Excessive RAM consumption with opacity mapped object

[AltoR]

Hello,

Here is the situation: I have to render a 7400 x 4900 pixel image of a quite simple scene containing some very basic low poly objects + some VRayProxy objects lit by a VRaySun and VRaySky. Settings are: Irr map + Light Cache on a dual Xeon X5680@3.33GHz and 48Go RAM on a Win 7 machine.
Everything runs fine until I put a particular VRayProxy in the scene: render is done in 4 hours for a 27Go RAM consumption. But then, when I put this opacity mapped VRayProxy object in the scene, it becomes catastrophic: 8 hours to render for 48Go RAM consumption + 15 Go memory swap on hard disk !! The culprit VrayProxy is a big plant composed of opacity mapped planes (15 500 000 faces total count). I did not forget to set the opacity map filtering to "none" instead of the default "pyramidal".
Anyway, I never saw such a huge RAM consumption using VRay for 5 years I use it so ... please help me, I am so disapointed.

Thank you a lot,
Regards

[tricky]

Mmm. Have you tried setting filtering an all the bitmaps to 'none' (i.e. not just the opacity map)? Not sure if it will help but might be worth a try.

[Slazzo]

I would break all apart, render the geometry with gray material without opacity, find out what makes the slowdown, if it's the opacity maps, maybe makes sense to edit them to be sure alpha channel is clean, and maybe use other format...

[AltoR]

@tricky: thank you. I converted all the original maps of the material from tiff to jpg (it is a free XFrog Juniperus plant). Then I set all these maps filtering to "none" but it is even worse: the render did not finish after a whole night calculating and hdd swap was about 15GB ... So my first conclusion at the moment is that using a format that supports transparency like .tiff works better than one that does not support it like .jpg.
As mentionned by Slazzo, I am now going to render with a grey override material to see if it renders fast and check there are no RAM problems, and, if it's ok, I will then go deeper with opacity/map format and filtering tests to see what works best.
Thank you both of you for helping me !
Richard: I had a look to your website, I very much like your work.

[Svetlozar Draganov]

Have you tried to reduce Max Transp. Levels or increase Trans. Cutoff values from Global Switches ?

[AltoR]

I reduced Max transparency levels (which has been set to 150 because of many tiny branches in my 3d trees models causing black spots on my RGB pass when set to 50) and increased Transparency cutoff and now I have acceptable render times and no more excessive RAM usage.

Thank you a lot !

[Svetlozar Draganov]

Thank you very much for your feedback.