Tutorial: Making of the Citroën Lacoste press kit

Tutorial: Making of the Citroën Lacoste press kit

by Charles-Antoine, September 3, 2011

Citroën Lacoste final renderThis small article is a simple Tutorial: Making of the Citroën Lacoste press kit. The Citroën Lacoste is a concept-car that was presented at the Paris International Motor show in September 2010. It consists in a minimalist, user-friendly casual vehicle, and our two-guy team had to create its press kit. I propose you to enter the Citroën Design department to discover how Laurent Nivalle and I made this press kit that required four weeks of work.

Art direction research

Before starting anything, it is a good idea to what direction to take. According to what this vehicle stands for, Laurent defines the art direction to give to the press kit. In this case, the speech is oriented towards a nice bright natural environment made of a sand beach that goes along with the message the brand wants to spread. An additional constraint came over this : the PSA green chart forbids to put a car in a natural environment, whether the vehicle is real or virtual. This small detail will appear to be quite critical in our search of environments and image composition.

This kind of image can easily be translated into a CGI context : the car, naturally rendered and lit by an HDR image, will be integrated over a photograph. Which means that we will have to shoot our backgrounds, and use a Spheron camera to make the HDRIs from the spots that will be shot.

CAD model preparation

Citroën CAD design team built the car in 3D using softwares such as Icem Surf and AutoStudio. Those softwares, mainly used in industry and especially by car manufacturers, allow the creation of Class A surfaces, the highest quality level for surfaces so that reflections on the car can be as perfect as possible. The car is actually made of NURBS surfaces, which is not the best format for images. Therefore, the first step consists in converting this purely mathematical model into a polygonal mesh after having organized it according to our needs.

Once imported in 3dsMax (often after quite some work to obtain clean surfaces), we can start the real work. The first materials are applied according to the Colors and Trims department indications. This department is in charge of creating the color palettes and defining the materials of the cars. We already know that we will have to take changes into account later, but at this point nothing is fixed as the car does not physically exist yet. We have to wait for decisions to be made and for references to be available. Anyway, the current draft is enough to be used to look for nice points of view. This step of creating the different cameras is quite critical as it defines not only the composition of our images but also the way people will feel and understand the shapes of the vehicle. Every shot must evidence the volume while playing with shapes. We therefore try to make descriptive shots that allow to understand the car as well as graphical shots that are intended to be more artistic.

Overview of the different angles

Overview of the different angles

After the art direction got the agreement of everybody, it is time to make the images itself. The most simple procedure in our case was to integrate the car onto a photograph and to lit the scene with and HDR image taken on the same spot as the background in order to get the best integration. We extracted all the required information from the validated 3D cameras (distance to the car, height, roll angle, focal length) ; these information will be used during the backgrounds shooting to make them match perfectly with the car.

Live action shots

After having carefully checked the weather, we leave our desks on a sunny day of August to go in the North of France with Laurent and a computing engineer. Weather is hopefully on our side. The program is quite intense : we have to locate the spots that will be used as backgrounds, to take the shots according to the different cameras (distance to the car, focal length, roll angle), to shot the HDR images with the Spheron cam and to check all this in live 3D. At this point, we have to consider the PSA green chart ; we therefore took a few pictures of sand roads that will later be integrated under the car.

HDRI shot with a Spheron camera

HDR image shot with a Spheron camera

Picture that will later be used as a background

Picture that will later be used as background

Road to be placed under the car in compositing

Road to be placed under the car in compositing

Scene setup

We now have all the elements to start the real work, that is setting up the 3D scene. It will be quite simple as the one light source is a VRay Sky Dome that allows light emission and shadow casting directly from an HDRI without needing any additional light source, which is a very interesting and convenient specificity. Using this light will lead to a clean and accurate integration of the car onto the back plates. For the ground, a simple plane with a VRay MtlWrapper applied to it to get global illumination and shadows information.

Screenshot of a very empty 3DSMax scene

Screenshot of a very empty 3dsMax scene…

The only trick is that, as we have a lot of images to make, we also have a lot of backgrounds and we had to find workarounds so that we only have one scene file to render, which is more convenient that having one scene file per camera. This was done using scene states and playing with an animated HDRI rotation and environment states.

Model detailing

In the meantime, the prototype manufacturing is going on and we finally get samples and references for the materials : fabric and leather samples that will be scanned and used as textures, reference pictures, materials repartition. The Colors and Trims designer also assists us and keeps us updated about the latest changes.

CAD model with an interior that dramatically lacks details

CAD model with an interior that dramatically lacks details

As shown in the previous image, interior is currently made of a few surfaces. As it is a concept-car, only one is made and a lot of parts are therefore hand-made. CAD is only used for main pieces and parts, which means that the interior model is not detailed enough to get photo-realistic images from it, and does not match with the real trims work, which also changed along with the project. In addition, UV unfolding of a thousand-polygon mesh is clearly not the easiest task ever… This is why the only solution consists in re-modeling those elements in 3dsMax using the classic low poly + smooth technique.

Classic low poly modeling

Classic low poly modeling

Finished interior modeling

Finished interior modeling

Final interior render

Final interior render

The mesh we then get is not only more detailed and easily unfoldable, it also gives a smoother and more realistic aspect to the garment made elements. For more convenience, I often work displaying the final result of the modifier stack that contains the Symmetry and TurboSmooth modifiers. Nevertheless, when mapping needs to be done, I have to collapse the symmetry modifier in order to get rid of texture stretching.

Texture streching problem caused by the symmetry modifier

Texture streching problem caused by the symmetry modifier

UV's of the bench once the modifiers stack has been collapsed

UV’s of the bench once the modifiers stack has been collapsed

In addition of being used for modeling and texturing, the samples are also used to refine our materials to achieve a result as accurate as possible. But we often have to extrapolate as, until the very last minute, live modifications on the car itself are quite numerous.

Rendering the images

Model is detailed, textured and ready, all the chosen back plates are set for each camera, scene is ready including all the required mattes, masks and passes for compositing. As the deadline is approaching, we cannot wait any longer for further modifications of the car. If any, it is now too late !

Our scene is quite simple, so render times won’t be too long. For instance, it takes an average 5 hours for a 5 000 x 2 500 px image. But there are 26 of them to render, and as much to work in compositing and post-production… Concerning our render settings, I used classic Irradiance Map and Light Cache combination for global illumination and an Area anti-aliasing filter to slightly blur the edges for a better blend of the car in the back plates. I usually avoid using sharpening anti-aliasing filters because they tend to give a more “CGI” fake look.

Raw image rendered in approximately 5h

Raw image rendered in approximately 5h

Compositing

We start working on post-production as images are rendered. Images are saved as 32-bit floating point OpenEXR files to keep all the lighting information. It avoids to get burnt or under-exposed areas. For this project, I also extracted a shadow pass to be used as a mask to give the shadows the blueish tint we can notice in a sunny environment. This trick will slightly exaggerate the sensation of light, give a more realistic and subtle aspect and balance the warm light of the sun with a cold color in the shadow areas.

The shadow pass allows to give the shadows a blueish tint

The shadow pass allows to give the shadows a blueish tint

All this work is done in Photoshop. Laurent defines the color touch and the post effects in order to give our images a specific atmosphere. As our images will be used for brand communication, we take extreme care of having accurate materials and colors. 3D renders provide us a working base, but we refine everything using a calibrated screen.

Final image after compositing

Final image after compositing

Conclusion

This project was definitely not the hardest we had, as all we had to do was integrating the CG car into an environment we shot. However, while creating a concept-car press kit, we usually have to create images of a car that does not physically exist yet. Therefore, we are often stuck between the delivery deadline at which our work has to be achieved and waiting for critical information concerning the physical aspect of the car : colors, used materials, material samples, knowing that the aspect itself is meant to evolve until the end. Eventually, even if we fly blind without an existing reference of the car we can base our work on, we are hopefully never too far from the truth.

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