In any project it is important to maintain a productive workflow that allows for tweaks and amends to a render without it being too time consuming. One of the most common is the use of render elements in V-Ray. A final render is made up of various layers that when composted together produce what is known as a beauty pass. By using render elements you can save out each layer as a separate image and then you can simply tweak a reflection, shadow, diffuse colour and even light intensity.
Use render elements to separate render layers
There are several core render elements that make up a common beauty pass. In Photoshop certain render elements are multiplied and others are added to complete the beauty pass:
VrayDiffuseFilter (Multiply) VrayRawLighting (Add)
VrayDiffuseFilter (Multiply) VRayRawGlobalIllumination
Set up render elements in Photoshop
When compositing your final render in Adobe Photoshop make sure your elements are saved as 16-bit at least so that no colour information is lost.
Use Material ID as a mask
One of the other most useful render elements is VRayMtlID. Once a material has been assigned unique ID, this render element will show an object as a block colour. This allows for simple mask selection in Photoshop. Depending on your workflow you may wish to have your mask anti-aliased, in which case it would be better to use a different render element such as VRayWireColor. This element will create block colour masks for each object according to their wire colour. However this will render all objects within the camera view. If you want to render a mask for a single object or a selection of objects it would be best to assign material ID’s and use VRayMtlID.
Exclude an object from the camera view
You can also exclude objects from a render. To do this, select the objects you do not wish to see in your final render and go to their object properties. Here you can un-tick visible to camera, if you marquee select all objects you wish to hide you can make them invisible in one click. You may wish to use this method when you need to re-render a particular object but to still have the lighting, reflection and shadow still affecting it. You can then overlay this render onto your existing render in Photoshop.
Faster feedback using active shade in V-Ray RT
One of the new features of V-Ray is V-Ray RT. It is an interactive renderer that uses progressive path tracing technology. The render starts at a very low quality and the longer you leave the render the cleaner the noise becomes as the quality improves. You do not need to worry about settings such as Irradiance map or light cache because in V-Ray RT these are not used. This allows for a much simpler rendering process and the results can be of a production level quality. One of the main speed advantages V-Ray RT has over the standard V-ray renderer is the ability to use GPU rendering. Rendering can be much faster on the GPU than it is on the CPU, this allows for almost real-time feedback in your scene.
There are added features within V-Ray RT one of which is the draw region tool which is available by right clicking in the active shade window. Similar to how draw region works on the standard V-Ray renderer. This allows you to draw a small region which is then re-calculated whilst the remainder of the scene stays the same. Particularly on much larger scene such as interiors the feedback from V-Ray RT can still be a little slow, the draw region tool allows you work much faster. V-Ray RT allows you to be more interactive when it comes to amending areas within your scene and you can get good results in very little time.
Use real zoom in the active shade window for amending small areas. This allows you to keep the same camera view and all render power goes to the selected region for much faster feedback.