HDRI lighting causing speckled Reflections/Highlights from strong sun

[simifinnie]

Hello fellow 3D Artists,

 

I am new to the forums but have been lurking around in the shadows for awhile now, often using this site to find solutions to many problems I have faced in the last few years. I am hoping you can provide some insight into my current problem as I have tried and failed to rectify this issue over the last few days, resulting in me to finally make my presence known...

 

I use Mental Ray renderer with 3DS Max/Design 2014 at work.

I had some downtime so was playing around with a "daylight" scene and using HDRI map to light and also provide reflections for my scene. Normally HDRIs provide soft shadows for lighting which I never had problems with, but I really wanted to speed up daylight workflow without using Daylight System just swap HDRI maps instead to get soft shadows for those cloudy days or strong clear day sun shadows.

 

I downloaded a sample of CG-Source hdri map which is capable of producing strong shadows to test my scene before committing to buying it.

 

I placed the hdri map inside Environment Map, and told Skylight to use it. Did my test render and the hdri map is perfect- gives me nice strong shadows! Yet my test Arch&Design material with blurred glossiness is looking awful, and speckled no matter how many samples I give it. It seems that the lower the glossiness value is the more speckled the sun reflection appears in the render.

 

Why is this happening? Is it at all possible to sort out? (The only way I could get more blurry reflections was to blur the hdri map by tons, but then my sun shadows become blurry too, which is the opposite of what I wanted to produce)

 

I did a similar test using vray at home, and I am not getting the same problem-but sadly at work we do not use vray so I must find a Mental Ray solution to this.

 

Mental Ray example:

Vray Example:

 

Thank you for your time!

[MarcellusW]

George,

 

Using this method, have you been able to get strong shadows (similar to vray) when only using the HDRI map/skydome combo to light your scene? If so, have you done this in 3ds max versions prior to 2014?

 

When I use HDRIs, I previously would put them in the sky color slot. Am excited to try what may be the correct way! If it casts shadows, then this is a million dollar answer!

[simifinnie]

Thanks for the reply George,

 

Unfortunately I am already using the Autodesk recommended way of using HDRI's after watching their youtube video on introducing IBL method as it seems to work best with HDRI workflow. (Skylight is using scene environment) I never had problems with normal interior renders where soft shadows are more desired, only with strong sun + shadow HDRI.

 

I just did a few tests with HDRI placed in Color Map slot for lighting + HDRI instance in Environment Map = same speckly reflection as I posted before.

 

Another method I tried, is just keeping HDRI in the Color Map to only get lighting from it, and removing environment map completely. I'm still getting strong shadows this way with no problems.

 

So now I know it's the issue with the Enivornment Map when it''s using HDRI for reflections.

 

I managed to achieve a more desired look by Creating 2 HDRI materials, keeping original in Skylight- Sky Color Map- so it won't use it for reflections. Then creating a copy of the material and setting Bur value to 100 and placing it in the Environment Map slot. This way there's no more speckles from the sun...The lower the Blur value the more speckles I get, hence why 100 produced best results.

 

However this is not an ideal solution, as now any other material, like chrome would have extremely blurred reflections- so clouds would simply blur into the blue of the sky...pretty much pointless?

 

 

I just had a EUREKA moment.

If I load the Environment map HDRI as 16bit and not 32 real Pixels (in the Setup of HDRI load settings), I am still getting correct non-blurred reflections without the speckles! So I just need to have 2 seperate HDRI materials, one at correct pixel depth and one lower.

 

 

 

This solutions works so far, will have to test it further at work, but I hope everyone else can find this useful too, because I spent so much time searching for answers on this issue )

[MarcellusW]

Simona,

 

I just realized, what are your sampling per pixel settings in the main renderer dialogue? Try increasing the min and the max. It will take a lot longer but it usually helps with the speckles.

[simifinnie]

Marcellus,

 

I had default sampling per pixel setting. Min 1 and Max 128 I think, sampling quality set at 8. I messed around with increasing the min and max values as you suggested but no change in speckles effect.

 

I found out I can Clamp my HDRI which is used for reflections, which gets rid of these speckles! Just have to make sure I'm not clamping the Skylight map HDRI to get those strong sharp shadows. (reference https://elementalray.wordpress.com/category/optimization/)

 

The cause seems to be that the HDRI has a too high value for the sun which mental ray is struggling with for reflections, yet that high value is a must to receive strong shadows....

 

I'm just a bit annoyed I can't simply use 1 HDRI for both lighting and reflections without any changes as Vray seems to be able to handle this!

 

At least we have a workaround now, so I'm pretty pleased with that.

 

Ps. I wrote another solution to this a few days ago, it hasn't been approved yet by moderators but it's basically to load in HDRI not at Real Pixel 32 bpp, but at 16 bit/chan linear, this also solves the speckling. Once again, keep original real pixels HDRI for Skylight map.

[miguelcalvo]

Hello.

 

Just some words to thank you, Simona, your post. It helped me to solve an identical problem we had with a project.

 

 

Miguel A.

[SgWRX]

simona, did you find that when you clamp the hdri used in the environment slot that the specular highlights were dull compared to un-clamping it?

[simifinnie]

simona, did you find that when you clamp the hdri used in the environment slot that the specular highlights were dull compared to un-clamping it?

 

I haven't been able to test this much further, but yes I noticed "clamp" option makes reflections more dull, especially the bright whites. I think, and don't quote me on this, but a better option was to load HDRI map for reflections only as 16bit and not 32? This way there was no speckles but colours were bright and not dull. Again, I could be wrong as I don't remember which option was the best, as I never ended up working with the original test scene again...

 

I'm glad others have found this topic useful, at least we have a few ways of working around this problem. I wonder if 3ds Max 2016 is much better at handling high quality HDRIS?

[SgWRX]

yes, very helpful thread, thanks for your work. i do find that the option of two maps being used helpful! based on that, i've tried setting my frame buffer window to be 16bit and that seems to have similar results without having to use two maps. thanks.

 

oh, i'm in max 2016 and getting the same. when i load the hdri i set gamma to 1, in the bitmap parameters i set "blur" to minium 0.01 and leave "blur offset" to 0.0.

[SgWRX]

one thing i remembered, the Environment Blur. http://mentalraytips.blogspot.com/2007/11/more-hidden-gems-miaenvblur-gloss.html

 

here are 4 test images:

[ATTACH=CONFIG]53770[/ATTACH]

[ATTACH=CONFIG]53771[/ATTACH]

[ATTACH=CONFIG]53772[/ATTACH]

[ATTACH=CONFIG]53773[/ATTACH]