Purple tips of tress with HDR Skies

[Archvis]

Hi all,

New to the forums, I wanted to ask and comment on an issue i'm having with trees in Corona.

I'd like to address 2 main issues and also request for Mental Ray Textures conversion of some type. (I have so many questions like how to make realistic water with caustics, and tiles with different coloured grout etc...)

1. Tops of trees Presenting as purple around the Alpha foreground of Skymaps. Also the Gum Leaves are also purple so it looks like a Euro Renders instead of Australian.
2. Background modelled grass seems to be coming in front of foreground. Very Strange.

Requests:

Mental Ray conversion / backwards support of some kind. (Most Architectural Practices workflow in Australia is Revit to Max with the Revit Textures shared.)

Other things I've noticed:

I've noticed Civil View for vehicles doesn't render as they are not CoronaMTL's which really is a logistical nightmare for everyone using 3DS max as we have to manually make car textures or convert the mental ray ones into corona ones - this cannot be I will never be able to do an urban visualisation with this workflow.

Similarly with Populated scenes, People and various "entourage" come up as blank unless I retexture them in corona. We need a mental ray conversion thats automated.

Positively, I must say this engine has pushed my renders forward in realism, however having to start again from mental ray materials is a pain, I WISH IT SUPPORTED OR CONVERTED MENTAL RAY TEXTURES!

I have attached the image for you to see. Please let me know.

Thank you.

Scott

[romullus]

2. Background modelled grass seems to be coming in front of foreground. Very Strange.

This is known bug. It is fixed in latest builds and upcoming V1.0 will render fine. Meanwhile you can solve this problem by setting refraction level of your grass material to 0.

As for Mental Ray materials conversion: https://forum.corona-renderer.com/index.php/topic,126.0.html

[Ludvik Koutny]

Autodesk integrated 3ds Max's feature set closely with CAD/Civil imported data. That's what only Autodesk can do. So not third party renderer will be ever able to implement proper support for all the possible CAD/Civil import stuff those files can bring in.

Also, writing in Comic Sans is an unwritten internet crime.

[Archvis]

Thanks Romullus.

Is there also a fix for version 1 regarding the purple tips on the trees?

[Javadevil]

That purple fringing is odd, whats the material setup ?

[Archvis]

Its nothing special, just a diffuse map set to 1 (TIF) with an opacity Map set to 1 (Greyscale TIF cutout of leaves) with Bump map (TIF) Set to 0.05.

I also have rendered off at 4000px 13 hours straight and I'm noticing not only am I seeing a transparency on the leaves with the same Purple Tint but I also have these odd white artifacts. I've used the Script to convert all materials from Standard to CoronaMTL's still with these odd artifacts.

I'm assuming they are reflections from Vegetation. I'll re-render tonight without Vegetation and see if it produces the same image. I have a feeling Its incompatible with my Trees and grass.

I've also been checking the render and I compared a screen shot at 9 hours to the 13 hours render and I can't see a difference, same amount of artifacts and still same semi transparent leaves.

Any ideas? Is this a bug or have do I need to switch over to a different engine?

Thanks.

[racoonart]

Have you checked the materials after conversion? Opacity maps in Corona work differently than for example in Vray or MR. My guess is that those are causing the purple tint. You can even see that the leafs themselves are half transparent. It should also be pretty prominent in the Material editor already when you check the leaf material.

Probable cause may be that Corona uses the RGB channels instead of the embedded alpha in the opacity slot and that can has to be fixed manually at the moment.

[Archvis]

Hi mate,

thanks for your comments, I appreciate it.

It seems all in order, however I've noticed a checkbox which I'm not familiar with in MR, a "Premultiplied Alpha" set to on by default.

Is this the checkbox you're referring to?

I have attached a screenshot of my opacity map settings, let me know if anything here seems to be the culprit.

Thank you.

[racoonart]

No, premultiplied alpha is fine. What you have to do is change the "Mono Channel Output" setting on the left. It's currently set to Alpha, but this is exactly causing the problem described above. Vray and mental ray are using the alpha embedded in the tif - Corona does not, Corona uses the RGB channels of the map.
There are multiple ways to fix this.
A) use a seperate alpha map
B) try to set the "RGB channel output" to "Alpha as gray"
C) Add a CoronaMix texture in the opacity slot and set this tif as mix amount

I have implemented method C) as an additional tool in the Converter which will be released after Corona 1.0 is out.

[Archvis]

Thanks for your reply,

I tried A and B to no change at all.

Do you think its possible the HDRI Environment I have as a background (with a purple sunset) is influencing this? Because I have turned off the Environment map and the trees work fine.

So theres someting to do with the Environment.

Unfortunately C isn't really feasible as I do a lot of Urban Design and need to have accurate plant species specified by Landscape Architects and theres no room for error or time consuming remapping. I could have over 10-20 species in a render and the focus is not really on the tips of trees lol.

I'll try C anyway and hope for a fix in the future.

Thanks for your tips.

Do you know what the artifacts are as well?

Also does anyone have any tips for standards for outdoor renders?

I'm using Mental ray Exposure (this is what I'm most comfortable using) As theres no Corona Exclusive tool for exposure I'd love for there to be some kind of way to understand lighting settings.

At the moment I've chosen 10.5 on MR exposure, with a 0.3 light setting for daytime renders, and a setting of .15 for night renders.
But I am getting a fair bit of bleed on the wall textures which are super high res but not showing quite pixelated.

Last question. Is there a script to convert Photometric lights into Corona Lights?

Thank you!

[racoonart]

Do you think its possible the HDRI Environment I have as a background (with a purple sunset) is influencing this? Because I have turned off the Environment map and the trees work fine.

The environment shines through a colored opacity, so sure, disabling environment ( = black) will make the issue invisible, but it will reappear as soon as you change the background (even in post). It doesn't have anything to do with the issue (as explained above).

Unfortunately C isn't really feasible as I do a lot of Urban Design and need to have accurate plant species specified by Landscape Architects and theres no room for error or time consuming remapping. I could have over 10-20 species in a render and the focus is not really on the tips of trees lol.

Trusting a complete automatic material conversion sounds a lot like "room for error" ;) The fix won't make your plant less accurate than before - it's a fix - so it fixes the problem.

Do you know what the artifacts are as well?

Could have a lot of reasons, too high MSI, Reflections from sundisk etc.
There are a lot of topics considering noise here: https://coronarenderer.freshdesk.com/support/home

I'm using Mental ray Exposure (this is what I'm most comfortable using) As theres no Corona Exclusive tool for exposure I'd love for there to be some kind of way to understand lighting settings.

At the moment I've chosen 10.5 on MR exposure, with a 0.3 light setting for daytime renders, and a setting of .15 for night renders.
But I am getting a fair bit of bleed on the wall textures which are super high res but not showing quite pixelated.

I don't know what happens if you do that, it's definitely not recommended, Corona has it's own exposure settings in the render settings dialog / Vfb

Last question. Is there a script to convert Photometric lights into Corona Lights?

The converter for 1.0 will have it

[Archvis]

Version 1, still having purple trees.

I have tried to use corona mix and I can't get it to work.

Is there a script you could make that converts all xfrog trees opacity maps into black and white? I have a feeling its because its a coloured opacity map its causing half transparency...

I'm going to photoshop the tiff file myself and convert it into black and white and see if that fixes it.

Please see attachement.

Also my background contrast is so much darker than my exposure. Is there a faster way determine the correct balance (also I am using automatic exposure now - under exposure) which one should I be using for corona?

Thanks.

[racoonart]

Is there a script you could make that converts all xfrog trees opacity maps into black and white? I have a feeling its because its a coloured opacity map its causing half transparency...

The material/lights converter has a button for it, called  'fix opacity maps w. "Mono Channel Output" on'
https://forum.corona-renderer.com/index.php/topic,126.0.html
It only works after conversion btw.

Also my background contrast is so much darker than my exposure. Is there a faster way determine the correct balance (also I am using automatic exposure now - under exposure) which one should I be using for corona?

Again, don't use these exposure control settings. You can either control it via CoronaVfb (click on the tools button and then the ColorMap tab on the right) or directly in the rendersettings in the "scene" tab.

Apart from that you can use the "CoronaOutput" map in combination with your background to exclude it from colormapping (so exposure won't change the background brightness)

[PROH]

I honestly think you're making your life much more difficult by using Max's exposure control. Use the exposure in Corona VFB or render setup - it's interactive, so you can see your changes while rendering.

Regarding your alpha channel/cut out mask, then don't convert the colored image itself in PS, but use the alpha channel to make a black & white mask image.

NB - "Premultiplied Alpha" is part of Max standard, and therefore it has been present in mr for ages. Nothing related to Corona

Hope it helps

[Archvis]

Awesome the Script works! Thank you Sir.

I found a reason why this is happening if people are reluctant to use the script and want a quick easy fix.

1. Convert the Opacity map into a black and white map (usually named *_a.tif) for Xfrog.
2. Goto output for the map and click invert. As the black bits need to be white and visa versa.

This will fix it, and perhaps the real problem is xfrog got lazy when making opacity maps and should have used the _a.tiff map instead of the same as the diffuse!

Anyway, Excellent job guys, you have all the solutions even before I have the problems :)

Corona has finally won me over.

Now all I need is a better material library instead of making glass from scratch each time.

*** For some reason I can't reply to you PROH as a new message so I'll respond with an edit:

The problem is the background to foreground brighness ratio is wrong and i'm getting a very white foreground when the background is at a good exposure, and visa versa.

So to create a good balance of the HDRI / TIFF landscape backgrounds I'm using, I need to use the environment exposure to create this balance.

I've attached a screenshot for you to comment.

How do you suggest I get the background brighter without messing around with environment exposure? (Which is how i've been doing it for mental ray for 9 years, using MR exposure).

Do you suggest I set it to <no exposure>?