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Vray 1.1 Matte Comping Tag
This quick tutorial outlines a basic technique used to merge mesh and photograph, employing Vray's matte comping tag properties.
Pic A - The pre-rendered background image or photograph. This image is put into the Environmental Background slot with frontal mapping.
Pic B - The scene in wire frame. A simple set of balls with a plane object ground.
Pic C - The basic rendered scene. The lighting properties for this example were lifted directly from the original background image scene. No reflections, just basic shadow and GI. The ground has no material yet, just the VR Comp tag with all Matte Properties activated.
Pic D - All reflections now activated, but suffers the ground object reflecting the background image. You cant switch off reflections from any of the scene objects as that effects the rest of the scene. So, a barrier is needed to mask out the background environment.
Pic E - This image shows where a vertical plane has been inserted into the scene. It's positioned just behind the spheres. It only has a VR Comp tag assigned to it (no materials), with Cast Shadow and Generate GI switched off, and all Matte Properties switched on.
Pic F - When rendered, the lighting, GI and more importantly the reflections, are now all correct.
The background is correctly masked off, but still provides scene reflections. The Environmental Reflection channel can also be used to enhance scene reflection, as can spherical mesh sections.
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