Material opactiy adds minutes to render time??

[DJTravisty]

Basic night scene with one quixel grass object scattered and one light. Opacity map plugged into the the material is over a 6 minute render. Unplug the opacity map and the render is under 40 seconds.. This has to be a bug right? Of course I'm in the middle of client work when I realize this. Thanks for any input! Oh and I have two 3090's

[bepeg4d]

Hi DJTravisty,
this is expected.

If you disable the Alpha Shadow option in kernel panel, the speed is back, but the result is wrong.

Octane doesn't like scattered opacity maps, much better to scatter real geometry for grass, leaves, ecc.

ciao,
Beppe

[boxfx]

Octane doesn't handle transparent object very well is our general experience. it seems that the level of opacity seems to determine how many samples that object gets. For example if an object normally receives 1000 samples, giving it a 50% opacity material drops this to 500 samples for the object and 500 samples for whatever's behind it. If you have a 1-2% visible object but it was very bright with emission then the object itself receives so few samples that you have to crank the sample count, or depending on your settings, the automatic sample modes may be assigning the object many more samples.

For blades of grass you'll be better off with real geometry rather than many, many overlapping transparent surfaces.

If you can provide the ground object and texture we can have a look

[SSmolak]

As I remember Redshift has special material for this type of tree leaves with opacity channel.

[elsksa]

Opacity is known for not being “renderer friendly”. Regardless of the renderer. Octane, as well as any other.