writing a compressed texture that's loaded in memory to disk

test.cs

using System.IO;

using UnityEditor;

using UnityEngine;

public class test : EditorWindow
{

    [MenuItem("CONTEXT/Material/Rip Texture")]
    static void GetTexture(MenuCommand command)
    {
        Material m = command.context as Material;
        Texture x = m.GetTexture("_TextureName");
        Texture2D y = x as Texture2D;
        Texture2D tex = new Texture2D(x.width, x.height, TextureFormat.ARGB32, false);
        RenderTexture a = RenderTexture.GetTemporary(x.width, x.height, 0, RenderTextureFormat.ARGB32);
        Graphics.Blit(y, a);
        RenderTexture.active = a;
        tex.ReadPixels(new Rect(0, 0, x.width, x.height), 0, 0);
        byte[] bytes = tex.EncodeToPNG();
        File.WriteAllBytes(Application.dataPath + "/tex.png", bytes);
        RenderTexture.ReleaseTemporary(a);
    }
}