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One of the great things about lighting with Twilight is the versatility and diversity of the options available. As well as the Physical Sun and Sky system and the ability to mimic artificial light sources using some very specific light types, we also have the option to use image- based, or HDRI, lighting if we want to. The initials HDRI stands for High Dynamic Range Image. This is a specialized image format that holds a far higher amount of data, including luminance data, than can be captured by a typical film or digital camera in a single shot.
In this video, we are going to walk you through the steps required to set up image-based lighting in Twilight. Our start scene is once again in complete darkness, so we will be building our scene lighting from scratch. To do this, our first port of call needs to be Twilight's Light Editor, so let's come up to the Twilight toolbar and click on the icon to open that. Straight away we are taken into our Sun/Sky tab, which is exactly where we want to be, because we want to access the options for our Sky type. Which of these we choose to work with will depend very much on what type of HDRI we have available to us.
If we have, as I will be working with, a full 360-degree map, then the Spherical Sky option is the one we are going to want to pick. Of course HDRIs do come in Hemispherical or even Light Probe formats, Light Probe often being referred to as mirror ball HDRIs. If we have one of those, then we just need to choose the appropriate option, but as we say, we are going to be working with Spherical Sky. Once that is set, we of course need to load our HDRI into our environment, so let's click on the Browse button for the Background Image option.
Now, of course, as with IES files, there are lots of sites around the Internet that offer free high-quality images that can even be freely used in commercial work. I am using a renamed image from the free sIBL set entitled BasketballCourt, downloaded from HDRLabs.com. You of course will need to supply your own HDRI. With the image loaded in, we can now work with our Sky Rotation Angle. This control allows us to rotate our HDRI environment around our scene geometry.
This means we can set our scene lighting to suit and then use SketchUp Shadow settings to match the sunlight in our scene. After performing a number of tests with this image, I know that I want to set my Rotation Angle to something around about 90 degrees. Of course at this point we could go and enable our Sunlight options, but typically, when working with an image-based lighting setup, we will want to take a render with just our HDRI in situ. This means we can try and get a sense of where any directional light in the image may be coming from and again, we can use SketchUp Shadows settings to match things up.
So let's go and do just that. Let's open up the Render dialog. I want to render in this instance with the Easy 07 preset. Even though this is a high quality setting, because of the simplicity of our scene, we should still get fast renders back. With that set then, let's take a test render. And in just 34 seconds we have a very nice representation of the scene render. You can most certainly see the coloration that is coming from our High Dynamic Range Image that is being pulled into our scene lighting, and you can hopefully just make out the directional shadows that are occurring in the scene.
So get a rough idea of how we want to position our sunlight. We can do that of course using SketchUp Shadows options. So let's come up to our View menu, into the Toolbars, and let's turn on the Shadows controls. The first thing you will probably want to do is enable those in the viewport, just so you can see how things are working. Again, because I have performed a number of tests, I know exactly what settings I want to use here, so I am going to set my time of day to around about 16:00 p.m., and we are going to set our month to September and indeed choose the 1st of September.
As you can see in the SketchUp viewport, this places our shadows pretty much where we want them. Of course we still need to enable the Sunlight options in our Twilight controls, but before we go and do that, just a word of caution: make certain that you turn this Sunlight setting off in the SketchUp viewport; otherwise, you will find your Twilight user interface becoming very slow to respond. In fact, because we are finished with these controls, we can just go and turn them off and close down our dialog. Jumping back then into Twilight's Light Editor, we can go and enable our three Sunlight options.
I will want to make a quick change to the softness of the shadows in the scene. I want to sharpen them up just a little bit from the default, so I am going to set my slider to a value of 30. As I also want to reduce the harshness of the sunlight in the scene, I am going to set my Maximum Sun Intensity to a value of 2.5. And with that done, we can once again go and take a render. What we see now is a very nice, very natural-looking daytime lighting setup. Now, you may be thinking that this looks very similar to our earlier Physical Sun and Sky setup, but if you were to make a very close examination, you would find that an IBL setup has subtle variations that don't exist in the Physical Sun and Sky system, subtle variations in color, particularly in the shadowed areas, even subtle variations in the illumination levels.
You will have noticed of course that at this moment in time we are rendering our HDRI as the background of our render. If this is how we want things, then that is absolutely fine. My preferred method would at this point be to render out an alpha mask of our scene geometry and then add my back plate in a compositing or image editing application. That just means we have a little more control over our foreground and background elements, but as I say, that is just a personal preference. To really finish off our image-based lighting setup, we would probably at this point want to switch over to one of our progressive render presets, such as Easy 09.
That would really maximize the subtleties of light and color that are coming from our High Dynamic Range Image. Hopefully though, you would agree, based on the results that we have so far that image-based lighting is yet another powerful lighting option that is available to us in the Twilight Render engine.
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