When you've done it correctly, this is what Photoshop will come up with. You can uncheck the green ticks and view the results. Because we've been building a synthetic HDRI, the results from unchecking can be a little strange, but don't mind: it will definitely work. Finally, click OK and Photoshop will build the HDRI for you, that you should save as a radiance document.



Next, load the HDRI in your 3D-app of choose. In Cinema 4D, the best place in a material would be the Luminance channel.

As you can see, our simple window casts quite a lot of interesting reflections. This render is far from perfect and needs more that it has now but I wanted to keep it simple and plain. With the use of extra lights, the results could be improved but I've made my point: It's possible to make your own HDRI from scratch. It goes without saying that you could draw anything that suits your needs.

Happy rendering!