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Shadow only renders are always off

mikekmikek Posts: 195
edited September 2018 in The Commons

I'm trying to render a object in iray and insert the result into a existing image. The difficult part with this is to get the shadows right. In the advanced iray material settings there is the iray matte option for this which can turn any object in the scene into a shadow catcher. This would allow me to create the needed shadows the problem is the result of the shadow catcher isn't like the normal shadows.

The following image is a scene with a simple ground and one object but no shadow catcher. This is how the shadows should look like for the crate:


In the next image the ground has been changed into a shadow catcher by enabling the iray matte option. This shows what the shadow catcher produces:



The problem here is the shadows are far stronger and the whole ground receives a visible gray overlay which isn't visible in the original scene. This gray overlay makes it unusable for me as each border of a shadow catcher gets visible by it.
As a reference the next image shows the shadow catcher result merged with a shadowless ground. If the shadow catcher would work right this would have to look like the first picture:

But the result has shadows so dark it looks like the crate is hovering and the whole ground is darker ever where there aren't really supossed to be shadows visible. Is there a way to fix this and get the same smooth shadows a surface would receive if rendered normally? I'm using the same materials for the shadow catcher and original surface. The only difference is the iray matte option enabled. 
Or is there any other approach to create the same shadows beside trying to fix everything manually in post processing?
 

Post edited by mikek on

Comments

  • FishtalesFishtales Posts: 6,212

    You don't need a shadow catcher in Iray the ground is a built in one. To get the shadows on your ground plane make sure it is sitting on the Iray ground, Ctrl D, and then you can adjust the shadow intensity using the shadow slider at the bottom of the Environment Plane. Below 1.0 makes them lighter, greater than 1.0 makes them darker.

  • mikekmikek Posts: 195

    Ok this creates the expected smooth shadows:



    It would be nice if the shadow catcher would work like this to create correct shadows on walls and objects but having the ground working helps me a lot. Thank you.

  • FishtalesFishtales Posts: 6,212

    Lights in Iray cast shadows on any objects in the scene. To change the intensity of the shadow you change the light geometry e.g. point, sphere or plane etc. and raise or lower the Lumen value. For use in an HDRI scene, no geometry, you can use a primitive with a Matte function to catch the shadows.

  • mikekmikek Posts: 195

    I use only HDRI in the scene. Something they did different in the video is changing the shadow catcher diffuse to black. It's still a little bit darker in direct comparsion to the version with ground but it's by far bettern than my old shadow catcher:

     Thank you. This one should work for me.

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