Now that the scene is prepared and the basic lighting parameters are set, we will finally start to work the the HDR image. The first thing we need to do is assign our HDRI to the GI Environment and Reflection/Refraction Environment Override slots:

Turn on both the GI Environment override, and the Reflection/refraction Environment override. Click on None in the map slot for the GI Environment and select VRayHDRI as the map type. Drag an instance of this map to the Reflection/refraction map slot beneath it. Now, in order for us to be able to manipulate this map, we will need an instance of it in the Material Editor. Drag from one of these two map slots to an empty material slot in the material editor. Click on the Browse button for your new map, and navigate to the HDR image that you would like to use. Now you will see a thumbnail of your HDRI map, as well as a number of new parameters to work with.

The first thing you will need to do if using the Rectilinear/Spherical style HDRI map employed by HDR Mill is to select the Spherical environment map type. The next item to address is the Gamma setting. Depending on the method of image capture, some images will look fine at the default 1.0 gamma setting, while others will look dark and oversaturated. If your image appears incorrect, then its gamma has not been pre-adjusted for viewing on monitors. The setting of 2.2 is the typical correction used for viewing these images in monitor color space.

Now, if you do a quick test render you will see that your model is nicely lit, but that the background is still your default Max environment color. We could simply drag an instance of the HDR image from the material editor into the Environment Map slot of the Environment dialog. However, in order for the background map to look decent, you would need to use a very large hdr image. This would consume a large amount of your computer's resources, and slow down the rendering process. Instead, we can use a larger low dynamic range (ldr) image such as a .jpeg to fill this slot. This ldr image will usually be a tonemapped version of the hdr image, but with higher resolution.

Go to your Rendering>Environment dialog and click on "None" in the map slot. Choose Bitmap map type and navigate to the regular image that matches the scene in your hdr image. Then, drag an instance of this map from the Environment map slot to another empty material slot in your Material Editor (select "instance" when prompted). In this new material's Coordinates rollout, make sure and select Environ mapping, and Spherical Environment type.

Now, if you are using an hdr and ldr of the same scene, you would expect the two respective thumbnails to match. They do not, so go into the Parameters rollout for your VRayHDRI map and enter a horizontal rotation of 90 degrees. This rotation amount works nine times out of ten, however, if it does not, you may have to experiment a little.