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This example shows how the use of a GI material affects the rendering.

 As

you can see, the This simple interior scene represents a square-type room. There are window openings in one of the wall. There is a Direct Light coming through, which simulates the Sun. The floor has a texture in the Diffuse map slot. All the rest - the walls, the ceiling and the teapots have a Default VRayMtl with a Diffuse Color (200, 200, 200).room lit by two rectangle VRayLights - one hidden top light and another back fill light - as well as by three disc VRayLights for the pendant lamps above the sinks.

A wooden VRayMtl from the Chaos Cosmos library is applied on the floor, and a default VRayMtl with Diffuse color (128, 128, 128) is applied on the rest of the scene objects, except for the glass objects (mirror and pendant lamp plafonds).

In the first image, it is visible that all walls, objects, and the ceiling are On the first render, it is absolutely visible that all the walls, the ceiling, and the teapots have been rendered in some light brown (pale pumpkin) color, although they have despite having a light-gray material assigned to them. This is because of due to the Color Bleeding, which is generated by the GI calculations.

On In the second pictureimage, the scene is rendered with a VRayOverride a VRayOverride GI material assigned material assigned to the Floor.This material floor. The VRayOverrideMtl contains in itself the initial 2 two V-Ray materials - the floor's and the walls' ones. So now assigned on the floor object, : the wooden VRayMtl as base and the default VRayMtl as GI material. The rest of the scene objects keep the default gray VRayMtl. So now V-Ray knows that while calculating the GI it the GI it has to use the GI material the GI material (in our this case:  walls - VRayMtl with Diffuse Color (200, 200, 200)) VRayMtl with Diffuse color (128, 128, 128) and during rendering it uses the Base material the Base material (in our this case:  floor - VRayMtl with texture in the Diffuse Slotthe wooden VRayMtl). The  The result of that is quite different from the previous render as the Color Bleeding has is gone. Of  Of course this depends entirely on our your choice for the GI material. For instance, if we you had chosen a bluish colored material, the final result would also be tinted slightly to blue, like in the first render with the pale brown colors.

In this simple scene, the result of the second render can be produced, with a pre-saved irradiance map, calculated with just the walls' material assigned to all the geometry.

For a much more complex scene, with lots of different geometry, shaders, textures, etc., using the VRayOverride material can be very helpful.

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Now each of the chairs has a different material assigned in their VRayOverride Reflect material. The first one has a green diffuse color, the second one has black, the third one has blue, the fourth - purple, and the fifth has a red diffuse color. V-Ray uses those materials when the objects are seen in reflections. In our this scene, the environment is actually a reflective surface, so the chairs are being reflected. On the other hand, you can also notice that the base material of the chairs is also reflective, and the fourth chair is seen with its Override Reflect material in the middle chair.

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