Two hopefully really easy Nuke questions.

#1

I’m VERY new to nuke…hopefully two really easy questions.

  1. Imagine two images connected to a merge node. What’s different between connecting with A and B, or other way around, B then A?

Is one always on top or it reads from left to right?

  1. I have a render from 3dsMax. The background is grey. How do I make the grey an alpha?

In a tutorial I saw from maya, a constant node was added, the colour changed, and the background seemed to automatically change like the object already has an alpha?

(I’m rendering multi passes in Max so have lots of layers)

Thanks!!!

#2

  1. depends on blending mode, but with default, A is over B.

  2. make a shuffle node, set alpha to a color channel.

#3
  1. Do you want to make the grey transparent? Alpha is a channel name, and this channel contains transparency values.
    In order to work with the image correctly in Nuke, the background needs to be black and alpha value on the background has to be 0.
#4

Yes, I want the background to be transparent. At the moment the background is grey, but I can make it Black (0)

I followed the other advice, I made the red channel the alpha, using a grade node too. Maybe I’m doing something wrong here, because the result was rubbish, the background is a plain colour so should be easy, but the red channel didn’t work correctly around my object… the edges fuzzy.

Not being funny but… Seeing as you can render out alpha’s in Max, why is there not a simple alpha node?! Or just attach it to the mask? Or can you?

I have a perfect alpha ready (black and white), can I just attach it to the mask?

GringoFX, how do I do that?, I have a mask (black-0)

http://www.youtube.com/watch?v=CCzzp5tG4Eg

On 20mins, 20 seconds… all he does is add a merge node and saying, ‘as you can see the background is under the gun’…

I might have missed him clicking on something to make this possible?

Thanks!

#5

The background is grey. How do I make the grey an alpha?..
Yes, I want the background to be transparent. At the moment the background is grey, but I can make it Black (0)

If you don’t have any object completely blocking the background, the background from your 3ds Max is transparent by default, no matter what color or bitmap you use in your Environment menu. You’ll need to save into an image format that does support alpha channels. exr, tif, tga, png for instance do save an alpha channel, jpegs don’t.

I have a perfect alpha ready (black and white), can I just attach it to the mask?

You can use a merge node’s various blend modes to attach an alpha channel to an existing mask.

In a tutorial I saw from maya, a constant node was added, the colour changed, and the background seemed to automatically change like the object already has an alpha?
Should be the same with an image from 3ds Max.
Create a constant, select both your read node and constant node, hit ‘m’ to create a merge node and you should be good(assuming there’s an alpha channel). When using ‘over’ A will be your image, B your background color in nuke.

I attached a nuke script, just pipe you read node into the dot where it says READ_IN.

#6

OK thanks! I’ve had a quick read, that will put me on the right path.

I am using ‘exr’ files.

I will spend a good few hours going through all these notes…

thanks!

(thanks everyone!)