Creating a 3D Box Shot with Carrara

[Thomas]

This short tutorial is going to show us how to realize a typical job where 3D is pretty essential: creating a Box Shot (for websites, product presentation, catalogs, magazines, and more) pretty quickly, using Carrara.


At first thought, it seems to be a simple task, but we are quickly going to see that some issues will occur, especially if we want to utilize the result in an image editing tool (like Photoshop®) and outline the box while keeping the shadow projected on the floor.

[Thomas]

Part One: Scene creation and first considerations.

Here is the scene on which we will be working: a 3D object (fake Carrara 5 box), a floor and several light sources. For this tutorial, no lighting effects will be used, (e.g. no HDRI, no Global Illumination) only a soft skylight (20%), which allows us to get a soft ambient light which will look nicer than the default ambient lighting. Note that we have created 4 light sources: 3 spots for the box and a vertical light source to light the floor and the top face of the box.

Before doing the first render, think about selecting, in the Render Output Parameters, the two options "Render Alpha Channel" and "Use Premultiplied Alpha" of the PSD file format. Let's generate a render, open the created .PSD file in Photoshop and look at the result: If we look closely, several problems appear: first of all on the right, in the Alpha channel, the floor is clearly visible. It is impossible to completely outline the box in a clean manner. This means that it will require tedious work by hand. The other problem appears on the floor render itself. We can see that it is over-illuminated (we would say "burned"). The shadow is even brighter just behind the box than in its extremity, which is far from the effect we are looking for. This is due to the lighting, composed of several light sources, converging on the same place. Below, the rendered image outlined through the alpha channel. We can throw out this result, because it is simply not usable.

[Thomas]

Part Two: Improvements

Let's go back to Carrara to fix that problem. Let's select the floor and change its material properties. The main trick of this tutorial consists of using a “Shadow Catcher” material, which will be invisible on the rendered image, but that (as its name means) catches (receives) the projected shadows. Note as well that 3D objects located behind it are invisible, but it lets the background color/environment pass through. Very convenient for special effects! Lets'go into the Material Editor, with the floor selected, to edit its properties. As shown in the above snap shot, let's click in the pull-down menu on the top of the shader tree and change the type (the "Lighting Model") from "Multi Channel" to "Shadow Catcher". You should get a shader tree like the one shown on the right side of the snap shot, indicated by the red arrow. You can also put all the other channels on "none" if you wish (this is not mandatory).

It's now time to do a new render. But before we proceed, let's change the backdrop color to white, as shown in the snapshot below. Click in the Scene Tree located in the Assembly Room, on the "Scene" (1) name, then in the "Backdrop" field, choose a white color (2) Let's render a new image now, open the new file into Photoshop and look at the result: We immediately see that the render is much better: we have a more natural shadow, with a perfect alpha channel that lets us see that the outlining will be much easier. This is due to the floor material properties that only display the shadows and not the object itself. The shadow is thus absolutely perfect. Below, the outlined render through the alpha channel. A perfectly usable result! Note the shadow indicated by the arrow, and which is almost invisible.

A last final problem remains which we are going to fix in the third and final part of this tutorial.

[Thomas]

Part Three: Finish

In many cases, we will perhaps need a different background color, a pattern or a background image. We could always change the Carrara Backdrop, but generating a new render can be time consuming and is not a very productive approach for this kind of piece. So instead, let's change the background color in Photoshop andsee the result: Left, with a black background, the shadow appears, and right, the shadow is displayed, but in blue-gray. This does not look very natural... The problem in fact comes from the Carrara Backdrop color, which influences the shadow color at rendering time. It is an important point to take into account. Below, new renders generated with a black backdrop and then, in Photoshop, different background colors, with the result always being a black shadow. In conclusion: if you wish to test different background colors or patterns in your image editing tool, use a Black Backdrop color when generating the render in Carrara. This will give you much more freedom to experiment with various incarnations, while keeping the shadow effect natural.

Now you know how to create renders with uniform backgrounds very quickly with Carrara. You will be pleased to know that there is a lighting work around with the new Carrara 5: you can include and exclude objects from the lighting. For example, you can include only the box shot in the lighting and exclude the floor. Then you would create a light that will light only the floor, excluding all the other elements. This is very useful to create uniform floors very easily. But it does not solve the issue of a quick outlining!