(Chaos Corona Team,

In this article, we catch up with Francesco Legrenzi, the author of what would go on to be the definitive guide for V-Ray back in 2008. Francesco has spent the last 4 years dedicating himself to writing a similar guide for Chaos Corona, with the aim of making it just as definitive! We spoke with him about the book, and the work that has gone in to writing it.


My name is Francesco Legrenzi, I was born in Bergamo valley located in northern Italy (Fig. 1.1), and I am the owner of the studio “Legrenzi Studio” (

I graduated as a construction engineer at the Faculty of Engineering in Milan in 1999. A teacher there made us discover the fascinating world of 3D, and it was during his last two AutoCAD R14 lessons (back in 1998!) that my passion for CG began. Since AutoCAD did not offer advanced modeling and rendering tools, he showed us 3D Studio MAX Release 1. From that day on, my close “friendship” with 3ds Max started.

I worked for three years as a structural engineer before realizing my true passion, and then I gave up my long-term job, devoting myself to the world of 3D graphics instead. In 2001 I was asked to participate in the management of a famous Italian graphics forum, where I remained active until 2010. In the meantime, in 2001 I became aware of a small plug-in, V-Ray, developed by Chaos Group, a Bulgarian software house. In 2005, I began writing what became one of the most referenced books for learning VRay: “VRay – LA GUIDA COMPLETA” (Fig. 1.2).

Fig. 1.1
Fig. 1.2 - VRay - LA GUIDA COMPLETA (2008).

The success was unexpected, and three reprints and an English version were made (Fig. 1.3).

Since then, I immersed myself in the world of 3D, with a special focus on the render engines available for 3ds Max. After years spent directing the Modeling & Lighting department in an architecture firm in Milan, I began working as a freelancer. In 2013, I discovered Corona Renderer, when it was at the Alpha 4 version. It was relatively unknown, but I decided to use it on a professional level. From that encounter, a close collaboration was born with Chaos Czech a.s., which led to the creation of this book.

Fig. 1.3 - English version of the book: “VRay - LA GUIDA COMPLETA”.


After writing the world’s first guide to V-Ray (2008), my adventure as a freelancer began, leaving my comfortable 3D graphic job in Milan. It was not easy, especially because I had to introduce my studio to potential clients. However, it didn’t take long, thanks to the word of mouth and visibility that the V-Ray book gave me. We worked actively until 2013. Unfortunately, the world of “arch-viz” rendering was flattening out, and it no longer gave me the joy satisfaction that made me change my life back in 2001. All the products we made were monotonous, as were the kinds of projects we were asked to work on. In 2012, I saw the possibility of using UDK3 at an architectural level, but hardware and software were not yet ready. In the meantime, I began to experiment with Corona Renderer, which gave me the new energy I needed. In 2016, I started writing the world’s first guide to Chaos Corona. During the first few months, I worked part-time on this project. Then, from 2017, writing became my main activity, abandoning almost entirely the world of 3D architectural visualization.


I first discovered it many years ago, I think in 2014, when a strange script appeared on I’m talking about LightLister script that allowed us to manage and control the lights of a certain “Corona Renderer”! Initially, I didn’t pay much attention to it, but something attracted me. In fact, we already used a similar script for V-Ray, which we continued to use for all our professional projects. The real breakthrough was when Ondra released the Alpha 4 benchmark for Corona Renderer. It was a small compressed file of around 40 MB. Intrigued, I downloaded it. The benchmark consisted of a folder containing the files needed for the test render: the Corona Renderer software, the 3d file of a room in .obj, format, the textures, and a file “!runme.bat”. I clicked on the small .bat file and was immediately amazed. In just twenty seconds I had an excellent preview of the scene (Fig. 1.4).

In two minutes the render was almost perfect; after four minutes and thirty seconds the rendering was finished, all without stains or artifacts. The noise of the image (from now on “noise”) was really low! At the time it was a real revolution – a truly efficient and CPU-based progressive rendering system. V-Ray had not yet integrated a progressive “biased” system (BF+LC), and this really made me think.

So, I installed my first version of Corona Renderer, the Alpha 4 for 3ds Max 2011, 2012, and 2013 (Fig. 1.5).

Fig. 1.4 - Render produced from the first Corona Renderer benchmark.
Fig. 1.5 - The Corona Renderer "ALPHA 4" interface.

It was totally free, and working 100%, with no time or resolution limits. I was pleasantly surprised by its simplicity, though the interface needed a rework, as it was poorly organized at the time. In any case, coming from a complex engine like V-Ray, I immediately felt at ease. In less than a day, I’d learned how to manage the main parameters of Corona Renderer. Furthermore, the CoronaMtl shader was effortless and intuitive. But the feature that really struck me was the real-time preview, including of Global Illumination directly inside the Material Editor: we could finally see the material exactly as if it were in the final render.

The first time I met Ondra was in April 2015 (Fig. 1.6). He was chairing a workshop at the University of Venice. Immediately, I realized that I was face to face with a unique man with a wonderful mind. On that occasion, we discussed the possibility of creating a guide to Chaos Corona.

The project was under development and would be subject to numerous changes in the following months, which allowed me to take my time. I started writing the first pages in March 2016 with their support, using Corona v1.3 (3 November 2015).

Fig. 1.6 - The author of the book. Venice, April 2015.


For customers who have already bought the V-Ray book, the Chaos Corona guide will instantly familiar – the style used is quite faithful to my earlier book. I used a similar format, with colors and layouts that recall the V-Ray book. More than a guide, it is a technical manual in which ALL the Chaos Corona parameters are explained.

The web is full of video tutorials or online courses for Chaos Corona, which are often expensive, sloppy, and very similar to each other. Usually, they want to explain how to generate an interior, such as a living room or bathroom, or an architectural exterior as quickly as possible. They say, “Click here… Do this… Do that”, but without explaining the reasons for certain choices, and without explaining the technical basics of Chaos Corona. The important thing for them is to use captivating pre-set scenes to prevent the viewer from getting bored, but without providing much substance in the actual lesson.

I have known many 3D graphic designers in my career, but those I can call true experts are rare. Very few stand out from the crowd, while many designers are satisfied with mediocre tutorials found on the web, produced by lackluster “professionals” who offer certifications of dubious utility.

With Corona: THE COMPLETE GUIDE I wanted to go beyond the basics – I wanted to analyze in detail, with many renders and images, all the parameters of our favorite rendering engine, and explain every single button. Who among us has never asked, “What is this parameter for? What happens if I change it? ” To find the answers, we’ve become used to searching the internet, browsing through dozens and dozens of pages, looking in the Corona forum, or even opening a new discussion there, hoping to find someone willing to help us, all the while wasting valuable time.

Now all this is no longer necessary – you have, next to your keyboard, a 700-page, physical book for immediate reading! Within it, you’ll find all the answers to your questions, with a detailed index, and frequent references, to make it all the easier to use. The hundreds of comparative images (Fig. 1.7, Fig. 1.8, Fig. 1.9, Fig. 1.10, Fig. 1.11) will simplify and speed up your understanding of Chaos Corona, allowing you to browse the guide anywhere and at any time of day, without the need for electronics. Being able to read peacefully on the train, on the bus, or on vacation, without the hassle of carrying a computer with limited battery life, is a luxury that only a book can offer. But beyond that, the act of reading – of owning, and holding in your hands, a real book – is in itself a rich and rewarding experience, and increasingly rare nowadays.

Fig. 1.7 - "Zoom" parameter of the new "Custom aperture" tool introduced with Corona Renderer v6.0.
Fig. 1.8 - "S" parameter of the "Mandelbox" object.
Fig. 1.9 - Use of the "Channel color mapping…" tool to define the colors of the "CoronaVolumeGrid" object.
Fig. 1.10 - "Eye separation" parameter of "Corona Camera".
Fig. 1.11 - Changing the "Distance" parameter of the "CoronaMtl" shader.


Passion first. I made my very first renders with a Pentium MMX and 32 MB of RAM with AutoCAD R14. I started my career back in 2000, when a Pentium III 733Mhz and the Brazil, rendering engine were the standard setup, when the computation resolutions were 1024×768 px, and when we used the Radiosity or Photon Map algorithms to generate GI (if the budget allowed). Without a sincere and unconditional passion, the experience gained in a more than 20-year career, and a pinch of madness, it would not have been possible to realize such a huge project.

The second ingredient is a deep self-knowledge. I knew it would be a mammoth task, and there were moments of doubt. The thought of working for four years on a project that could turn out to be below my expectations was a “travel friend” that accompanied me throughout this period. Through page after page, however, I was aware of the high quality of my creation, supported by the exciting reviews of some of the users who’d followed me over the years (Andrea Calzaferri and Emilio Seghezzi).

Finally, I have to thank Ondra and his whole team. Compared to the V-Ray guide – which, as a personal project, Chaos Group was totally unaware (I’d never expected such international enthusiasm) – this time Chaos Czech have been an active and fundamental figures from the very first pages, offering me constant support, offering me their constant support.

For example, when I wrote about the CoronaHairMtl shader, I had the privilege of being in direct contact with the programmer responsible for its development, and was able to ask him about unique technical details; or when I wrote about 2.5D displacement, I could speak to its writer, Ondra, who often suggested how best to write about it and other parts of the book.

Finally, I cannot fail to mention Marcin Miodek, Rowan Manns, and George Karampelas, who I spoke to hundreds of times, receiving advice on how and what to write for many parts of the guide. Having the Chaos Corona guys available on Skype, in real-time, over the last four years has been invaluable to the book’s final outcome. Many thanks to all of you.


Having written the world’s first guide to V-Ray, I was aware of the enormous difficulty  in making a book. I didn’t want to write a rough 200-page booklet with topics repeated ad nauseam, but a 700-page volume with the aim of being the first and only true manual in the world for Chaos Corona. I started writing the book in 2016, when Corona Renderer was in its version 1.3 (Fig. 1.12).

Fig. 1.12 - Image used in chapter 01. Note the number of groups: the first refers to Corona Renderer v1.3.

Month after month, year after year, the book slowly took shape, but it was a constant “battle” against Chaos Czech, as the speed at which Corona Renderer was developing was much faster than the speed I was able to maintain in making the book. So, version after version, I always had to start over, re-reading each page, redoing many of the screenshots already created, adding new pages and eliminating outdated concepts. I still remember well when, between v1.5 and v1.6, the new TAB called Camera was added, which forced me to add a new chapter and transfer numerous pages; or when the old CoronaOutput map was split in two, generating the CoronaTonemapControl and the CoronaColorCorrect maps (Fig. 1.13).

Fig. 1.13 - "CoronaTonemapControl" and "CoronaColorCorrect" maps.

Version 6.0 brought with it a lot of changes – in about two months, I had to regenerate 90% of all renders, as this was the version the book was sold with. The continuous revision of the entire book was an extremely complex and stressful job, much more than I would have expected: it is as if I had rewritten the entire book 4-5 times from scratch (Fig. 1.14).

Fig. 1.14 - "Corona Scatter". Again, note the numerous updates.

Another big challenge was to be able to summarize the topics as much as possible, but without going too far in-depth. The V-Ray book was a great success, but some users complained that it was far too complete and complex. In fact, we’re talking about a book in A4 format, consisting of more than 1,000 pages and weighting 3Kg.

I would have liked this new book to have no more than 500-600 pages and a total weight of 1.5kg. Unfortunately I had too many things to write, though I still managed to stay below the 700 page threshold, and its weight doesn’t exceed 1.75kg.

Finally, a lot of time was dedicated to the production of the assets (file .max, .psd, .aep, .vdb, cache files) and to the creation of technical animations in .mov format. I’ll tell you about them shortly.


I started writing the book in early 2016 (Fig. 1.15).

Initially, the content of the guide was slightly different. I wanted to include some short tutorials that users could use as verification tools (Fig. 1.16).

Fig. 1.15 - The very first versions of the book.
Fig. 1.16 - First version of “Corona - THE COMPLETE GUIDE”.

Unfortunately, the manual was getting too long, and I didn’t want to risk creating a 3kg book again: increasing the number of pages, with an increase in weight and price, was not a mistake wanted to male.

Along with the Italian version, I also wanted to create an English version (Fig. 1.17), a decision that exponentially multiplied the difficulties of the entire project.

Fig. 1.17 - Same page written in Italian and English.

In the summer of 2019, I started upgrading to Corona Renderer v4.0, while the v5.0 update began to take shape at the end of March 2020 (Fig. 1.18, Fig. 1.19, Fig. 1.20). During the writing of the book, I wore out many notebooks in which I took daily notes. I used this “analogue” system because it gave me more control over the production process.

Fig. 1.18 - In the figure you can see the beginning of the v5.0 update (20 March 2020).
Fig. 1.19 - Notes taken when updating the book to Corona Renderer v5.0.
Fig. 1.20 - Notes taken when updating the book to Corona Renderer v5.0.

In those months, I was finish the translation and proofreading of the English version, which took up most of 2019 and 2020. On 9 June, 2020, I started updating both versions to v6.0 (Fig. 1.21, Fig. 1.22, Fig. 1.23).

Fig. 1.21 - Start of v6.0 update.
Fig. 1.22 - Notes taken when updating the book to Corona Renderer v6.0.
Fig. 1.22 - Notes taken when updating the book to Corona Renderer v6.0.

The update ended in the first week of October. At the time this article was published (November 2020), the guide was in production at a printing house in the city of Brescia (Italy) (Fig. 1.24, Fig. 1.25, Fig. 1.26, Fig. 1.27, Fig. 1.28, Fig. 1.29, Fig. 1.30).

Fig. 1.24 - The first step is to print the cyan, magenta, yellow, and black colors of each page on metal plates, using an expensive laser machine.
Fig. 1.25 - The huge printer, capable of producing 13,000 sheets per hour.
Fig. 1.26 - Each sheet has to go through the machine four times in order to add one color at a time.
Fig. 1.27 - Close-up of the section dedicated to red printing.
Fig. 1.28 - Sheets ready to be sent to the cutting machine.
Fig. 1.29 - Quality control workstation.
Fig. 1.30 - Quality control: the operator is analyzing the four-color process alignment.


The translation phase was quite complex. At first, I wanted to rely on translation agencies. After some research, I found a company that seemed suitable to a complex task such as translating a 3D graphics technical manual. The initial test looked great, but I couldn’t say the same about the later chapters. In addition, the constant revisions of the Italian book, due to the speed of Corona Renderer’s updates, made communication between our studio and the agency problematic.

Realizing that the quality of the product was not good enough, I decided to take matters into my own hands and personally carry out the translation, supported daily by three talented and patient native speakers (Angelica, Chris, and Carlos) and by Tom Grimes (Corona Team). A big thanks to all of them! In conclusion, I am very satisfied with the result obtained, as confirmed by some users who had the pleasure of reading the preview of the English version (Chris Langeveldt and Zdenka).


Buyers of the book “VRay: THE COMPLETE GUIDE” had complained that the 3D scenes shown in the manual were not attached. I didn’t think it was a big problem at the time because those files were really simple and achievable in seconds. With my second book, I didn’t want to make the same mistake. That’s why I produced 117 scenes for 3ds Max (there is no book in the world dedicated to a rendering engine with so many scenes available), designed and engineered to exemplify each parameter or concept, offering the user effective tools to test their knowledge (Fig. 1.31).

Corona - THE COMPLETE GUIDE - Interview
Fig. 1.31 - Contents of the two Dual Layer DVDs. In total, 20GB of data is available.

The files are not particularly complicated or heavy, however. This is for two reasons. First, I wanted to give everyone a chance to practice, even users with low-end computers. The second relates to practicality. The purpose of the manual is to explain, in concrete terms, how Chaos Corona works, and hundreds of MB files are not needed for this purpose. As I always tell my students:   to understand a certain parameter, you have to practice with simple, fast, and easy-to-manage files.

Thanks to my decades of experience in creating complex scenes (especially exteriors), the structure of the files attached to the guide is logical and comprehensive, and  names of its objects and materials are self-explanatory. All scenes are organized with layers specially named to offer perfect navigation within the file structure.

The book was developed using 3ds Max 2015, when Corona Renderer v1.3 was compatible with 3ds Max 2011. All files are tested with 3ds Max2014 and 2021, ensuring full compatibility with all 3ds Max versions supported by Corona Renderer v6.0.

In addition to the .max files, I made dozens of technical videos in .mov format, all available in low resolution at our YouTube channel. Thanks to these animations, understanding the more complex parameters will be simplier and hopefully more enjoyable (Fig. 1.32, Fig. 1.33, Fig. 1.34).

Fig. 1.32 - Scene used to explain indoor static animations (fly through).
Fig. 1.33 - Scene used to explain indoor dynamic animations.
Fig. 1.34 - Scene used to explain outdoor dynamic animations.

Also included are .psd (Photoshop) and .aep (After Effects) files, developed during the writing of the Render Elements chapter (Fig. 1.35). I made an animation and saved some REs “frame-by-frame” in 32-bit depth in order to understand, in practical terms, how to compose the various REs together. No one has ever made such accurate post-production tutorials for Chaos Corona, explaining all its thirty-two REs one by one.

Finally, there are animations in OpenVDB format used for the analysis of the CoronaVolumeGrid object (Fig. 1.36). I devoted an enormous amount of time to developing the DVD content, and I am sure these files will become faithful companions on the long journey towards learning Chaos Corona.

Fig. 1.35 - "Adobe After Effects" file used for the explanation of many "Render Elements".
Fig. 1.36 - Animation used to explain the "CoronaVolumeGrid" object.


At the moment, I want to take a break from these long and tiring four years, during which the writing of the book, its translation and the creation of the new website absorbed all my energies. But the life of Corona: THE COMPLETE GUIDE will be long, and I will try to offer small updates with each new Chaos Corona version. I’m also preparing a surprise for Chaos Corona users. Meanwhile, we are always active in experimenting with new technologies.


At the time this interview took place (November 2020), the book was being printed. You can stay informed by going to the website for news, and you can sign up to be notified when the book is ready for shipping at the following page:

The book will be on sale exclusively on our website via our e-commerce at the following link:

The price is 119 euros plus shipping. You can pay by wire transfer, PayPal, or credit card. Shipments are traceable via a tracking number provided by email. For international orders, shipping will be available by air freight for faster service



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