Rendering speed difference - real-time vs. maximum time (offline)??

[DriesV]

I always suspected this to be the case, but now I tested it more thoroughly.

The real-time renderer seems much faster than the offline rendering methods that use the same engine (maximum time/maximum samples). It takes considerably longer for the noise to disappear when doing offline renderings compared to real-time rendering at the same resolution.

Why is this happening?
I thought the real-time renderer and the time/sample limit offline methods used the same algorithms?
Below you can see a few side-by-side comparisons of the same scene rendered in real-time for 10 minutes and rendered offline by setting a 10 minute limit.

Dries

[DriesV]

On a side note:
On my dual Xeon E5-2680 machine, quite oddly, during real-time rendering the CPU temperature never exceeds 75 deg C (hottest core), while during an offline rendering the CPU temperature goes as high as 81 deg C.
The reported power per single CPU in Watts (monitoring software) is nearly identical for both rendering methods (114W during real-time, 118W during offline rendering).
My system also feels a bit more responsive when real-time is running, than when an offline render job is running.

In fact, the offline rendering methods using time and sampling limit are the most stressing things I can throw at my system.
No other application gets the CPU cores that hot or get my system that less responsive.

In contrast, offline rendering with advanced settings is less stressing than any other rendering method in KeyShot. My hottest core is 74 deg C and max. power for a single CPU is 108.5W

SO... when comparing offline time limit rendering to real-time rendering:
How can it be that my CPU's are running hotter, while the rendering seems slower?

Dries

[DriesV]

On build 4.1.35 I'm still noticing a significant difference in rendering speed between realtime and max. time/samples rendering.
Anyone else making the same observations?

Dries

[PhilippeV8]

I reported a while back that if you set 10min render time, it renders less fine than when you just let it render with not time limit and stop it after exactly 10min.  Is this the same issue ?

[DriesV]

I'm not sure, Philippe. I will try to recreate your conditions.
This speed difference is especially noticeable in scenes with lots of render 'hogs': DOF, physical lights, translucent materials...

Translucent materials can take much, much longer to get artifact-free, compared to realtime rendering (in which translucent materials are actually blazing fast ).
I'm just puzzled as to why this happens, because both rendering methods use the same algorithms (I guess?).

Dries

[malayutou]

hi ,DriesV.I notice this during my renderings too.In my work,I often had to offer the product renderings without background to the client.So I often render with an alpha channel.A screenshot is faster,but I will have to pick out the product in Photoshop.
Thanks for sharing it with us.

[evilmaul]

yeah me too have notice this 'issue'. I am a big fan of the interactive render and when I render offline I do use mostly max time but never get exactly the same results as the interactive render which you would of course expect for the same amount of time allocated for it. 

[guest84672]

We will definitely take a look at this.

[hitesh.m]

yup me too feel same render diamond with 16 raybounce taking too much time n with 32 rendering not even starting.......

[guest84672]

There is definitely an issue here. The team is digging deeper to try and nail down the details. Stay tuned.

[Robb63]

Any update on a fix for this??

[DriesV]

Yeah, I'm really hoping this will be fixed by 4.2 ...

Recently I had a few scenes with fine geometric details that caused 'splotches', even with GI quality maxed out at 5.
Rendering with max. time/samples would just take too long to get rid of the noise...

I'm confident it will be fixed in the near future though.

Dries

[Gerard_Mike]

Same problem here, I've also noticed that the skin shader have more line artifacts with the offline render than with the realtime preview...



These line artifacts are very hard to get rid off with the offline render, I've also noticed these on Evilmaul female character, hope you don't mind me posting it

So I take the opportunity here to ask if it's possible to use a different refinement pattern? Ideally it would be better a less mechanical line pattern, maybe random noise?

[KeyShot]

This is all resolved in 4.2. Contact beta@luxion.com if you would like to test.