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Creating different alpha groups for the car body, the wheels and the whole car object
You can also indicate if the transparent objects will.... Opaque
The indicated As with the regular Alpha channel, you can render a completely white alpha also for transparent objects by enabling the Opaque option, useful if you want to maintain the full look of the transparency from the render instead of blending it with any other images in your composite, or leave it unchecked so the alpha grey value shows the transparency of the material.
The masks will be exported as independent alpha images in the desired indicated format.
The Custom Alpha channel feature allows you to get independent masks for the selected group of objects. Here the car body, the wheels and the whole car
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