Scene Tab

The Scene tab includes render settings which affect the appearance of the rendered scene. Additionally, it provides quick access to some of Corona's features such as the VFB, interactive rendering, and LightMix.

Show VFB – Displays the Corona VFB with the last rendered image.

Start interactive – Starts interactive rendering in the Corona VFB.

Setup LightMix – Displays the Corona Interactive LightMix Setup dialog which can be used to set up LightMix with a single click.

Open Material Library – Opens the Corona Material Library window if it's currently installed.

Reset settings – Resets all Corona render settings to their safe, factory defaults.

Progressive Rendering Limits

Pass limit – Number of passes after which the rendering will stop.

Time limit – The time after which the rendering will stop (hours, minutes, seconds).

Noise level limit – Sets the target error (noise level) at which the rendering stops.

Save/Resume Rendering

Save CXR... – Saves the current render output to the hard drive with additional data, so that the rendering can be resumed later or opened with the Corona Image Editor. Can be used any time after starting rendering at least once in the current 3ds Max session.

Resume from file... – Resumes rendering from a file previously saved with the Save CXR function.

Resume last render – Resumes the last rendering in this session.

Render Overrides

Render hidden lights – When enabled, even hidden lights in the scene will be rendered.

Render only masks (disable shading) – When enabled, only render elements which are not dependent on the beauty pass (such as masks and normals) will be rendered. This makes the rendering process almost instant.

Mtl. override – When enabled, allows overriding all scene materials with a single specified material.

"None" slot – When the Mtl. override checkbox is enabled, the override material should be placed in this slot.
"+" button – When clicked, it adds the currently selected scene objects to the material override include/exclude list.
Preserve... – Shows a dialog box where specific material types and their properties can be excluded from the material override.

Denoising

Mode – Specifies the post-render image denoising. If enabled, the beauty element will be replaced after rendering with its denoised version. You can then use the Denoise Amount option to interactively control strength of the effect. The following denoising modes are available:

None – Disables any kind of denoising.
Only firefly removal – A fast filter that just removes very bright pixels from the image (created by any source - noise, caustics, sun reflections, etc.).
NVIDIA GPU AI – A Very fast denoiser which also denoises the image during rendering, not just at the end. Not suitable for denoising animations. Available only on NVIDIA GPUs when the optional NVIDIA AI Denoiser Corona component has been installed.
Intel CPU / GPU AI – Also known as Intel Open Image Denoiser – a fast denoiser applied when the rendering ends. If you have an NVIDIA GPU in your machine, then it runs on the GPU. Otherwise, it runs on the CPU. Both AMD and Intel CPUs are supported. As a rule of thumb, if your CPU can run Corona, it can also run this denoiser. In the CPU mode it is slower than the NVIDIA GPU AI denoiser, but can achieve a better quality. 
Corona High Quality – A more memory and CPU intensive filter available exclusively in Corona. It takes longest to compute, but produces the best denoising quality of all integrated denoisers.
Gather data for later – This option just gathers denoising data for later processing via the Corona Image Editor. For this to work, the image must be saved as a Corona EXR (.cxr).

Amount – Mixing coefficient between the original (noisy) and processed (non-noisy) image. It allows fine-tuning the effect strength to find the sweetspot between preserving the finest details and removing excessive noise. This parameter can be changed interactively after render.

Radius – Controls the blurring radius of the Corona High Quality denoiser. Increasing the value can prevent splotches when denoising extremely noisy images, and lowering it can prevent loss of details, but the default value usually works best. This parameter must be set before rendering - it cannot be changed interactively after rendering like the Denoise amount.

Render Selected (Pixel Mask)

Mode – An extension to 3ds Max "Area to render: Selected" feature. Render a cutout region of only some scene objects while keeping indirect shading contribution of the others. When "Clear VFB between renders" is ON, this feature will render a cutout of the selection against a black background with alpha channel - useful for quick fixes. When "Clear VFB between renders" is OFF, this feature will render a cutout on top of the previous render - useful for rapid re-rendering individual objects when tweaking their materials. The mode selector sets how the selection is defined - it can be the current selection in viewport, an include/exclude list, or a specific object GBuffer ID.

None – Disables the Render Selected feature.
Include/Exclude list – Uses an Include/Exclude list to specify the area to be rendered.
Viewport selection – Uses the current viewport selection as the area to be rendered.
Object GBuffer ID – Uses the objects with the Specified Object GBuffer ID as the area to be rendered.

Scene Environment

3ds Max settings (Environment tab) – When selected, Corona uses the environment color or map specified in the 3ds Max Environment and Effects window.

Single map – When selected, Corona uses the environment color or map slot next to this radio button.

Multiple maps (LightMix) – When selected, multiple environment maps are used. They should be split into multiple Light Select render elements.

Excluding Objects from Environment Illumination

0 objects excluded... – Exclude/Include list of scene objects lit by the environment.

"+" button – Adds the currently selected objects to the Exclude/Include list of objects lit by the environment.

Accurate sampling (slower) – This option enables accurate sampling of environment maps. It is slower but more accurate for high detail maps. This can make lighting and shadows from environment maps sharper, specifically for small light sources(s) in the map (e.g. the sun). Enable it if there is flickering in the lighting.

Overrides

Direct visibility override – When enabled, the color or map next to this checkbox is used as an override for the environment map visible directly from the camera.

Reflections override – When enabled, the color or map next to this checkbox is used as an override for the environment map visible in reflections.

Refractions override – When enabled, the color or map next to this checkbox  is used as an override for the environment map visible in refractions.

Global volume material – When enabled, the material placed next to this checkbox is used as the global volumetric medium for the scene. Useful for simulating fog or aerial perspective.