How to use cryptomatte to select objects in fusion

Hello.. I'm starting to use cryptomatte in fusion.. very powerful feature, but, I'm stuck...

I have an hourglass that I need to make bluish and the sand needs to stay sand color..

I see my cryptomatte color differences, but if I move the cursor over the sand or a character inside the hourglass, it doesn't select that object, but rather the glass...

So how to I go about to isolate object inside a glass with my cryptomatte...

thx.

Marc.

It may not work because I've never tried to select an object behind another object, because that's technically what you're trying to do BUT Cryptomattes are bases on either a material name or an object name. So if you know the name of what it is you're trying to select, you can just type it in instead of using the eyedropper. You may be able to do it in this case because it's still visible? Otherwise I would suggest using puzzle mattes for those objects. It will give you options for allowing refractions.

Hello.. thx for the answer.. I did not try to select the object by name.. Will definitely try that..

And is "puzzle mattes" within Fusion? or it's something I need to export or setup in my 3D software.. (Using Blender and Cinema 4D).

thx.

Marc.

You didn't mention if you were using the cryptomatte plugins for Fusion or if you were just loading cyrptomatte renders in a regular loader.

I’m using the reactor plugin indeed

Ah well, I was hoping that not using it was the magic source for a solution.

It might help to open this thread over on WSL since the Cryptomatte expertise over there is slightly higher.

So a puzzle matte is just a generic name for the red, green and blue matte you can generate from a 3D rendering set up. It was the standard before Cryptomattes came along gave us all back a bit of sanity. You assign an ID of 1, 2 or 3 to all the objects you want rendered in either red, green or blue. Then, in your compositor of choice, you'd select one of the three colors as a key and away you go. With all the sub pixel issues you can imagine.

The other trick with Cyptomattes is to assign an override color of black to you entire scene and turn off all your lights. The scene will render a beauty of black ultra fast and then output the Cryptomattes as normal since they are object based and not color based. Since your trying to get to something hidden by some glass, you can hide the glass object and render a specific Crypto pass with the intended objects visible.

The only trick becomes the refraction index of the glass and using the Crypto in the warpped reflections. This is where a puzzle pass with the colors reflected accurately will probably be a better choice?

I actually got it going by typing the object's name in the cryptomatte object name... Selected my character behind the glass, and I was able to color correct only that !!

Thanks for your help!!

Out of curiosity, did you use materials or objects to define the Cryptomattes? I wonder if using materials allows it to be selectable in reflections vs "object" that would have created a matte from the glass geometry.

Material vs object would probably make no difference. How picking is implemented here I don’t know exactly but if it selects the id with biggest coverage per pixel you will still get glass, because material samples give same coverage as objects.

Out of curiosity, did you use materials or objects to define the Cryptomattes? I wonder if using materials allows it to be selectable in reflections vs "object" that would have created a matte from the glass geometry.

I use both.. in case I needed to call all the same materials, that were not necessarily the same objects.

But for that case, I typed in the object name..

cheers