In brief
- V-Ray's next 3.5 service pack brings Resumable Rendering first to 3ds Max; bucket rendering uses a .vrimg sidecar file, while progressive rendering uses a .vrprog sidecar file.
- In VFB 2.0, introduced with Corona 12, the Resume File option in the Render button menu continues rendering from a previously saved CXR file, while Resume Last continues the most recent render.
- Corona Render Elements (including CESSENTIAL, CGeometry, CMasking, Cryptomatte) split the scene into components, allowing fixes in post-production without re-rendering.
- Corona Image Editor (CIE) lets you apply LightMix, denoising, bloom/glare and LUTs to CXR files without opening the scene or 3D software; since Corona 11 it supports batch processing via the --batch parameter.
One of the biggest time sinks in interior and archviz rendering workflows is having a render that takes hours interrupted midway by a power outage, a cloud server being reclaimed, or user intervention. Chaos's V-Ray and Corona Renderer product family offers two complementary mechanisms to mitigate this risk: Resumable Rendering on the V-Ray side, and VFB 2.0 plus Corona Image Editor (CIE), which work through the CXR file format, on the Corona side. Based on the official documentation for both tools, this guide explains how a render studio can set up and use these features.
How to enable Resumable Rendering in V-Ray
Resumable Rendering, to be introduced in V-Ray's next 3.5 service pack, allows interrupted renders to continue where they left off. The feature is coming first to V-Ray for 3ds Max, and will later be extended to other platforms. According to the documentation, since the feature is still in development, some details may change in the final release.
To enable it, activate the Resumable Rendering option in the VFB settings within the render dialog; V-Ray Standalone users can instead pass the following command:
-resume=1It works differently depending on the rendering mode:
Bucket rendering: As each bucket completes, progress is written to a
.vrimgsidecar file; the light cache is also stored in this file, so it doesn't need to be recalculated.Progressive rendering: Here, a time interval must be defined; V-Ray saves the image state and light cache to a
.vrprogfile at that interval.
The documentation notes that in both cases these sidecar files can become large, and that when a render is resumed, scene preparation and texture loading need to be redone; the irradiance map, however, is not saved and must be recalculated. It's recommended not to attempt resuming at very short intervals (e.g. 30 seconds), since reloading the scene on each resume takes time.
Flexible post-production with Corona's Render Elements
Corona Renderer's Render Elements split the image into its components, enabling post-production edits without re-rendering. The main groups added from the Render Setup › Render Elements tab are:
CESSENTIAL: Light components such as Direct, Indirect, Reflect, Refract, Emission, Translucency, and Volumetrics; summed in linear color space, these can reconstruct the Beauty image.
CGeometry: Geometry data such as Z-Depth, normal, UVW, world position, and velocity; used for DOF and motion blur simulation or masking.
CMasking: Masking elements such as Cryptomatte, ID, and WireColor.
Cryptomatte can generate masks based on object names, hierarchy, layer, or material; however, the documentation notes that each added render element increases RAM usage during rendering, so it's best to avoid adding elements that aren't needed.
VFB 2.0 and the CXR format
In VFB 2.0, introduced with Corona 12, the menu next to the Render button offers two resume options: Resume Last continues the most recent render, while Resume File continues rendering from a previously saved CXR file. The Save CXR command stores LightMix, tone mapping, and denoising data alongside the Beauty pass in a single file, allowing all post-production settings to be readjusted even after rendering is complete.
Editing without opening the scene: Corona Image Editor
Corona Image Editor (CIE) is a standalone application that lets you edit a CXR file without opening any 3D software. LightMix, denoising, bloom/glare, and LUT applications can all be done through CIE, enabling post-production work on lower-spec machines. Since Corona 11, a --batch parameter has been added for batch processing:
CoronaImageCmd.exe [arguments] --batch <input-1> <output-1> <input-2> <output-2>With this command, for example, 100 frames of an animation can be denoised at once and exported as PNG.
| Setting | Recommended value | Effect |
|---|---|---|
| Resumable Rendering (Bucket) | Enabled, .vrimg sidecar | Light cache is preserved, resumes from the last bucket |
| Resumable Rendering (Progressive) | Not-too-short time interval | Very short intervals (e.g. 30 sec) increase scene reload overhead |
| CMasking_Cryptomatte Levels | Increase as needed | Each level requires a separate memory buffer, increasing RAM |
| CShading_Beauty Denoise amount | Between 0 and 1 | 0 gives original, 1 gives fully denoised image |
Impact on architectural visualization workflows
For interior and archviz rendering teams, these features provide significant time savings, especially for long renders running overnight on a farm or on interruption-prone cloud servers (such as preemptible virtual machines). Since the scene must be reloaded each time a render is stopped and resumed, very short pause-resume cycles are not recommended. Additionally, the CXR-based workflow allows teams to share LightMix and tone mapping settings through a single file, enabling quick changes during client revisions without reopening the scene.
Common mistakes
Setting the save interval too short in progressive rendering, unnecessarily increasing scene reload time.
Adding heavy render elements like CMasking_Cryptomatte to the scene without need, needlessly increasing RAM consumption.
Saving only a single render element (e.g. Beauty) and not using the CXR format, which causes LightMix and post-production data to be lost.
Attempting to use the
--batchparameter together with the<weight>argument; the documentation states these two are incompatible.
Sources
3 sourcesSource texts are not republished; short quotes are marked, everything else is our own summary and commentary.
For offices in Turkey running overnight renders or using cloud render farms, these two features together form a practical safety net: a power outage or a preemptible cloud server being reclaimed no longer means hours of lost rendering. That said, it's worth remembering that sidecar files (.vrimg, .vrprog, CXR) consume disk space; storage planning is especially necessary for high-resolution animation projects.
On the Corona side, the CXR format's ability to carry all post-production data in a single file after rendering saves time particularly on interior projects with heavy client revision traffic; adjusting settings through Corona Image Editor without reopening the scene is possible even on lower-spec machines. Still, it should be kept in mind that this feature (on the V-Ray side) is still in development, and behavior may change before release.
Frequently asked questions
When is Resumable Rendering coming to V-Ray?
The feature will be introduced first for V-Ray for 3ds Max in V-Ray's next 3.5 service pack, and will later be extended to other platforms. The documentation notes the feature is still in development and may change in the final release.
Why is the CXR file important in Corona?
Since the CXR file stores all render elements alongside the Beauty image, as well as LightMix, tone mapping, and denoising data in a single file, it allows post-production work via Corona VFB or Corona Image Editor without restarting the render.
What should you watch out for when using Resumable Rendering?
Very short save intervals (e.g. 30 seconds) are not recommended for progressive rendering, since scene preparation and texture loading are redone on every resume; also, the resulting .vrimg/.vrprog files can take up significant disk space.
