Certain Frames on the cache are larger and more motion blured

[johnnelsonvfx]

Certain Frames on the cache are larger then others and they cause a massive change in the sim. I currently have no idea why this is happening. It doesnt happen to the smoke of the fire sim just the fire.

This is a bad Frame - frame 1065



This is an image of the correct frame - Frame 1066, the frames before and after look similar and are correct to the rest of the sim. I have checked there are no keyframes in this area




Here is what the cache looks like

[Morbid Angel]

a guess would be its a backup interval frame which is every 15th frame or so...Did you check use uvw for motion blur before running a simulation?

either way it looks like a bug.

[johnnelsonvfx]

thats interesting cause it happens every fifteen frames. so checking uvw for motion blur would fix this?

[Morbid Angel]

not sure if it will. From what I recall (this was years ago) I was told that you have to actually check that option if you want to render with motion blur before simulating. I don't know how this works now (I haven't used phoenix in a long time). But it seems that every 15th frames the velocity information is stored for a restore point. It could some how have impact on your render.

I would suggest re-running the sim with uvw for motion blur on, and no backup interval.

[johnnelsonvfx]

Thank you very much testing right now. I am assuming the uvw for motion blur is the velocity output button?

[Morbid Angel]

sorry, I was thinking this was in maya (where this option exists). I can't see it in max. One would think that without backup interval this should work then

[Svetlin.Nikolov]

Hey guys,

That's right - UVW for MB is not in Max yet. The backup frames are what that you can use to continue (Restore) the simulation from a certain frame onward.

If you try to render with motion blur, you would get a warning if you have no Velocity simulated in the caches. Does the moblur work okay now since I see you have Velocity (you need to simulate the sequence again after you've enabled it in the Output panel)?

Cheers!

[anthonyh]

hi,
i had a similar issue rendering an ocean sim before with backup on, the backup frame would render brighter than the others. it was explained to me what/why/how but it didn`t really solve the issue of it rendering differently which made the frames useless so i always have to sim without using backup. now i`m sure i`m doing it wrong and didn`t really understand the issue or the explanation at the time, ensuing deadlines meant i didn`t have a choice but to switch it off and resim. i also haven`t checked if it still does it since v3 came out. i`m keen to learn what i`m doing wrong though.
anthonyh

[johnnelsonvfx]

Yes this solved my issues as well. I just shut it off and it solved. I am also using v3.0 . Sadly this is not a solved issue . Thank you for your response.

[johnnelsonvfx]

Thank you for your response !!!

[Ivaylo Katev]

the rendering difference between backup frame and normal frame in the most cases means render settings requiring some info that is not exported, in the most cases velocity, but sometimes is not that simple.
in phoenix 3.0 many of these situations are detected and warnings are displayed, but it's very probably that still exist cases that are not handled. so, my recommendation is in all cases with phoenix 3.0 when no warning appears and there is rendering difference, send it to support describing the situation, this may help to improve the detection of these cases