Corona shadow catcher! Urgent question! Please help

[Daria Kaurova]

Good afternoon!
There were 2 problems! When doing object rendering, there is such a dark rim around the light object. If this is a dark object, there are no such problems. This is very important, because I'm working on a catalog and I can not admit such things. Background - Corona shadow catcher mtl. The settings changed in different ways and nothing helps. Maybe I did not understand something about this material?
The second problem is the gray background. When I used Vray, there were no such problems. At any settings of light and the material of the Corona shadow catcher, mtl still has a gray background, and I only need a drop shadow. It is very uncomfortable, because the printing is done on a white background. Further I can not twist fixtures and settings because the object is not realistic. Can you help me?
Sorry for my English, I'm from Russia.)
All pictures are attached.

[romullus]

AFAIK CoronaShadowCatcher for compositing mode only gives correct result when saved and comped in linear, i.e. 16/32 bit float.

[Daria Kaurova]

So I can not save in png format? I tried to save in Tiff 16 and 32. The gray bezel decreased a bit, but the contour is still visible. The background remains still gray.

[romullus]

Save it to exr. If done right, it should not produce any visible contour.
Regarding the grey background, i'm not sure what i see. If you applied shadowcatcher to a vertical wall, placed near to your furniture, then i think it's simply a shadow from GI of the furniture.

[Daria Kaurova]

Excellent! With the format ex worked! Thank you so much. As for the gray background, yes this is a normal render studio, probably to be perfectly clean and the shadows were only on the floor, I need to clean it manually in Photoshop via the alpha channel.
Thanks again)

[romullus]

Glad to help you :]
As for the render studio object, i would simply replace it to flat plane, that way there would be no need, or at most very small cleanup needed in photoshop.