create 3D LUT


can someone help me how in fusion to create a 3D LUT that i could use in photoshop and in Vray. Vray supports loading 3d LUTs into the frame buffer. in fusion i created a color correction of my linear render and i would like to test my renders inside vray before going into fusion. vray supports only .cube LUT files. i think i am doing something wrong because the LUT makes everything black.