunction([Slot(0, Binding.None)] DynamicDimensionVector A,
        [Slot(1, Binding.None)] Vector1 gamma,
        [Slot(2, Binding.None)]  out DynamicDimensionVector Out)
    {
        return @" { 
                    Out = pow(A,(1.0 / gamma));
                  }";
    }
}