How to brighten shadows in a white scenery?

[lightwriter]

Hi there!

Me and my colleagues have been trying to create the "perfect" white background for pieces of furniture. This set must be transparent (in order for the renders to blend in with the website background) and the objects must cast shadow on the floor.

With the first setting (diffuse lounge - corona shadow catcher material with enviro/backplate set to black), I am able to have a transparent background when saving with the alpha checked in PNG, but the shadow doesn't appear
With the second setting (cadeirão transparente - corona shadow catcher material with enviro/backplate set to grey) I am able to have a transparent background when saving with the alpha checked in PNG, and the shadow appears, but it's often too dark.
When I apply a Corona Ray Switcher Material to the background, the environment is uniformly white and the shadow is light, but I don't have a transparent background.

What can I do to achieve a transparent background, with light shadows (or at least the ability to lighten the shadows without going to Photoshop?)

[Aram Avetisyan]

Hi,

You are doing everything correctly. If shadow amount does not do the trick for you, try changing the material for shadow catcher, making it brighter, or tweak it using raySwitch.
Ultimately you need to control the opacity for the shadow, so you need to tweak the Alpha value (given that shadows are not full white or black) - this can be easily done right in the alpha channel of the image. You can either save it, tweak and then apply to the image, or you can tweak it directly as a channel inside Photoshop, if that is were the final compositing is going to happen.

Hope this helps.

[lightwriter]

Hi,

You are doing everything correctly. If shadow amount does not do the trick for you, try changing the material for shadow catcher, making it brighter, or tweak it using raySwitch.
Ultimately you need to control the opacity for the shadow, so you need to tweak the Alpha value (given that shadows are not full white or black) - this can be easily done right in the alpha channel of the image. You can either save it, tweak and then apply to the image, or you can tweak it directly as a channel inside Photoshop, if that is were the final compositing is going to happen.

Hope this helps.

Thank you for your insight. I was trying to avoid going to Photoshop, since there are times when I have to render dozens of furniture pieces, and doing it by hand is very time consuming. Maybe there's a way to record a macro in Photoshop?

Other think I noticed is the fact that, while the mesh looks good when the noise is roughly at 2,5%, the shadow often only cleans up at values close to 1% or even lower. If I try to select the noisy shadow in Photoshop to brighten it up, I almost always have to blur it, otherwise the discrepancy is too big.

However, if I use Corona Ray Switcher Material for the background, the shadow is light and not noisy at all, even in the first seconds of preview (unfortunately, this method doesn't give me transparency). Is there something I can do to minimize the shadow noise directly in Corona (without having to wait for it)?

[Aram Avetisyan]

Is there something I can do to minimize the shadow noise directly in Corona (without having to wait for it)?

Denoising? :)

The speed/noise difference may be exactly because of raySwitch (maybe no GI or other ray type is dismissed). There should be ways to have transparent shadows with rayswitch as well.
You can simply change the visibility (object properties) of the object. This should work in any case, with any material.

[lightwriter]

Is there something I can do to minimize the shadow noise directly in Corona (without having to wait for it)?

Denoising? :)

The speed/noise difference may be exactly because of raySwitch (maybe no GI or other ray type is dismissed). There should be ways to have transparent shadows with rayswitch as well.
You can simply change the visibility (object properties) of the object. This should work in any case, with any material.

Yeah, I was waiting for the denoise answer ;)

I tried to change the Object Properties of the background, unchecking Visible to Camera, among others. However, as it's possible to see in the attachment, the shadow never appears in the alpha...all this with CoronaRaySwitcherMaterial as a shader for the background.

[Aram Avetisyan]

Keep the shadowCatcher as it was - for compositing. Change only the visibility parameter (or opacity) of the object. Making an object invisible to camera will of course remove it from view.

[Aram Avetisyan]

Sorry, my bad, apparently visibility does not affect alpha (I may report this), but here is a good way to change the shadow density (alpha), using a trick - a light which illuminates only the shadow catcher.
Scene attached.

[lightwriter]

Thanks for your help!

I'm having an issue, though; when I try to open the file a popup appears that says "An error has ocurred and the application will now close. Do you want to attempt to save a copy of the current scene?"
I'm using 3ds Max 2024.2.5 Security Fix, with Corona 10 (Hotfix 2)

[Aram Avetisyan]

You should have mentioned the Corona version earlier. The scene was made with latest public Corona 12 Update 1 Hotfix 1.

Try merging the scene. If it doesn't work, I will prepare the same scene with earlier version of Corona, newer version should be irrelevant for your case.

[lightwriter]

Sorry for haven't had mentioned the Corona version in the first post. I merged the scene and then it worked, thanks.

I was playing with the scene, and the trick works great. However, in my scene I have several lights; should I exclude all of them from casting shadows on the plane, and create a new one just for the shadow?

[Aram Avetisyan]

Good to hear!

I would say keep the scene as is. Just do the trick to your scene as well - create a single rectangular light, which illuminates just the shadowcatcher (include list).
Increasing the light intensity will make the shadows cast to shadowcatcher (no matter how many there are, where they are placed, you are illuminating the shadow receiving surface) lighter or stronger through alpha channel.

[lightwriter]

I tried with one of my models and it's exactly the solution that I was looking for.

Thank you again for your patience!

P.S.: I modified the material of my object to have a strong color, in order to see if the shadow would inherit the same color. The results were positive; I would like to have my shadows always in shades of grey - is it possible to have those without having to edit the render in Photoshop?

[Aram Avetisyan]

Yes, it is possible. RaySwitch with no color (greyscale) base color should do it.

It is not simply shadows, it is global illumination, and objects' surface color do affect it. So you may need to rayswitch the objects which cast shadow and also the shadowcatcher (but probably not).

Anyway, a very slight tint in the shadows won't do much harm in my opinion, as it is used with some opacity, so see if the current workflow suffices.

[lightwriter]

It worked. Thank you again for all your help!

[Aram Avetisyan]

You are welcome!