Shadow catcher problem.

[vermu]

Hi,
I am doing a house render and my goal is to edit the house picture in ps so that the house is agains pure white bg and shadows are casting from the house.
So I tried to use shadow catcher material and use composite option. The problem is that I get my direct shadow but I also get a lot of unwanted noise shadow. It kinda looks like the light is coming from every direction.
I am using hdri map to light the scene. Can you give any tips how to get only direct shadow casting to shadow catcher material. If I change my shadow catcher plane to solid white color it does not have those weird shadows that shadow catcher material is getting.

[romullus]

Did you try to compose shadow catcher image with white background in post? If you'll do it right (i.e. linearly), it should exactly match the image rendered with ordinary white material.

[vermu]

Yes, I tried to compose shadow catcher image in post.

Can you explain abit that linearly thing?

I have tried to alter all the settings in catcher material but it's just not working. Obviously I am doing something wrong here.

[romullus]

You need to export rendered image with gamma 1 to floating or half-floating format and with all tonemapping, except exposure,  turned off. And of course you need to perform composing in linear too with blending mode set to add.

Can you show what you're getting in 3ds max and in comp?