Multipass

Hi Tim.

After testing how the OpenEXR plugin works I found that it's much much simpler to render the layers to separate image sequences using PNG/TIFF files.
But, if you prefer OpenEXR be aware that Blender has two different flavors of it. If you select the reender to use OpenEXR the resulting files will only have one layer. If you use the "Multilayer" output format then you will have an OpenEXR file with all the layers that you have selected in the "Render Layers" tab.
Remember that you have to explicitly name the render file and to give them the ".exr" extension because the Multilayer option doesn't do that for you.


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Paolo Ciccone
Pret-A-3D
http://www.preta3d.com
http://www.paolociccone.com

I was afraid that you would ask :)
The workflow goes like this:

- The combined pass is the only one for which you can directly set a file name in the output tab. You also must have a default pass so the combined is a good example but you could use it to render directly the Color/Diffuse pass. Up to you.

- If you need to create a separate pass, for example for the shadows, you need to create a new render layer in the "Render Layer" tab.
First rename the default layer, which is called "1 RenderLayer" something like "Combined" or "Color".
Drop down the list of render layers and select "ADD NEW".
Rename the new render layer "Shadow"
In that "Shadow" layer deselct "Solid, Halo" etc. and select only the shadow pass.
- Now open a Node Editor window. You will need to use Blender's compositor for the multipass.
In the Node Editor click on the button with the little face, it activates the Compositor
- Make the "Use Node" button active if it's not already
- Press "Home" to see the default Noddles and nodes. It should show a network of a render layer node, defaulting to the first layer, connected to a "Composite" output layer. Leave them alone.
- Press Shift-A, select Add/Input/Render Layers
- In the newly created node drop down the list of the layer names and select "Shadow". Now the output sockets of the node should show Image, Alpha and Shadow.
- Shift-A and select Add/Output/File Output. The new node shoudl be already connected. If not Drag a noodle from the Image socket of the Shadow Layer node, to the image input socket of the File Output node.
- In the File Output node set the file format to PNG and to a location of your choice, possibly a separate directory.
- Go back to the output tab and, below the "Anim" button, find the "Do Composite" button. That tells Blender to go through the Compositor whenever it renders a frame. That in turn will pass the action to each of the Render Layer node and that in turn will output the shadow pass via the File Output node.
- Click on the "Anim" button and Blender will render all the layer per each frame.
- Collect the files and start compositing.

Hope this helps.

--
Paolo Ciccone
Pret-A-3D
http://www.preta3d.com
http://www.paolociccone.com

Sorry, my mistake, disconnect the noode from the Shadow Layer and create a new one from the Shadow socket to the File Output node.

--
Paolo Ciccone
Pret-A-3D
http://www.preta3d.com
http://www.paolociccone.com

Very cool Bartek!

I've been trying to get my head wrapped around the nodes in Blender and this is very helpful. Along with Paolo's AE export script and render passes, this is a very powerful workflow.

Thanks again guys!!



Improper planning on your part doesn't necessarily constitute and emergency on my part

Well - that's right, but every render layer requires another analysis of the scene by the render engine, so the scene simply renders longer.
In simple scenes you can afford this, but in more complicated ones? Well...
Changing settings of the render layer takes about a minute, or two.
Render time difference may be several hours.

Bartek Skorupa
Warszawa, Poland

Hi,
It is very good to have such discussions in public, as many other users can have a look at it and take what's useful for him or her.
Every scene is different and before you hit Ctl-F12 it's good to take some time to make analysis.

Let me present the way I like to work on scenes that require a lot of rendering time:

First I prepare the scene, set up Render Layers and render passes.
I chose to have as little amount of render layers as possible.
I don't do any compositing. I just chose MultiLayer as the output format and render the sequence.
Then I open fresh, new blend file (or create new scene), set the Render Layer so that it renders nothing, activate "Do Composite", add an input node of "image", select the sequence of *.exr (MultiLayer), and take a look at the passes. (Just add a viewer node and link it to what I want).
Because all those passes are already rendered, I don't wait hours for the frame to render, I just chose the frame to look at, and see if I like the result or not.
When I like what I see, I just link File Output nodes to the passes. (This additional render takes seconds, so it's worth doing it in many cases).
If I don't like what I get as passes - I try to fix it by adding some nodes. If I have to - I rerender some passes. I just reopen the file with my scene and then create render layer that I need to rerender the pass.

Most of the scenes require compositing. I do compositing both in blender and in After Effects. I just try to take advantage of both apps.
Having rendered MultiLayer gives me possibility to go back to the fresh render without any blender compositing any time I want.
That's just a way I like to work. It may seem weird at first, but believe me... I tested it, tried many other workflows - and the one I just presented suits me best.

Bartek Skorupa
Warszawa, Poland

It IS working better. Much better.
In fact in After Effects CS4 you don't have to install any additional stuff to have the access to the passes stored in MultiLayer exr. You just select "Extractor" from 3D channel, but I don't recommend using it, because it takes ages even to see the single frame.
I extract the passes using blender, and then composite separate sequences in AE.
Try also this one:
Render the MultiLayer from blender. Include the vector pass.
Composite the stuff in AE. Render it out.
Go back to blender and add vector blur to the result from AE using vector pass from your Multi Layer.
You will need the input of the MultiLayer to have the vector data, and your final render from AE as the image.
Add a "vector blur" node. Connect the image to your final render from AE, and Speed to vector socket of the MultiLayer, and Z to the Z socket of your MultiLayer.
You have the nice motion blur in seconds.


Bartek Skorupa
Warszawa, Poland

I must say that I don't really remember why I do this. I know that I had a problem once, so just to be sure I don't have that problem again - I Set Alpha of 1 to the vector data. If it has Alpha of 1 anyway - nothing will change, but sometimes it has Alpha of zero in some places, so this limits the blur to the borders of the object. Setting alpha doesn't change color values, so I just do it to be sure everything goes right.

Bartek Skorupa
Warszawa, Poland