Попробуйте это
private void SaveImage(Texture t, string path)
{
RenderTexture rt = new RenderTexture(t.width, t.height, 0);
Graphics.Blit(t, rt);
Texture2D t2d = new Texture2D(rt.width, rt.height, TextureFormat.RGB24, false);
t2d.ReadPixels(new Rect(0, 0, rt.width, rt.height), 0, 0);
File.WriteAllBytes(path, t2d.EncodeToPNG());
}
Использование
SaveImage(yourQuad.GetComponent<MeshRenderer>().material.mainTexture, "yourSavePath.png");