Fake HDRI lighting using a ramp node in Maya

Using HRDI map is great for realistic lighting, but its difficult to get them for the desired lighting setup you would like in your scene, unless you wish to take HDRI photos every time you lighting digitally. There's many ways to fake HDRI, and here's a very common approach I use to fake out door HDRI lighting. It is flexible that you can't get by using photos.

Below is a digital model of Toyota yaris 2007, I'm going to use IBL node in Maya7 and Mental Ray's final gather to light it, this is what I get with the standard IBL(with white colour) + Final gather approach.

First of all car doesn't have reflections, and HDRI is all about reflection. If you look at the reference image below, the reflection of a car in day light in a city is made of a some trees, ground objects and a bright sky above. The sky is meet with the ground with a bright and sharp line, this is caused by highly dynamic lighting as the light shines through foliage or between houses and sips through gaps.

To mimic the above I setup a nurb sphere, with a ramp texture, for the ramp I need to have a dark region and a bright region, the dark part would represent ground objects, usually at half way point on the ramp, the bright part on the ramp would represent the sky. In the bright region of the ramp you must hit dynamic range with the "value"(in HSV), so for values above 1, here I have pushed it to 2. Also notice I have two white points on the ramp, the first is 1.4 and the next is 2, so to create a bit of fall off, from high dynamic range to lower dynamic range.

Also I have thrown in standard lights, without them FG is only an ambient lighting effect, and will look rather fake. Usually if you use standard lights be careful with specular, because mixing it with real reflections like this setup below, can look out of place and fake. Because specular highlights are fake reflections and we got real reflections already, you don't really need them. Below is a render with this setup.

its a fake ground and sky line, but here's a nice bit, you can add noise on the ramp to fake some what random objects or trees that makes the reflection line not so regular. Try adjusting the U wave, noise and noise frequency, but be careful is you a bit of noise the bottom colour will wrap to the top, so you may need to add bottom colour to be same as top most colour, to fix the seam.

And below is the render with noise and I have added two bounce cards, to give more reflection. Bounce cards are made of a plane and a surface shader with white colour. For the bounce cards I also push values above 1 to add more dynamic lighting.

In the above image you can also clearly see where the noise created a shape on the sphere that now reflected on the car.

~ by yinako on May 16, 2006.