Ground shadow falloff?

[carterhickmandesigns]

So here is my scenerio.  I have a product that uses a custom hdr and an emissive geometry for lighting.  The problem comes in on the plane that is under the product that has a 'Ground' material.  I have tried adding a blurred circle as opacity map to the 'Ground' material but that messes up the shadow.  I need these to be .png files with transparency with the shadow clipped back some so the shadow does not run to the edges of the plane or the edges of the image (see the good and bad images attached)  I have to do hundreds of these a month so adding a shadow in post is not really an option.  Any ideas?

[Esben Oxholm]

If you have KeyShot 7 you can try and enable the 'occlusion  shadow' just beneath the checkbox for the ground shadow in the environment tab.

[carterhickmandesigns]

Well I upgraded to version 7 (which I needed to do anyway) and the Occlusion Ground Shadow only works with the default ground shadow and I need it to work on a plane with the Ground Shadow material.  When I render out the image as .png with transparency and then place that file into another photoshop document the shadows are cut off by the bounds of the render size(see below).  I have tried using a circular gradient to limit the show falloff but that only makes things worse.   I need to somehow clamp the shadow falloff with out using photoshop.  Any thoughts?

I really need to find a solution for this as this is keeping me from rendering the product shots in Keyshot.

[carterhickmandesigns]

I got it figured out.  I used a technique from NM-92 https://www.keyshot.com/forum/index.php?topic=18973.0 that uses an occlusion shader on the opacity channel of a plastic material.  In the material graph I added a color adjust utility node to help shorten the shadow length out and it works PERFECT!

[Esben Oxholm]

I got it figured out.  I used a technique from NM-92 https://www.keyshot.com/forum/index.php?topic=18973.0 that uses an occlusion shader on the opacity channel of a plastic material.  In the material graph I added a color adjust utility node to help shorten the shadow length out and it works PERFECT!

Cool. Thanks for sharing how you solved it!

[TGS808]

Richard goes over a technique (maybe the one you settled on) in this video. If it's not the one you're using, it's another option. He starts the shadow stuff at about 11 minutes, 30 seconds in.

https://www.youtube.com/watch?v=athFOgZPjCY