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What is the exact difference between 'Fast Mode' and 'Accurate Mode'?

Question asked by Saurabh Nayak on Jul 3, 2016
Latest reply on Sep 15, 2017 by Brian Hillner

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Hi All,

I understand that 'Fast Mode' renders only 100 passes and in 'Accurate Mode', you can pick the number of passes.

However, in 'Fast Mode', Visualize does not give you any options to pick the render device, i.e. CPU, GPU or Hybrid, while 'Accurate Mode' allows for the same.

My main concern is, when in 'Fast Mode', is the software making use of the GPU as well as the CPU or is it only the CPU that is used for rendering? If the former, how is it different from 'Accurate Mode' set to 100 passes, because I seem to get better renders in 'Fast Mode' than in 'Accurate Mode' set to 100 passes.

Any details on how exactly this works would be greatly appreciated.

Regards,

Saurabh

Bastian Krueckeberg

Jul 19, 2016 4:52 AM

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Hi Saurabh,

I'd like to confirm your discovery that Fast Render Mode does NOT support Hybrid. If Hybrid is selected, it will default internally to using only the GPU.

Fast Render Mode:

CPU, GPU

Accurate Render Mode:

CPU, GPU, Hybrid

I understand from this thread that our user interface is ambiguous with that respect. We should not offer "Hybrid" for Fast Render Mode to make this more obvious.

Thanks,

Bastian

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Brian Muhlbach Jul 12, 2016 2:12 PM
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Fast Mode (Nvidia's Iray Interactive) processes the image using an advanced approximation algorithms to mimic realism while minimizing unwanted noise - maximizing performance during interaction. Renders can take half the time or less depending on lighting and other conditions with great results.

A pass in Fast mode and a pass in Accurate mode are not equal. Noise removal and refinement in Fast mode is typically complete by 100 passes which is why Fast mode is set to complete at that point. Because Accurate mode is designed to handle more complex and varied scenarios, users have the flexibility to adjust the pass count accordingly.

The biggest difference between the Accurate render (Iray Photoreal) and Fast Mode (Iray Interactive) is the shadow quality and reflectivity in appearances.

If a CUDA enabled GPU is detected, the Fast render will automatically default to GPU, otherwise if a CUDA GPU is not detected, Fast Mode will default to CPU.
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- Saurabh Nayak @ Brian Muhlbach on Jul 13, 2016 8:57 AM
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  Hi,
  
  Thanks for the reply Brian.
  
  In my experience with the software and the models I deal with, Fast Mode is more than sufficient for my renders. One frame in my animation takes about 30 seconds to render in Fast Mode, but 2 minutes in Accurate Mode (500 passes). However, the quality of the render is much better in Fast Mode!
  
  Is there any way that I can get the software to utilize both the CPU and the GPU in Fast Mode? Currently, it is making use of the GPU only, while the CPU sits idle. This would help increase the speed of the renders as I currently have to wait around 12 hours to complete a 1 minute animation at only 15fps!
  
  Brian Hillner, if this isn't currently possible, any way this can be implemented in the next SP or SW Visualize 2017?
  
  Thanks,
  Saurabh
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  - Ron Bates @ Saurabh Nayak on Jul 13, 2016 9:23 AM
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    Hi Saurabh,
    
    You are correct that the render device is locked in FAST mode. Although i thought it used Hybrid...it could be true that it is GPU only.
    
    In any case, the ability to choose a render device for FAST will be available in the next SP of Visualize and is available in 2017 Beta. If you're on current subscription, you can try it out now in the Beta... Visit beta.solidworks.com to get started...
    
    Also - it' s not unexpected that accurate mode take a lot longer, and require a lot more passes to achieve clean results. If FAST suits you're needs; then that's great...and the recommended way to go anyhow.
    
    R
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    - Saurabh Nayak @ Ron Bates on Jul 15, 2016 9:49 AM
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      Hi Ron,
      
      I was pretty excited to hear that the Beta version of Visualize 2017 is out with the option to pick the render device in Fast Mode, right up until I actually tried it out. Unfortunately, even after picking Hybrid Mode, the CPUs are still lying idle while the GPUs are running at around 70-80%.
      
      I tried another render in Fast Mode picking CPU as the render device, and it did complete the render, albeit slower than when the render device was only GPU, which is completely expected.
      
      However, in Accurate Mode, picking Hybrid as the render device immediately shoots up the CPU and GPU utilization over the 90% mark.
      
      Any thoughts?
      
      Regards,
      Saurabh
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      - Ron Bates @ Saurabh Nayak on Jul 15, 2016 1:18 PM
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        Hi Saurabh
        
        I tried myself today...
        
        On my machine:
        CPU ONLY - GPU remains idle, ~0%. CPU runs 90-100%.
        GPU ONLY - GPU run 70-90%. CPU's run about 20-30% consistently.
        HYBRID - GPU run 70-90%. CPU's run about 20-30% consistently.
        
        So i'm basically seeing the opposite issue; where CPU's are never idle. Meanwhile both Hybrid and GPU seem to use about the same amount of CPU... I'd expect CPU to remain idle in GPU only mode, and approach >50% at least in Hybrid.
        
        Hmm????
        
        Let's clarify a couple other things:
        - How are you clocking CPU and GPU usage (what tool are using to monitor usage)?
        - Are you switching just the viewport renderer (Tools, Options, 3D Viewport, Render Device)? Or are you choosing the render device for a final/offline render in the Output Tools, Render Settings before starting final render?
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        Saurabh Nayak @ Ron Bates on Jul 17, 2016 9:03 PM
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        Hi Ron,
        
        -I'm monitoring CPU usage through Task Manager and GPU usage through the Nvidia Control Panel.
        
        -I'm selecting the render device for the final/offline render in the Output Tools, Render settings before starting the final render.
        
        From the looks of your test, it seems that you have other programs running as well, which is probably why your CPU is running about 20-30% even in GPU only mode. But as you can see, even in your case, there is absolutely no difference in GPU only and Hybrid Mode. In my case, I have practically nothing else running on this computer other than Visualize, which is probably why my CPU is sitting idle (around 2-3%).
        
        I tried another test where I rendered the same image in GPU only and Hybrid Mode separately. The render took the exact same time, which indicates that the CPU is not being utilized at all.
        
        Any chance this could be a bug in the Beta?
        
        Regards,
        Saurabh
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Bastian Krueckeberg Jul 19, 2016 4:52 AM
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Hi Saurabh,
I'd like to confirm your discovery that Fast Render Mode does NOT support Hybrid. If Hybrid is selected, it will default internally to using only the GPU.

Fast Render Mode:
CPU, GPU

Accurate Render Mode:
CPU, GPU, Hybrid

I understand from this thread that our user interface is ambiguous with that respect. We should not offer "Hybrid" for Fast Render Mode to make this more obvious.

Thanks,
Bastian
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- Saurabh Nayak @ Bastian Krueckeberg on Jul 19, 2016 5:56 AM
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  Hi Bastian,
  
  Well that's a bummer. I was hoping to utilize both my Xeon CPUs as well as the GPUs to speed up the render animations, as in Accurate Mode, Hybrid tends to save me around 15-20% of my time over GPU only.
  
  Is there any particular reason as to why Fast Mode will not utilize the CPUs at all, while Accurate Mode makes full use of both CPU and GPU?
  
  Regards,
  Saurabh
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  - Bastian Krueckeberg @ Saurabh Nayak on Jul 19, 2016 6:10 AM
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    Hi Saurabh,
    
    it is a limitation of our underlying render engine (NVIDIA Iray) and their internal way of handling things which are beyond my expertise. Please understand that the Fast Mode Renderer is completely different from Accurate Render. Fast Mode is highly interactive and chances are high that the additional performance gain would be minimal with respect to the overhead of utilizing different render devices at the same time.
    
    I will address this with our partners from NVIDIA and explore possible future options with them.
    
    Sorry for the inconvenience,
    Bastian
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    - Saurabh Nayak @ Bastian Krueckeberg on Jul 19, 2016 8:25 AM
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      Hi Bastian,
      
      Thanks for the quick reply.
      
      I guess upgrading my GPU is the only way to speed up the animations now
      
      Regards,
      Saurabh
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      - Brian Hillner @ Saurabh Nayak on Sep 15, 2017 5:01 PM
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        For anyone else visiting this forum thread, here is a great description from our fellow Visualizer Tianping Ma on another forum thread:
        
        In Visualise, there are two mode "fast" and "accurate" which are very different.
        
        The fast mode use "biased renders" whose algorithm are simplified which make it more easy to get rid of the noise and come to the convergence. This kind of "biased renders" will sacrifice the quality of the image but be more faster. Usually, the biased renders are already very excellent (for example simple case as the desk you show).
        
        The accurate mode, on the other hand, use "physically accurate rendering tool", which don't take the "shortcuts" in the algorithm. This will give better quality of the image. Maybe this is only meaningful since GPU function in Visualise make the rendering much faster. But, using the accurate mode, the algorithm is more difficult to get rid of the noises. You can find more related information at the attached Youtube link, at 3:43. SOLIDWORKS Visualize - Lesson 1 - YouTube
        
        Simple conclusion is that, when we just want to take the advantage of the high calculation speed of GPU, we can use the fast mode of the Visualize to replace PV360. In some cases, when we want better image quality in complex designs/structures, we can use the accurate mode of Visualize, but remember to enter high enough pass counts to get rid of the noise.
        
        Also, please my suggestion on this forum thread below for using Photoshop's built in noise removal features. Saves hours of render time!
        
        Rending in Accurate mode and choosing the right pass count depends on 2 main aspects of your projects:
        1) LIGHTING: if you are in a fully enclosed interior, then 5,000+ passes might be necessary.*
        2) COMPLEXITY: this is material complexity. Stacked transparent objects (glass bottles behind one another) and some metals require a bit more passes to achieve the subjective "it's done" look.
        
        I would first try 1000 passes for your project. Then if that's not enough, rather than wasting hours of render time, use this trick below:
        
        There's this awesome trick I use in Adobe Bridge (comes with Photoshop). You can use the noise reduction tools to keep render time short with lower passes, and then 'fix it in post.' This little trick literally saves HOURS of render time!
        
        *NEW for 2018 are Area Lights that work in Fast mode! This translates to ~70% faster interior renders!
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What is the exact difference between 'Fast Mode' and 'Accurate Mode'?

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