How to blur a single object, Layers dont exist anymore? (2.92)(Permanent interface changes confuse every new user)

Question

I've tried to find a solution for 2.92. As the title suggests I am not able to do this simple thing. I want to blur a single object, not motion blur with he camera I mean simply blur an object.

I have looked around forever and as usual every video is either too old or the blender version has changed and the buttons are somewhere else, or the way layers work has changed or something else... It is REALLY hard for newcomers to learn properly since it gets so frustrating after searching for up to date tutorials.

So all i could find out (thanks to Stackexchange) is that the render layers don't exist anymore and that i have to work with collections now, i created a collection, put my object in there but all tutorials only talk about render layer nodes in the compositor, but that doesn't let me pick the collection, I also changed the pass ID to greater than 0 and if i pick the pass node i cant connect it to my collection since its so confusing to find out what combo works atm..

Can someone please explain to me where i can find actual up to date infos about blender or a place in general where changes are shown or explained, I wouldn't have any problem with old tutorials if there would be a clear way of checking how to replicate the steps in the newer version.

This is really sucking out the fun of learning.

All help is appreciated.

Answer 1

I am by no means used to work much with the compositor, that said, I hope what I am going to show here is not too far from what others would do.

Object Index method:

1. Activate the Object Index in the View Layer Properties:
2. Make sure the object in question has its own Object Properties -> Relations->Pass Index:
3. Render the image with F12 if only that one object needs special treatment, otherwise give each object that needs it its own Pass Index like in step 2.
4. Go in the Compositor and activate Use Nodes: simple example of a cube and sphere, whereas the sphere has pass index 1 and cube has pass index 2 Using the ID Mask node you can get the mask for the specific object or objects(same pass index objects are in the same mask)
5. Multiplying the rendered image with the mask we obtain the separate object and adding a Blur node we can then blur the specific object: This would be blurring a specific object

Cryptomatte method:

1. Activate View Layer Properties->Passes->Cryptomatte->Object:
2. With the object already having its own pass, you can then render and get new output sockets on the Render Layers node in the compositor.
3. Connecting those to a Cryptomatte node and later the Blur node you get this: The Cryptomatte node needs to be set up first
4. With the Pick output used, you can easy use the eyedropper Add to select the wanted object and switching to the Matte output this will show the mask created.
5. Switching now to the Image output you get only the selected object from the entire render.
6. Routing this image through the Blur node will then result in the same as above Object Index method.

UPDATE (Compositing the blurred object back into the image)

While not 100% sure, I believe this should be the result asked for: All the difference is an Alpha Over node