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

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?

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!