# Two-phase rendering

### **The two-phase system**

V-Nova PresenZ generates images through a two-phase system consisting of a detection phase and a render phase. Once these two phases are complete, we get one or several “.PrzRender” files. \
Then PresenZ Merger, also called the Prz\_Maker, combines the results to create a “.PRZ” file that can be viewed in VR by the PresenZ player. \
This “.prz” file is a compressed file, think of this like a “.jpeg” file, while a “.PrzRender” file is more like an “.exr” with all the aov and colour data present for compositing.

####  1. **Detection phase**

During the detection phase, V-Nova PresenZ gathers all the necessary information to cover whatever is visible from the ZOV, optimizing this information to obtain the proper detail level as seen from the ZOV. This phase probes the 3D scene to define what render origins and directions have to be performed during the next phase (the render phase). At the end of the detection phase, V-Nova PresenZ generates a “.przDetect” file that is stored in the przDetect subfolder created automatically at your output render pass.

{% hint style="info" %}
*Note: Depending on the render engine, there might be multiple detect passes, for example, one for transparent and one for opaque objects.*
{% endhint %}

####  **2. Render phase**

In the render phase, V-Nova PresenZ shoots sampling rays according to the origin and direction given by the detection phase. This phase applies lighting and shading, resulting in colour data and other AOVs (Arbitrary Output Variables) computations for the final output. The render phase generates a “.przRender” file that is stored in the przRender subfolder created automatically at your output render pass. The “.przRender” file is a RAW PresenZ image file that contains all the colour and AOV information in half float precision. This file can be manipulated for colour calibration and compositing. It supports  V-Ray colour correction for V-Ray users, but also other colour grading techniques like  [OCIO (OpenColorIO)](https://support.presenzvr.com/docs/html/Utilities/OCIOSupport.html#ociosupport), for instance.

{% hint style="info" %}
*Note: All compositing, tweaking, and post-processing will be done on the .prZRender files that ultimately will become your "master" copy of the movie before compression.*
{% endhint %}

**Prz\_Maker**

The PresenZ Merger/ Prz\_Maker converts the previously created “.przRender” file(s) to a “.PRZ” image file that can be viewed in the PresenZ player. The .przRender files carry uncompressed pixel data, which is compressed during the merging process, resulting in the .prz file in a smaller file size that can be easily handled by the player.

In summary, V-Nova PresenZ uses a two-phase system to generate images for the PresenZ player. The detection phase gathers information on what is visible from the ZOV, while the render phase applies lighting and shading to create colour data and other output variables. The PresenZ Merger/Prz\_maker transforms those "raw" images into a ".PRZ" file that can be viewed in the PresenZ player.


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