Handling Shadow Masks in VFB

[DCHA34]

Hi,
I would like to be able to lighten/darken or tint only the shadows of the objects in the VFB.
Would someone have a tuto or the kindness to explain me how to manipulate the shadow masks in the VFB ?
I don't understand how Matte/RAW Shadow masks work.

[natalia.gruzdova]

Hello DCHA34,
Thank you for your question.
Perhaps the easiest way to do what you describe would be by adding Shadows Render Element.

Shadows RE works as a reverse mask for shadows. It is a color image that can be used to lighten, darken or tint shadows.

Shadows can be lightened in the composite by adding this render element, or darkened by subtracting this render pass from the final composite.



This Shadows RE is the product of multiplying the Raw Shadow RE with the Diffuse RE in the composite.

So by multiplying the Diffuse RE by Raw Shadows RE and adding them on top of the RGB channel will give you similar\same to Shadows RE results.



And the third option is to add Matte Shadows RE to Raw Lights RE.
Matte Shadows RE shows areas where light doesn't reach. Compared to the Raw Shadow RE, which gives areas of cast shadows.



Multiplier and add amount depends on what results you want to achieve.
I am also attaching the test scene with settings, hope it helps.
Shadows_compositing.zip

[DCHA34]

Hi Natalia,
thank you for this detailed explanation.
While trying quickly different blending modes, I found this "artifact" (see photo) with the Raw_Shadows RE and the Shadows RE.
Is it a bug?

[DCHA34]

Natalia,
I just took a closer look at all this. It's not exactly what I expected.
In fact, I would have liked to have a classic black and white or grayscale shadow mask.
Exactly like the attached image. This is a save of the Sketchup screen in shadow mode only.
In summary, can we have the shadows in Cryptomatte mask format.
I hope I've been clear enough.

[wzfwzfwzf]

I think this is the effect you want, just follow the screenshot. The test file is below. tast.rar

[wzfwzfwzf]

rendering result

[DCHA34]

Hi wzfwzfwzf
thanks for taking time to look for a solution, but it's not a style of rendering I'm looking for.
It's the possibility in V-Ray to have a Cryptomatte mask of the shadows and thus have the possibility to " tweak" the shadows only in the VFB.

Here is an example made with the "Sketchup mask" in Photoshop

[natalia.gruzdova]

Hello DCHA34,

While trying quickly different blending modes, I found this "artifact" (see photo) with the Raw_Shadows RE and the Shadows RE. Is it a bug?

Thanks for sharing, I will need to look further into it.

It's the possibility in V-Ray to have a Cryptomatte mask of the shadows and thus have the possibility to " tweak" the shadows only in the VFB.

The Shadow Select feature (that is perhaps most close to what you are describing) is logged as a feature request for evaluation. Cryptomatte Render Element can select only objects for masking and also can be added to Lens Effects.

Here is an example made with the "Sketchup mask" in Photoshop.

Similar results are possible with all three approaches I have shared previously. This is example for Shadows RE compositing in the VFB:



The render elements itself look different from what you give as an example, but combining Matte Shadow (10%) + Raw Light gives similar results, please see here: