LWRP OnRenderImage

Hello, I wanted to test out LWRP. I have an effect i like that uses OnRenderImage but that doesnt get called when using LWRP. Does anyone know how I can achieve the same thing without OnRenderIamge?

using UnityEngine;

[ExecuteInEditMode]
public class SimpleBlit : MonoBehaviour
{
    public Material TransitionMaterial;

    void OnRenderImage(RenderTexture src, RenderTexture dst)
    {
		if (TransitionMaterial != null)
		{
			Graphics.Blit(src, dst, TransitionMaterial);
		}
    }
}

I solved it myself by implementing something like this Writing Custom Effects · Unity-Technologies/PostProcessing Wiki · GitHub. I did need to create my own material parameter, and then i used

context.command.Blit(context.source, context.destination, settings.mat);