This week, we studied how to do a CG beauty rebuild, using channels or passes of our CG to see its layers to then adjust them separately, relight them, and put them back together.
To start with the CG beauty rebuild, first we need our CG layers (usually the CG has already been exported like this). We can see all these layers separated in the ‘layer contact sheet‘ which contains a view of passes in EXR (e.g. diffuse, specular, reflection, etc). The separation of the EXR in layers or passes (channels) is used for adjusting each pass separately to match the lighting and colour conditions of the background. In order to adjust each pass, we first need a ‘shuffle‘ node set with the specific pass (input layer) we need to then ‘merge (plus)‘ (+) for the lights (diffuse, indirect, specular, and reflections) and ‘merge (multiply)‘ (*) for shadows (AO or ambient occlusion, and shadow). Every pass must be graded separately and then we could add a final ‘grade’ or/and ‘colour correct’ to the entire asset if needed.
There are several types of ‘render passes’ or ‘AOVs’ (Arbitrary Output Variable):
- Beauty Rebuilt Passes:
- Material AOVs. To adjust material attributes (shader).
- Light Groups. To adjust individual lights of a scene.
- Data Passes:
- Utilities. Combined with tools to get various effects (e.g. motion blur, defocus, etc.).
- IDs. To create alphas or mattes for different areas of the render.
There are some elements that can be used to double check or improve our CG beauty rebuild quality:
- Cryptomatte. To see different parts of the scene colours.
- KeyID. To create a mask of the ID pass.
- AO pass. It creates a fake shadow, produced by proximity of geometry to other geometry or background.
- Motion pass. It let us see the blur of the motion clearly.
The process to subtract a pass to edit it is the following:
- Unpremult (all)
- Link to ‘shuffle’ node (set with pass needed)
- ‘Grade’ and make adjustments needed
- Add back with ‘merge (plus)’ or ‘merge (multiply)’
- ‘Remove (keep)’ node
- ‘Permult’
Once we have our colour correction and grading made, we can relight the scene with ‘position pass’ which is the 3D scene but in colour values (red=X, green=Y, blue=Z). In order to have a reference of the 3D space, we could use a ‘position to points’ node set with ‘surface point’ to ‘position’ and ‘surface normal’ to ‘normal’. We then adjust the point size how we want and we will see a 3D representation of colour values. Once the representation is made we can start to add lights with ‘points’ nodes linked to the ‘scene’ node to put them together. This scene is then connected to a ‘relight’ node which puts light, colour, material, and camera together (use alpha, and link ‘normal vector’ to ‘normal’ and ‘point positions’ to ‘point’). To merge over original background, we then ‘shuffle’ and ‘merge’.
As a homework of the week, we need to composite a 3D modelled car in a background of out choice:
I feel like this practice was simpler than last week’s homework, however, I still encountered some challenges that I would like to research and study, such as the addition of ‘fake’ lights to the car lights to look like they are turned on, and also to get rid of a specific area glow like the one on the right door of the car which does not really make sense it shows there.