How to process reflection + shadow

[Tok_Tok]

Hello,

I've been trying to get this for a while but can't figure it out. How can I save a png files where the shadow and reflections are transparent. Keyshot has this feature build in and you can directly save PNG's with transparent shadows and reflections. I tried to use the reflection and shadow pass for this in Photoshop but that gave me weird results. How do I use these correctly? Is there maybe a tutorial on that?

Best,
Joep

[TomG]

Linear Add in post for reflections (to overlay them onto a layer without reflections). For the Shadows pass, it contains the energy subtracted from that point to make the shadow, so a Linear Add will "cancel out" the shadows (then adjusting the opacity of the layer will let you lighten the shadows rather than just cancel them out altogether). I guess the biggest question is what effect you are trying to achieve?

[Tok_Tok]

Yes that's what I tried but I need the reflections to be transparent. The renders are product renders with a reflective ground, my client wants to be able to use them in a presentation so they need to be cut out but with shadows and reflections semi-transparent.

This is what I want to achieve:

He talks about the shadow only in this tut but Keyshot can also do this with the reflections.

[sprayer]

We thought you talking about reflection pass. Just render shadowcatcher with reflection in compose mode on black background for proper mask. also add wire color mask pass this may help later

[Tok_Tok]

Yes I am, like I said: "He talks about the shadow only in this tut but Keyshot can also do this with the reflections."

So it's for both, I would like to have an image with both reflections and shadows semi-transparent.

So I tried what you suggested and it sort of worked. When I set shadowcatcher to compositing with a black BG I indeed got the shadow pass in the png's alpha channel, so that's nice! But when I turned on the reflection on in the shadow catcher material the reflection was only there when the glossiness was set to 1.0. Anything below that and the reflection disappears in the PNG file. Is this suppose to happen?

I also tried it with a white BG and that worked but when I render it, the plane with the shadow catches material stays black, which makes it hard to work with when you are doing visualization work which is supposed to have a white (back)ground. The same thing also happens when I lower the glossiness of the material.

[Tok_Tok]

I still can't find a solution or reason why the reflection is not saved in the png if the roughness is set to something lower than 1.0. Somebody can help me with that?

[sprayer]

What roughness? o_O

Here example.
https://i.imgur.com/YNHD6dA.jpg

i suggest do not save as png but EXR or at least tiff\tga with all layers and compose in photoshop, you can adjust levels for alpha channel to control shadows. For EXR you will need plugin loader - Exr-IO_1.04.00 this one is good

[Tok_Tok]

With roughness, I meant Glossiness, sorry I use multiple render engines, it gets confusing sometimes.

So I tried what you said, using the same settings and savings a tiff but that does not help, the reflection is not visible in the file. When I set the Glossiness to 1.0 I keep the reflection but I lose the shadow. In the example you sent I see the reflection blurred but no shadow, there should be shadow in alpha channel as well right?

Edit: Also when I change the Glossiness the alpha channel in the VFB changes from having a shadow, or reflection, to having no shadow but having the reflection.... What am I missing?

[sprayer]

Sorry my bad example, just make brighter backplate color on shadowcatcher
https://i.imgur.com/tnD0rrI.jpg

[Tok_Tok]

No still not working... Am I overlooking something here? These are my settings:

https://i.postimg.cc/X7xX45GD/Reflection-0-8.png
https://i.postimg.cc/W13z340p/Reflection-1-0.png

The first image is with a Glossiness set to 0.8 and the second to 1.0. I'm showing you the alpha channel. So why is the reflection showing up in the G1.0 image and not in the G0.8?

[sprayer]

Can you send scene what is not showing reflection? I was used corona 2.0

You can check reflection without compose mode if you do not see reflection with turn it on it is definitely something wrong.

[Tok_Tok]

Yes of course. I'm using the latest 3.0. If you are using 2.0 then I guess something has changed. This is the scene:

https://1drv.ms/u/s!Aj60xGOaJtrFiZYMB5DD8jwXX9_wMg

I see the reflection the Beauty pass when I don't use For Compositing mode (and also when I do use it) but then the Alpha channel won't work.  The only problem I have is the reflection not showing up in the Alpha channel.

[sprayer]

i think it's another couple bugs here, if set light source to 0 it will reflects in alpha.

To solve your issue, make more realistic light setup, add hdri or color to environments,  this bug i think is from one light source and black environment color, if you change something from this it's start to reflect, i was never render with only one light and never saw this bug.

[Frood]

Could you please report this issue? I can confirm it for Max2018+Corona 2.0 and Max2016 + current daily.


Good Luck

[Tok_Tok]

When I use multiple lights or set the BG color to something lighter than black it still won't work. Also when I set the light source to 0 it does not work. But I tried it on an existing scene and it works in there. So I guess this is solved, thank you for your help!

Sorry but I'm very busy and don't have time to report this, I think it's clearly described in this post though.