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Render Elements can be used to:

The Corona render elements are specified in the 3ds Max Render Elements tab of the Render Setup window. Corona does not support native 3ds Max render elements and offers its own elements instead.

UI Path: ||Render Setup window|| > Render Elements tab

These elements represent the standard (but not the only possible) way to assemble the final image: you need to render all elements starting with CESSENTIAL and stack them one by one using the "add" operation in linear color space (i.e. before adding gamma). All of them are only computed when using regular rendering; they show as black when using the Render only masks option. 

CESSENTIAL_Direct – All diffusely bounced direct illumination (light that bounced exactly once in the scene before hitting camera). 

CESSENTIAL_Emission – All light that is emitted directly into the camera, with no bounces (i.e. directly visible lights sources/scene environment). 

CESSENTIAL_Indirect – All diffusely bounced indirect illumination (light that bounced at least twice in the scene before hitting camera).

CESSENTIAL_Reflect – All light specularly reflected into the camera (both direct and indirect). Includes imperfect and perfectly glossy (mirror) reflections.

CESSENTIAL_Refract – All light refracted into camera (both direct and indirect). Includes imperfect and perfectly glossy (e.g. glass) refractions. 

CESSENTIAL_Translucency – All translucency lighting (both direct and indirect). 

CESSENTIAL_Volumetrics – All volumetrics (scene objects using volumetric effects and the global volume material). 

An example rendered image (BEAUTY element).

CESSENTIAL_Direct render element.

These elements contain additional geometry information. They can be used for masking, DOF and motion blur simulation in post-processing, denoising, or visual debugging of the scene. 

CGeometry_NormalsDotProduct – Outputs the angle between the surface normal and ray direction (similarly to the 3ds Max native Falloff map). White indicates surface directly facing the view; surfaces facing away from the view (grazing angles) are black. This quickly shows what the scene looks like without shading.

CGeometry_NormalsGeometry – Outputs the surface normal vectors as color values (with transformation RGB = (XYZ+[1,1,1])/2). Uses normals directly calculated from the geometry, with no bump mapping or smoothing groups. 

CGeometry_NormalsShading – Outputs the surface normal vectors as color values (with transformation RGB = (XYZ+[1,1,1])/2). Uses the final shading normals from the lighting calculation, which includes the effects of bump mapping and smoothing groups. 

CGeometry_UvwCoords – Outputs the surface mapping coordinates for selected channel. This can be used to check for mapping discontinuities and objects lacking mapping. 

Channel ID – Specifies the UVW map channel to output the coordinates from.

CGeometry_Velocity – Outputs the surface velocity vector as an RGB color. 

Mode – Velocity element mode. In "Camera" mode the movement relative to screen is shown, with movement to right being red, and movement up being green. Both object and camera movement is taken into account. In "World" mode the object movement in world space (XYZ represented as RGB) is shown. Camera movement is ignored in this mode.
Multiplier – Intensity multiplier that scales the velocity globally up or down.
Offset – Constant offset added to the velocity pass. Some postprocessing tools require offset 0.5 to bring negative values to positive ones.

CGeometry_WorldPosition – Outputs the surface world position XYZ vector directly as an RGB color.

CGeometry_ZDepth – Outputs the Z-Buffer channel, with adjustable min (white) and max (black) depths. 

Clip output to 0-1 range – Brings any values lower than 0 or higher than 1 to the 0-1 range.
Use camera environment range – When enabled, uses the current camera object environment range to define the min and max depth. When disabled, uses the custom values under Min Z and Max Z.
Min Z (white) – This distance from the camera is treated as the minimum Z distance (white color).
Max Z (black) – This distance from the camera is treated as the maximum Z distance (black color).
Override enviro distance – When the override is enabled, all environment will be reported as if it was geometry at this specified distance.
Allow propagation through reflection/refraction – When enabled, this render element will propagate through reflection and/or refraction according to the propagation settings of the materials. When disabled, this render element will be computed based on the first visible object.

CGeometry_NormalsShading render element.

These elements show information related to the rendering process and its performance. Useful mostly for debugging, creating comparisons, investigating performance issues. 

CInfo_NetworkRenderDebugging – Shows the name of the computer where the image was rendered and the version of Corona installed on it. Useful in troubleshooting network rendering issues. 

CInfo_RenderStamp – Stores the render stamp only. Useful for saving rendering statistics without having to keep the render stamp visible in the actual image. 

CInfo_SamplingFocus – Shows how Corona distributes samples in the image during rendering. Brighter colors show areas where more samples are used. Darker color shows areas where less samples are used. This element is available only if adaptivity is enabled (it is enabled by default). It updates each time adaptivity is recalculated (by default every 5 passes). 

Intensity – Linear brightness multiplier of the displayed values.

CInfo_TimePerSample – Shows how much time is spent on sampling each pixel during rendering. The specific time value to show as pure white can be defined in this element's settings (by default it is 100 microseconds). Darker colors mean shorter time per sample. Higher sampling time is sometimes expected (e.g. when using complex effects such as subsurface scattering) but may also indicate that the scene could be optimized for faster rendering (e.g. simplifying a specific material). Single white spots appearing in this element are expected and are caused by the CPU working on some other tasks than rendering (other processes running in the background). 

Time per sample to show as white [microseconds] – Sets the time in microseconds that is displayed as white.

CInfo_SamplingFocus render element.

These render elements are used primarily for masking individual scene elements for postprocessing. They are all rendered when using the Render only masks option.

CMasking_Cryptomatte – An advanced masking element. Cryptomatte is an industry-standard, which allows to render masks based on object Names, Materials, Layers, or Names with Hierarchy, all saved into an EXR. Cryptomatte exports are able to properly handle Depth of Field and Motion Blur effects (which otherwise can cause fringing or blurring at the edges of other mask types). 

Levels – Determines how many different objects can be identified by the cryptomatte render element in a single pixel. Increasing this value will significantly increase memory consumption (separate image buffer is required for every two levels).
ID Type – Determines how the different objects are distinguished in the cryptomatte render element:

Name – Only objects with the same name will have the same color.
Hierarchy – Only objects that have the same and and are in the same group will have the same color.
Layer name – Only objects in the same layer will have the same color.
Material – Only objects with same material will have the same color.

CMasking_ID – Assigns a random color to each pixel using one of the available modes. The most important ones are:

Primitive ID – Each primitive (typically a triangle) in a mesh receives different color. 
Material ID – Each assigned material receives a different color.
Instance ID – Each scene object receives a different color.
Geometry group ID – Each geometry group receives a different color.
Allow propagation through reflection/refraction – When enabled, this render element will propagate through reflection and/or refraction according to the propagation settings of the materials. When disabled, this render element will be computed based on the first visible object.

CMasking_Mask – Creates a custom set of rules for including/excluding each object from the mask. The available conditions are: Material GBuffer ID, Object GBuffer ID, and manual object selection. 

CMasking_WireColor – Assigns colors to scene objects based on their 3ds Max viewport wire colors (object colors). 

Allow propagation through reflection/refraction – When enabled, this render element will propagate through reflection and/or refraction according to the propagation settings of the materials. When disabled, this render element will be computed based on the first visible object.

CMasking_WireColor render element.

These render elements are related to scene shading.

CShading_Albedo – This element shows the total percentage of incoming light that is reflected or scattered by the material in any way (diffuse, reflection, refraction, translucency). Objects displayed in red have very high albedo and very bright diffuse and/or translucency component. Such materials, when applied to major portions of the scene (walls, floors, ceilings) can cause problems: excessive render times, noise, overall bad result with washed-up look.

High albedo (red) – Albedo values above this threshold are considered high and marked red in this render element. The default value of 0.85 is generally considered as a too high albedo value.
Low albedo (blue) – Albedo values below this threshold are considered low and marked blue in this render element. The default value is 0.

CShading_Alpha – Duplicates the built-in alpha channel, so it can be saved to a separate location. 

CShading_Beauty – An additional Beauty element, which can be added multiple times to get different versions of the final image: with and without denoising, with and without bloom, with and without glare. 

Denoise amount – Specifies the amount of denoising to apply to this render element.
Apply bloom – Toggles the bloom affect.
Apply glare – Toggles the glare effect.

CShading_BloomGlare – This element contains only the Corona's bloom and glare effect (against a black background). It can be used to compose and adjust bloom and glare in post production. 

Apply bloom – Toggles the bloom affect.
Apply glare – Toggles the glare effect.

CShading_Caustics – Shows only reflective and refractive caustics coming from the fast caustics solver. It can be used to compose and adjust caustics in post production. 

Apply denoising also to this render element – toggles denoising for this render element.
Apply bloom – Toggles the bloom affect.
Apply glare – Toggles the glare affect.
Include direct – Includes caustics that are directly visible from the camera.
Include reflected – Includes all caustics that are visible from the camera through a series of specular reflections/refractions, where the first interaction (first bounce after the camera) is reflection.
Include refracted – Includes all caustics that are visible from the camera through a series of specular reflections/refractions, where the first interaction (first bounce after the camera) is refraction.
Include GI – Includes caustics that are not in the other 3 categories (e.g. caustics visible from the camera through diffuse reflection).

CShading_Components – This versatile render element allows selecting a custom subset of lighting components. It can include diffuse, reflect, refract, and translucency lighting, in both direct and indirect (GI) variants. It can be used for basic as well as advanced image decomposition (e.g. separating lighting into direct and indirect reflections). 

Apply denoising also to this render element – toggles denoising for this render element.

CShading_LightMix – This render element is required to show the interactive LightMix in the VFB. It is possible to add multiple elements of this type, however each one of them will show exactly the same LightMix setup. 

Apply bloom – Toggles the bloom affect.
Apply glare – Toggles the glare effect.

CShading_LightSelect – This render element is required to show scene lights as adjustable items of the interactive LightMix. It stores information about the specific lights included in this element's settings. Saving a LightSelect element will always save the light intensity and color as it is defined in the scene itself, without the LightMix adjustments. 

Include lights not assigned to other LightSelect elements – Automatically includes lights which are not added to other LightSelect render elements.
Include specific light sources – Allows manually adding specific lights to the include list.
Include Environment Light – When enabled, the scene environment (e.g. Corona Sky or an HDRI) is included in this LightSelect element. Otherwise, the scene environment is excluded.
Open multi enviro setup dialog... – Opens a tool which allows for setting up multiple environments in the scene.
Apply denoising also to this render element – toggles denoising for this render element.

CShading_RawComponent – This shows one component (diffuse, reflect, refract, translucency) color divided by the corresponding CShading_SourceColor (input texture) value. This results in a "raw" lighting, not containing the surface color/texture. 

Apply denoising also to this render element – toggles denoising for this render element.

CShading_Shadows – Shows the shadows (energy subtracted from the image due to shadow ray occlusion). This is the complement to the beauty element, showing white where there are black shadows. If this element is linearly added to the beauty pass, it negates the visible shadows. Note that the shadows from environment lighting are always shown, resulting in a washed-out element in typical interior renders. 

Apply denoising also to this render element – toggles denoising for this render element.

CShading_SourceColor – The input color of a selected component (diffuse, reflect, refract, translucency, opacity). This is the value read from the texture, clamped to obey energy conservation laws.

CShading_SourceColor render element.

CTexmap – Allows the evaluation of an arbitrary texmap on all scene surfaces and environment. For example, the Ambient Occlusion element can be easily created by adding a CoronaAO texmap into this element's map slot.

Texmap – Drag and drop a texmap into this slot to show it applied to all surfaces in this render element.
0 objects excluded... – This list can be used to exclude specific objects from showing in this render element.
Override background color – When enabled, uses the specified solid color for the scene background rather than applying the custom texmap to it.
Apply denoising also to this render element – toggles denoising for this render element.
Allow propagation through reflection/refraction – When enabled, this render element will propagate through reflection and/or refraction according to the propagation settings of the materials. When disabled, this render element will be computed based on the first visible object.

CTexmap render element showing scene geometry covered with a procedural 3ds Max Checker map and the environment overridden with blue color.

When enabled, only the render elements which do not require shading are rendered (such as masks and normals). This option is useful, for example, if you do not need to render the full image, but you need some masking element. Since no shading is calculated, this option makes the rendering process almost instant, so you do not need to spend additional time on re-rendering the whole image.

There are multiple ways of saving render elements:

Specifying the main output file and render element paths in 3ds Max – Once the rendering is completed, the main output file and all render elements are saved in the file formats and locations specified in 3ds Max.

Clicking the "Save" button in the Corona VFB once – Only saves the render element currently visible in the VFB. For example, if the Beauty element is selected in the Corona VFB, this element is saved. If a CGeometry_NormalsShading element is selected in the Corona VFB, this element is saved, and so on.

Clicking and holding the "Save" button in the Corona VFB – Shows the following two options:

Save all – Saves the beauty element and every other available render element as separate files in the location of your choice, using the file format of your choice. The main output file will include additional data such as LightMix layers and denoising information so that you can post-process it in the Corona Image Editor, however no other render elements will include these data.
Save CXR – Stores all the information from the Corona VFB (all render elements, including the LightMix, tone mapping, denoising data, etc) inside a single CXR file. This file can be then used to resume rendering later, post-process in the Corona Image Editor, perform denoising later, and so on.

Clicking "Save CXR..." button in the Scene tab of the Render Setup window – Just like the Save CXR button in the Corona VFB, stores all the information from the Corona VFB (all render elements, including the LightMix, tone mapping, denoising data, etc) inside a single CXR file. This file can be then used to resume rendering later, post-process in the Corona Image Editor, perform denoising later, and so on.