To access Thea Render Settings, go to Render Settings > Renderer > Thea Render. Here you will see all the parameters that allow you to configure the complex algorithms based on which Thea Render operates.
The groups Main, Advanced, Ambient Occlusion and Clay Render refer to general engine settings. In Termination group you can set the termination criteria of your renders based on Time and Sample limit (Time format: 1h 15m 30s). Distribution group allows you to set the Network Rendering settings and last, Devices group allows you to configure you rendering devices. You can choose to enable or disable each device or set their priority. The groups Termination and Distribution are visible only in Production Rendering.
The data in the above groups refer directly to Thea Render and they are explained in detail in Thea Render manual (Link). Nevertheless, Denoise and Execute Preceded Passes parameters affect directly the plugin.
Thea For Cinema 4D utilizes both Production and Interactive render modes of Thea Render. You can switch between Interactive and Production mode either in Render Settings or in the Darkroom. Not all parameters are functional in both modes. For example, Termination Criteria or Distribution settings are ignored in Interactive mode.
Thea Render offers a large variety of render engines to choose from depending on your needs. Presto MC is set as the default engine in Interactive Render and Unbiased TR1 in Production.
Allows you to select the Denoise method that will be used during Production Rendering. Denoising is a technique that allows the user to produce noise-free images with low sample count. It is produced as a post-process effect after a series of calculations based on certain render channels. Basically, it utilizes the channel information to reduce the noise making highly-demanding scenes easier and faster to render. Thea Render supports two denoise methods:
Non-Local Means (NLM) and Nvidia's OptiX. In case a user wants to render with any denoiser, they must enable it in Render Settings before rendering. That's necessary since the engine needs to know prior to rendering if it has to also produce the channels related to the Denoiser. The requiring channels are activated and generated transparently in order to calculate the Denoise effect. The user doesn’t have to do any further action regarding the channels since it is taken care of automatically by the engine.
After that you can switch it on/off as a post-process effect in Display settings.
Execute Preceded Passes
Due to dynamics and simulations, hair animation is quite hard to transfer into Thea on a specific frame. This option forces the calculation of all the frames that precede the current one. That way hair will have the form when they are about to be transferred into the engine.
Important note: Enabling this option will affect the scene conversion time, so it must be used only when hair animation is necessary.
Here you can select which channels you want to produce along with RGB for any post-processing effect.
Channel Custom Depth: Select the bit depth for each channel (8 and 32 bit)
These parameters refer to EXR options in Thea Render. They are stored into the engine and they are taken into consideration only when the image is saved into EXR.
To render in 32-bit images in Picture Viewer, first you must select Channels > Channel Custom Depth > 32 Bits. That way you directly command Thea to produce 32-bit renders. Then, go to Save page in Render Settings and select a format that can store images in 32 bits (such as OpenEXR).