Well, you’re not alone. I would prefer to have all dpi mentions removed from KeyShot since they are only confusing. A digital photo camera doesn’t ask you how much DPI you want your image to be as well, it’s just pixels.
I think Will Gibbons made a nice cheat-sheet for the confusing dpi/resolution things 
Hi @dan.spore
I’m facing exactly the same issue, with a RTX 4090.
Resolution 1920x1080, 30s to reach 1’000 sample in realtime view then 10 minutes in the render window. I enabled motion blur and I guess it’s why the gap is much more important than you.
Did you find why and/or a workaround ?
Best.
Did you try simply saving the scene and reloading it using recent files?
Hi Oscar,
Yes I tried that after reading your previous message, no changes. Same if I import the file in a blank file.
I had a couple of critical error with ‘bad triangles’ after switching back to CPU, but I had to kill KS process because it was not responding. Back in the scene I tried to re-tesselate all the parts, but no changes.
I’ve tried to delete all parts/animations/lights/studios/cameras/environments to keep only 1 main geometry with basic plastic material and 1 basic environment and I still have quite strong differences between realtime (which I found quite slow regarding the ‘empty’ scene) and render windows. A strange thing was that KS still shown me an ‘actualise displacement’ icon on top right corner like I still had a geometry somewhere with displacement material.
In the color mode, there is still many colors in the swatch although there is only one material which not uses named colors. Maybe a point ?
Another weird point is later in the animation, at least after frame 501 where I rendered a first image range previously, the gap drop to a bit less than twice the time, and I can render a frame in 1 to 2 minutes (which is much more acceptable for my deadline).
Models are the same with same materials, only physical lights changed.
I’m almost sure you did but you also tried the September 2024 driver from Nvidia?
Difficult to guess what the issue is, I’m also quite sure you don’t put in a HUGE resolution by accident?
edit if you want/can I can try the scene here to see what happens with my 4090 and config.
No I didn’t change driver’s version, and I’ll not have time for that exploration. Maybe Monday if issue still makes me crazy. I’ll render the animation’s end first and the begining where the bug is the strongest then and hope it will be finished monday. I don’t really get how to install previous nvidia drivers.
I cleaned all my file with duplicated material, duplicated color swatches, unused color modes but no changes.
No, resolution is 1920x1080px.
It will be complicated for me to share that client file as the product isn’t on the market yet. Thanks.
Sometimes I get this error, it should be linked I guess but no idea how to fix that.
In another hand, I often have the ‘gpu setup’ window infinity loop when I close the rendering window, and I must kill and restart the KS process to get my scene back.
Best.
Reason I ask about the driver is that the actual recommended Nvidia driver is still the one from September 2024. I had a scene where first 150 frames rendered fast and than suddenly it slowed down like crazy. That was solved by installing the older drivers.
It’s not much work, just go to Nvidia.com/drivers and download the old studio driver from September. There’s a link on that page pointing to the older ones.
Than just double click the installer and if it installs say you want a custom install. Just select the drivers and not the Nvidia app/GeForce experience. And select the button clean install after a minute or five it’s done.
Worth trying is you have so much issues.
@pierre.kairn I looked for direct link for that driver for you but Nvidia site gives a internal server error, saw I had it still in my downloads so if you want, I uploaded it here:
Thanks, I’ll try it monday if rendering isn’t finished as I’m not at work for the week-end.
I’ve tried this afternoon to install an old driver but it was stucked at the hardware compatibility window … Let test this new one monday
I’ve tried your driver, and it’s worst. GPU crashes at the render window opening.
I’ll try another driver if it could changes something.
Hi @pierre.kairn,
Really odd, reason I suggested it was because I had render speed suddenly reducing in the beta as mentioned here: 2025.1 Beta | GPU Render in background - For Beta Testers - Luminaries
When I switched to the Sep 2024 driver it didn’t drop the render speed anymore.
If your client is ok I could render some frames just to keep some progress (if it works here)
Hi Oscar,
Thanks for your time.
I think I found something connected to NURBS rendering.
I’va made a blank file, imported my STEP model and realtime was fast and final slow. I deleted some parts and gap went smaller as I deleted more parts. > It isn’t linked to a specific part.
In another file, I imported the model, unchecked the ‘import nurbs’ box this time and I didn’t notice speed reduction, rendering is even faster. (realtime : 10s > 4’200samples vs final render 10s > 5’200s)
I guess KS is bugging and uses NURBS data in the final rendering even if that is not checked. Which could make sense.
@dan.spore Can you tell me if your file had NURBS file imported ?
Thanks.
If I look at the top screenshot of Dan it sure does look like he has nurbs imported. I know there’s a GPU limitation with Nurbs like:
But that shouldn’t give weird render times. Would be an interesting one for the developers I think to look into. If I’ve some time I’ll check if I can create such a scene as well.
I remember I had some complications with the STEP file from my client, with surfaces errors, even when I imported it inside Rhino or Solidworks.
Maybe it’s something between KS and the file.
I’ll re-importe my file without NURBS in my final scene and check if I still have speed reduction.
I’ll ask my client if I can share the file to KS for developers.
EDIT : First : Classic imported model, with NURBS included.
Second : I clicked ‘remove nurbs’ in the model’s menu in the scene tree. No NURBS in the file
Third : I duplicated the model set with the nurbs, removed them in the first one, disable the NURMBS’ one. No NURBS visible, but NURBS in the file. Render seems to be impacted by NURBS from other model sets, even if they’re disabled.
For each tries, I set a rotation on the root model and motion blur at 1/50s for camera and parts.
I think that’s really interesting information for KS! Since you’re in GPU mode I would say the existence of NURBS shouldn’t impact your render times at all. So I think it’s even more strange not having those model sets selected having such an impact on the render time.
I don’t use NURBS models that often, but I wonder if that has caused me some issues in the past as well.
@dries.vervoort and @jan.simon.1 sorry to tag you guys but I think the findings of Pierre are really worth some investigation looking at the difference in render times.
Hi,
Thanks for tagging developers.
I’ve removed all NURBS in my file but I still get speed reduction.
I saved my material and make a new file by imported all my parts without nurbs, and rebuild my animation opening with same lights and material. It seems to not have speed reduction.
I’ll continue to rebuild my scene and launch rendering step after step to figure when rendering time drops.
I’m guessing if it could be something linked to huge amount of datas duplicated/deleted in the file and multiple incremental saves that could corrupte the file, but I have some doubt.
Best
EDIT : After rebuilding my file, it seems that is still an issue with the planar lights. I’ve added my planar light to my scene with curve powered material and that makes the sample rate drop.
I added a standard plane to see if an area light makes same behaviour and I copy paste the planar light material (to keep the power curve) to the plane, then make the render and sample rate came back to normal. Maybe something linked to the ‘geometry’ of the ‘planar light’ object.
EDIT 2 : I should miss something, use planar with planar light material doesn’t change speed reduction but area light with curve animation for power works instead of curve powered planar light.
@oscar.rottink is right in his reply below this one - my file does have Nurbs data, but none of the objects are set to “render nurbs.”
Thank you for all of your investigation into this, and thanks to @oscar.rottink as well! I’ve moved on from the issue due to production schedules, etc., but for me it was never resolved. KS support wanted my scene file, but the need for an NDA complicates this.
I remember deleting a model set at one point and gaining the speed back a bit. There was nothing special or notable about the model set - it was just not needed. My renders were still slower than realtime, but not quite as slow. I could not find a link anywhere as to the cause.
I have some big animations projects coming up soon and I am dreading it a bit. And now you mention a problem with planar lights. Sigh.
Hi @dan.spore,
Pierre put also a topic here:
[BUG] GPU, NURBS & Motion blur - For Beta Testers - Luminaries
If you’ve not seen it, it’s interesting since he found out that actually getting rid of the Nurbs seems to help a lot. Of course that’s not an actual solution but they are working on it. At least it will hopefully reduce the render times compared to the real time window.
He also found out that even inactive model sets still impacted the render times if there were Nurbs present. His suggestion to import models without any Nurbs is I think the best way for now to prevent you from getting rid of Nurbs afterwards.