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View Full Version : Smooth Dissolve problems with glass item



Johnny
12-04-2009, 12:09 PM
I have a glass which I need to fade gently from view...I used Dissolve on the object, and enveloped a nice, smoooooth curve, but when I play back the resulting clip, their is a very abrupt change in opacity from one frame to the next which you notice..it's nasty.

no other object in the same scene to which I've applied dissolve behaves this way; they all fade out smoothly and gently with no sudden jumps in opacity.

So, I enveloped every aspect of the glass, and of it's air polys and it makes no change!

I tinkered with the Dissolve envelope. No improvement.

Can anyone suggest how I can make this glass item fade out properly?

thank you!

J

toby
12-04-2009, 05:20 PM
Seems to work ok for me, are you using dialectric? What properties of glass are you using, reflection, refraction? Can you post a video?

or a scene might be easier.

Johnny
12-04-2009, 05:34 PM
Seems to work ok for me, are you using dialectric? What properties of glass are you using, reflection, refraction? Can you post a video?


regular glass..martini, in fact...has air polys, and all the usual stuff...thin film, I believe, raytraced reflection.

The martini glass is just to the left of the magazine on the red table.

here are the last frame (right), and the one before it...I hope that gives an idea of how abrupt; I'd expect the frame before invisibility to be far more ghosty than what is shown here.

one thing that might be affecting it is that I have a volumetric light making smoke in this scene, but as I watch the clip, there was a definite jump between those last 2 frames.

thank you!


J

http://www.coffeeonmars.com/glas.jpg

toby
12-04-2009, 06:03 PM
It's hard to tell from stills, why is the martini glass obscuring the box behind it but nothing else? Have you tried it without the volumetric light just in case -

Johnny
12-04-2009, 06:31 PM
It's hard to tell from stills, why is the martini glass obscuring the box behind it but nothing else? Have you tried it without the volumetric light just in case -

haven't tried w/o volumetric, but that is a good idea.


as for why it's obscuring the box, that's just it! it's the last frame of visibility..should be almost like vapor..

in the hi-rez frame, the glass' shape can be fully seen, so it is obscuring what's behind it...that wall is blue, and the glass is kind of blue...

I will try to get a clip together so that you can see the "jump" I saw.

J

Johnny
12-04-2009, 06:44 PM
OK...here's a clip...even tho it's small, you can clearly see the abrupt transition I'm talking about.

thanks!

J


http://www.coffeeonmars.com/johnny.mov

toby
12-04-2009, 06:52 PM
I see what you mean, odd that the upper half of the glass obscures even after the lower half is invisible. Are the settings on that object different, is it unseen by rays, or is your ray recursion too low? Are you raytracing refraction?

Johnny
12-04-2009, 06:55 PM
I see what you mean, odd that the upper half of the glass obscures even after the lower half is invisible. Are the settings on that object different, is it unseen by rays, or is your ray recursion too low? Are you raytracing refraction?


raytracing is at 8 recursions, and it's worked throughout the development of the scene..not unseen by rays, and yes, raytraced refraction.

you are right that the top is still visible...the stem and base fade out nicely a couple frames earlier...

J

toby
12-04-2009, 07:23 PM
There's no reason for the glass to be that opaque so near the end, I would use that second-to-last frame to test with. If that box was unseen by rays it could explain it -

Johnny
12-04-2009, 07:25 PM
There's no reason for the glass to be that opaque so near the end, I would use that second-to-last frame to test with. If that box was unseen by rays it could explain it -

that is an excellent idea....I do need to check that aspect of the scene....

more I think about it, and in relation to your comments, the box is seeming more like the possible culprit.

thank you!

J

toby
12-04-2009, 07:42 PM
I just found out that the shadow from glass with Color Filter on doesn't fade, even when the glass is 99% dissolved, then pops out on the last frame. HV has been known to do this too, so try removing any effects like that from the material.

Johnny
12-04-2009, 07:44 PM
lousy news to hear...

does it make it worse to know that there are no such effects in that scene?


J

Johnny
12-05-2009, 07:02 AM
OK....just re-opened that scene after others finished rendering...

that box WAS "seen by Rays." dang..hoping that was it.

I wonder if it would make sense for me to somehow render that scene without the martini glass, then render it again with ONLY the martini glass, and have the glass be its own layer whose opacity I could fade in Final Cut Pro (NLE)?

would this work, or would the results be crummy?

dwburman
12-05-2009, 11:20 AM
Doing the dissolve in Final Cut should work just fine and may be the simplest, and quickest solution (depending on render times). Heck, that's how you'd do it in the real world (shoot it without the glass, add the glass and shoot it again and do the dissolve in the editor).

I'd try raising the Ray Recursions to something higher and flipping the "Raytrace Transparency" setting. I might try isolating the air polys, and liquid (if any) from the glass to see which bit geometry is causing the problem.

Johnny
12-05-2009, 12:32 PM
Doing the dissolve in Final Cut should work just fine and may be the simplest, and quickest solution (depending on render times).

is doing this as simple as:

1. rendering the sequence without the glass

2. rendering the sequence with ONLY the glass

then

3. pulling both clips into FCP, then dialing down the opacity of the glass layer as I want?

I have never done this before, and was imagining how the glass would behave in a scene where all the other things were "turned off" during render time...

or, does the glass "know" that the other stuff is there?

J

dwburman
12-05-2009, 08:03 PM
Rendering it without the glass and then with the glass turned on is the simplest way. You could possibly use limited region to keep render times down.

You can do it with rendering only the glass. You just need to set all of the other objects to Unseen by Camera... I think the glass would still catch all the reflections, but I'm not 100% sure about that. If you DO isolate just the glass then you need to do extra stuff to put the shadow (and caustics) on the table.

Johnny
12-05-2009, 08:07 PM
OK...good to know...doesn't sound too difficult...no caustics in my scene..and shadows aren't really needed.

thank you for helping me with that info.

J

toby
12-05-2009, 08:12 PM
It's even simpler than that - one pass with the glass unseen by camera, one pass with everything else unseen by camera. That will take care of shadows and caustics, unless of course you get the same pop in the render, which could happen. I'd still want to figure out why it's doing what it's doing, for next time -

Johnny
12-05-2009, 08:15 PM
yeah..I do, too...

I don't like to say "oh, well" when these problems pop up....

maybe if I step away from the issue for a bit, an idea will pop into my head.

you *know* this issue will come up again..sometime...somewhere...


J