Shadow Catcher anomalies?

HI. I am rendering a few scenes to place into PowerPoint. The images are png with transparent backgrounds, and I am using a shadow catcher. But somehow, I get some outer area on a lighter grey as a falloff. This does not allow me to place the render on a background since I can still see the limits of my render due to this framed shadow.

This is my viewport:

This is the issue:

I need to “merge” the png seamlessly onto the background. I know I could use Photoshop to mask that, but I wonder if this is the correct behavior or if I am missing how to set it in Blender.

Thank you

What is your lighting setup? It looks like a double shadow from more than one light source.


I think this might be color bleeding from the cylinder. Try using a glossy shader for the floor, with high roughness so that it almost resembles a diffuse shader

I have an hdri and an area light. The area light is facing the z axis.
Is there any way to turn off the shadow generated by the hdri to verify is the hdri creating those shadows?

Thank you

You can probably just set the environment color to black to test it

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In the World Properties tab set the Surface Strength to 0.

Sorry, I misread your question. There may be a node setup for the World in the Shader Editor that can achieve that, but I’m not familiar with it. But it might be worth reconsidering the need for an HDRI for the lighting of this scene. I think you can achieve this with a simple white Background with a low Surface Strength like .100. You’ll get fill light on the object, but the only shadow will be the one cast by the area light.

Hi. Thank you.
I tested with a black background and a smaller size in my area light. Still, I get a gradient hitting the frame limits.

Thank you! Not exactly about the hdri. I tried now with and without it, and I can say the lighting of the hdri, although not contrasty, gives a lot of depth to the image. There are a lot of subtle reflections in my scene. Be aware the cylinder is a test sample for the forum. I can not post the scene due to NDA reasons.

How does it look with a sun light size 0 instead ? Seems to me this is caused by the area light.

In that case I think a 2 layer composite is what you need. Layer 1 being the object only, full lighting setup; layer 2 the shadow catcher only, object set to holdout or invisible to camera, HDRI strength @ 0.

I will try, but if I use a sun light size 0…isn’t it like it’s not there? I wonder if I should play with the area light spread angle…maybe that helps.

I meant the size property, sorry. Sun lights have no size, since they’re considered to be infinitely far away. They have an angular size instead.

Basically if you set it to 0 degrees your shadows will be infinitely sharp. Increase it and your shadows will be blurred. I think that’s what’s happening with your area light : consider one end of your area light rectangle (assuming it’s a rectangle), it casts the shadow of the part of the model that’s directly under it, right ? but it also casts the shadow of the opposite part of the object, at a very steep angle, producing very long and blurry shadows in those directions.

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Ok, the issue was that the light spread of the area light (180) was creating the falloff in the shadow. The hdri also had a subtle effect on it.

I turned the hdri to black and 0 power and light with a narrower angle, and now I can see it works as expected.

Thank you

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Oh, right, didn’t think of the spread. Good catch.