DFD1022 4.3 Look Development – 3D-Tracking with After Effects and Blender – Audi A6 by Nick Mez
MultiLayer #EXR compositing in Adobe After Effects with #OCIO #AgX.
I bought the wonderful #Audi A6 model from Nick Mez and used it to further develop the integration. Integrating a 3D model with reflective surfaces onto a filmed #backplate with a photographed #HDR image at the model's position is not an easy task, as you need a properly matched #environment for the reflective parts. The #equirectangular #HDRI is usually the key to this, but it cannot simulate the #texture of the ground, which is important for a convincing #reflection in combination with the #shadow of the object, which is created by a so-called shadow catcher pass.
The first idea is a camera projection of the filmed #backplate onto a floor plane with an adjusted #PBR #material and some color corrections to adjust the reflection intensity of the HDRI image. However, this results in a clipped floor due to the lack of information outside the frame, which we will see in the reflections. Also, the texture blends with the HDRI reflection, resulting in a shape boundary between the clipped camera projection and the HDRI.
Extending the texture with tiles with mirrors is the next idea, but the kaleidoscope effect due to the camera movement is visible in the reflections of the car, which makes it look like a coding error.
The actual solution in the result is a modification of the HDRI environment mapping by compressing the bottom of the sphere to a flat plane with a special #vector node tree and a vector transform node to project the equirectangular HDRI onto the ground plane. The tricky part is to match the image detail as well as possible with the detail of the backplate to prevent specific parts of the backplate under the #car from being reflected in the doors. This can be adjusted by additionally animating the parameters of the #mapping node over the whole #sequence.
The next step is to adjust the #intensity of the projected HDRI map to the image-based #rendering result. This is necessary because the HDRI map illuminates the scene and this affects the result of the textured PBR material of the floor. It will be too bright. To compensate for this, I used a chrome sphere and added color correction to the HDRI texture projection until it is very close to the color and intensity of the original HDRI environment reflection. Finally, I switch between the shadow catcher model and the HDRI result to compare the chrome sphere and car renderings in the viewport.
It would be easier if the shadow catcher in #Blender rendered a transparency-mapped shadow catcher. This means the shadow is opaque and the rest transparent for the HDRI lighting and reflection from below. If I turn off "Visibility: Glossy" for the shadow catcher model, the shadow is also disabled, but the shadow is important to block the lighting and reflection coming from below the HDRI environment map.
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