Different objects rendered to different files with transparency

Hi,
I’m new to blender, so please treat me like a total noob :slight_smile:
I want to render my first Blender project. I understand the basics and I know how to render a single PNG file.
I’m trying to render 120frames animation in few variants. Every variant has the same camera and objects. Objects are placed on a plane. I want to create a few version where plane colour is different in every shot, the rest of the elements stay the same. Objects throw shadows on my plane. So ideally I would like to have two separate PNG files with aplha (objects + shadows) and a second file with plane only. Is it possible and if so then how to do it :slight_smile: ?

You render the sequence once and use compositing to change color of plane.
With cryptomatte, it is relatively easy to isolate an object rendered.
https://wiki.blender.org/wiki/Reference/Release_Notes/2.80/Cycles#Cryptomatte

By using cryptomatte node, you can isolate the plane in the image and only apply nodes modifying its color to it.
You can create as many color modifications as wanted in one single nodetree and use a file output node per variant.

But if you absolutely want a set of images (Object+Shadow on a transparent background), youcan set plane as a shadow catcher in 3D View.
https://docs.blender.org/manual/en/latest/render/cycles/object_settings/object_data.html#shadow-catcher.

You are not forced to create 2 blend files.
You can create 2 view layers or you can link object of one scene into another one.

And if you are not annoyed by rendering several times same scene with just a variant of color in material, you are not forced to create as many files as variants needed. You can create fake users for alternative materials of plane and save everything in one .blend file.
Then, switch material of plane at each re-rendering.

Thanks for a quick reply. I would like to go this shadow catcher route, but I need some more help. Let’s say I would like to have separate files for my objects / shadows (plane with objects shadows only / clean colour plane. The question is how to render shadows as a separate file (without the objects)? I want to change colour of my plane in AE or Fusion on a composing stage.

Additional question: because my plane will have different colours the light reflected from it on my objects should also those colour to make it more realistic. Is there a way to export it as a speratare file (layer)?

You can render your image sequence as .exr files.
Basically, you can store compositing passes of your render as layers of a multilayer OpenEXR file or you can save them as separate files of any kind of format using multiples File Output nodes.

You have to define desired passes in View Layer Properties tab.
https://docs.blender.org/manual/en/latest/render/layers/passes.html