MULTI PASS RENDERING AND COMPOSITING WITH ROBBY BRANHAM tutorial series 03

 

Video 3 of the series was about exporting the scene to Nuke. The Aronorld hyper shade in Maya is like Nuke, where there are branches that must be connected for the information to be presented adequately, such as colour and imported images. This video started to introduce that. The branches in Nuke are called RE:nodes and they can be set up by the project trajectory.

Branham "A shuffle node is when you select one channel like the lighting pass and it is shuffled out into the RGBA. The RGBA becomes the lighting pass and it can now visually change the picture"

The coloured R(ed)G(reen)B(lue)A(lpha) are the incoming channels.

The non-coloured R(ed)G(reen)B(lue)A(lpha) are the outcoming channels.

If you click on the black it will pour pure black into the RGBA, the same applies if you click the white.

When you select the colours it will shuffle them into all the channels.

To do the beauty pass, copy the shuffle lighting and change the in 1 to GI pass.

You then combine both shuffle lighting by pressing M in Nuke. The operation that you use is plus (+).

Then copy the merge and GI pass but this time change GI to reflect.

Copy again to change reflect to specular.

selecting the shuffle means it automatically hooks up to the branch/node you've made before.

Following passes: refract,  SelfIlum, SSS and atmosphere all this together gets back to the beauty of the Maya render. 

In read 1, if you press A the alpha shows black and white which changes all the work you've done, but there's a way to solve this. This alpha error is more visibible with renders that don't cover the full frames.

To fix this you search unpremult to divide the alpha by the RGBA then premult after.

Press ctrl + shift + x to connect premult to bottom of chain (connected to atmosphere). This means you are working between the unpremult and premult.

When you go from start to the end of the premults it gets darker. This destroys the alphas. To save the alphas you need to store the original RGBA into the read1 alpha ad shuffle it back out into the chain's end (premult).

Adding a shuffle node in between unpremult and read 1  which shuffles the RGBA into a new channel.

In the new channel select new (where the RGB tab would be) which gives us a new layer option. 

Then type (_startRGBA)

Underscores separate utility passes from RGBA passes.

Hit rgb preset and it will do the channels for us.

A channel is a RGBA and layers are SSS, atmosphere ect.

This restore the RGBA but we really want to unpremult all the channels. This will help later on with matte passes. This helps prevents bad edges around renders like pixels.

Unpremulting the channels makes the alphas innefective.

To stop this drop ion a copy node. The copy node copies the layers from a tree, specifically A (alpha) tree.

Hit period to make a dot. Hit A  which brings it to the start RGB layer. (above unpremult and between read 1). This copies in our channel.

Selecting _startRGBA gives us out original RGBA channel.

The rest of the passes like lighting will be unpremulted which is what we want.

The actual _startRGBA will be left untouched.

Select shuffle, unpremult and copy and hit tab to backdrop them (search backdrop) this will be new unpremult.

Something similar for premult.

Go shuffle leave 1 (RGBA) the same but change 2 to _startRGBA as we only want to take the alpha from that channel.

This helps to rebuild the beauty more.

With the alpha restore a full white image is made.

Taking off the premult makes us go 1 for 1 for the original image (removing premult makes it more fuzzy of an image after all of these steps have been taken).

Backdrop premult and shuffle RGBA at bottom.

Everything will run smoothly as long as the work is in between the unpermult backdrop and the premult backdrop.

Switching back to read 2, there is much more control over the original image.

If there is wireframe on the render you can remove it in Nuke. select selfIlum and press G which gives you grade. selecting multiply and bring it down will take to the wireframe.

If you want an object to be more brimmed up go to the specular pass. Hit G. You can boost up the multiply. if you search glow a nice specular glow is formed.

If you want to play with the atmosphere to bring contrast between the foreground and background you would hit G and multiply up. Bringing the game lower creates stronger contrast. Scrolling up and down shows the different ranges and it's usually between 1 and 7.

This is the simplest way to rebuild the image. If you wanted greater control of the colours in the image or lights themselves you would have to dive into overall passes.