Corona - Noise and HDRIs

[shortcirkuit]

Hi guys

ive done an interior scene and rendered it overnight on 2 machines.  The final noise level was 2.89 which in most cases would be super clean.  As you can see, its quiet noisy in the shadow areas - ive used a HDRI to illuminate the scene.
Do you think a coronaportal material will fix this if i put it over the window opening?

the scene has 3 window openings so plenty of light to come through - the HDRI itself is 10,000 x 5,000 - so not sure if that is considered low res and adds to the noise?  the passes indicate that the noise come from the hdri/indirect lighting and another light source - the reflection pass was good.

any advice would be appreciated.

[Njen]

Use a much smaller HDRI for lighting your scene. Less pixels means less potential variance, which means less noise. I recommend you resize it down to something like 1024x512 if possible. I personally saw render times decrease by about 9% using a smaller HDRI (16384x8192 -> 1024x512), and noise clean up a little smoother with practically no image quality degradation.

[shortcirkuit]

interesting theory - and do you put a higher resolution one in the override for reflections?

Wouldnt the sun from the HDRI blur and affect shadows?  it would blur them wouldnt it?

[ChrisMyatt]

Hey there,

You could maybe try Light portals over the openings of your windows in your interior scene.

They help force the computational power to focus on the room the light in the room and less on the whole scene. Remember, there is always noise in real life, so a little doesn't affect the image :).

Or take some out in photoshop with CameraRAW, Details tab/Noise reduction, at the sacrifice of a bit of detail.

Similarly use a little bit of denoise on the image in corona

Chris

[sprayer]

Do not know why people using hdri for interior scene, you won't see it and for light is enough sun+sky
portal  also good idea, it may decrease noise. Hdri may also produce noise depend of loader and how you adjust it

[maru]

If the windows are small, using portals would probably help. It should be easy to check by just rendering a small region of the most noisy area for a given time with portals hidden and unhidden.

I don't think lowering HDRI resolution should impact render times, but it would be actually interesting to benchmark this, so if you do decide to do it, please do share your results.

[shortcirkuit]

thanks for the responses - some scenes it works perfect and other scenes not so.... ahhh the joys!
I will report back if i come across any interesting findings.