How to do UV paint on the reverse side

I am new in Blender. I importing a TGA file in the UV image editor an it looks fine. The only problem is that it is showing the painting in the external side of the cylinder I am using, but I want to project this painting in the inner side of the cylinder. How can I paint in the interior of 3d figures?

I just did this by recalcultaing the Normals inside. Select the cylinder and in Edit mode, if I’m correct, press Ctrl+Shift+N.

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