Multipass channels increasing render-time ?

[ASIMO]

Hello Community

Usually I render some interior images with sizes like 3000 x 3000 px. Depending on complexity it takes around 2-6 hours to have satisfying results. At the moment one render takes up to 12-16 hours. I thought maybe it could be the multi-pass channels that can be added like Alpha / Reflect / Translucency and so on. Are they evaluated during the render (on the fly) or are they separately calculated ?

In fact my question is : Do this extra added channels in multi-pass increase the render time dramatically ? Any experience on this ?
Is there a way to post-render them ?

Thank you
best - A

[maru]

No, additional render elements (or multi-pass channels as C4D users call them ;) ) should not have any impact on rendering speed. There are some exceptions like the CTexmap element (which may just need additional computing power to calculate something - like AO), but other than that, the "compositing" elements should not slow down rendering.
What might happen though, is that you will run out of RAM, and then rendering may become orders of magnitude slower. Each render element requires some RAM. Additionally, each denoised render element requires twice as much RAM.
If running out of RAM is not the case here, then we would be interested in checking your scene. You can upload it using the uploader in my signature.

[ASIMO]

Hello. Thank you for your support and comments. I checked on it a few hours ago and finally came up with the same result. The Multi-Pass Channels have not increased the render time at all. It was more or less a bump map used in glass reflection as well as the changed GI Solver. Rendered with the use of UHD Cashe it was much faster then. Everything alright. Also running low an RAM could have been the case. I will upgrade soon.

Thank you again.
A