Render Series
Introduction to AOVs in Octane
Version 2.0, Updated September 2024 using Octane 2024.1 and Cinema 4D 2025.0
About this Guide
This guide serves as an introduction to the AOV (Render Pass) system in Octane. It has been fully rewritten to account for recent changes in Octane 2024 and Cinema 4D 2025.
Part I gives an overview of what AOVs are and why we might want to use them. There’s also a quick overview of how Octane treats them. This is valid for any DCC, not just C4D.
Part II is a dive into Octane’s AOV settings as they exist in Cinema 4D. The concepts should apply to other DCCs like Blender, Maya, etc., but the location of the settings will probably vary pretty wildly from DCC to DCC
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- PDF Version of this guide can be found here
Part I: AOV Overview
When we go to render an image with all settings at default, we end up with a flat image for each frame. If we picked a format meant to be displayed on the web or sent in an email like a PNG or JPEG, we have a little flexibility when it comes to altering it in an image or video editor. We can change some of the colors to some extent, or make it a little brighter or more contrasty. If we rendered out 16- or 32-bit TIF or EXR files, we have a bit more flexibility because we have more data to work with, but we’re still limited to mostly color grading, contrast/levels, and a few other adjustments to the overall image as a whole.
After doing the basic edits, we export our final PNGs or MP4s to be displayed somewhere. This workflow is fine if we’re happy with the results of our render and don’t need to do much more than some basic edits.
What if we want to do some serious alterations to the final image though? Let’s say our render is only a small piece in a bigger scene that has video footage, other image data, text, or other elements and we want to adjust only some aspects of the render to better combine it with all that. What if we just want to take down the intensity of one light, or color grade one particular material, or completely remove the reflections that we now see are pretty overpowering once we’re in the edit?
This is where the AOV (or render pass) system comes into play.
When we render using AOVs, rather than getting one flat image per frame, we end up with either a series of images that each contain a certain isolated property of the render, or we get a single multi-layered file (EXR, PSD, TIF), that has each of those isolated properties on a different layer.
A file or layer that contains a particular isolated property of an overall render is referred to as either an AOV (arbitrary output variable) or a render pass (or simply “a pass”). These terms are used interchangeably in the industry, with pass usually being a little more common.
Our AOVs can either be edited directly in Octane, or exported (typically as EXRs) to be further edited and/or recombined in another external app like Photoshop, After Effects, Affinity Photo, Resolve, Nuke, or any other of the myriad of still and video compositors out there.
Render Passes (AOVs)
The final composited output from Octane is called a Beauty render. There are two paths to get to the beauty render, each involving breaking it up into different stacks of passes. Typically we choose one path or the other, but we can mix and match if needed.
The Beauty Pass stack breaks the render into the contribution of each material property. When combined with the Post Processing pass (bloom/glare/stuff like that), these form the beauty pass.
The Lighting Pass stack breaks the render into the contribution of each light source. Each light can be on its own pass, or we can make custom groupings. The scene above has 3 area lights, each on their own pass, an HDRI which shows in the Ambient Light pass, and one emissive material. Emitters always show in Light Pass 1 in Octane. When combined with the Post pass, these also form the beauty pass.
There are also various masking, data, and utility passes that don’t contribute to the beauty render directly. We can use these to see information about our render, mask out parts of it, drive effects in external compositing software, or sometimes composite them back into the render for interesting looks. These are often referred to as Info Passes.
Color Spaces
You didn’t think we’d get through a guide without talking about this, right?
Don’t worry, we’ll be quick here… the thing to remember is that choosing the right color space is extremely important when dealing with AOVs. Most of the time we want to use a high bit depth file saved in a linear color space so we have the maximum amount of data and flexibility when editing in post. Usually this means either Linear sRGB (not regular ol’ sRGB), or ACES, or some other wide gamut OCIO color space, and saving our files as 16- or 32-bit EXR. More on that whole thing in the color spaces overview and color management for Octane guides.
Recombining AOVs
Merging standard AOV stacks (lighting or beauty) is an additive process. This means we start with black, and then each pass adds some sort of contribution to the beauty render. So when we think of it that way, the Add blend mode starts to make sense, which is what we need to set all our AOVs to.
The naming for this can get a little confusing though. The Linear Dodge and Add blend modes work the same way when the layer is 100% opaque (which is usually the case when we’re recombining passes). Some apps only have Add like Affinity, some only have Linear Dodge like Photoshop (though it has Add in parens), and some have both Linear Dodge and Add separately like After Effects. Both do what we want, so we just need to pick the one the software has. If we start to mess with layer opacity or fill, there is a difference between the two.
There are other, more advanced techniques where we use other blend modes like Multiply if we’re doing a shadow or ambient occlusion pass, but we’ll go into those in another guide.
One of the nice things about an additive process is that the layer order in the post app doesn’t matter. As long as we have a full stack of beauty or lighting passes, they can be in whatever order makes sense to us and it will still look the same.
The other thing to think about when exporting passes is whether to use a single, layered file for all the passes, or separate files for each pass. Both have advantages and disadvantages and are treated differently depending on the post app of choice and particular workflow. There’s no right answer here, so it’ll probably take some trial and error to see which one tends to work best.
AOVs in Octane
Octane actually has two AOV systems.
Render AOV System
The first one is the Render AOV system which we can think of as “basic mode”.
This is what we just went over in the last section - it breaks the render up into beauty passes, lighting passes, info passes, or some combination of those.
Render AOVs can be exported directly as individual files or layers in multi-layer files so they can be edited and composited in an external app like Photoshop, After Effects, Resolve, Affinity Photo, or the like. The external compositor is responsible for recombining the frame(s) for final delivery.
Output AOV System
The second one is the Output AOV system which uses Octane’s built-in compositor.
After we specify a bunch of Render AOVs, they can then be fed back into a different node structure within Octane that allows us to further edit them. This system contains a number of editing/compositing AOVs like color correction/image editing, external textures, and other things that aren’t derived from the Render AOVs themselves.
We can then either export final composited files from Octane for delivery, or stacks of edited AOVs for an external compositing program to further mess with.
Part II: The AOV System in Octane for C4D
C4D Render Settings
Octane’s AOV management is almost entirely handled in C4D’s render settings (not Octane’s settings). We can get to those by hitting the little clapboard icon with the gear in the upper right corner of the UI, or Control-B (Win) / Command-B (Mac) on the keyboard.
The first thing to do is be sure we choose Octane Renderer from the Renderer dropdown. This reveals the Octane Renderer section on the left. When we select this, we’ll see four tabs across the top on the right.
The Render AOV group tab contains settings for the Render AOV system, as well as file export settings. There’s also a section toward the bottom twirled up by default called Render AOVs. If we twirl that down, we can add and remove render AOVs.
There’s also a button that launches the Render AOV manager popup window which makes this a lot easier. We can see a list of available AOVs on the left, and also quickly load in standard preset stacks for both lighting and beauty passes without having to dig through and add each one individually which is nice. In fact, we can go a step further and make our own presets if we’re working with a particular set on a lot of different projects. This also allows us to quickly move AOVs around in the stack and delete them.
Important: There’s an option here called Enable. This must, must, MUST be checked if we want to use Render AOVs at all. If we’re ever in a situation where we can’t view or export Render AOVs, it’s because we forgot to do this.
The AOV groups tab is where we manage the Output AOV system. Output AOVs get complicated really fast, so really the best place to deal with them is the node editor, which there’s a button for. When we open the node editor we see both the Render AOVs if we have any and the Output AOVs.
Important: These two systems are not directly compatible. For example, we can’t take a Diffuse Render AOV and run it into an Output AOV group - we need to use a special Render AOV node made for the Output AOV system instead. We’ll look at this in depth later, but it’s good to know right from the start that we really are dealing with two different systems.
Viewing AOVs in the Live Viewer
Once we have a few AOVs set up, we can view them in the Live Viewer after we render the scene. The AOVs show up as tabs at the bottom of the Live Viewer window near all the information readouts. We can select each one to see its contribution.
The Beauty render is always the first tab called Main. If we’re using the Denoiser, there should be another tab to the right of that called DeMain which is the denoised beauty render. If we’re using Adaptive Sampling, there will be a Noise pass as well.
Render AOVs show up next and are called things like Dif (Diffuse) or Ref (Reflectance) or Li1, Li2, etc. for lighting passes. Output AOVs show up to the right of Render AOVs and are called Out 1, Out 2, etc.
Important: Render AOVs will not show unless “Enable” is checked in the Render AOV group tab. Output AOVs will always show, regardless of this setting.
Exporting AOVs
When doing any kind of post production, we want the highest fidelity output we can get within reason. High resolution, high bit depth files that have been encoded in a linear fashion give us the most flexibility when it comes to altering colors, adjusting light levels, or anything else we want to do in post.
Exporting from the Live Viewer
There are two menu options in the File menu of the Live Viewer that allow us to save our AOVs:
Save render passes as EXR makes a no-frills 32-bit ZIPS-compressed layered EXR of the current state of the Live Viewer. If we render 10 samples and hit pause and use this, we’ll have a gritty file with 10 samples. If we let the render complete and then use this, we’ll get a final frame.
Save image sequence will render each specified frame to the max samples and then save it in whatever format/compression/bit depth we want. This is more versatile, but comes with a several quirks:
Quirk 1: The Use Render Settings option ONLY refers to using the Output section of C4D’s Render Settings (Ctl/Cmd-B>Output) to determine the frame range. It doesn’t pull in any other render settings.
Quirk 2: As of this writing (2024.1), Octane will render ALL frames if only one frame is specified in the Frame Range. So even though C4D defaults to Current Frame, Octane will default to rendering them all. If we set this to Manual, From: 2F to 2F, Octane will render ALL frames in the timeline. If we set it to Manual, From: 2F to 3F, Octane will render frames 2 and 3 as expected.
Quirk 3: If we’re rendering to EXR, the File Type dropdown’s bit depth options don’t work. Both EXR (16-bit) and EXR (32-bit) will render as 32-bit UNLESS we enable EXR Half Float at the bottom. If we check that, then it’ll be 16-bit regardless if we pick 16-bit or 32-bit from the dropdown.
Quirk 4: The color space defaults to sRGB - this is only valid for PNG. If we’re using EXR, we MUST change this to Linear sRGB or it will tonemap the passes in a destructive way and hose our files.
Quirk 5: Save Render passes is OFF by default - If we’re using this method to render our AOVs, we want to make sure we turn it ON.
Exporting from the Picture Viewer
If we want the most control over our exports, we can use C4D’s Picture Viewer to set all the settings we need and render. Does this come with quirks too? But of course! Not too bad though.
First off, we’re going to want to turn OFF C4D’s Save section on the left. This will create unnecessary renders. All the EXRs are going to be generated directly from Octane, so we don’t need this. Multi-Pass will be checked as soon as we do the next step. That’s fine, and not something we have to worry about.
On to the Octane Renderer settings…
Important: Again, Enable MUST be checked in the Render AOV group tab. No enable, no Render AOVs. Output AOVs will still export regardless of this setting.
Also Important: In the Main tab, the Color space defaults to sRGB. This will cause weird tone mapping with our high bit depth EXRs and ruin them. We need to make sure to set this to Linear sRGB (or OCIO or ACES if we’re using one of those).
Back to the Render AOV group tab. If we’re creating AOVs, odds are good we’re going to want to save our files as EXR. In the Live Viewer, there’s only one option for this, but in the Picture Viewer settings, there’s Octane’s EXR format and C4D’s EXR format. Because of reasons, we want to ALWAYS use Octane’s EXR format (called EXR (Octane)). C4D’s EXR format is known to cause problems like missing passes, etc, so we need to avoid it.
Save Beauty is off by default. If we want that as a reference pass, we need to turn it on. Also, if we want the Beauty pass to be denoised, we need to enable Denoised Beauty.
The one main difference when using the Picture Viewer is the ability to export each AOV as its own file, rather than its own layer in a multi-layer EXR if we want to work that way. To do this, we just need to uncheck Multilayer file, and decide whether we want separate folders for each pass or not. As of this writing, the other two methods from the Live Viewer do not support this.
The Picture Viewer also supports tokens, which are really handy for procedurally generating file names. There are several good youtube videos out there for how to use them.
Wrap Up
That’s it for the overview. At this point, you should have a basic understanding of what AOVs are, why you’d want to use them, and how Octane treats them. The next guides in this series will cover what the individual passes do and explore the Output AOV system in more detail.