Cycles render is grainy (but it wasn't last time)

[brightwanderer]

I’m still in the first section of the course so I haven’t got to any details about rendering yet. For my first project, I found that switching from Eevee to Cycles gave me better lighting and shadows…

Eevee:

Cycles:

But now I’ve tried to do the same thing with my next (in progress) project and the Cycles result is grainy and full of static.

Eevee:

Cycles:

What gives? Obviously I don’t want to get too side-tracked right now into the details of the render settings but I’m confused as to why the second project isn’t getting the same results.

[GPas]

This is noise generated from cycles rendering.

You can try the denoise function or increase the sampling. But inreasing sampling also increases render times.

Playing around with your lighting setup could also have an effect on the noise.

[brightwanderer]

The denoise seems to have done the job, thanks!

[FedPete]

@brightwanderer

but I’m confused as to why the second project isn’t getting the same results.

Noise depend on many things, like how much light (intensity) is available. How light is bouncing through the scene (reflection). Do you use large flat surfaces, where you can easily see inconsistencies. How many sample (lightrays) does cycles use (128 is very very low, try 2000 but then is took many hours to complete).
And yes, de-noising with solve this problem a bit, but introduces other problems too (less sharp).

[brightwanderer]

So in this case, perhaps because the second scene has smaller, dimmer lights, and maybe because of the extra effects from that standing lamp? The farmhouse had one “sun” lamp and then three point lamps set up in the Key/Fill/Backlight configuration, whilst the room had the standing lamp and fireplace, and then two point lamps as Key/Fill, and everything was much dimmer. And does it make a difference that it was an “internal” scene, i.e. the light is bouncing off the ceiling and walls etc rather than just sort of raining straight down on the exterior of an object?

[FedPete]

Yes.

The SUN is also a beam of light in one direction. While a POINT light shine in all directions, but it’s light intensity will drop huge (x2). So a ceiling lamp give too much light on the spot it self, so you make it less, but then the light on the floor (from the ceiling lamp) has low intensity, hence noise.

Also the world lighting has less influence in a building room, etc. But help in evenly distributing light everywhere.
That’s why many people are struggling with dark scene, because it’s mystical, lights, fires, gloom. But for Cycles there are not many lightrays to calculate (of importance). So fireflies and noise become a problem. Only solvable by increasing the sample size of Cycles rays. Showing down your render fun. Hoping for some budget to buy a fast realtime video card ($10.000).

Or learn tricks to cope with this type of render problems. De-noising is one of them. All depending on your project goals; realism, catroon, video games …

[dragoneyes97]

This is probably a way too in depth explanation, but this does a pretty good job of explaining it and providing a fix.
Andrew Price at Blender Guru is someone I’ve been following for a long time. He’s also gotten really good at explaining what’s behind the hood of Blender.