This page provides a step-by-step tutorial on using Render Channels in your projects.
In this tutorial we’ll go over how to output Render Channels for flexibility to improve your workflow.
To follow this tutorial, you will need to have the V-Ray for Revit plugin installed.
This tutorial page is a companion that goes with the QuickStart video posted on our YouTube channel and is available here:
To download the files used in this tutorial, please click on the button below.
Open the Example Scene
Open the channels.rvt project, which you can download through the link above. In this tutorial, Revit 2017 is being used, however, you will be able to use this project with Revit versions 2015 and up.
With the project loaded, go into the V-Ray tab, and click the Settings icon to load a few settings.
Select Sharing and click on Load Settings.
Choose the file channels.xml from the downloaded assets and click Open.
Click Import Selected to import the settings into the file.
If some of your geometry shows up as Fuchsia, then click on Settings and then click Paths. From the Path Settings choose Add and then browse to the location of the VRayRevit_QS11_Channels folder on your machine.
Prepping the Example Scene
Change the Current View to Render. Leave Quality to Medium and set Resolution to Crop Region with Printer set to a DPI of 300.
Click Settings and click Fog for the Fog Settings.
Turn on Aerial Perspective and set the View Distance to 8000m. The interface will automatically convert 8000 meters to whatever units you are using.
Now click on Engine for the Engine Settings.
Change the Image Sampler from Progressive to Buckets. You can do it just for the Medium setting, but we will do all of them here just for fun.
Click Channels for the Render Channel Settings.
Go ahead and turn on all the render channels available. These include Diffuse, Global Illumination, Lighting, Reflection, Refraction, Self Illumination, Specular, Sample Rate, Background, Atmosphere, Normals, Bump Normals, and DR Buckets.
Rendering in Channels will not impact the render time very much, but the flexibility you gain for editing the image after the fact is substantial.
In the Render Channel Settings, enable the Denoiser Channel. This channel is essentially a post-processing effect that reduces noise in renders.
Leave the Mode to Generate Denoise Channel as opposed to Replace RGB Channel to see the difference between the original raw render and the denoised result. The Radius Preset allows you set how much denoising you want, though you can also enter more specific values as well. Turn on Use GPU if you have a powerful video card to make the process a bit faster.
Now Enable the ZDepth Channel. This generates a grayscale image that gives a brightness value in the render, that shows the distance a surface is away from the camera. This is useful for a number of compositing effects such as depth of field or adjusting the look of the atmosphere.
Set the White point of the ZDepth to be at 12 ft from the camera, and the Black point at 26 ft. These values are in project units, so if you are in feet these numbers represent feet. If you are set to meters, these will represent 12m and 26m respectively. We are working in feet in this project.
Close the Settings window. We are going to enable Swarm to make the rendering faster. Enable Swarm if you have it installed and setup, otherwise you can leave this off; you do not need to have Swarm enabled for Render Channels to work.
After the render resolves, the Denoiser pass kicks in as you can see in the Progress window
The render is complete!
Primary Render Channels
Now, let’s go over the different Channels we just output. In the upper left of the VFB is the Channel List. Selecting a channel here displays its result in the VFB.
Some Render Channels are advanced workflows for a lot of control in the composite, so let’s go over the primary channels, that when properly combined in image editing (like Photoshop or After Effects) re-assemble into the final RGB render, often called the Beauty.
RGB Color Channel
RGB Color is your final render, also known as the beauty.
The Alpha Channel is a grey-scale matte that shows where solid surfaces are in the scene as white. We can see here through the window to the sky, so that part is black in the Alpha Channel, denoting transparency, or empty space.
The Diffuse channel is the flat color of the project, devoid of any lighting or other surface properties, such as reflections.
Global Illumination Channel
The Global Illumination channel is the lighting contribution from bounced/indirect light in the scene.
The Lighting channel is the contribution from the direct lighting in the project, which in this case is the sun.
The Reflection channel isolates the reflections rendered into the surfaces per their material settings.
The Refraction channel shows parts of the image that are shown through refractive objects such as glass; in this case, the windows and the table.
The Self-Illumination channel shows objects that have illuminated materials. Here, our lamp shades’ material was set to emit some illumination, so they show up in this channel.
The Specular channel shows the reflection of highlights in the scene from light sources, which again, is the sun in this project. This adds the gloss, for example, to the leather seat.
The Background is the direct line of sight to the background of the project, which is the blue sky in this example.
The Atmosphere channel stores any Aerial Perspective or Environment Fog you added to the scene. For us, it’s the Aerial Perspective that we enabled.
You can save out these channels as their own images, through the VFB’s Save icon.
All the Channels listed above, when composited together properly, will get you back to the RGB color render. But this workflow gives you huge latitude to adjust any component along the way, like if you wanted to increase or tint the reflections in the floor, without re-rendering the entire project.
DR Buckets Channel
If you had Swarm enabled, the DR Buckets channel will show you which machine rendered what part of the image, which is great for troubleshooting if needed.
Z Depth Channel
The Z Depth channel shows the relative distance surfaces are from the camera using the values we specified earlier. Just as we specified earlier, white values are those that are 12 feet from the camera and closer, while black values are those that are 26 feet away and further. This pass is helpful for certain compositing filters to add depth of field blur, for example, to the final image as desired.
The Denoise channel is what V-Ray generates after removing noise and cleaning up renders. This avoids prolonged render times from very high Quality values. The channels below it in teh channel list drop-down menu in the VFB help V-Ray to properly denoise the image. When you click on the Denoiser channel, you essentially get a new RGB channel, but with less noise than the original RGB pass.
The images below show a close up view of the glass table to show the difference that denoiser makes in this render. Compared to the RGB Channel image on the left, you can easily see the grain in the image. Looking at the denoiser Channel image on the right, all that grainy noise is removed
Compare the results of this painting. The painting has a bump map applied to give it a textured look. The denoiser softens the bump map slightly when removing noise from this area.
The more noise the image has before the denoiser pass runs, the more detail could potentially be removed by the denoiser pass. Therefore, if you use a lower quality setting in the Quality setting, you may lose some texture data.
Zoom in and move around your image and switch between the RGB and Denoiser channels to compare how the Denoiser cleaned up your image.
Using Render Channels and image editing after a render gives you great control over your final output.