Fading hair to invisibility?

cobusp

I am busy with a CSI scene of a poached rhino (based on a real scene I visited here in South Africa) for a major news network.

I used the hair tool to create the long grass, which works well as you can see. My plan is to make it invisible over about 1 second to make the scene look more stylized (and a grid shader to replace the soil shader.

But, to make the hair vanish is more of a mission than I anticipated: As you will see in the sequencer, it is supposed to be gone after its visibility has turned to 0.

Can this effect only be obtained by making the hair shader invisible?

Side note: I find it rather frustrating that the visibility parameter for objects cannot be animated with spline tangents, i.e. make it to fade aeay over time.

Can anybody help please?

Sockratease

I'd "do it in post" for simplicity.

You could do two renders, then layer them in a video editor (one with grass on top, and without on bottom) and slowly fade the top layer. Even my old ULead gif animator could do it then export a png sequence for use elsewhere. This would work whether the scene is animated or not but works better on a still because of things like shadows and even etc.

Sorry, I know of no way to do that inherently in Cowrarra.

Hope that helps...

3DAGE

HI Cobusp :)

Yes,. you'd animate the hair shader
Carrara doesn't have any way to animate object visibility over time (Fade in / Fade out),. it's an on/off thing Visible or invisible on a single key-frame.

By animating the shader transparency, you can "fade" the visibility of the object.

However,...

The Hair shaderr doesn't have a Transparency option.....

What it does have,.. is Density / Length / and Thickness.

A quick test with a sphere would suggest that the Thickness , or Length is your best options for animating the disappearance of the grass.

Hope it helps :)

DUDU

It's very easy to do a grass texture.
Why not use a multichannel texture and tweek the alpha channel which can be animated ?

cobusp

Ah, thanks for the feedback. I thought it would have something to do with the hair shader.

Pity that one cannot fade object visibility - I guess there would probably be a reason for only making it work only with an on/off function?

Socrates -- now there is a good second option! I should have though about it. But, if it is quite a complex scene to animate that takes long to render, then this will obviously have to be plan B only.

3DAGE

Actually,. I think DUDU's idea is simpler,. easier.

Just change the shader on the grass, to a normal Multichannel shader, ..rather than the "Hair shader"

That'll give you the options for Alpha value,. or Transparency Value, which can be easily key-framed.

way too early on a Sunday morning for my brain to get past the problem of using the hair shader to realise that simply changing it was easier.

Nice DUDU

Sockratease

One advantage to doing it in post with two layers is the control over the fade. It can happen top to bottom, radially from the subject, in patches, or however else you want to make it fade.

Alpha animating is easiest, but I don't think the uniform fade will make for as satisfying a transition in a video project.

I guess it all depends on time, taste, and the needs of the client.

cobusp

3DAGE said:

Actually,. I think DUDU's idea is simpler,. easier.

Just change the shader on the grass, to a normal Multichannel shader, ..rather than the "Hair shader"

That'll give you the options for Alpha value,. or Transparency Value, which can be easily key-framed.

way too early on a Sunday morning for my brain to get past the problem of using the hair shader to realise that simply changing it was easier.

Nice DUDU

Sounds good. Is it possible to get a screen shot of such a multichannel breakdown?

cobusp

Sockratease said:

One advantage to doing it in post with two layers is the control over the fade. It can happen top to bottom, radially from the subject, in patches, or however else you want to make it fade.

Alpha animating is easiest, but I don't think the uniform fade will make for as satisfying a transition in a video project.

I guess it all depends on time, taste, and the needs of the client.

Yes I agree. This will give you most control during post-work. The only issue might be time.

Thanks

DUDU

Not shure you're asking for a grass shader especially but here a excellent tuto about the multichannel shader : https://www.youtube.com/watch?feature=player_embedded&v=0DQhtVZ1-8U#!

WendyLuvsCatz

I thought it HAD to be a hair shader to work on hair,( the exception being in Octane where I can actually use any Octane shader but not instead rather applied in the viewport or the option in effects)
Any attempt to change a hair shader to multichannel, terrain etc usually gives me black hair.

3DAGE

You're right Wendy. :)

Changing the Hair shader to a Multichannel, ..to get the Alpha or transparency options,... won't work.

Cobusp will need to try animating the thickness or length,. to fade it in Carrara,.
or do it in Post,. which is probably the easiest option.

DUDU

I return my medal to you Andy, I believed to have done it… Thikness is the best solution.
Is it an explanation for that ?

3DAGE

Explanation = Dumb Luck :)