Shadow Catcher Noise

[Xrotis]

Simple test scene:
1. Plane (Shadowcatcher material "For compositing", Default settings)
2. Corona spherical light source
3. Camera
4. Simple box with default corona material. Produces shadow to shadowcatcher material. (Problem not resolved if I remove this object)
All other settings by default.

Problem:
Alpha channel filled with noise. See picture.
Rendered over 250 passes.

Rendered to TGA.
To see this noise: I select Alpha channel (CTRL+click on alpha channel in photoshop), then fill or erase multiple times.

[maru]

Hi, I am not sure what is happening here. I will try to recreate this, or maybe you could send us the scene?
Are you using DoF in this scene?

[Xrotis]

Sure, scene in attachment.
Thank you

No DOF in scene, all settings by default.

[maru]

Sorry but I am unable to recreate this. The only strange thing I got was the attached image, but the dots are not in alpha channel. It is only saved like this when I pick certain options while saving (also attached). Can you write step-by-step what you did to see this error?

[Xrotis]

These dots are not visible in frame buffer.

To see this:

1 - Select Alpha channel (CTRL+click on alpha channel in photoshop), then fill or erase multiple times.

Or

2 - You can catch in by the eyedropper tool in framebuffer.  (See screenshot)

[Xrotis]

I found out that it depends on the type of light source.

If I use "Rectangle" or "Disk" shape (Light) - all clean, no dots appears.

But if I choose "Cylinder" shape - Alpha channel looks funny) (screnshot).

[Ondra]

it looks like slight self intersections. Sadly there is no way to prevent them, they will always happen from time to time.