Create a "mask" PNG file that has negative space (black) where there would normally be no tubes, and clear/transparent where you want the tubes to actually be. You could make softer or feathered edge to the black areas to make the whole thing look more rounded.

Make this the "top" layer.

If it needs to look more "pixelated".....on the layer/layers behind simply Scale them up till it looks "pixelated" enough.

Hope this helps.