Flexibility

Flexible Lights
Users can make any light source invisible to the camera, as well as invisible to reflections/refractions. Shadows can be turned on/off and specific objects can be included/excluded from receiving illumination from any Corona light. Backplates can be easily created with the invisible to GI option. 3ds Max default lights are fully supported.

Rayswitcher Material
Rayswitcher material and texture allow a wide range of artistic tweaks when rendering with Corona. Use them to create materials invisible to camera or not affecting GI, to reduce or increase color bleeding, and more.

Environment Overrides
You can use different environment maps for reflections, refractions and direct visibility from the camera. For example you can use a clear sky HDRI as a light source and a second cloudy HDRI just for reflections and refractions.

Glass without Caustics
Caustics can be difficult to compute, especially when using path tracing. But in many cases, water or glass look plausible even without caustics, window glass panels being prime examples. Because of this, caustics have been disabled by default. This significantly reduces render times, and if caustics are needed they can easily be enabled with the “Caustics” checkbox in Corona material.

Shadow Catcher
Corona implements its own shadow catcher (matte/shadow) solution. It is a single material with all the necessary controls in one place – there is no need to combine special materials with other special texmaps. It works especially well with the interactive rendering for rapid camera and illumination matching. Advanced features, such as light illuminators and matte bump mapping, are of course supported.

Speed

Corona Renderer uses Intel Embree Ray Tracing Kernels, making the CPU-only Corona as fast as many GPU renderers - but without the memory and flexibility limitations.

Interactive Rendering

Corona Renderer brings you state of the art, fully-featured interactive rendering.

Interactive Capabilities
You can change materials, lights, and create or adjust geometry while rendering. There is no need to manually restart or update the rendering, as it happens automatically usually within less than a second. It runs completely on the CPU, so it has no limitations and does not require any special hardware.

Same Results
Interactive rendering is an integral part of the Corona core. In fact, it shares over 99.9% of the regular renderer code. This means that all features of Corona Renderer are supported, and that the results are exactly the same as with the non-interactive version. Users can render motion blur, DOF, create proxies, scatter systems and more, all with instant feedback.

Compatibility
Because our interactive and regular renderer are almost identical, all types of geometry and proxies are supported. The same goes for all the 3ds Max maps and third party maps. Even the advanced third party plugins such as Itoo Forest Pack work as expected.

Materials

Material Preview
Material preview uses the same rendering engine as the final frame rendering. The default 3ds Max material preview scene is replaced with a custom, more representative Corona scene, to get the real “What You See Is What You Get” material editor.

GGX
Corona Renderer uses the GGX microfacet model to deliver realistically looking metals and other glossy materials. This model produces much more plausible results than legacy models such as Blinn, Phong, or Ward.

Lights

The whole process of creating lights is designed to give artists complete control over their scene, while being fast and intuitive. There are no sampling multipliers, no differences between using light objects and materials, and no need to create artificial fill or dome lights. Users can use HDRI, IES files, Sun & Sky system, 3ds Max lights, Corona Lights, or turn any mesh object into light simply by assigning to it the Corona Light Material.

No Sampling Parameters
There are no sampling parameters that you would have to set by trial and error. Lights will always work as expected.

Corona Lights and Corona Light Material
There is no difference in behavior of Corona Lights and Corona Light Material. Both of them have almost the same options and deliver the same results. So it is up to the artist to use what is more convenient.

Lights and Rendering Speed
In Corona, there is very little penalization for using mesh lights with high polycount. They will perform as well as low-poly ones with the same shape. Additionally, the version 1.0 improves sampling of directional/IES lights. They now render almost as fast as regular diffuse lights.

No more Dome Lights for HDRI
Users do not need to set up any dome light object for HDR image-based rendering. Just put the HDRI into a 3ds Max environment and it's done. There is also no need to put downsampled/blurred versions of the map into a GI override slot – HDRIs in Corona work always fast and without splotches, regardless of resolution or complexity.

UHD Cache

Traditionally, users had to choose to either use unbiased algorithms without any caching and wait long time for all renders, or use biased caching algorithms, and deal with splotches, missing shadows, and sensitive input parameters. Corona merges the best of both worlds. Its cached solution, called “UHD cache”, is significantly faster than plain path tracing, but does not suffer from artifacts, missing contact shadows, or complicated UI controls.

Rendering Quality
UHD cache uses only partial caching, and does not try to interpolate everything. While this is slower than fully cached solution (such as irradiance caching), it does not create artifacts, only noise that eventually goes away.

Animation Support
The biggest difference between UHD cache (released in Corona 1.0) and its predecessor, the HD cache, is in the animations. UHD cache is much more accurate, so it significantly reduces flickering – even when light sources or geometry are moving. This is especially important when the cache cannot be precomputed.